Internet DRAFT - draft-ietf-storm-iscsi-cons
draft-ietf-storm-iscsi-cons
Storage Maintenance (storm) WG Mallikarjun Chadalapaka
Internet Draft Microsoft
draft-ietf-storm-iscsi-cons-10.txt
Intended status: Proposed Standard Julian Satran
Expires: January 2014 Infinidat Ltd.
Obsoletes: RFC3720, RFC3980, RFC4850, RFC5048
Updates: RFC3721 Kalman Meth
IBM
David Black
EMC
iSCSI Protocol (Consolidated)
Status of this Memo
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Abstract
This document describes a transport protocol for SCSI that works
on top of TCP. The iSCSI protocol aims to be fully compliant with
the standardized SCSI Architecture Model (SAM-2). RFC 3720
defined the original iSCSI protocol. RFC 3721 discusses iSCSI
Naming examples and discovery techniques. Subsequently, RFC 3980
added an additional naming format to iSCSI protocol. RFC 4850
followed up by adding a new public extension key to iSCSI. RFC
5048 offered a number of clarifications and a few improvements and
corrections to the original iSCSI protocol.
This document obsoletes RFCs 3720, 3980, 4850 and 5048 by
consolidating them into a single document and making additional
updates to the consolidated specification. This document also
updates RFC 3721. The text in this document thus supersedes the
text in all the noted RFCs wherever there is a difference in
semantics.
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1. Introduction.................................................... 14
2. Acronyms, Definitions and Document Summary...................... 15
2.1. Acronyms .................................................. 15
2.2. Definitions ............................................... 17
2.3. Summary of Changes ........................................ 24
2.4. Conventions ............................................... 25
3. UML Conventions................................................. 26
3.1. UML Conventions Overview .................................. 26
3.2. Multiplicity Notion ....................................... 26
3.3. Class Diagram Conventions ................................. 27
3.4. Class Diagram Notation for Associations ................... 28
3.5. Class Diagram Notation for Aggregations ................... 29
3.6. Class Diagram Notation for Generalizations ................ 29
4. Overview........................................................ 31
4.1. SCSI Concepts ............................................... 31
4.2. iSCSI Concepts and Functional Overview ...................... 32
4.2.1. Layers and Sessions ..................................... 33
4.2.2. Ordering and iSCSI Numbering ............................ 34
4.2.2.1. Command Numbering and Acknowledging ................. 34
4.2.2.2. Response/Status Numbering and Acknowledging ......... 38
4.2.2.3. Response Ordering ................................... 39
4.2.2.3.1. Need for Response Ordering ...................... 39
4.2.2.3.2. Response Ordering Model Description ............. 39
4.2.2.3.3. iSCSI Semantics with the Interface Model ........ 40
4.2.2.3.4. Current List of Fenced Response Use Cases ....... 41
4.2.2.4. Data Sequencing ..................................... 42
4.2.3. iSCSI Task Management ................................... 43
4.2.3.1. Task Management Overview ............................ 43
4.2.3.2. Notion of Affected Tasks ............................ 43
4.2.3.3. Standard Multi-task Abort Semantics ................. 44
4.2.3.4. FastAbort Multi-task Abort Semantics ................ 45
4.2.3.5. Affected Tasks Shared across Standard and FastAbort
Sessions ..................................................... 47
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4.2.3.6. Rationale behind the FastAbort Semantics ............48
4.2.4. iSCSI Login .............................................50
4.2.5. iSCSI Full Feature Phase ................................51
4.2.5.1. Command Connection Allegiance .......................52
4.2.5.2. Data Transfer Overview ..............................53
4.2.5.3. Tags and Integrity Checks ...........................54
4.2.5.4. Task Management .....................................55
4.2.6. iSCSI Connection Termination ............................55
4.2.7. iSCSI Names .............................................56
4.2.7.1. iSCSI Name Properties ...............................57
4.2.7.2. iSCSI Name Encoding .................................59
4.2.7.3. iSCSI Name Structure ................................60
4.2.7.4. Type "iqn." (iSCSI Qualified Name) ..................61
4.2.7.5. Type "eui." (IEEE EUI-64 format) ....................63
4.2.7.6. Type "naa." - Network Address Authority .............63
4.2.8. Persistent State ........................................64
4.2.9. Message Synchronization and Steering ....................65
4.2.9.1. Sync/Steering and iSCSI PDU Length ..................66
4.3. iSCSI Session Types .........................................66
4.4. SCSI to iSCSI Concepts Mapping Model ........................67
4.4.1. iSCSI Architecture Model ................................68
4.4.2. SCSI Architecture Model .................................71
4.4.3. Consequences of the Model ...............................73
4.4.3.1. I_T Nexus State .....................................74
4.4.3.2. Reservations ........................................74
4.5. iSCSI UML Model .............................................75
4.6. Request/Response Summary ....................................78
4.6.1. Request/Response Types Carrying SCSI Payload ............78
4.6.1.1. SCSI-Command ........................................78
4.6.1.2. SCSI-Response .......................................79
4.6.1.3. Task Management Function Request ....................79
4.6.1.4. Task Management Function Response ...................80
4.6.1.5. SCSI Data-out and SCSI Data-in ......................80
4.6.1.6. Ready To Transfer (R2T) .............................81
4.6.2. Requests/Responses carrying SCSI and iSCSI Payload ......82
4.6.2.1. Asynchronous Message ................................82
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4.6.3. Requests/Responses Carrying iSCSI Only Payload ..........82
4.6.3.1. Text Request and Text Response ......................82
4.6.3.2. Login Request and Login Response ....................83
4.6.3.3. Logout Request and Response .........................84
4.6.3.4. SNACK Request .......................................84
4.6.3.5. Reject ..............................................84
4.6.3.6. NOP-Out Request and NOP-In Response .................85
5. SCSI Mode Parameters for iSCSI................................. 86
6. Login and Full Feature Phase Negotiation....................... 87
6.1. Text Format ................................................ 88
6.2. Text Mode Negotiation ...................................... 92
6.2.1. List negotiations ...................................... 96
6.2.2. Simple-value Negotiations .............................. 97
6.3. Login Phase ................................................ 97
6.3.1. Login Phase Start ..................................... 101
6.3.2. iSCSI Security Negotiation ............................ 104
6.3.3. Operational Parameter Negotiation During the Login Phase105
6.3.4. Connection Reinstatement .............................. 106
6.3.5. Session Reinstatement, Closure, and Timeout ........... 106
6.3.5.1. Loss of Nexus Notification ........................ 107
6.3.6. Session Continuation and Failure ...................... 107
6.4. Operational Parameter Negotiation Outside the Login Phase . 108
7. iSCSI Error Handling and Recovery............................. 110
7.1. Overview .................................................. 110
7.1.1. Background ............................................ 110
7.1.2. Goals ................................................. 110
7.1.3. Protocol Features and State Expectations .............. 111
7.1.4. Recovery Classes ...................................... 112
7.1.4.1. Recovery Within-command ........................... 113
7.1.4.2. Recovery Within-connection ........................ 114
7.1.4.3. Connection Recovery ............................... 115
7.1.4.4. Session Recovery .................................. 116
7.1.5. Error Recovery Hierarchy .............................. 116
7.2. Retry and Reassign in Recovery ............................ 118
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7.2.1. Usage of Retry ....................................... 118
7.2.2. Allegiance Reassignment .............................. 119
7.3. Usage Of Reject PDU in Recovery .......................... 120
7.4. Error Recovery Considerations for Discovery Sessions ..... 121
7.4.1. ErrorRecoveryLevel for Discovery Sessions ............ 121
7.4.2. Reinstatement Semantics for Discovery Sessions ....... 121
7.4.2.1. Unnamed Discovery Sessions ....................... 122
7.4.2.2. Named Discovery Session .......................... 123
7.4.3. Target PDUs During Discovery ......................... 123
7.5. Connection Timeout Management ............................ 123
7.5.1. Timeouts on Transport Exception Events ............... 124
7.5.2. Timeouts on Planned Decommissioning .................. 124
7.6. Implicit Termination of Tasks ............................ 124
7.7. Format Errors ............................................ 125
7.8. Digest Errors ............................................ 126
7.9. Sequence Errors .......................................... 128
7.10. Message Error Checking .................................. 128
7.11. SCSI Timeouts ........................................... 129
7.12. Negotiation Failures .................................... 130
7.13. Protocol Errors ......................................... 130
7.14. Connection Failures ..................................... 131
7.15. Session Errors .......................................... 132
8. State Transitions............................................. 133
8.1. Standard Connection State Diagrams ....................... 133
8.1.1. State Descriptions for Initiators and Targets ........ 133
8.1.2. State Transition Descriptions for Initiators and Targets134
8.1.3. Standard Connection State Diagram for an Initiator .....138
8.1.4. Standard Connection State Diagram for a Target .........140
8.2. Connection Cleanup State Diagram for Initiators and Targets 142
8.2.1. State Descriptions for Initiators and Targets ..........144
8.2.2. State Transition Descriptions for Initiators and Targets145
8.3. Session State Diagrams .....................................147
8.3.1. Session State Diagram for an Initiator .................147
8.3.2. Session State Diagram for a Target .....................148
8.3.3. State Descriptions for Initiators and Targets ..........149
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8.3.4. State Transition Descriptions for Initiators and Targets 150
9. Security Considerations...................................... 152
9.1. iSCSI Security Mechanisms ............................... 152
9.2. In-band Initiator-Target Authentication ................. 153
9.2.1. CHAP Considerations ................................. 155
9.2.2. SRP Considerations .................................. 158
Kerberos Considerations ................................... 158
9.2.3. ..................................................... 158
9.3. IPsec ................................................... 159
9.3.1. Data Integrity and Authentication ................... 159
9.3.2. Confidentiality ..................................... 160
9.3.3. Policy, Security Associations, and Cryptographic Key
Management ................................................. 161
9.4. Security Considerations for the X#NodeArchitecture Key .. 163
9.5. SCSI Access Control Considerations ...................... 165
10. Notes to Implementers....................................... 166
10.1. Multiple Network Adapters ............................... 166
10.1.1. Conservative Reuse of ISIDs ......................... 166
10.1.2. iSCSI Name, ISID, and TPGT Use ...................... 167
10.2. Autosense and Auto Contingent Allegiance (ACA) .......... 169
10.3. iSCSI Timeouts .......................................... 169
10.4. Command Retry and Cleaning Old Command Instances ........ 170
10.5. Synch and Steering Layer and Performance ................ 171
10.6. Considerations for State-dependent Devices and Long-lasting
SCSI Operations ............................................... 171
10.6.1. Determining the Proper ErrorRecoveryLevel ........... 172
10.7. Multi-task Abort Implementation Considerations .......... 173
11. iSCSI PDU Formats........................................... 174
11.1. iSCSI PDU Length and Padding ........................... 174
11.2. PDU Template, Header, and Opcodes ...................... 174
11.2.1. Basic Header Segment (BHS) ......................... 175
11.2.1.1. I .............................................. 176
11.2.1.2. Opcode ......................................... 176
11.2.1.3. Final (F) bit .................................. 178
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11.2.1.4. Opcode-specific Fields ......................... 178
11.2.1.5. TotalAHSLength ................................. 178
11.2.1.6. DataSegmentLength .............................. 178
11.2.1.7. LUN ............................................ 178
11.2.1.8. Initiator Task Tag ............................. 179
11.2.2. Additional Header Segment (AHS) ................... 179
11.2.2.1. AHSType ....................................... 179
11.2.2.2. AHSLength ..................................... 180
11.2.2.3. Extended CDB AHS .............................. 180
11.2.2.4. Bidirectional Expected Read-Data Length AHS ... 180
11.2.3. Header Digest and Data Digest ..................... 181
11.2.4. Data Segment ...................................... 181
11.3. SCSI Command .......................................... 181
11.3.1. Flags and Task Attributes (byte 1) ................ 182
11.3.2. CmdSN - Command Sequence Number ................... 183
11.3.3. ExpStatSN ......................................... 184
11.3.4. Expected Data Transfer Length ..................... 184
11.3.5. CDB - SCSI Command Descriptor Block ............... 185
11.3.6. Data Segment - Command Data ....................... 185
11.4. SCSI Response ......................................... 185
11.4.1. Flags (byte 1) .................................... 186
11.4.2. Status ............................................ 187
11.4.3. Response .......................................... 188
11.4.4. SNACK Tag ......................................... 189
11.4.5. Residual Count .................................... 189
11.4.5.1. Field Semantics ............................... 189
11.4.5.2. Residuals Concepts Overview ................... 190
11.4.5.3. SCSI REPORT LUNS and Residual Overflow ........ 190
11.4.6. Bidirectional Read Residual Count ................. 192
11.4.7. Data Segment - Sense and Response Data Segment .... 192
11.4.7.1. SenseLength ................................... 193
11.4.7.2. Sense Data .................................... 193
11.4.8. ExpDataSN ......................................... 194
11.4.9. StatSN - Status Sequence Number ................... 194
11.4.10. ExpCmdSN - Next Expected CmdSN from this Initiator 195
11.4.11. MaxCmdSN - Maximum CmdSN from this Initiator ...... 195
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11.5. Task Management Function Request ....................... 196
11.5.1. Function ........................................... 196
11.5.2. TotalAHSLength and DataSegmentLength ............... 200
11.5.3. LUN ................................................ 200
11.5.4. Referenced Task Tag ................................ 200
11.5.5. RefCmdSN ........................................... 200
11.5.6. ExpDataSN .......................................... 201
11.6. Task Management Function Response ...................... 201
11.6.1. Response ........................................... 202
11.6.2. TotalAHSLength and DataSegmentLength ............... 204
11.7. SCSI Data-out & SCSI Data-in ........................... 204
11.7.1. F (Final) Bit ...................................... 207
11.7.2. A (Acknowledge) bit ................................ 207
11.7.3. Flags (byte 1) ..................................... 208
11.7.4. Target Transfer Tag and LUN ........................ 209
11.7.5. DataSN ............................................. 209
11.7.6. Buffer Offset ...................................... 209
11.7.7. DataSegmentLength .................................. 210
11.8. Ready To Transfer (R2T) ................................ 211
11.8.1. TotalAHSLength and DataSegmentLength ............... 213
11.8.2. R2TSN .............................................. 213
11.8.3. StatSN ............................................. 213
11.8.4. Desired Data Transfer Length and Buffer Offset ..... 213
11.8.5. Target Transfer Tag ................................ 213
11.9. Asynchronous Message ................................... 214
11.9.1. AsyncEvent ......................................... 215
11.9.2. AsyncVCode ......................................... 218
11.9.3. LUN ................................................ 218
11.9.4. Sense Data and iSCSI Event Data .................... 218
11.9.4.1. SenseLength .................................... 219
11.10. Text Request .......................................... 219
11.10.1. F (Final) Bit ..................................... 221
11.10.2. C (Continue) Bit .................................. 221
11.10.3. Initiator Task Tag ................................ 221
11.10.4. Target Transfer Tag ............................... 221
11.10.5. Text .............................................. 222
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11.11. Text Response ....................................... 223
11.11.1. F (Final) Bit ................................... 224
11.11.2. C (Continue) Bit ................................ 225
11.11.3. Initiator Task Tag .............................. 225
11.11.4. Target Transfer Tag ............................. 225
11.11.5. StatSN .......................................... 226
11.11.6. Text Response Data .............................. 226
11.12. Login Request ....................................... 226
11.12.1. T (Transit) Bit ................................. 227
11.12.2. C (Continue) Bit ................................ 228
11.12.3. CSG and NSG ..................................... 228
11.12.4. Version ......................................... 228
11.12.4.1. Version-max .................................. 228
11.12.4.2. Version-min .................................. 229
11.12.5. ISID ............................................ 229
11.12.6. TSIH ............................................ 231
11.12.7. Connection ID - CID ............................. 231
11.12.8. CmdSN ........................................... 231
11.12.9. ExpStatSN ....................................... 232
11.12.10. Login Parameters ............................... 232
11.13. Login Response ...................................... 232
11.13.1. Version-max ..................................... 233
11.13.2. Version-active .................................. 234
11.13.3. TSIH ............................................ 234
11.13.4. StatSN .......................................... 234
11.13.5. Status-Class and Status-Detail .................. 234
11.13.6. T (Transit) bit ................................. 238
11.13.7. C (Continue) Bit ................................ 239
11.13.8. Login Parameters ................................ 239
11.14. Logout Request ...................................... 239
11.14.1. Reason Code ..................................... 242
11.14.2. TotalAHSLength and DataSegmentLength ............ 243
11.14.3. CID ............................................. 243
11.14.4. ExpStatSN ....................................... 243
11.14.5. Implicit termination of tasks ................... 243
11.15. Logout Response ..................................... 244
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11.15.1. Response ........................................ 245
11.15.2. TotalAHSLength and DataSegmentLength ............ 246
11.15.3. Time2Wait ....................................... 246
11.15.4. Time2Retain ..................................... 246
11.16. SNACK Request ....................................... 247
11.16.1. Type ............................................ 248
11.16.2. Data Acknowledgement ............................ 249
11.16.3. Resegmentation .................................. 249
11.16.4. Initiator Task Tag .............................. 250
11.16.5. Target Transfer Tag or SNACK Tag ................ 250
11.16.6. BegRun .......................................... 251
11.16.7. RunLength ....................................... 251
11.17. Reject .............................................. 252
11.17.1. Reason .......................................... 253
11.17.2. DataSN/R2TSN .................................... 254
11.17.3. StatSN, ExpCmdSN and MaxCmdSN ................... 254
11.17.4. Complete Header of Bad PDU ...................... 255
11.18. NOP-Out ............................................. 255
11.18.1. Initiator Task Tag .............................. 256
11.18.2. Target Transfer Tag ............................. 256
11.18.3. Ping Data ....................................... 257
11.19. NOP-In .............................................. 258
11.19.1. Target Transfer Tag ............................. 259
11.19.2. StatSN .......................................... 259
11.19.3. LUN ............................................. 259
12. iSCSI Security Text Keys and Authentication Methods......... 260
12.1. AuthMethod ........................................... 260
12.1.1. Kerberos ......................................... 262
12.1.2. Secure Remote Password (SRP) ..................... 263
12.1.3. Challenge Handshake Authentication Protocol (CHAP) 265
13. Login/Text Operational Text Keys............................ 267
13.1. HeaderDigest and DataDigest .......................... 267
13.2. MaxConnections ....................................... 270
13.3. SendTargets .......................................... 270
13.4. TargetName ........................................... 270
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13.5. InitiatorName ......................................... 271
13.6. TargetAlias ........................................... 272
13.7. InitiatorAlias ........................................ 272
13.8. TargetAddress ......................................... 273
13.9. TargetPortalGroupTag .................................. 274
13.10. InitialR2T ........................................... 274
13.11. ImmediateData ........................................ 275
13.12. MaxRecvDataSegmentLength ............................. 276
13.13. MaxBurstLength ....................................... 277
13.14. FirstBurstLength ..................................... 277
13.15. DefaultTime2Wait ..................................... 278
13.16. DefaultTime2Retain ................................... 278
13.17. MaxOutstandingR2T .................................... 279
13.18. DataPDUInOrder ....................................... 279
13.19. DataSequenceInOrder .................................. 280
13.20. ErrorRecoveryLevel ................................... 280
13.21. SessionType .......................................... 281
13.22. The Private Extension Key Format ..................... 282
13.23. TaskReporting ........................................ 282
13.24. iSCSIProtocolLevel Negotiation ....................... 283
13.25. Obsoleted Keys ....................................... 283
13.26. X#NodeArchitecture ................................... 284
13.26.1. Definition ....................................... 284
13.26.2. Implementation Requirements ...................... 285
14. Rationale for revised IANA Considerations................... 286
15. IANA Considerations......................................... 288
Appendix A. Examples ........................................... 295
Read Operation Example ...................................... 295
Write Operation Example ..................................... 296
R2TSN/DataSN Use Examples ................................... 296
CRC Examples ................................................ 300
Appendix B. Login Phase Examples ............................... 302
Appendix C. SendTargets Operation .............................. 312
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Appendix D. Algorithmic Presentation of Error Recovery Classes . 317
D.2.1. Procedure Descriptions ............................... 319
Appendix E. Clearing Effects of Various Events on Targets ...... 336
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1. Introduction
The Small Computer Systems Interface (SCSI) is a popular family of
protocols for communicating with I/O devices, especially storage
devices. SCSI is a client-server architecture. Clients of a SCSI
interface are called "initiators". Initiators issue SCSI
"commands" to request services from components, logical units of a
server known as a "target". A "SCSI transport" maps the client-
server SCSI protocol to a specific interconnect. An Initiator is
one endpoint of a SCSI transport and a target is the other
endpoint.
The SCSI protocol has been mapped over various transports,
including Parallel SCSI, IPI, IEEE-1394 (firewire) and Fibre
Channel. These transports are I/O specific and have limited
distance capabilities.
The iSCSI protocol defined in this document describes a means of
transporting of the SCSI packets over TCP/IP, providing for an
interoperable solution which can take advantage of existing
Internet infrastructure, Internet management facilities and
address distance limitations.
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2. Acronyms, Definitions and Document Summary
2.1. Acronyms
Acronym Definition
--------------------------------------------------------------
3DES Triple Data Encryption Standard
ACA Auto Contingent Allegiance
AEN Asynchronous Event Notification
AES Advanced Encryption Standard
AH Additional Header (not the IPsec AH!)
AHS Additional Header Segment
API Application Programming Interface
ASC Additional Sense Code
ASCII American Standard Code for Information Interchange
ASCQ Additional Sense Code Qualifier
BHS Basic Header Segment
CBC Cipher Block Chaining
CD Compact Disk
CDB Command Descriptor Block
CHAP Challenge Handshake Authentication Protocol
CID Connection ID
CO Connection Only
CRC Cyclic Redundancy Check
CRL Certificate Revocation List
CSG Current Stage
CSM Connection State Machine
DES Data Encryption Standard
DNS Domain Name Server
DOI Domain of Interpretation
DVD Digital Versatile Disk
EDTL Expected Data Transfer Length
ESP Encapsulating Security Payload
EUI Extended Unique Identifier
FFP Full Feature Phase
FFPO Full Feature Phase Only
Gbps Gigabits per Second
HBA Host Bus Adapter
HMAC Hashed Message Authentication Code
I_T Initiator_Target
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I_T_L Initiator_Target_LUN
IANA Internet Assigned Numbers Authority
IB InfiniBand
ID Identifier
IDN Internationalized Domain Name
IEEE Institute of Electrical & Electronics Engineers
IETF Internet Engineering Task Force
IKE Internet Key Exchange
I/O Input-Output
IO Initialize Only
IP Internet Protocol
IPsec Internet Protocol Security
IPv4 Internet Protocol Version 4
IPv6 Internet Protocol Version 6
IQN iSCSI Qualified Name
iSCSI Internet SCSI
iSER iSCSI Extensions for RDMA
ISID Initiator Session ID
iSNS Internet Storage Name Service (see [RFC4171])
ITN iSCSI Target Name
ITT Initiator Task Tag
KRB5 Kerberos V5
LFL Lower Functional Layer
LTDS Logical-Text-Data-Segment
LO Leading Only
LU Logical Unit
LUN Logical Unit Number
MAC Message Authentication Codes
NA Not Applicable
NAA Network Address Authority
NIC Network Interface Card
NOP No Operation
NSG Next Stage
OS Operating System
PDU Protocol Data Unit
PKI Public Key Infrastructure
R2T Ready To Transfer
R2TSN Ready To Transfer Sequence Number
RDMA Remote Direct Memory Access
RFC Request For Comments
SAM SCSI Architecture Model
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SAM2 SCSI Architecture Model - 2
SAN Storage Area Network
SAS Serial Attached SCSI
SCSI Small Computer Systems Interface
SLP Service Location Protocol
SN Sequence Number
SNACK Selective Negative Acknowledgment - also
Sequence Number Acknowledgement for data
SPDTL SCSI-Presented Data Transfer Length
SPKM Simple Public-Key Mechanism
SRP Secure Remote Password
SSID Session ID
SW Session-Wide
TCB Task Control Block
TCP Transmission Control Protocol
TMF Task Management Function
TPGT Target Portal Group Tag
TSIH Target Session Identifying Handle
TTT Target Transfer Tag
UA Unit Attention
UFL Upper Functional Layer
ULP Upper Level Protocol
URN Uniform Resource Names
UTF Universal Transformation Format
WG Working Group
2.2. Definitions
- Alias: An alias string can also be associated with an iSCSI
Node. The alias allows an organization to associate a user-
friendly string with the iSCSI Name. However, the alias string is
not a substitute for the iSCSI Name.
- CID (Connection ID): Connections within a session are identified
by a connection ID. It is a unique ID for this connection within
the session for the initiator. It is generated by the initiator
and presented to the target during login requests and during
logouts that close connections.
- Connection: A connection is a TCP connection. Communication
between the initiator and target occurs over one or more TCP
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connections. The TCP connections carry control messages, SCSI
commands, parameters, and data within iSCSI Protocol Data Units
(iSCSI PDUs).
- I/O Buffer:A buffer that is used in a SCSI Read or Write
operation so SCSI data may be sent from or received into that
buffer. For a read or write data transfer to take place for a
task, an I/O Buffer is required on the initiator and at least one
is required on the
target.
- INCITS: INCITS stands for InterNational Committee of Information
Technology Standards. The INCITS has a broad standardization scope
within the field of Information and Communications Technologies
(ICT), encompassing storage, processing, transfer, display,
management, organization, and retrieval of information. INCITS
serves as ANSI's Technical Advisory Group for the ISO/IEC Joint
Technical Committee 1 (JTC 1). See http://www.incits.org.
- InfiniBand: An I/O architecture originally intended to replace
PCI and to address high performance server interconnectivity [IB].
- iSCSI Device: A SCSI Device using an iSCSI service delivery
subsystem. Service Delivery Subsystem is defined by [SAM2] as a
transport mechanism for SCSI commands and responses.
- iSCSI Initiator Name: The iSCSI Initiator Name specifies the
worldwide unique name of the initiator.
- iSCSI Initiator Node: The "initiator" device. The word
"initiator" has been appropriately qualified as either a port or a
device in the rest of the document when the context is ambiguous.
All unqualified usages of "initiator" refer to an initiator port
(or device) depending on the context.
- iSCSI Layer: This layer builds/receives iSCSI PDUs and
relays/receives them to/from one or more TCP connections that form
an initiator-target "session".
- iSCSI Name: The name of an iSCSI initiator or iSCSI target.
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- iSCSI Node: The iSCSI Node represents a single iSCSI initiator
or iSCSI target or a single instance of each. There are one or
more iSCSI Nodes within a Network Entity. The iSCSI Node is
accessible via one or more Network Portals. An iSCSI Node is
identified by its iSCSI Name. The separation of the iSCSI Name
from the addresses used by and for the iSCSI Node allows multiple
iSCSI nodes to use the same address, and the same iSCSI node to
use multiple addresses.
- iSCSI Target Name: The iSCSI Target Name specifies the worldwide
unique name of the target.
- iSCSI Target Node: The "target" device. The word "target" has
been appropriately qualified as either a port or a device in the
rest of the document when the context is ambiguous. All
unqualified usages of "target" refer to a target port (or device)
depending on the context.
- iSCSI Task: An iSCSI task is an iSCSI request for which a
response is expected.
- iSCSI Transfer Direction: The iSCSI transfer direction is
defined with regard to the initiator. Outbound or outgoing
transfers are transfers from the initiator to the target, while
inbound or incoming transfers are from the target to the
initiator.
- ISID: The initiator part of the Session Identifier. It is
explicitly specified by the initiator during Login.
- I_T nexus: According to [SAM2], the I_T nexus is a relationship
between a SCSI Initiator Port and a SCSI Target Port. For iSCSI,
this relationship is a session, defined as a relationship between
an iSCSI Initiator's end of the session (SCSI Initiator Port) and
the iSCSI Target's Portal Group. The I_T nexus can be identified
by the conjunction of the SCSI port names; that is, the I_T nexus
identifier is the tuple (iSCSI Initiator Name + ',i,'+ ISID, iSCSI
Target Name + ',t,'+ Portal Group Tag).
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- I_T_L nexus: An I_T_L nexus is a SCSI concept, and is defined as
the relationship between a SCSI Initiator Port, a SCSI Target
Port, and a Logical Unit (LU).
- NAA: Network Address Authority, a naming format defined by the
INCITS T11 Fibre Channel protocols [FC-FS3].
- Network Entity: The Network Entity represents a device or
gateway that is accessible from the IP network. A Network Entity
must have one or more Network Portals, each of which can be used
to gain access to the IP network by some iSCSI Nodes contained in
that Network Entity.
- Network Portal: The Network Portal is a component of a Network
Entity that has a TCP/IP network address and that may be used by
an iSCSI Node within that Network Entity for the connection(s)
within one of its iSCSI sessions. A Network Portal in an initiator
is identified by its IP address. A Network Portal in a target is
identified by its IP address and its listening TCP port.
- Originator: In a negotiation or exchange, the party that
initiates the negotiation or exchange.
- PDU (Protocol Data Unit): The initiator and target divide their
communications into messages. The term "iSCSI protocol data unit"
(iSCSI PDU) is used for these messages.
- Portal Groups: iSCSI supports multiple connections within the
same session; some implementations will have the ability to
combine connections in a session across multiple Network Portals.
A Portal Group defines a set of Network Portals within an iSCSI
Network Entity that collectively supports the capability of
coordinating a session with connections spanning these portals.
Not all Network Portals within a Portal Group need participate in
every session connected through that Portal Group. One or more
Portal Groups may provide access to an iSCSI Node. Each Network
Portal, as utilized by a given iSCSI Node, belongs to exactly one
portal group within that node.
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- Portal Group Tag: This 16-bit quantity identifies a Portal Group
within an iSCSI Node. All Network Portals with the same portal
group tag in the context of a given iSCSI Node are in the same
Portal Group.
- Recovery R2T: An R2T generated by a target upon detecting the
loss of one or more Data-Out PDUs through one of the following
means: a digest error, a sequence error, or a sequence reception
timeout. A recovery R2T carries the next unused R2TSN, but
requests all or part of the data burst that an earlier R2T (with a
lower R2TSN) had already requested.
- Responder: In a negotiation or exchange, the party that responds
to the originator of the negotiation or exchange.
- SAS: Serial Attached SCSI. The Serial Attached SCSI (SAS)
standard contains both a physical layer compatible with Serial
ATA, and protocols for transporting SCSI commands to SAS devices
and ATA commands to SATA devices [SAS].
- SCSI Device: This is the SAM2 term for an entity that contains
one or more SCSI ports that are connected to a service delivery
subsystem and supports a SCSI application protocol. For example, a
SCSI Initiator Device contains one or more SCSI Initiator Ports
and zero or more application clients. A Target Device contains one
or more SCSI Target Ports and one or more device servers and
associated logical units. For iSCSI, the SCSI Device is the
component within an iSCSI Node that provides the SCSI
functionality. As such, there can be, at most, one SCSI Device
within a given iSCSI Node. Access to the SCSI Device can only be
achieved in an iSCSI normal operational session. The SCSI Device
Name is defined to be the iSCSI Name of the node.
- SCSI Layer: This builds/receives SCSI CDBs (Command Descriptor
Blocks) and relays/receives them with the remaining command
execute [SAM2] parameters to/from the iSCSI Layer.
- Session: The group of TCP connections that link an initiator
with a target form a session (loosely equivalent to a SCSI I-T
nexus). TCP connections can be added and removed from a session.
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Across all connections within a session, an initiator sees one and
the same target.
- SCSI Port: This is the SAM2 term for an entity in a SCSI Device
that provides the SCSI functionality to interface with a service
delivery subsystem. For iSCSI, the definition of the SCSI
Initiator Port and the SCSI Target Port are different.
- SCSI Initiator Port: This maps to the endpoint of an iSCSI
normal operational session. An iSCSI normal operational session is
negotiated through the login process between an iSCSI initiator
node and an iSCSI target node. At successful completion of this
process, a SCSI Initiator Port is created within the SCSI
Initiator Device. The SCSI Initiator Port Name and SCSI Initiator
Port Identifier are both defined to be the iSCSI Initiator Name
together with (a) a label that identifies it as an initiator port
name/identifier and (b) the ISID portion of the session
identifier.
- SCSI Port Name: A name consisting of UTF-8 [RFC3629] encoding of
Unicode [UNICODE] characters and includes the iSCSI Name + 'i' or
't' + ISID or Portal Group Tag.
- SCSI-Presented Data Transfer Length (SPDTL): SPDTL is the
aggregate data length of the data that the SCSI layer logically
"presents" to the iSCSI layer for a Data-In or Data-Out transfer
in the context of a SCSI task. For a bidirectional task, there are
two SPDTL values -- one for Data-In and one for Data-Out. Note
that the notion of "presenting" includes immediate data per the
data transfer model in [SAM2], and excludes overlapping data
transfers, if any, requested by the SCSI layer.
- SCSI Target Port: This maps to an iSCSI Target Portal Group.
- SCSI Target Port Name and SCSI Target Port Identifier: These are
both defined to be the iSCSI Target Name together with (a) a label
that identifies it as a target port name/identifier and (b) the
portal group tag.
- SSID (Session ID): A session between an iSCSI initiator and an
iSCSI target is defined by a session ID that is a tuple composed
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of an initiator part (ISID) and a target part (Target Portal Group
Tag). The ISID is explicitly specified by the initiator at session
establishment. The Target Portal Group Tag is implied by the
initiator through the selection of the TCP endpoint at connection
establishment. The TargetPortalGroupTag key must also be returned
by the target as a confimation during connection establishment.
- T10: A technical committee within INCITS that develops standards
and technical reports on I/O interfaces, particularly the series
of SCSI (Small Computer Systems Interface) standards. See
http://www.t10.org.
- T11: A technical committee within INCITS responsible for
standards development in the areas of Intelligent Peripheral
Interface (IPI), High-Performance Parallel Interface (HIPPI) and
Fibre Channel (FC). See http://www.t11.org.
- Target Portal Group Tag: A numerical identifier (16-bit) for an
iSCSI Target Portal Group.
-Target Transfer Tag (TTT): An iSCSI protocol field used in a few
iSCSI PDUs (e.g. R2T, NOP-In) which is always sent from the target
to the initiator first and then quoted as a reference in
initiator-sent PDUs back to the target relating to the same
task/exchange. So effectively, TTT acts as an opaque handle to an
existing task/exchange to help target associate the incoming PDUs
from the initiator to the proper execution context.
- Third-party: A term used in this document as a qualifier to
nexus objects (I_T or I_T_L) and iSCSI sessions, to indicate that
these objects and sessions reap the side effects of actions that
take place in the context of a separate iSCSI session. One
example of a third-party session is an iSCSI session discovering
that its I_T_L nexus to an LU got reset due to an LU Reset
operation orchestrated via a separate I_T nexus.
- TSIH (Target Session Identifying Handle): A target assigned tag
for a session with a specific named initiator. The target
generates it during session establishment. Other than defining it
as a 16 bit binary string, its internal format and content are not
defined by this protocol but for the all 0 value that is reserved
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and used by the initiator to indicate a new session. It is given
to the target during additional connection establishment for the
same session.
2.3. Summary of Changes
1) Consolidated RFCs 3720, 3980, 4850 and 5048, and made the
necessary editorial changes
2) iSCSIProtocolLevel is specified as "1" in Section 13.24, and
added a related normative reference to [iSCSI-SAM] draft
3) Markers and related keys were removed
4) SPKM authentication and related keys were removed
5) Added a new Section 13.25 on responding to obsoleted keys
6) Have explicitly allowed initiator+target implementations
throughout the text
7) Clarified in Section 4.2.7 that implementations SHOULD NOT
rely on SLP-based discovery
8) Added UML diagrams and related conventions in Section 3
9) FastAbort implementation is made a "SHOULD" requirement in
Section 4.2.3.4 from the previous "MUST" requirement.
10) Required in Section 4.2.7.1 that iSCSI Target Name must be
the same as iSCSI Initiator Name for SCSI (composite) devices
with both roles
11) Changed the "MUST NOT" to "should avoid" in Section 4.2.7.2
regarding usage of characters such as punctuation marks in
iSCSI Names.
12) Updated Section 9.3 to require the following: MUST implement
IPsec, 2400-series RFCs (IPsec v2, IKEv1) and SHOULD implement
IPsec, 4300-series RFCs (IPsec v3, IKEv2).
13) Clarified in Section 10.2 that ACA is a SHOULD requirement
only for iSCSI targets
14) Prohibited usage of X# name prefix for new public keys in
Section 6.2
15) Prohibited usage of Y# name prefix for new digest extensions
in Section 13.1, and Z# name prefix for new authentication
method extensions in Section 12.1
16) Added a SHOULD requirement in Section 6.2 that initiators and
targets support at least six (6) exchanges during text
negotiation.
17) Added a clarification that Appendix.C is normative.
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18) Added a normative requirement on [IPSEC-IPS] draft, and made
a few related changes in Section 9.3 to align the text in this
document with that of [IPSEC-IPS]
19) Added a new Section 9.2.3 covering Kerberos authentication
considerations
2.4. Conventions
In examples, "I->" and "T->" show iSCSI PDUs sent by the initiator
and target respectively.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL"
in this document are to be interpreted as described in RFC 2119
[RFC2119].
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3. UML Conventions
3.1. UML Conventions Overview
The SCSI Architecture Model (SAM) uses class diagrams and object
diagrams with notation that is based on the Unified Modeling
Language [UML]. Therefore, this document also uses UML to model
the relationships for SCSI and iSCSI objects.
A treatise on the graphical notation used in UML is beyond the
scope of this document. However, given the use of ASCII drawing
for UML static class diagrams, a description of the notational
conventions used in this document is included in the remainder of
this Section.
3.2. Multiplicity Notion
Not specified The number of instances of an attribute is not
specified.
1 One instance of the class or attribute exists.
0..* Zero or more instances of the class or attribute exist.
1..* One or more instances of the class or attribute exist.
0..1 Zero or one instance of the class or attribute exists.
n..m n to m instances of the class or attribute exist
(e.g., 2..8).
x, n..m Multiple disjoint instances of the class or
attribute exist (e.g., 2, 8..15).
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3.3. Class Diagram Conventions
+--------------+ +--------------+ +--------------+
| Class Name | | Class Name | | Class Name |
+--------------+ +--------------+ +--------------+
| | | |
+--------------+ +--------------+
| |
+--------------+
The previous three diagrams are examples of a class with no
attributes and with no operations.
+-------------------+ +-------------------+
| Class Name | | Class Name |
+-------------------+ +-------------------+
| attribute 01[1] | | attribute 01[1] |
| attribute 02[1] | | attribute 02[1] |
+-------------------+ +-------------------+
| |
+-------------------+
The preceding two diagrams are examples of a class with attributes
and with no operations.
+------------------------+
| Class Name |
+------------------------+
| attribute 01[1..*] |
| attribute 02[1] |
+------------------------+
| operation 01() |
| operation 02() |
+------------------------+
The preceding diagram is an example of a class with attributes
that have a specified multiplicity and operations.
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3.4. Class Diagram Notation for Associations
+-----------------+
| Class A |
+-----------------+ association_name +-----------------+
| attribute 01[1] |<------------------>| Class B |
| attribute 02[1] | 1..* 0..1 +-----------------+
+-----------------+ | attribute 03[1] |
| operation 1() | +-----------------+
+-----------------+
The preceding diagram is an example where Class A knows about
Class B (i.e., read as "Class A association_name ClassB") and
Class B knows about Class A (i.e., read as "Class B
association_name Class A"). The use of association_name is
optional. The multiplicity notation (1..* and 0..1) indicates the
number of instances of the object.
+--------------------+
| Class A |
+--------------------+ +--------------------+
| attribute 01[1] |<-------------| Class B |
| attribute 02[1] | 1 0..1 +--------------------+
+--------------------+ | attribute 03[1] |
| operation 1() | +--------------------+
+--------------------+
The preceding diagram is an example where Class B knows about
Class A (i.e., read as "Class B knows about Class A") but Class A
does not know about Class B.
+----------------------+
| Class A |
+----------------------+ +--------------------+
| attribute 01[1] |----------->| Class B |
| attribute 02[1] | 0..* 1 +--------------------+
+----------------------+ | attribute 03[1] |
| operation 1() | +--------------------+
+----------------------+
The preceding diagram is an example where Class A knows about
Class B (i.e., read as "Class A knows about Class B") but Class B
does not know about Class A.
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3.5. Class Diagram Notation for Aggregations
+---------------+ +--------------+
| Class whole |o------------| Class part |
+---------------+ +--------------+
The preceding diagram is an example where Class whole is an
aggregate that contains Class part and where Class part may
continue to exist even if Class whole is removed (i.e., read as
"the whole contains the part").
+---------------+ +--------------+
| Class whole |@------------| Class part |
+---------------+ +--------------+
The preceding diagram is an example where Class whole is an
aggregate that contains Class part where Class part only belongs
to one Class whole, and the Class part does not continue to exist
if the Class whole is removed (i.e., read as "the whole contains
the part").
+-------------+
| |
+-------------+
| |
+ =(a)= +
| |
The preceding diagram is an example where there is a constraint
between the associations where the (a) footnote describes the
constraint.
3.6. Class Diagram Notation for Generalizations
+---------------+
| Superclass |
+-------^-------+
/_\
|
+---------------+
| Subclass |
+---------------+
The preceding diagram is an example where the subclass is a kind
of superclass. A subclass shares all the attributes and
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operations of the superclass (i.e., the subclass inherits from the
superclass).
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4. Overview
4.1. SCSI Concepts
The SCSI Architecture Model-2 [SAM2] describes in detail the
architecture of the SCSI family of I/O protocols. This Section
provides a brief background of the SCSI architecture and is
intended to familiarize readers with its terminology.
At the highest level, SCSI is a family of interfaces for
requesting services from I/O devices, including hard drives, tape
drives, CD and DVD drives, printers, and scanners. In SCSI
terminology, an individual I/O device is called a "logical unit"
(LU).
SCSI is a client-server architecture. Clients of a SCSI interface
are called "initiators". Initiators issue SCSI "commands" to
request services from components, logical units, of a server known
as a "target". The "device server" on the logical unit accepts
SCSI commands and processes them.
A "SCSI transport" maps the client-server SCSI protocol to a
specific interconnect. Initiator is one endpoint of a SCSI
transport. The "target" is the other endpoint. A target can
contain multiple Logical Units (LUs). Each Logical Unit has an
address within a target called a Logical Unit Number (LUN).
A SCSI task is a SCSI command or possibly a linked set of SCSI
commands. Some LUs support multiple pending (queued) tasks, but
the queue of tasks is managed by the logical unit. The target uses
an initiator provided "task tag" to distinguish between tasks.
Only one command in a task can be outstanding at any given time.
Each SCSI command results in an optional data phase and a required
response phase. In the data phase, information can travel from the
initiator to target (e.g., WRITE), target to initiator (e.g.,
READ), or in both directions. In the response phase, the target
returns the final status of the operation, including any errors.
Command Descriptor Blocks (CDB) are the data structures used to
contain the command parameters that an initiator sends to a
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target. The CDB content and structure is defined by [SAM2] and
device-type specific SCSI standards.
4.2. iSCSI Concepts and Functional Overview
The iSCSI protocol is a mapping of the SCSI command, event and
task management model (see [SAM2]) over the TCP protocol. SCSI
commands are carried by iSCSI requests and SCSI responses and
status are carried by iSCSI responses. iSCSI also uses the request
response mechanism for iSCSI protocol mechanisms.
For the remainder of this document, the terms "initiator" and
"target" refer to "iSCSI initiator node" and "iSCSI target node",
respectively (see iSCSI) unless otherwise qualified.
As its title suggests, Section 4 presents an overview of the iSCSI
concepts, and later Sections in the rest of the specification
contain the normative requirements - in many cases covering the
same concepts discussed in Section 4. Such normative requirements
text overrides the overview text in Section 4 if there is a
disagreement between the two.
In keeping with similar protocols, the initiator and target divide
their communications into messages. This document uses the term
"iSCSI protocol data unit" (iSCSI PDU) for these messages.
For performance reasons, iSCSI allows a "phase-collapse". A
command and its associated data may be shipped together from
initiator to target, and data and responses may be shipped
together from targets.
The iSCSI transfer direction is defined with respect to the
initiator. Outbound or outgoing transfers are transfers from an
initiator to a target, while inbound or incoming transfers are
from a target to an initiator.
An iSCSI task is an iSCSI request for which a response is
expected.
In this document "iSCSI request", "iSCSI command", request, or
(unqualified) command have the same meaning. Also, unless
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otherwise specified, status, response, or numbered response have
the same meaning.
4.2.1. Layers and Sessions
The following conceptual layering model is used to specify
initiator and target actions and the way in which they relate to
transmitted and received Protocol Data Units:
- The SCSI layer builds/receives SCSI CDBs (Command Descriptor
Blocks) and passes/receives them with the remaining command
execute parameters ([SAM2]) to/from
- the iSCSI layer that builds/receives iSCSI PDUs and
relays/receives them to/from one or more TCP connections;
the group of connections form an initiator-target "session".
Communication between the initiator and target occurs over one or
more TCP connections. The TCP connections carry control messages,
SCSI commands, parameters, and data within iSCSI Protocol Data
Units (iSCSI PDUs). The group of TCP connections that link an
initiator with a target form a session (equivalent to a SCSI I_T
nexus, see Section 4.4.2). A session is defined by a session ID
that is composed of an initiator part and a target part. TCP
connections can be added and removed from a session. Each
connection within a session is identified by a connection ID
(CID).
Across all connections within a session, an initiator sees one
"target image". All target identifying elements, such as LUN, are
the same. A target also sees one "initiator image" across all
connections within a session. Initiator-identifying elements, such
as the Initiator Task Tag, are global across the session
regardless of the connection on which they are sent or received.
iSCSI targets and initiators MUST support at least one TCP
connection and MAY support several connections in a session. For
error recovery purposes, targets and initiators that support a
single active connection in a session SHOULD support two
connections during recovery.
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4.2.2. Ordering and iSCSI Numbering
iSCSI uses Command and Status numbering schemes and a Data
sequencing scheme.
Command numbering is session-wide and is used for ordered command
delivery over multiple connections. It can also be used as a
mechanism for command flow control over a session.
Status numbering is per connection and is used to enable missing
status detection and recovery in the presence of transient or
permanent communication errors.
Data sequencing is per command or part of a command (R2T-triggered
sequence) and is used to detect missing data and/or R2T PDUs due
to header digest errors.
Typically, fields in the iSCSI PDUs communicate the Sequence
Numbers between the initiator and target. During periods when
traffic on a connection is unidirectional, iSCSI NOP-Out/In PDUs
may be utilized to synchronize the command and status ordering
counters of the target and initiator.
The iSCSI session abstraction is equivalent to the SCSI I_T nexus,
and the iSCSI session provides an ordered command delivery from
the SCSI initiator to the SCSI target. For detailed design
considerations that led to the iSCSI session model as it is
defined here and how it relates the SCSI command ordering features
defined in SCSI specifications to the iSCSI concepts see
[RFC3783].
4.2.2.1. Command Numbering and Acknowledging
iSCSI performs ordered command delivery within a session. All
commands (initiator-to-target PDUs) in transit from the initiator
to the target are numbered.
iSCSI considers a task to be instantiated on the target in
response to every request issued by the initiator. A set of task
management operations including abort and reassign (see Section
11.5) may be performed on an iSCSI task - however an abort
operation cannot be performed on a task management operation, and
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usage of reassign operation has certain constraints. See Section
11.5.1 for the details.
Some iSCSI tasks are SCSI tasks, and many SCSI activities are
related to a SCSI task ([SAM2]). In all cases, the task is
identified by the Initiator Task Tag for the life of the task.
The command number is carried by the iSCSI PDU as CmdSN (Command-
Sequence-Number). The numbering is session-wide. Outgoing iSCSI
PDUs carry this number. The iSCSI initiator allocates CmdSNs with
a 32-bit unsigned counter (modulo 2**32). Comparisons and
arithmetic on CmdSN use Serial Number Arithmetic as defined in
[RFC1982] where SERIAL_BITS = 32.
Commands meant for immediate delivery are marked with an immediate
delivery flag; they MUST also carry the current CmdSN. CmdSN MUST
NOT advance after a command marked for immediate delivery is sent.
Command numbering starts with the first login request on the first
connection of a session (the leading login on the leading
connection) and CmdSN MUST be incremented by 1, in a Serial Number
Arithmetic sense as defined in [RFC1982], for every non-immediate
command issued afterwards.
If immediate delivery is used with task management commands, these
commands may reach the target before the tasks on which they are
supposed to act. However their CmdSN serves as a marker of their
position in the stream of commands. The initiator and target MUST
ensure that the SCSI task management functions specified in [SAM2]
act in accordance with the [SAM2] specification. For example, both
commands and responses appear as if delivered in order. Whenever
CmdSN for an outgoing PDU is not specified by an explicit rule,
CmdSN will carry the current value of the local CmdSN variable
(see later in this Section).
The means by which an implementation decides to mark a PDU for
immediate delivery or by which iSCSI decides by itself to mark a
PDU for immediate delivery are beyond the scope of this document.
The number of commands used for immediate delivery is not limited
and their delivery to execution is not acknowledged through the
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numbering scheme. An iSCSI target MAY reject immediate commands,
e.g., due to lack of resources to accommodate additional commands.
An iSCSI target MUST be able to handle at least one immediate task
management command and one immediate non-task-management iSCSI
command per connection at any time.
In this document, delivery for execution means delivery to the
SCSI execution engine or an iSCSI protocol specific execution
engine (e.g., for text requests with public or private extension
keys involving an execution component). With the exception of the
commands marked for immediate delivery, the iSCSI target layer
MUST deliver the commands for execution in the order specified by
CmdSN. Commands marked for immediate delivery may be delivered by
the iSCSI target layer for execution as soon as detected. iSCSI
may avoid delivering some commands to the SCSI target layer if
required by a prior SCSI or iSCSI action (e.g., CLEAR TASK SET
Task Management request received before all the commands on which
it was supposed to act).
On any connection, the iSCSI initiator MUST send the commands in
increasing order of CmdSN, except for commands that are
retransmitted due to digest error recovery and connection
recovery.
For the numbering mechanism, the initiator and target maintain the
following three variables for each session:
- CmdSN - the current command Sequence Number, advanced by 1
on each command shipped except for commands marked for
immediate delivery (see Section 4.2.2.1). CmdSN always
contains the number to be assigned to the next Command PDU.
- ExpCmdSN - the next expected command by the target. The
target acknowledges all commands up to, but not including,
this number. The initiator treats all commands with CmdSN
less than ExpCmdSN as acknowledged. The target iSCSI layer
sets the ExpCmdSN to the largest non-immediate CmdSN that it
can deliver for execution "plus 1" per [RFC1982]. There
MUST NOT be any holes in the acknowledged CmdSN sequence.
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- MaxCmdSN - the maximum number to be shipped. The queuing
capacity of the receiving iSCSI layer is MaxCmdSN - ExpCmdSN
+ 1.
The initiator's ExpCmdSN and MaxCmdSN are derived from target-to-
initiator PDU fields. Comparisons and arithmetic on ExpCmdSN and
MaxCmdSN MUST use Serial Number Arithmetic as defined in [RFC1982]
where SERIAL_BITS = 32.
The target MUST NOT transmit a MaxCmdSN that is less than
ExpCmdSN-1. For non-immediate commands, the CmdSN field can take
any value from ExpCmdSN to MaxCmdSN inclusive. The target MUST
silently ignore any non-immediate command outside of this range or
non-immediate duplicates within the range. The CmdSN carried by
immediate commands may lie outside the ExpCmdSN to MaxCmdSN range.
For example, if the initiator has previously sent a non-immediate
command carrying the CmdSN equal to MaxCmdSN, the target window is
closed. For group task management commands issued as immediate
commands, CmdSN indicates the scope of the group action (e.g., on
ABORT TASK SET indicates which commands are to be aborted).
MaxCmdSN and ExpCmdSN fields are processed by the initiator as
follows:
-If the PDU MaxCmdSN is less than the PDU ExpCmdSN-1 (in
Serial Arithmetic Sense), they are both ignored.
-If the PDU MaxCmdSN is greater than the local MaxCmdSN (in
Serial Arithmetic Sense), it updates the local MaxCmdSN;
otherwise, it is ignored.
-If the PDU ExpCmdSN is greater than the local ExpCmdSN (in
Serial Arithmetic Sense), it updates the local ExpCmdSN;
otherwise, it is ignored.
This sequence is required because updates may arrive out of order
(e.g., the updates are sent on different TCP connections).
iSCSI initiators and targets MUST support the command numbering
scheme.
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A numbered iSCSI request will not change its allocated CmdSN,
regardless of the number of times and circumstances in which it is
reissued (see Section 7.2.1). At the target, CmdSN is only
relevant while the command has not created any state related to
its execution (execution state); afterwards, CmdSN becomes
irrelevant. Testing for the execution state (represented by
identifying the Initiator Task Tag) MUST precede any other action
at the target. If no execution state is found, it is followed by
ordering and delivery. If an execution state is found, it is
followed by delivery if it has not already been delivered.
If an initiator issues a command retry for a command with CmdSN R
on a connection when the session CmdSN value is Q, it MUST NOT
advance the CmdSN past R + 2**31 -1 unless the connection is no
longer operational (i.e., it has returned to the FREE state, see
Section 8.1.3), the connection has been reinstated (see Section
6.3.4), or a non-immediate command with CmdSN equal or greater
than Q was issued subsequent to the command retry on the same
connection and the reception of that command is acknowledged by
the target (see Section 10.4).
A target command response or Data-in PDU with status MUST NOT
precede the command acknowledgement. However, the acknowledgement
MAY be included in the response or the Data-in PDU.
4.2.2.2. Response/Status Numbering and Acknowledging
Responses in transit from the target to the initiator are
numbered. The StatSN (Status Sequence Number) is used for this
purpose. StatSN is a counter maintained per connection. ExpStatSN
is used by the initiator to acknowledge status. The status
sequence number space is 32-bit unsigned-integers and the
arithmetic operations are the regular mod(2**32) arithmetic.
Status numbering starts with the Login response to the first Login
request of the connection. The Login response includes an initial
value for status numbering (any initial value is valid).
To enable command recovery, the target MAY maintain enough state
information for data and status recovery after a connection
failure. A target doing so can safely discard all of the state
information maintained for recovery of a command after the
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delivery of the status for the command (numbered StatSN) is
acknowledged through ExpStatSN.
A large absolute difference between StatSN and ExpStatSN may
indicate a failed connection. Initiators MUST undertake recovery
actions if the difference is greater than an implementation
defined constant that MUST NOT exceed 2**31-1.
Initiators and Targets MUST support the response-numbering scheme.
4.2.2.3. Response Ordering
4.2.2.3.1. Need for Response Ordering
Whenever an iSCSI session is composed of multiple connections, the
Response PDUs (task responses or TMF responses) originating in
the target SCSI layer are distributed onto the multiple
connections by the target iSCSI layer according to iSCSI
connection allegiance rules. This process generally may not
preserve the ordering of the responses by the time they are
delivered to the initiator SCSI layer.
Since ordering is not expected across SCSI responses anyway, this
approach works fine in the general case. However, to address the
special cases where some ordering is desired by the SCSI layer, we
introduce the notion of a "Response Fence": Response Fence is
logically the attribute/property of a SCSI response message handed
off to a target iSCSI layer which indicates that there are special
SCSI-level ordering considerations associated with this particular
response message - whenever Response Fence is set or required on a
SCSI response message, we define the semantics in 4.2.2.3.2 with
respect to target iSCSI layer's handling of such SCSI response
messages.
4.2.2.3.2. Response Ordering Model Description
The target SCSI protocol layer hands off the SCSI response
messages to the target iSCSI layer by invoking the "Send Command
Complete" protocol data service ([SAM2], clause 5.4.2) and "Task
Management Function Executed" ([SAM2], clause 6.9) service. On
receiving the SCSI response message, the iSCSI layer exhibits the
Response Fence behavior for certain SCSI response messages
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(Section 4.2.2.3.4 describes the specific instances where the
semantics must be realized).
Whenever the Response Fence behavior is required for a SCSI
response message, the target iSCSI layer MUST ensure that the
following conditions are met in delivering the response message to
the initiator iSCSI layer:
- Response with Response Fence MUST be delivered
chronologically after all the "preceding" responses on the
I_T_L nexus, if the preceding responses are delivered at
all, to the initiator iSCSI layer.
- Response with Response Fence MUST be delivered
chronologically prior to all the "following" responses on
the I_T_L nexus.
The "preceding" and "following" notions refer to the order of
handoff of a response message from the target SCSI protocol layer
to the target iSCSI layer.
4.2.2.3.3. iSCSI Semantics with the Interface Model
Whenever the TaskReporting key (Section 13.23) is negotiated to
ResponseFence or FastAbort for an iSCSI session and the Response
Fence behavior is required for a SCSI response message, the target
iSCSI layer MUST perform the actions described in this Section for
that session.
a) If it is a single-connection session, no special
processing is required. The standard SCSI Response PDU
build and dispatch process happens.
b) If it is a multi-connection session, the target iSCSI
layer takes note of the last-sent and unacknowledged
StatSN on each of the connections in the iSCSI session,
and waits for an acknowledgement (NOP-In PDUs MAY be used
to solicit acknowledgements as needed in order to
accelerate this process) of each such StatSN to clear the
fence. The SCSI response requiring Response Fence
behavior MUST NOT be sent to the initiator before
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acknowledgements are received for each of the
unacknowledged StatSNs.
c) The target iSCSI layer must wait for an acknowledgement
of the SCSI Response PDU that carried the SCSI response
requiring the Response Fence behavior. The fence MUST be
considered cleared only after receiving the
acknowledgement.
d) All further status processing for the LU is resumed only
after clearing the fence. If any new responses for the
I_T_L nexus are received from the SCSI layer before the
fence is cleared, those Response PDUs MUST be held and
queued at the iSCSI layer until the fence is cleared.
4.2.2.3.4. Current List of Fenced Response Use Cases
This Section lists the situations in which fenced response
behavior is REQUIRED in iSCSI target implementations. Note that
the following list is an exhaustive enumeration as currently
identified - it is expected that as SCSI protocol specifications
evolve, the specifications will specify when response fencing is
required on a case-by-case basis.
Whenever the TaskReporting key (Section 13.23) is negotiated to
ResponseFence or FastAbort for an iSCSI session, the target iSCSI
layer MUST assume that the Response Fence is required for the
following SCSI completion messages:
1. The first completion message carrying the UA after the
multi-task abort on issuing and third-party sessions. See
Section 4.2.3.2 for related TMF discussion.
2. The TMF Response carrying the multi-task TMF Response on
the issuing session.
3. The completion message indicating ACA establishment on the
issuing session.
4. The first completion message carrying the ACA ACTIVE status
after ACA establishment on issuing and third-party
sessions.
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5. The TMF Response carrying the Clear ACA response on the
issuing session.
6. The response to a PERSISTENT RESERVE OUT/PREEMPT AND ABORT
command.
Note:
- Due to the absence of ACA-related fencing requirements in
[RFC3720], initiator implementations SHOULD NOT use ACA on
multi-connection iSCSI sessions with targets complying only
with [RFC3720]. This can be determined via TaskReporting key
(Section 13.23) negotiation - when the negotiation results
in either "RFC3720" or "NotUnderstood".
- Initiators that want to employ ACA on multi-connection iSCSI
sessions SHOULD first assess response-fencing behavior via
negotiating for "ResponseFence" or "FastAbort" value for the
TaskReporting (Section 13.23) key.
4.2.2.4. Data Sequencing
Data and R2T PDUs transferred as part of some command execution
MUST be sequenced. The DataSN field is used for data sequencing.
For input (read) data PDUs, DataSN starts with 0 for the first
data PDU of an input command and advances by 1 for each subsequent
data PDU. For output data PDUs, DataSN starts with 0 for the first
data PDU of a sequence (the initial unsolicited sequence or any
data PDU sequence issued to satisfy an R2T) and advances by 1 for
each subsequent data PDU. R2Ts are also sequenced per command. For
example, the first R2T has an R2TSN of 0 and advances by 1 for
each subsequent R2T. For bidirectional commands, the target uses
the DataSN/R2TSN to sequence Data-In and R2T PDUs in one
continuous sequence (undifferentiated). Unlike command and status,
data PDUs and R2Ts are not acknowledged by a field in regular
outgoing PDUs. Data-In PDUs can be acknowledged on demand by a
special form of the SNACK PDU. Data and R2T PDUs are implicitly
acknowledged by status for the command. The DataSN/R2TSN field
enables the initiator to detect missing data or R2T PDUs.
For any read or bidirectional command, a target MUST issue less
than 2**32 combined R2T and Data-In PDUs. Any output data sequence
MUST contain less than 2**32 Data-Out PDUs.
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4.2.3. iSCSI Task Management
4.2.3.1. Task Management Overview
iSCSI task management features allow an initiator to control the
active iSCSI tasks on an operational iSCSI session that it has
with an iSCSI target. Section 11.5 defines the task management
function types that this specification defines - ABORT TASK, ABORT
TASK SET, CLEAR ACA, CLEAR TASK SET, LOGICAL UNIT RESET, TARGET
WARM RESET, TARGET COLD RESET, and TASK REASSIGN.
Out of these function types, ABORT TASK and TASK REASSIGN
functions manage a single active task, whereas ABORT TASK SET,
CLEAR TASK SET, LOGICAL UNIT RESET, TARGET WARM RESET and TARGET
COLD RESET functions can each potentially affect multiple active
tasks.
4.2.3.2. Notion of Affected Tasks
This Section defines the notion of "affected tasks" in multi-task
abort scenarios. Scope definitions in this Section apply to both
the Standard Multi-task Abort semantics (Section 4.2.3.3) and the
FastAbort Multi-task Abort semantics behavior (Section 4.2.3.4).
ABORT TASK SET: All outstanding tasks for the I_T_L nexus
identified by the LUN field in the ABORT TASK SET TMF Request PDU
(Section 11.5).
CLEAR TASK SET: All outstanding tasks in the task set for the LU
identified by the LUN field in the CLEAR TASK SET TMF Request PDU.
See [SPC3] for the definition of a "task set".
LOGICAL UNIT RESET: All outstanding tasks from all initiators for
the LU identified by the LUN field in the LOGICAL UNIT RESET
Request PDU.
TARGET WARM RESET/TARGET COLD RESET: All outstanding tasks from
all initiators across all LUs to which the TMF-issuing session has
access on the SCSI target device hosting the iSCSI session.
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Usage: An "ABORT TASK SET TMF Request PDU" in the preceding text
is an iSCSI TMF Request PDU with the "Function" field set to
"ABORT TASK SET" as defined in Section 11.5. Similar usage is
employed for other scope descriptions.
4.2.3.3. Standard Multi-task Abort Semantics
All iSCSI implementations MUST support the protocol behavior
defined in this Section as the default behavior. The execution of
ABORT TASK SET, CLEAR TASK SET, LOGICAL UNIT RESET, TARGET WARM
RESET, and TARGET COLD RESET TMF Requests consists of the
following sequence of actions in the specified order on the
specified party.
The initiator iSCSI layer:
a. MUST continue to respond to each TTT received for the
affected tasks.
b. SHOULD process any responses received for affected tasks in
the normal fashion. This is acceptable because the
responses are guaranteed to have been sent prior to the TMF
response.
c. SHOULD receive the TMF Response concluding all the tasks in
the set of affected tasks unless the initiator has done
something (e.g., LU reset, connection drop) that may
prevent the TMF Response from being sent or received. The
initiator MUST thus conclude all affected tasks as part of
this step in either case, and MUST discard any TMF Response
received after the affected tasks are concluded.
The target iSCSI layer:
a. MUST wait for responses on currently valid target-transfer
tags of the affected tasks from the issuing initiator. MAY
wait for responses on currently valid target-transfer tags
of the affected tasks from third-party initiators.
b. MUST wait (concurrent with the wait in Step a) for all
commands of the affected tasks to be received based on the
CmdSN ordering. SHOULD NOT wait for new commands on third-
party affected sessions -- only the instantiated tasks have
to be considered for the purpose of determining the
affected tasks. In the case of target-scoped requests
(i.e., TARGET WARM RESET and TARGET COLD RESET), all of the
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commands that are not yet received on the issuing session
in the command stream however can be considered to have
been received with no command waiting period -- i.e., the
entire CmdSN space up to the CmdSN of the task management
function can be "plugged".
c. MUST propagate the TMF request to and receive the response
from the target SCSI layer.
d. MUST provide the Response Fence behavior for the TMF
Response on the issuing session as specified in Section
4.2.2.3.2.
e. MUST provide the Response Fence behavior on the first post-
TMF Response on third-party sessions as specified in
Section 4.2.2.3.3. If some tasks originate from non-iSCSI
I_T_L nexuses, then the means by which the target ensures
that all affected tasks have returned their status to the
initiator are defined by the specific non-iSCSI transport
protocol(s).
Technically, the TMF servicing is complete in Step d. Data
transfers corresponding to terminated tasks may however still be
in progress on third-party iSCSI sessions even at the end of Step
e. The TMF Response MUST NOT be sent by the target iSCSI layer
before the end of Step d, and MAY be sent at the end of Step d
despite these outstanding data transfers until after Step e.
4.2.3.4. FastAbort Multi-task Abort Semantics
Protocol behavior defined in this Section SHOULD be implemented by
all iSCSI implementations complying with this document, noting
that some steps below may not be compatible with [RFC3720]
semantics. However, protocol behavior defined in this Section MUST
be exhibited by iSCSI implementations on an iSCSI session when
they negotiate the TaskReporting (Section 13.23) key to
"FastAbort" on that session. The execution of ABORT TASK SET,
CLEAR TASK SET, LOGICAL UNIT RESET, TARGET WARM RESET, and TARGET
COLD RESET TMF Requests consists of the following sequence of
actions in the specified order on the specified party.
The initiator iSCSI layer:
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a. MUST NOT send any more Data-Out PDUs for affected tasks on
the issuing connection of the issuing iSCSI session once
the TMF is sent to the target.
b. SHOULD process any responses received for affected tasks in
the normal fashion. This is acceptable because the
responses are guaranteed to have been sent prior to the TMF
response.
c. MUST respond to each Async Message PDU with FAST_ABORT
AsyncEvent as defined in Section 11.9.
d. MUST treat the TMF response as terminating all affected
tasks for which responses have not been received, and MUST
discard any responses for affected tasks received after the
TMF response is passed to the SCSI layer (although the
semantics defined in this Section ensure that such an out-
of-order scenario will never happen with a compliant target
implementation).
The target iSCSI layer:
a. MUST wait for all commands of the affected tasks to be
received based on the CmdSN ordering on the issuing
session. SHOULD NOT wait for new commands on third-party
affected sessions - only the instantiated tasks have to be
considered for the purpose of determining the affected
tasks. In the case of target-scoped requests (i.e., TARGET
WARM RESET and TARGET COLD RESET), all the commands that
are not yet received on the issuing session in the command
stream can be considered to have been received with no
command waiting period -- i.e., the entire CmdSN space up
to the CmdSN of the task management function can be
"plugged".
b. MUST propagate the TMF request to and receive the response
from the target SCSI layer.
c. MUST leave all active "affected TTTs" (i.e., active TTTs
associated with affected tasks) valid.
d. MUST send an Asynchronous Message PDU with AsyncEvent=5
(Section 11.9) on:
i) each connection of each third-party session to
which at least one affected task is allegiant if
TaskReporting=FastAbort is operational on that third-
party session, and,
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ii) each connection except the issuing connection of
the issuing session that has at least one allegiant
affected task.
If there are multiple affected LUs (say, due to a target
reset), then one Async Message PDU MUST be sent for each
such LU on each connection that has at least one allegiant
affected task. The LUN field in the Asynchronous Message PDU
MUST be set to match the LUN for each such LU.
e. MUST address the Response Fence flag on the TMF Response on
the issuing session as defined in Section 4.2.2.3.3.
f. MUST address the Response Fence flag on the first post-TMF
Response on third-party sessions as defined in Section
4.2.2.3.3. If some tasks originate from non-iSCSI I_T_L
nexuses, then the means by which the target ensures that
all affected tasks have returned their status to the
initiator are defined by the specific non-iSCSI transport
protocol(s).
g. MUST free up the affected TTTs (and STags, if applicable)
and the corresponding buffers, if any, once it receives
each associated NOP-Out acknowledgement that the initiator
generated in response to each Async Message.
Technically, the TMF servicing is complete in Step e. Data
transfers corresponding to terminated tasks may however still be
in progress even at the end of Step f. A TMF Response MUST NOT be
sent by the target iSCSI layer before the end of Step e, and MAY
be sent at the end of Step e despite these outstanding Data
transfers until Step g. Step g specifies an event to free up any
such resources that may have been reserved to support outstanding
data transfers.
4.2.3.5. Affected Tasks Shared across Standard and FastAbort Sessions
If an iSCSI target implementation is capable of supporting
TaskReporting=FastAbort functionality (Section 13.23), it may end
up in a situation where some sessions have TaskReporting=RFC3720
operational (RFC 3720 sessions) while some other sessions have
TaskReporting=FastAbort operational (FastAbort sessions) even
while accessing a shared set of affected tasks (Section 4.2.3.2).
If the issuing session is an RFC 3720 session, the iSCSI target
implementation is FastAbort-capable, and the third-party affected
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session is a FastAbort session, the following behavior SHOULD be
exhibited by the iSCSI target layer:
a. Between Steps c and d of the target behavior in Section
4.2.3.3, send an Asynchronous Message PDU with AsyncEvent=5
(Section 11.9) on each connection of each third-party
session to which at least one affected task is allegiant.
If there are multiple affected LUs, then send one Async
Message PDU for each such LU on each connection that has at
least one allegiant affected task. When sent, the LUN field
in the Asynchronous Message PDU MUST be set to match the
LUN for each such LU.
b. After Step e of the target behavior in Section 4.2.3.3,
free up the affected TTTs (and STags, if applicable) and
the corresponding buffers, if any, once each associated
NOP-Out acknowledgement is received that the third-party
initiator generated in response to each Async Message sent
in Step a.
If the issuing session is a FastAbort session, the iSCSI target
implementation is FastAbort-capable, and the third-party affected
session is an RFC 3720 session, iSCSI target layer MUST NOT send
Asynchronous Message PDUs on the third-party session to prompt the
FastAbort behavior.
If the third-party affected session is a FastAbort session and the
issuing session is a FastAbort session, the initiator in the
third-party role MUST respond to each Async Message PDU with
AsyncEvent=5 as defined in Section 11.9. Note that an initiator
MAY thus receive these Async Messages on a third-party affected
session even if the session is a single-connection session.
4.2.3.6. Rationale behind the FastAbort Semantics
There are fundamentally three basic objectives behind the
semantics
specified in Sections 4.2.3.3 and 4.2.3.4.
1. Maintaining an ordered command flow I_T nexus abstraction
to the target SCSI layer even with multi-connection
sessions.
- Target iSCSI processing of a TMF request must
maintain the single flow illusion. Target behavior in
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Step b of Section 4.2.3.3 and Step a of Section 4.2.3.4
correspond to this objective.
2. Maintaining a single ordered response flow I_T nexus
abstraction to the initiator SCSI layer even with multi-
connection sessions when one response (i.e., TMF response)
could imply the status of other unfinished tasks from the
initiator's perspective.
- The target must ensure that the initiator does not
see "old" task responses (that were placed on the wire
chronologically earlier than the TMF Response) after
seeing the TMF response. The target behavior in Step d
of Section 4.2.3.3 and Step e of Section 4.2.3.4
correspond to this objective.
- Whenever the result of a TMF action is visible across
multiple I_T_L nexuses, [SAM2] requires the SCSI device
server to trigger a UA on each of the other I_T_L
nexuses. Once an initiator is notified of such an UA,
the application client on the receiving initiator is
required to clear its task state (clause 5.5 in [SAM2])
for the affected tasks. It would thus be inappropriate
to deliver a SCSI Response for a task after the task
state is cleared on the initiator, i.e., after the UA
is notified. The UA notification contained in the first
SCSI Response PDU on each affected Third-party I_T_L
nexus after the TMF action thus MUST NOT pass the
affected task responses on any of the iSCSI sessions
accessing the LU. The target behavior in Step e of
Section 4.2.3.3 and Step f of Section 4.2.3.4
correspond to this objective.
3. Draining all active TTTs corresponding to affected tasks in
a deterministic fashion.
- Data-Out PDUs with stale TTTs arriving after the
tasks are terminated can create a buffer management
problem even for traditional iSCSI implementations, and
is fatal for the connection for iSCSI/iSER
implementations. Either the termination of affected
tasks should be postponed until the TTTs are retired
(as in Step a of Section 4.2.3.3), or the TTTs and the
buffers should stay allocated beyond task termination
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to be deterministically freed up later (as in Steps c
and g of Section 4.2.3.4).
The only other notable optimization is the plugging. If all tasks
on an I_T nexus will be aborted anyway (as with a target reset),
there is no need to wait to receive all commands to plug the CmdSN
holes. The target iSCSI layer can simply plug all missing CmdSN
slots and move on with TMF processing. The first objective
(maintaining a single ordered command flow) is still met with this
optimization because the target SCSI layer only sees ordered
commands.
4.2.4. iSCSI Login
The purpose of the iSCSI login is to enable a TCP connection for
iSCSI use, authentication of the parties, negotiation of the
session's parameters and marking of the connection as belonging to
an iSCSI session.
A session is used to identify to a target all the connections with
a given initiator that belong to the same I_T nexus. (For more
details on how a session relates to an I_T nexus, see Section
4.4.2).
The targets listen on a well-known TCP port or other TCP port for
incoming connections. The initiator begins the login process by
connecting to one of these TCP ports.
As part of the login process, the initiator and target SHOULD
authenticate each other and MAY set a security association
protocol for the session. This can occur in many different ways
and is subject to negotiation - see Section 12.
To protect the TCP connection, an IPsec security association MAY
be established before the Login request. For information on using
IPsec security for iSCSI see Section 9, [RFC3723] and [IPSEC-IPS}.
The iSCSI Login Phase is carried through Login requests and
responses. Once suitable authentication has occurred and
operational parameters have been set, the session transitions to
Full Feature Phase and the initiator may start to send SCSI
commands. The security policy for whether, and by what means, a
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target chooses to authorize an initiator is beyond the scope of
this document. For a more detailed description of the Login Phase,
see Section 6.
The login PDU includes the ISID part of the session ID (SSID). The
target portal group that services the login is implied by the
selection of the connection endpoint. For a new session, the TSIH
is zero. As part of the response, the target generates a TSIH.
During session establishment, the target identifies the SCSI
initiator port (the "I" in the "I_T nexus") through the value pair
(InitiatorName, ISID). We describe InitiatorName later in this
Section. Any persistent state (e.g., persistent reservations) on
the target that is associated with a SCSI initiator port is
identified based on this value pair. Any state associated with the
SCSI target port (the "T" in the "I_T nexus") is identified
externally by the TargetName and portal group tag (see Section
4.4.1). ISID is subject to reuse restrictions because it is used
to identify a persistent state (see Section 4.4.3).
Before the Full Feature Phase is established, only Login Request
and Login Response PDUs are allowed. Login requests and responses
MUST be used exclusively during Login. On any connection, the
login phase MUST immediately follow TCP connection establishment
and a subsequent Login Phase MUST NOT occur before tearing down a
connection.
A target receiving any PDU except a Login request before the Login
phase is started MUST immediately terminate the connection on
which the PDU was received. Once the Login phase has started, if
the target receives any PDU except a Login request, it MUST send a
Login reject (with Status "invalid during login") and then
disconnect. If the initiator receives any PDU except a Login
response, it MUST immediately terminate the connection.
4.2.5. iSCSI Full Feature Phase
Once the two sides successfully conclude the Login on the first -
also called the leading - connection in the session, the iSCSI
session is in the iSCSI Full Feature Phase. A connection is in
Full Feature Phase if the session is in Full Feature Phase and the
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connection login has completed successfully. An iSCSI connection
is not in Full Feature Phase
a) when it does not have an established transport
connection,
OR
b) when it has a valid transport connection, but a
successful login was not performed or the connection is
currently logged out.
In a normal Full Feature Phase, the initiator may send SCSI
commands and data to the various LUs on the target by
encapsulating them in iSCSI PDUs that go over the established
iSCSI session.
4.2.5.1. Command Connection Allegiance
For any iSCSI request issued over a TCP connection, the
corresponding response and/or other related PDU(s) MUST be sent
over the same connection. We call this "connection allegiance". If
the original connection fails before the command is completed, the
connection allegiance of the command may be explicitly reassigned
to a different transport connection as described in detail in
Section 7.2.
Thus, if an initiator issues a READ command, the target MUST send
the requested data, if any, followed by the status to the
initiator over the same TCP connection that was used to deliver
the SCSI command. If an initiator issues a WRITE command, the
initiator MUST send the data, if any, for that command over the
same TCP connection that was used to deliver the SCSI command. The
target MUST return Ready To Transfer (R2T), if any, and the status
over the same TCP connection that was used to deliver the SCSI
command. Retransmission requests (SNACK PDUs) and the data and
status that they generate MUST also use the same connection.
However, consecutive commands that are part of a SCSI linked
command-chain task (see [SAM2]) MAY use different connections.
Connection allegiance is strictly per-command and not per-task.
During the iSCSI Full Feature Phase, the initiator and target MAY
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interleave unrelated SCSI commands, their SCSI Data, and responses
over the session.
4.2.5.2. Data Transfer Overview
Outgoing SCSI data (initiator to target user data or command
parameters) is sent as either solicited data or unsolicited data.
Solicited data are sent in response to R2T PDUs. Unsolicited data
can be sent as part of an iSCSI command PDU ("immediate data") or
in separate iSCSI data PDUs.
Immediate data are assumed to originate at offset 0 in the
initiator SCSI write-buffer (outgoing data buffer). All other Data
PDUs have the buffer offset set explicitly in the PDU header.
An initiator may send unsolicited data up to FirstBurstLength
(see Section 13.14) as immediate (up to the negotiated maximum PDU
length), in a separate PDU sequence or both. All subsequent data
MUST be solicited. The maximum length of an individual data PDU or
the immediate-part of the first unsolicited burst MAY be
negotiated at login.
The maximum amount of unsolicited data that can be sent with a
command is negotiated at login through the FirstBurstLength (see
Section 13.14) key. A target MAY separately enable immediate data
(through the ImmediateData key) without enabling the more general
(separate data PDUs) form of unsolicited data (through the
InitialR2T key).
Unsolicited data on write are meant to reduce the effect of
latency on throughput (no R2T is needed to start sending data). In
addition, immediate data is meant to reduce the protocol overhead
(both bandwidth and execution time).
An iSCSI initiator MAY choose not to send unsolicited data, only
immediate data or FirstBurstLength bytes of unsolicited data with
a command. If any non-immediate unsolicited data is sent, the
total unsolicited data MUST be either FirstBurstLength, or all of
the data if the total amount is less than the FirstBurstLength.
It is considered an error for an initiator to send unsolicited
data PDUs to a target that operates in R2T mode (only solicited
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data are allowed). It is also an error for an initiator to send
more unsolicited data, whether immediate or as separate PDUs, than
FirstBurstLength.
An initiator MUST honor an R2T data request for a valid
outstanding command (i.e., carrying a valid Initiator Task Tag)
and deliver all the requested data provided the command is
supposed to deliver outgoing data and the R2T specifies data
within the command bounds. The initiator action is unspecified for
receiving an R2T request that specifies data, all or part, outside
of the bounds of the command.
A target SHOULD NOT silently discard data and then request
retransmission through R2T. Initiators SHOULD NOT keep track of
the data transferred to or from the target (scoreboarding). SCSI
targets perform residual count calculation to check how much data
was actually transferred to or from the device by a command. This
may differ from the amount the initiator sent and/or received for
reasons such as retransmissions and errors. Read or bidirectional
commands implicitly solicit the transmission of the entire amount
of data covered by the command. SCSI data packets are matched to
their corresponding SCSI commands by using tags specified in the
protocol.
In addition, iSCSI initiators and targets MUST enforce some
ordering rules. When unsolicited data is used, the order of the
unsolicited data on each connection MUST match the order in which
the commands on that connection are sent. Command and unsolicited
data PDUs may be interleaved on a single connection as long as the
ordering requirements of each are maintained (e.g., command N+1
MAY be sent before the unsolicited Data-Out PDUs for command N,
but the unsolicited Data-Out PDUs for command N MUST precede the
unsolicited Data-Out PDUs of command N+1). A target that receives
data out of order MAY terminate the session.
4.2.5.3. Tags and Integrity Checks
Initiator tags for pending commands are unique initiator-wide for
a session. Target tags are not strictly specified by the protocol.
It is assumed that target tags are used by the target to tag
(alone or in combination with the LUN) the solicited data. Target
tags are generated by the target and "echoed" by the initiator.
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These mechanisms are designed to accomplish efficient data
delivery along with a large degree of control over the data flow.
As the Initiator Task Tag is used to identify a task during its
execution the iSCSI initiator and target MUST verify that all
other fields used in task related PDUs have values that are
consistent with the values used at the task instantiation based on
Initiator Task Tag (e.g., the LUN used in an R2T PDU MUST be the
same as the one used in the SCSI command PDU used to instantiate
the task). Using inconsistent field values is considered a
protocol error.
4.2.5.4. Task Management
SCSI task management assumes that individual tasks and task groups
can be aborted solely based on the task tags (for individual
tasks) or the timing of the task management command (for task
groups) and that the task management action is executed
synchronously - i.e, no message involving an aborted task will be
seen by the SCSI initiator after receiving the task management
response. In iSCSI initiators and targets interact asynchronously
over several connections. iSCSI specifies the protocol mechanism
and implementation requirements needed to present a synchronous
view while using an asynchronous infrastructure.
4.2.6. iSCSI Connection Termination
An iSCSI connection may be terminated by use of a transport
connection shutdown or a transport reset. Transport reset is
assumed to be an exceptional event.
Graceful TCP connection shutdowns are done by sending TCP FINs. A
graceful transport connection shutdown SHOULD only be initiated by
either party when the connection is not in iSCSI Full Feature
Phase. A target MAY terminate a Full Feature Phase connection on
internal exception events, but it SHOULD announce the fact through
an Asynchronous Message PDU. Connection termination with
outstanding commands may require recovery actions.
If a connection is terminated while in Full Feature Phase,
connection cleanup (see Section 7) is required prior to recovery.
By doing connection cleanup before starting recovery, the
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initiator and target will avoid receiving stale PDUs after
recovery.
4.2.7. iSCSI Names
Both targets and initiators require names for the purpose of
identification. In addition, names enable iSCSI storage resources
to be managed regardless of location (address). An iSCSI node name
is also the SCSI device name contained in the iSCSI Node. The
iSCSI name of a SCSI device is the principal object used in
authentication of targets to initiators and initiators to targets.
This name is also used to identify and manage iSCSI storage
resources.
iSCSI names must be unique within the operation domain of the end
user. However, because the operation domain of an IP network is
potentially worldwide, the iSCSI name formats are architected to
be worldwide unique. To assist naming authorities in the
construction of worldwide unique names, iSCSI provides three name
formats for different types of naming authorities.
iSCSI names are associated with iSCSI nodes, and not iSCSI network
adapter cards, to ensure that the replacement of network adapter
cards does not require reconfiguration of all SCSI and iSCSI
resource allocation information.
Some SCSI commands require that protocol-specific identifiers be
communicated within SCSI CDBs. See SCSI for the definition of the
SCSI port name/identifier for iSCSI ports.
An initiator may discover the iSCSI Target Names to which it has
access, along with their addresses, using the SendTargets text
request, or other techniques discussed in [RFC3721].
iSCSI equipment that needs discovery functions beyond SendTargets
SHOULD implement iSNS (see [RFC4171]) for extended discovery
management capabilities and interoperability. Although [RFC3721]
implies an SLP ([RFC2608]) implementation requirement, SLP has not
been widely implemented or deployed for use with iSCSI in
practice. iSCSI implementations therefore SHOULD NOT rely on SLP-
based discovery interoperability.
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4.2.7.1. iSCSI Name Properties
Each iSCSI node, whether it is an initiator or target or both,
MUST have an iSCSI name. Whenever an iSCSI Node contains an iSCSI
Initiator Node and an iSCSI Target Node, the iSCSI Initiator Name
MUST be the same as the iSCSI Target Name for the contained Nodes
such that there is only one iSCSI Node Name for the iSCSI Node
overall. Note the related requirements in Section 9.2.1 on how to
map CHAP names to iSCSI Names in such a scenario.
Initiators and targets MUST support the receipt of iSCSI names of
up to the maximum length of 223 bytes.
The initiator MUST present both its iSCSI Initiator Name and the
iSCSI Target Name to which it wishes to connect in the first login
request of a new session or connection. The only exception is if a
discovery session (see Section 4.3) is to be established. In this
case, the iSCSI Initiator Name is still required, but the iSCSI
Target Name MAY be omitted.
iSCSI names have the following properties:
- iSCSI names are globally unique. No two initiators or
targets can have the same name.
- iSCSI names are permanent. An iSCSI initiator node or target
node has the same name for its lifetime.
- iSCSI names do not imply a location or address. An iSCSI
initiator or target can move, or have multiple addresses. A
change of address does not imply a change of name.
- iSCSI names do not rely on a central name broker; the naming
authority is distributed.
- iSCSI names support integration with existing unique naming
schemes.
- iSCSI names rely on existing naming authorities. iSCSI does
not create any new naming authority.
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The encoding of an iSCSI name has the following properties:
- iSCSI names have the same encoding method regardless of the
underlying protocols.
- iSCSI names are relatively simple to compare. The algorithm
for comparing two iSCSI names for equivalence does not rely
on an external server.
- iSCSI names are composed only of printable ASCII and Unicode
characters. iSCSI names allow the use of international
character sets but uppercase characters are prohibited. The
iSCSI stringprep profile [RFC3722] maps uppercase characters
to lowercase and SHOULD be used to prepare iSCSI names from
input that may include uppercase characters. No whitespace
characters are used in iSCSI names, see [RFC3722] for
details.
- iSCSI names may be transported using both binary and ASCII-
based protocols.
An iSCSI name really names a logical software entity, and is not
tied to a port or other hardware that can be changed. For
instance, an initiator name should name the iSCSI initiator node,
not a particular NIC or HBA. When multiple NICs are used, they
should generally all present the same iSCSI initiator name to the
targets, because they are simply paths to the same SCSI layer. In
most operating systems, the named entity is the operating system
image.
Similarly, a target name should not be tied to hardware interfaces
that can be changed. A target name should identify the logical
target and must be the same for the target regardless of the
physical portion being addressed. This assists iSCSI initiators in
determining that the two targets it has discovered are really two
paths to the same target.
The iSCSI name is designed to fulfill the functional requirements
for Uniform Resource Names (URN) [RFC1737]. For example, it is
required that the name have a global scope, be independent of
address or location, and be persistent and globally unique. Names
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must be extensible and scalable with the use of naming
authorities. The name encoding should be both human and machine
readable. See [RFC1737] for further requirements.
4.2.7.2. iSCSI Name Encoding
An iSCSI name MUST be a UTF-8 (see [RFC3629]) encoding of a string
of Unicode characters with the following properties:
- It is in Normalization Form C (see "Unicode Normalization
Forms" [UNICODE]).
- It only contains characters allowed by the output of the
iSCSI stringprep template (described in [RFC3722]).
- The following characters are used for formatting iSCSI
names:
- dash ('-'=U+002d)
- dot ('.'=U+002e)
- colon (':'=U+003a)
- The UTF-8 encoding of the name is not larger than 223 bytes.
The stringprep process is described in [RFC3454]; iSCSI's use of
the stringprep process is described in [RFC3722]. Stringprep is a
method designed by the Internationalized Domain Name (IDN) working
group to translate human-typed strings into a format that can be
compared as opaque strings. iSCSI names are expected to be used by
administrators for purposes such as system configuration - for
this reason, characters that may lead to human confusion among
different iSCSI names (e.g., punctuation, spacing, diacritical
marks) should be avoided, even when such characters are allowed as
stringprep processing output by [RFC3722]. The stringprep process
also converts strings into equivalent strings of lower-case
characters.
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The stringprep process does not need to be implemented if the
names are generated using only characters allowed as output by the
stringprep processing specified in [RFC3722]. Those allowed
characters include all ASCII lowercase and numeric characters, as
well as lowercase Unicode characters as specified in [RFC3722].
Once iSCSI names encoded in UTF-8 are "normalized" as described in
this Section, they may be safely compared byte-for-byte.
4.2.7.3. iSCSI Name Structure
An iSCSI name consists of two parts--a type designator followed by
a unique name string.
iSCSI uses three existing naming authorities in constructing
globally unique iSCSI names. Type designator in an iSCSI name
indicates the naming authority on which the name is based. The
three iSCSI name formats are the following:
a) iSCSI-Qualified Name: it is based on domain names to
identify a naming authority,
b) NAA format Name: it is based on a naming format defined
by [FC-FS3] for constructing globally unique identifiers,
referred to as the Network Address Authority (NAA), and,
c) EUI format Name: it is based on EUI names where the IEEE
Registration Authority assists in the formation of
worldwide unique names (EUI-64 format).
The corresponding type designator strings currently defined are:
a) iqn. - iSCSI Qualified name
b) naa. - Remainder of the string is an INCITS T11-defined
Network Address Authority identifier, in ASCII-encoded
hexadecimal.
c) eui. - Remainder of the string is an IEEE EUI-64
identifier, in ASCII-encoded hexadecimal.
These three naming authority designators were considered
sufficient at the time of writing this document. The creation of
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additional naming type designators for iSCSI may be considered by
the IETF and detailed in separate RFCs.
The following table summarizes the current SCSI transport
protocols and their naming formats.
SCSI Transport Protocol Naming Format
+----------------------------+-------+-----+----+
| | EUI-64| NAA |IQN |
|----------------------------|-------|-----|----|
| iSCSI (Internet SCSI) | X | X | X |
|----------------------------|-------|-----|----|
| FCP (Fibre Channel) | | X | |
|----------------------------|-------|-----|----|
| SAS (Serial Attached SCSI) | | X | |
+----------------------------+-------+-----+----+
4.2.7.4. Type "iqn." (iSCSI Qualified Name)
This iSCSI name type can be used by any organization that owns a
domain name. This naming format is useful when an end user or
service provider wishes to assign iSCSI names for targets and/or
initiators.
To generate names of this type, the person or organization
generating the name must own a registered domain name. This domain
name does not have to resolve to an address; it just needs to be
reserved to prevent others from generating iSCSI names using the
same domain name.
Since a domain name can expire, be acquired by another entity, or
may be used to generate iSCSI names by both owners, the domain
name must be additionally qualified by a date during which the
naming authority owned the domain name. A date code is provided as
part of the "iqn." format for this reason.
The iSCSI qualified name string consists of:
- The string "iqn.", used to distinguish these names from
"eui." formatted names.
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- A date code, in yyyy-mm format. This date MUST be a date
during which the naming authority owned the domain name used
in this format, and SHOULD be the first month in which the
domain name was owned by this naming authority at 00:01 GMT
of the first day of the month. This date code uses the
Gregorian calendar. All four digits in the year must be
present. Both digits of the month must be present, with
January == "01" and December == "12". The dash must be
included.
- A dot "."
- The reversed domain name of the naming authority (person or
organization) creating this iSCSI name.
- An optional, colon (:) prefixed, string within the character
set and length boundaries that the owner of the domain name
deems appropriate. This may contain product types, serial
numbers, host identifiers, or software keys (e.g, it may
include colons to separate organization boundaries). With
the exception of the colon prefix, the owner of the domain
name can assign everything after the reversed domain name as
desired. It is the responsibility of the entity that is the
naming authority to ensure that the iSCSI names it assigns
are worldwide unique. For example, "Example Storage Arrays,
Inc.", might own the domain name "example.com".
The following are examples of iSCSI qualified names that might be
generated by "EXAMPLE Storage Arrays, Inc."
Naming String defined by
Type Date Auth "example.com" naming authority
+--++-----+ +---------+ +--------------------------------+
| || | | | | |
iqn.2001-04.com.example:storage:diskarrays-sn-a8675309
iqn.2001-04.com.example
iqn.2001-04.com.example:storage.tape1.sys1.xyz
iqn.2001-04.com.example:storage.disk2.sys1.xyz
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4.2.7.5. Type "eui." (IEEE EUI-64 format)
The IEEE Registration Authority provides a service for assigning
globally unique identifiers [EUI]. The EUI-64 format is used to
build a global identifier in other network protocols. For example,
Fibre Channel defines a method of encoding it into a
WorldWideName. For more information on registering for EUI
identifiers, see [OUI].
The format is "eui." followed by an EUI-64 identifier (16 ASCII-
encoded hexadecimal digits).
Example iSCSI name:
Type EUI-64 identifier (ASCII-encoded hexadecimal)
+--++--------------+
| || |
eui.02004567A425678D
The IEEE EUI-64 iSCSI name format might be used when a
manufacturer is already registered with the IEEE Registration
Authority and uses EUI-64 formatted worldwide unique names for its
products.
More examples of name construction are discussed in [RFC3721].
4.2.7.6. Type "naa." - Network Address Authority
The INCITS T11 Framing and Signaling Specification [FC-FS3]
defines a format called the Network Address Authority (NAA) format
for constructing worldwide unique identifiers that use various
identifier registration authorities. This identifier format is
used by the Fibre Channel and SAS SCSI transport protocols. As FC
and SAS constitute a large fraction of networked SCSI ports, the
NAA format is a widely used format for SCSI transports. The
objective behind iSCSI supporting a direct representation of an
NAA-format name is to facilitate construction of a target device
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name that translates easily across multiple namespaces for a SCSI
storage device containing ports served by different transports.
More specifically, this format allows implementations wherein one
NAA identifier can be assigned as the basis for the SCSI device
name for a SCSI target with both SAS ports and iSCSI ports.
The iSCSI NAA naming format is "naa.", followed by an NAA
identifier represented in ASCII-encoded hexadecimal digits.
An example of an iSCSI name with a 64-bit NAA value follows:
Type NAA identifier (ASCII-encoded hexadecimal)
+--++--------------+
| || |
naa.52004567BA64678D
An example of an iSCSI name with a 128-bit NAA value follows:
Type NAA identifier (ASCII-encoded hexadecimal)
+--++------------------------------+
| || |
naa.62004567BA64678D0123456789ABCDEF
The iSCSI NAA naming format might be used in an implementation
when the infrastructure for generating NAA worldwide unique names
is already in place because the device contains both SAS and iSCSI
SCSI ports.
The NAA identifier formatted in an ASCII-hexadecimal
representation has a maximum size of 32 characters (128 bit NAA
format). As a result, there is no issue with this naming format
exceeding the maximum size for iSCSI node names.
4.2.8. Persistent State
iSCSI does not require any persistent state maintenance across
sessions. However, in some cases, SCSI requires persistent
identification of the SCSI initiator port name (See Section 4.4.2
and Section 4.4.3).
iSCSI sessions do not persist through power cycles and boot
operations.
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All iSCSI session and connection parameters are re-initialized on
session and connection creation.
Commands persist beyond connection termination if the session
persists and command recovery within the session is supported.
However, when a connection is dropped, command execution, as
perceived by iSCSI (i.e., involving iSCSI protocol exchanges for
the affected task), is suspended until a new allegiance is
established by the 'task reassign' task management function. (See
Section 11.5.)
4.2.9. Message Synchronization and Steering
iSCSI presents a mapping of the SCSI protocol onto TCP. This
encapsulation is accomplished by sending iSCSI PDUs of varying
lengths. Unfortunately, TCP does not have a built-in mechanism for
signaling message boundaries at the TCP layer. iSCSI overcomes
this obstacle by placing the message length in the iSCSI message
header. This serves to delineate the end of the current message as
well as the beginning of the next message.
In situations where IP packets are delivered in order from the
network, iSCSI message framing is not an issue and messages are
processed one after the other. In the presence of IP packet
reordering (i.e., frames being dropped), legacy TCP
implementations store the "out of order" TCP segments in temporary
buffers until the missing TCP segments arrive, upon which the data
must be copied to the application buffers. In iSCSI, it is
desirable to steer the SCSI data within these out of order TCP
segments into the pre-allocated SCSI buffers rather than store
them in temporary buffers. This decreases the need for dedicated
reassembly buffers as well as the latency and bandwidth related to
extra copies.
Relying solely on the "message length" information from the iSCSI
message header may make it impossible to find iSCSI message
boundaries in subsequent TCP segments due to the loss of a TCP
segment that contains the iSCSI message length. The missing TCP
segment(s) must be received before any of the following segments
can be steered to the correct SCSI buffers (due to the inability
to determine the iSCSI message boundaries). Since these segments
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cannot be steered to the correct location, they must be saved in
temporary buffers that must then be copied to the SCSI buffers.
Different schemes can be used to recover synchronization. The
details of any such schemes are beyond this protocol
specification, but it suffices to note that [RFC4297] provides an
overview of the direct data placement problem on IP networks, and
[RFC5046] specifies a protocol extension for iSCSI that
facilitates this direct data placement objective. Rest of this
document refers to any such direct data placement protocol usage
as an example of a "Synch and Steering layer".
Under normal circumstances (no PDU loss or data reception out of
order), iSCSI data steering can be accomplished by using the
identifying tag and the data offset fields in the iSCSI header in
addition to the TCP sequence number from the TCP header. The
identifying tag helps associate the PDU with a SCSI buffer address
while the data offset and TCP sequence number are used to
determine the offset within the buffer.
4.2.9.1. Sync/Steering and iSCSI PDU Length
When a large iSCSI message is sent, the TCP segment(s) that
contain the iSCSI header may be lost. The remaining TCP segment(s)
up to the next iSCSI message must be buffered (in temporary
buffers) because the iSCSI header that indicates to which SCSI
buffers the data are to be steered was lost. To minimize the
amount of buffering, it is recommended that the iSCSI PDU length
be restricted to a small value (perhaps a few TCP segments in
length). During login, each end of the iSCSI session specifies the
maximum iSCSI PDU length it will accept.
4.3. iSCSI Session Types
iSCSI defines two types of sessions:
a) Normal operational session - an unrestricted session.
b) Discovery-session - a session only opened for target
discovery. The target MUST ONLY accept text requests with
the SendTargets key and a logout request with reason
"close the session". All other requests MUST be rejected.
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The session type is defined during login with SessionType=value
parameter in the login command.
4.4. SCSI to iSCSI Concepts Mapping Model
The following diagram shows an example of how multiple iSCSI Nodes
(targets in this case) can coexist within the same Network Entity
and can share Network Portals (IP addresses and TCP ports). Other
more complex configurations are also possible. For detailed
descriptions of the components of these diagrams, see Section
4.4.1.
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+-----------------------------------+
| Network Entity (iSCSI Client) |
| |
| +-------------+ |
| | iSCSI Node | |
| | (Initiator) | |
| +-------------+ |
| | | |
| +--------------+ +--------------+ |
| |Network Portal| |Network Portal| |
| | 192.0.2.4 | | 192.0.2.5 | |
+-+--------------+-+--------------+-+
| |
| IP Networks |
| |
+-+--------------+-+--------------+-+
| |Network Portal| |Network Portal| |
| |198.51.100.21 | |198.51.100.3 | |
| | TCP Port 3260| | TCP Port 3260| |
| +--------------+ +--------------+ |
| | | |
| ----------------- |
| | | |
| +-------------+ +--------------+ |
| | iSCSI Node | | iSCSI Node | |
| | (Target) | | (Target) | |
| +-------------+ +--------------+ |
| |
| Network Entity (iSCSI Server) |
+-----------------------------------+
4.4.1. iSCSI Architecture Model
This Section describes the part of the iSCSI architecture model
that has the most bearing on the relationship between iSCSI and
the SCSI Architecture Model.
- Network Entity - represents a device or gateway that is
accessible from the IP network. A Network Entity must have
one or more Network Portals (see a following item), each of
which can be used by some iSCSI Nodes (see the following
item) contained in that Network Entity to gain access to the
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IP network.
- iSCSI Node - represents a single iSCSI initiator or iSCSI
target or an instance of each. There are one or more iSCSI
Nodes within a Network Entity. The iSCSI Node is accessible
via one or more Network Portals (see item d). An iSCSI Node
is identified by its iSCSI Name (see Section 4.2.7 and
Section 13). The separation of the iSCSI Name from the
addresses used by and for the iSCSI node allows multiple
iSCSI nodes to use the same addresses, and the same iSCSI
node to use multiple addresses.
- An alias string may also be associated with an iSCSI Node.
The alias allows an organization to associate a user
friendly string with the iSCSI Name. However, the alias
string is not a substitute for the iSCSI Name.
- Network Portal - a component of a Network Entity that has a
TCP/IP network address and that may be used by an iSCSI Node
within that Network Entity for the connection(s) within one
of its iSCSI sessions. In an initiator, it is identified by
its IP address. In a target, it is identified by its IP
address and its listening TCP port.
- Portal Groups - iSCSI supports multiple connections within
the same session; some implementations will have the ability
to combine connections in a session across multiple Network
Portals. A Portal Group defines a set of Network Portals
within an iSCSI Node that collectively supports the
capability of coordinating a session with connections that
span these portals. Not all Network Portals within a Portal
Group need to participate in every session connected through
that Portal Group. One or more Portal Groups may provide
access to an iSCSI Node. Each Network Portal, as utilized by
a given iSCSI Node, belongs to exactly one portal group
within that node. Portal Groups are identified within an
iSCSI Node by a portal group tag, a simple unsigned-integer
between 0 and 65535 (see Section 13.3). All Network Portals
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with the same portal group tag in the context of a given
iSCSI Node are in the same Portal Group.
Both iSCSI Initiators and iSCSI Targets have portal groups,
though only the iSCSI Target Portal Groups are used directly
in the iSCSI protocol (e.g., in SendTargets). For references
to the Initiator Portal Groups, see Section 10.1.1.
- Portals within a Portal Group should support similar session
parameters, because they may participate in a common
session.
The following diagram shows an example of one such configuration
on a target and how a session that shares Network Portals within a
Portal Group may be established.
----------------------------IP Network---------------------
| | |
+----|----------------|----+ +----|---------+
| +---------+ +---------+ | | +---------+ |
| | Network | | Network | | | | Network | |
| | Portal | | Portal | | | | Portal | |
| +--|------+ +---------+ | | +---------+ |
| | | | | | |
| | Portal | | | | Portal |
| | Group 1 | | | | Group 2 |
+--------------------------+ +--------------+
| | |
+--------|----------------|------------------|------------------+
| | | | |
| +----------------------------+ +----------------------------+ |
| | iSCSI Session (Target side)| | iSCSI Session (Target side)| |
| | | | | |
| | (TSIH = 56) | | (TSIH = 48) | |
| +----------------------------+ +----------------------------+ |
| |
| iSCSI Target Node |
| (within Network Entity, not shown) |
+---------------------------------------------------------------+
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4.4.2. SCSI Architecture Model
This Section describes the relationship between the SCSI
Architecture Model [SAM2] and constructs of the SCSI device, SCSI
port and I_T nexus, and the iSCSI constructs described in Section
4.4.1.
This relationship implies implementation requirements in order to
conform to the SAM2 model and other SCSI operational functions.
These requirements are detailed in Section 4.4.3.
The following list outlines mappings of SCSI architectural
elements to iSCSI.
a) SCSI Device - the SAM2 term for an entity that contains
one or more SCSI ports that are connected to a service
delivery subsystem and supports a SCSI application
protocol. For example, a SCSI Initiator Device contains
one or more SCSI Initiator Ports and zero or more
application clients. A SCSI Target Device contains one or
more SCSI Target Ports and one or more logical units. For
iSCSI, the SCSI Device is the component within an iSCSI
Node that provides the SCSI functionality. As such, there
can be one SCSI Device, at most, within an iSCSI Node.
Access to the SCSI Device can only be achieved in an
iSCSI normal operational session (see Section 4.3). The
SCSI Device Name is defined to be the iSCSI Name of the
node and MUST be used in the iSCSI protocol.
b) SCSI Port - the SAM2 term for an entity in a SCSI Device
that provides the SCSI functionality to interface with a
service delivery subsystem or transport. For iSCSI, the
definition of SCSI Initiator Port and SCSI Target Port
are different.
SCSI Initiator Port: This maps to one endpoint of an
iSCSI normal operational session (see Section 4.3). An
iSCSI normal operational session is negotiated through
the login process between an iSCSI initiator node and an
iSCSI target node. At successful completion of this
process, a SCSI Initiator Port is created within the SCSI
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Initiator Device. The SCSI Initiator Port Name and SCSI
Initiator Port Identifier are both defined to be the
iSCSI Initiator Name together with (a) a label that
identifies it as an initiator port name/identifier and
(b) the ISID portion of the session identifier.
SCSI Target Port: This maps to an iSCSI Target Portal
Group. The SCSI Target Port Name and the SCSI Target Port
Identifier are both defined to be the iSCSI Target Name
together with (a) a label that identifies it as a target
port name/identifier and (b) the portal group tag.
The SCSI Port Name MUST be used in iSCSI. When used in
SCSI parameter data, the SCSI port name MUST be encoded
as:
1. The iSCSI Name in UTF-8 format, followed by
2. a comma separator (1 byte), followed by
3. the ASCII character 'i' (for SCSI Initiator Port)
or the ASCII character 't' (for SCSI Target Port)
(1 byte), followed by
4. a comma separator (1 byte), followed by
5. a text encoding as a hex-constant (see Section 6.1)
of the ISID (for SCSI initiator port) or the
portal group tag (for SCSI target port) including
the initial 0X or 0x and the terminating null (14
bytes).
The ASCII character 'i' or 't' is the label that
identifies this port as either a SCSI Initiator
Port or a SCSI Target Port.
c) I_T nexus - a relationship between a SCSI Initiator Port
and a SCSI Target Port, according to [SAM2]. For iSCSI,
this relationship is a session, defined as a relationship
between an iSCSI Initiator's end of the session (SCSI
Initiator Port) and the iSCSI Target's Portal Group. The
I_T nexus can be identified by the conjunction of the
SCSI port names or by the iSCSI session identifier SSID.
iSCSI defines the I_T nexus identifier to be the tuple
(iSCSI Initiator Name + ",i,0x" + ISID in text format,
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iSCSI Target Name + ",t,0x" + Portal Group Tag in text
format) - an upper case hex prefix "0X" may alternatively
be used in place of "0x".
NOTE: The I_T nexus identifier is not equal to the
session identifier (SSID).
4.4.3. Consequences of the Model
This Section describes implementation and behavioral requirements
that result from the mapping of SCSI constructs to the iSCSI
constructs defined above. Between a given SCSI initiator port and
a given SCSI target port, only one I_T nexus (session) can exist.
No more than one nexus relationship (parallel nexus) is allowed by
[SAM2]. Therefore, at any given time, only one session with the
same session identifier (SSID) can exist between a given iSCSI
initiator node and an iSCSI target node.
These assumptions lead to the following conclusions and
requirements:
ISID RULE: Between a given iSCSI Initiator and iSCSI Target Portal
Group (SCSI target port), there can only be one session with a
given value for ISID that identifies the SCSI initiator port. See
Section 11.12.5.
The structure of the ISID that contains a naming authority
component (see Section 11.12.5 and [RFC3721]) provides a mechanism
to facilitate compliance with the ISID rule. (See Section 10.1.1)
The iSCSI Initiator Node should manage the assignment of ISIDs
prior to session initiation. The "ISID RULE" does not preclude the
use of the same ISID from the same iSCSI Initiator with different
Target Portal Groups on the same iSCSI target or on other iSCSI
targets (see Section 10.1.1). Allowing this would be analogous to
a single SCSI Initiator Port having relationships (nexus) with
multiple SCSI target ports on the same SCSI target device or SCSI
target ports on other SCSI target devices. It is also possible to
have multiple sessions with different ISIDs to the same Target
Portal Group. Each such session would be considered to be with a
different initiator even when the sessions originate from the same
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initiator device. The same ISID may be used by a different iSCSI
initiator because it is the iSCSI Name together with the ISID that
identifies the SCSI Initiator Port.
NOTE: A consequence of the ISID RULE and the specification for the
I_T nexus identifier is that two nexus with the same identifier
should never exist at the same time.
TSIH RULE: The iSCSI Target selects a non-zero value for the TSIH
at session creation (when an initiator presents a 0 value at
Login). After being selected, the same TSIH value MUST be used
whenever initiator or target refers to the session and a TSIH is
required.
4.4.3.1. I_T Nexus State
Certain nexus relationships contain an explicit state (e.g.,
initiator-specific mode pages) that may need to be preserved by
the device server [SAM2] in a logical unit through changes or
failures in the iSCSI layer (e.g., session failures). In order for
that state to be restored, the iSCSI initiator should reestablish
its session (re-login) to the same Target Portal Group using the
previous ISID. That is, it should reinstate the session via iSCSI
session reinstatement (Section 6.3.5) or continue via session
continuation (Section 6.3.6). This is because the SCSI initiator
port identifier and the SCSI target port identifier (or relative
target port) form the datum that the SCSI logical unit device
server uses to identify the I_T nexus.
4.4.3.2. Reservations
There are two reservation management methods defined in the SCSI
standards, reserve/release reservations, based on the RESERVE and
RELEASE commands [SPC2], and persistent reservations, based on the
PERSISTENT RESERVE IN and PERSISTENT RESERVE OUT commands [SPC3].
Reserve/release reservations are obsolete [SPC3] and should not be
used; persistent reservations are suggested as an alternative, see
Annex B of [SPC4].
State for persistent reservations is required to persist through
changes and failures at the iSCSI layer that result in I_T nexus
failures, see [SPC3] for details and specific requirements.
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In contrast, [SPC2] does not specify detailed persistence
requirements for reserve/release reservation state after an I_T
nexus failure. Nonetheless, when reserve/release reservations are
supported by an iSCSI target, the preferred implementation
approach is to preserve reserve/release reservation state for
iSCSI session reinstatement (see Section 6.3.5) or session
continuation (see Section 6.3.6).
Two additional caveats apply to reserve/release reservations:
- Retention of a failed session's reserve/release reservation
state by an iSCSI target, even after that failed iSCSI
session is not reinstated or continued, may require an
initiator to issue a reset (e.g., LOGICAL UNIT RESET, see
Section 11.5) in order to remove that reservation state.
- Reserve/release reservations may not behave as expected when
persistent reservations are also used on the same logical
unit; see the discussion of "Exceptions to SPC-2 RESERVE and
RELEASE behavior" in [SPC4].
4.5. iSCSI UML Model
This Section presents the application of the UML modeling concepts
discussed in Section 3 to the iSCSI and SCSI architecture model
discussed in Section 4.4.
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+----------------+
| Network Entity |
+----------------+
@ 1 @ 1
| |
+--------------------+ |
| |
| | 0..*
| +------------------+
| | iSCSI Node |
| +------------------+
| @ @
| | |
| +-----------+ =(a)= +-----------+
| | |
| | 0..1 | 0..1
| +------------------------+ +----------------------+
| | iSCSI Target Node | | iSCSI Initiator Node |
| +------------------------+ +----------------------+
| @ 1 @ 1
| +--------------+ |
| 1..* | | 1..*
| +-----------------------------+
| | Portal Group |
| +-----------------------------+
| O 1
| |
| | 1..*
| 1..* +------------------------+
+--------------------| Network Portal |
+------------------------+
(a) Each instance of an iSCSI Node class MUST contain one iSCSI
Target Node instance or one iSCSI Initiator Node instance, or
both.
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+----------------+
| Network Entity |
+----------------+
@ 1 @ 1
| | +-------------------+
+---------------------+ | | iSCSI Session |
| | +-------------------+
| | 0..* | SSID[1] |
| +--------------------+ | ISID[1] |
| | iSCSI Node | +-------------------+
| +--------------------+ @ 1
| | iSCSI Node Name[1] | |
| | Alias [0..1] | | 0..*
| +--------------------+ +------------------+
| | | | iSCSI Connection |
| +--------------------+ +------------------+
| @ 1 @ 1 | CID[1] |
| | | +------------------+
| +-------------+ ==(b)== +----------+ 0..* |
| | 1 | 1 |
| +------------------------+ +------------------------+ |
| | iSCSI Target Node | | iSCSI Initiator Node | |
| +------------------------+ +------------------------+ |
| | iSCSI Target name [1] | |iSCSI Initiator Name [1]| |
| +------------------------+ +------------------------+ |
| @ 1 @ 1 |
| | 1..* | 1..* |
| +--------------------------+ +------------------------+ |
| | Target Portal Group | | Initiator Portal Group | |
| +--------------------------+ +------------------------+ |
| |Target Portal Group Tag[1]| | Portal group tag[1] | |
| +--------------------------+ +------------------------+ |
| o 1 o 1 |
| +------------+ +---------+ |
| 1..* | | 1..* |
| +-------------------------+ |
| | Network Portal | |
| +-------------------------+ |
| 1..* | IP Address [1] | 1 |
+----------------| TCP Port [0..1] |<----------------------+
+-------------------------+
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(b) Each instance of an iSCSI Node class MUST contain one iSCSI
Target Node instance or one iSCSI Initiator Node instance, or
both. However, in all scenarios, note that an iSCSI Node MUST
only have a single iSCSI Name. Note the related requirement in
Section 4.2.7.1.
4.6. Request/Response Summary
This Section lists and briefly describes all the iSCSI PDU types
(request and responses).
All iSCSI PDUs are built as a set of one or more header segments
(basic and auxiliary) and zero or one data segments. The header
group and the data segment may each be followed by a CRC (digest)
(see [CRC]).
The basic header segment has a fixed length of 48 bytes.
4.6.1. Request/Response Types Carrying SCSI Payload
4.6.1.1. SCSI-Command
This request carries the SCSI CDB and all the other SCSI execute
command procedure call (see [SAM2]) IN arguments such as task
attributes, Expected Data Transfer Length for one or both transfer
directions (the latter for bidirectional commands), and Task Tag
(as part of the I_T_L_x nexus). The I_T_L nexus is derived by the
initiator and target from the LUN field in the request and the I_T
nexus is implicit in the session identification.
In addition, the SCSI-command PDU carries information required for
the proper operation of the iSCSI protocol - the command sequence
number (CmdSN) and the expected status number (ExpStatSN) on the
connection it is issued.
All or part of the SCSI output (write) data associated with the
SCSI command may be sent as part of the SCSI-Command PDU as a data
segment.
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4.6.1.2. SCSI-Response
The SCSI-Response carries all the SCSI execute-command procedure
call (see [SAM2]) OUT arguments and the SCSI execute-command
procedure call return value.
The SCSI-Response contains the residual counts from the operation,
if any, an indication of whether the counts represent an overflow
or an underflow, and the SCSI status if the status is valid or a
response code (a non-zero return value for the execute-command
procedure call) if the status is not valid.
For a valid status that indicates that the command has been
processed, but resulted in an exception (e.g., a SCSI CHECK
CONDITION), the PDU data segment contains the associated sense
data. The use of Autosense ([SAM2]) is REQUIRED by iSCSI.
Some data segment content may also be associated (in the data
segment) with a non-zero response code.
In addition, the SCSI-Response PDU carries information required
for the proper operation of the iSCSI protocol:
- The number of Data-In PDUs that a target has sent (to enable
the initiator to check that all have arrived).
- StatSN - the Status Sequence Number on this connection.
- ExpCmdSN - the next Expected Command Sequence Number at the
target.
- MaxCmdSN - the maximum CmdSN acceptable at the target from
this initiator.
4.6.1.3. Task Management Function Request
The Task Management function request provides an initiator with a
way to explicitly control the execution of one or more SCSI Tasks
or iSCSI functions. The PDU carries a function identifier (which
task management function to perform) and enough information to
unequivocally identify the task or task-set on which to perform
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the action, even if the task(s) to act upon has not yet arrived or
has been discarded due to an error.
The referenced tag identifies an individual task if the function
refers to an individual task.
The I_T_L nexus identifies task sets. In iSCSI the I_T_L nexus is
identified by the LUN and the session identification (the session
identifies an I_T nexus).
For task sets, the CmdSN of the Task Management function request
helps identify the tasks upon which to act, namely all tasks
associated with a LUN and having a CmdSN preceding the Task
Management function request CmdSN.
For a Task Management function, the coordination between responses
to the tasks affected and the Task Management function response is
done by the target.
4.6.1.4. Task Management Function Response
The Task Management function response carries an indication of
function completion for a Task Management function request
including how it completed (response and qualifier) and additional
information for failure responses.
After the Task Management response indicates Task Management
function completion, the initiator will not receive any additional
responses from the affected tasks.
4.6.1.5. SCSI Data-out and SCSI Data-in
SCSI Data-out and SCSI Data-in are the main vehicles by which SCSI
data payload is carried between initiator and target. Data payload
is associated with a specific SCSI command through the Initiator
Task Tag. For target convenience, outgoing solicited data also
carries a Target Transfer Tag (copied from R2T) and the LUN. Each
PDU contains the payload length and the data offset relative to
the buffer address contained in the SCSI execute command procedure
call.
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In each direction, the data transfer is split into "sequences". An
end-of-sequence is indicated by the F bit.
An outgoing sequence is either unsolicited (only the first
sequence can be unsolicited) or consists of all the Data-Out PDUs
sent in response to an R2T.
Input sequences enable the switching of direction for
bidirectional commands as required.
For input, the target may request positive acknowledgement of
input data. This is limited to sessions that support error
recovery and is implemented through the A bit in the SCSI Data-in
PDU header.
Data-in and Data-out PDUs also carry the DataSN to enable the
initiator and target to detect missing PDUs (discarded due to an
error).
In addition, StatSN is carried by the Data-In PDUs.
To enable a SCSI command to be processed while involving a minimum
number of messages, the last SCSI Data-in PDU passed for a command
may also contain the status if the status indicates termination
with no exceptions (no sense or response involved).
4.6.1.6. Ready To Transfer (R2T)
R2T is the mechanism by which the SCSI target "requests" the
initiator for output data. R2T specifies to the initiator the
offset of the requested data relative to the buffer address from
the execute command procedure call and the length of the solicited
data.
To help the SCSI target associate the resulting Data-out with an
R2T, the R2T carries a Target Transfer Tag that will be copied by
the initiator in the solicited SCSI Data-out PDUs. There are no
protocol specific requirements with regard to the value of these
tags, but it is assumed that together with the LUN, they will
enable the target to associate data with an R2T.
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R2T also carries information required for proper operation of the
iSCSI protocol, such as:
- R2TSN (to enable an initiator to detect a missing R2T)
- StatSN
- ExpCmdSN
- MaxCmdSN
4.6.2. Requests/Responses carrying SCSI and iSCSI Payload
4.6.2.1. Asynchronous Message
Asynchronous Messages are used to carry SCSI asynchronous events
(AEN) and iSCSI asynchronous messages.
When carrying an AEN, the event details are reported as sense data
in the data segment.
4.6.3. Requests/Responses Carrying iSCSI Only Payload
4.6.3.1. Text Request and Text Response
Text requests and responses are designed as a parameter
negotiation vehicle and as a vehicle for future extension.
In the data segment Text Requests/Responses carry text information
using a simple "key=value" syntax.
Text Request/Responses may form extended sequences using the same
Initiator Task Tag. The initiator uses the F (Final) flag bit in
the text request header to indicate its readiness to terminate a
sequence. The target uses the F (Final) flag bit in the text
response header to indicate its consent to sequence termination.
Text Request and Responses also use the Target Transfer Tag to
indicate continuation of an operation or a new beginning. A target
that wishes to continue an operation will set the Target Transfer
Tag in a Text Response to a value different from the default
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0xffffffff. An initiator willing to continue will copy this value
into the Target Transfer Tag of the next Text Request. If the
initiator wants to restart the current target negotiation (start
fresh) will set the Target Transfer Tag to 0xffffffff.
Although a complete exchange is always started by the initiator,
specific parameter negotiations may be initiated by the initiator
or target.
4.6.3.2. Login Request and Login Response
Login Requests and Responses are used exclusively during the Login
Phase of each connection to set up the session and connection
parameters. (The Login Phase consists of a sequence of login
requests and responses carrying the same Initiator Task Tag.)
A connection is identified by an arbitrarily selected connection-
ID (CID) that is unique within a session.
Similar to the Text Requests and Responses, Login
Requests/Responses carry key=value text information with a simple
syntax in the data segment.
The Login Phase proceeds through several stages (security
negotiation, operational parameter negotiation) that are selected
with two binary coded fields in the header -- the "current stage"
(CSG) and the "next stage" (NSG) with the appearance of the latter
being signaled by the "transit" flag (T).
The first Login Phase of a session plays a special role, called
the leading login, which determines some header fields (e.g., the
version number, the maximum number of connections, and the session
identification).
The CmdSN initial value is also set by the leading login.
StatSN for each connection is initiated by the connection login.
A login request may indicate an implied logout (cleanup) of the
connection to be logged in (a connection restart) by using the
same Connection ID (CID) as an existing connection as well as the
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same session identifying elements of the session to which the old
connection was associated.
4.6.3.3. Logout Request and Response
Logout Requests and Responses are used for the orderly closing of
connections for recovery or maintenance. The logout request may be
issued following a target prompt (through an asynchronous message)
or at an initiators initiative. When issued on the connection to
be logged out no other request may follow it.
The Logout response indicates that the connection or session
cleanup is completed and no other responses will arrive on the
connection (if received on the logging out connection). In
addition, the Logout Response indicates how long the target will
continue to hold resources for recovery (e.g., command execution
that continues on a new connection) in the Time2Retain field and
how long the initiator must wait before proceeding with recovery
in the Time2Wait field.
4.6.3.4. SNACK Request
With the SNACK Request, the initiator requests retransmission of
numbered-responses or data from the target. A single SNACK request
covers a contiguous set of missing items, called a run, of a given
type of items. The type is indicated in a type field in the PDU
header. The run is composed of an initial item (StatSN, DataSN,
R2TSN) and the number of missed Status, Data, or R2T PDUs. For
long data-in sequences, the target may request (at predefined
minimum intervals) a positive acknowledgement for the data sent. A
SNACK request with a type field that indicates ACK and the number
of Data-In PDUs acknowledged conveys this positive
acknowledgement.
4.6.3.5. Reject
Reject enables the target to report an iSCSI error condition
(e.g., protocol, unsupported option) that uses a Reason field in
the PDU header and includes the complete header of the bad PDU in
the Reject PDU data segment.
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4.6.3.6. NOP-Out Request and NOP-In Response
This request/response pair may be used by an initiator and target
as a "ping" mechanism to verify that a connection/session is still
active and all of its components are operational. Such a ping may
be triggered by the initiator or target. The triggering party
indicates that it wants a reply by setting a value different from
the default 0xffffffff in the corresponding Initiator/Target
Transfer Tag.
NOP-In/NOP-Out may also be used "unidirectional" to convey to the
initiator/target command, status or data counter values when there
is no other "carrier" and there is a need to update the
initiator/target.
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5. SCSI Mode Parameters for iSCSI
There are no iSCSI specific mode pages.
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6. Login and Full Feature Phase Negotiation
iSCSI parameters are negotiated at session or connection
establishment by using Login Requests and Responses (see Section
4.2.4) and during Full Feature Phase (Section 4.2.5) by using Text
Requests and Responses. In both cases the mechanism used is an
exchange of iSCSI-text-key=value pairs. For brevity, iSCSI-text-
keys are called just keys in the rest of this document.
Keys are either declarative or require negotiation and the key
description indicates if the key is declarative or requires
negotiation.
For the declarative keys the declaring party sets a value for the
key. The key specification indicates if the key can be declared by
the initiator, target or both.
For the keys that require negotiation, one of the parties (the
proposing party) proposes a value or set of values by including
the key=value in the data part of a Login or Text Request or
Response. The other party (the accepting party) makes a selection
based on the value or list of values proposed and includes the
selected value in a key=value in the data part of the following
Login or Text Response or Request. For most of the keys, both the
initiator and target can be proposing parties.
The login process proceeds in two stages - the security
negotiation stage and the operational parameter negotiation stage.
Both stages are optional but at least one of them has to be
present to enable setting some mandatory parameters.
If present, the security negotiation stage precedes the
operational parameter negotiation stage.
Progression from stage to stage is controlled by the T
(Transition) bit in the Login Request/Response PDU header. Through
the T bit set to 1, the initiator indicates that it would like to
transition. The target agrees to the transition (and selects the
next stage) when ready. A field in the Login PDU header indicates
the current stage (CSG) and during transition, another field
indicates the next stage (NSG) proposed (initiator) and selected
(target).
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The Text negotiation process is used to negotiate or declare
operational parameters. The negotiation process is controlled by
the F (final) bit in the PDU header. During text negotiations, the
F bit is used by the initiator to indicate that it is ready to
finish the negotiation and by the Target to acquiesce the end of
negotiation.
Since some key=value pairs may not fit entirely in a single PDU,
the C (continuation) bit is used (both in Login and Text) to
indicate that "more follows".
The text negotiation uses an additional mechanism by which a
target may deliver larger amounts of data to an enquiring
initiator. The target sets a Target Task Tag to be used as a
bookmark which when returned by the initiator, means "go on". If
reset to a "neutral value", it means "forget about the rest".
This Section details types of keys and values used, the syntax
rules for parameter formation, and the negotiation schemes to be
used with different types of parameters.
6.1. Text Format
The initiator and target send a set of key=value pairs encoded in
UTF-8 Unicode. All the text keys and text values specified in this
document are to be presented and interpreted in the case in which
they appear in this document. They are case sensitive.
The following character symbols are used in this document for text
items (the hexadecimal values represent Unicode code points):
(a-z, A-Z) ) (0x61-0x7a, 0x41-0x5a) - letters
(0-9) (0x30-0x39) - digits
" " (0x20) - space
"." (0x2e) - dot
"-" (0x2d) - minus
"+" (0x2b) - plus
"@" (0x40) - commercial at
"_" (0x5f) - underscore
"=" (0x3d) - equal
":" (0x3a) - colon
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"/" (0x2f) - solidus or slash
"[" (0x5b) - left bracket
"]" (0x5d) - right bracket
null (0x00) - null separator
"," (0x2c) - comma
"~" (0x7e) - tilde
Key=value pairs may span PDU boundaries. An initiator or target
that sends partial key=value text within a PDU indicates that more
text follows by setting the C bit in the Text or Login Request or
Text or Login Response to 1. Data segments in a series of PDUs
that have the C bit set to 1 and end with a PDU that have the C
bit set to 0, or include a single PDU that has the C bit set to 0
have to be considered as forming a single logical-text-data-
segment (LTDS).
Every key=value pair, including the last or only pair in a LTDS,
MUST be followed by one null (0x00) delimiter.
A key-name is whatever precedes the first = in the key=value pair.
The term key is used frequently in this document in place of key-
name.
A value is whatever follows the first = in the key=value pair up
to the end of the key=value pair, but not including the null
delimiter.
The following definitions will be used in the rest of this
document:
- standard-label: A string of one or more characters that
consist of letters, digits, dot, minus, plus, commercial at,
or underscore. A standard-label MUST begin with a capital
letter and must not exceed 63 characters.
- key-name: A standard-label.
- text-value: A string of zero or more characters that consist
of letters, digits, dot, minus, plus, commercial at,
underscore, slash, left bracket, right bracket, or colon.
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- iSCSI-name-value: A string of one or more characters that
consist of minus, dot, colon, or any character allowed by
the output of the iSCSI string-prep template as specified in
[RFC3722] (see also Section 4.2.7.2).
- iSCSI-local-name-value: A UTF-8 string; no null characters
are allowed in the string. This encoding is to be used for
localized (internationalized) aliases.
- boolean-value: The string "Yes" or "No".
- hex-constant: A hexadecimal constant encoded as a string
that starts with "0x" or "0X" followed by one or more digits
or the letters a, b, c, d, e, f, A, B, C, D, E, or F. Hex-
constants are used to encode numerical values or binary
strings. When used to encode numerical values, the excessive
use of leading 0 digits is discouraged. The string following
0X (or 0x) represents a base16 number that starts with the
most significant base16 digit, followed by all other digits
in decreasing order of significance and ending with the
least-significant base16 digit. When used to encode binary
strings, hexadecimal constants have an implicit byte-length
that includes four bits for every hexadecimal digit of the
constant, including leading zeroes. For example, a hex-
constant of n hexadecimal digits has a byte-length of (the
integer part of) (n+1)/2.
- decimal-constant: An unsigned decimal number with the digit
0 or a string of one or more digits that start with a non-
zero digit. Decimal-constants are used to encode numerical
values or binary strings. Decimal constants can only be used
to encode binary strings if the string length is explicitly
specified. There is no implicit length for decimal strings.
Decimal-constant MUST NOT be used for parameter values if
the values can be equal or greater than 2**64 (numerical) or
for binary strings that can be longer than 64 bits.
- base64-constant: base64 constant encoded as a string that
starts with "0b" or "0B" followed by 1 or more digits or
letters or plus or slash or equal. The encoding is done
according to [RFC4648].
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- numerical-value: An unsigned integer always less than 2**64
encoded as a decimal-constant or a hex-constant. Unsigned
integer arithmetic applies to numerical-values.
- large-numerical-value: An unsigned integer that can be
larger than or equal to 2**64 encoded as a hex constant, or
base64-constant. Unsigned integer arithmetic applies to
large-numeric-values.
- numeric-range: Two numerical-values separated by a tilde
where the value to the right of tilde must not be lower than
the value to the left.
- regular-binary-value: A binary string not longer than 64
bits encoded as a decimal constant, hex constant, or base64-
constant. The length of the string is either specified by
the key definition or is the implicit byte-length of the
encoded string.
- large-binary-value: A binary string longer than 64 bits
encoded as a hex-constant or base64-constant. The length of
the string is either specified by the key definition or is
the implicit byte-length of the encoded string.
- binary-value: A regular-binary-value or a large-binary-
value. Operations on binary values are key specific.
- simple-value: Text-value, iSCSI-name-value, boolean-value,
numeric-value, a numeric-range, or a binary-value.
- list-of-values: A sequence of text-values separated by a
comma.
If not otherwise specified, the maximum length of a simple-value
(not its encoded representation) is 255 bytes not including the
delimiter (comma or zero byte).
Any iSCSI target or initiator MUST support receiving at least 8192
bytes of key=value data in a negotiation sequence. When proposing
or accepting authentication methods that explicitly require
support for very long authentication items, the initiator and
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target MUST support receiving of at least 64 kilobytes of
key=value data.
6.2. Text Mode Negotiation
During login, and thereafter, some session or connection
parameters are either declared or negotiated through an exchange
of textual information.
The initiator starts the negotiation and/or declaration through a
Text or Login request and indicates when it is ready for
completion (by setting the F bit to 1 and keeping it to 1 in a
Text Request or the T bit in the Login Request). As negotiation
text may span PDU boundaries, a Text or Login Request or Text or
Login Response PDU that have the C bit set to 1 MUST NOT have the
F/T bit set to 1.
A target receiving a Text or Login Request with the C bit set to 1
MUST answer with a Text or Login Response with no data segment
(DataSegmentLength 0). An initiator receiving a Text or Login
Response with the C bit set to 1 MUST answer with a Text or Login
Request with no data segment (DataSegmentLength 0).
A target or initiator SHOULD NOT use a Text or Login Response or
Text or Login Request with no data segment (DataSegmentLength 0)
unless explicitly required by a general or a key-specific
negotiation rule.
There MUST NOT be more than one outstanding Text Request, or Text
Response PDU on an iSCSI connection. An outstanding PDU in this
context is one that has not been acknowledged by the remote iSCSI
side.
The format of a declaration is:
Declarer-> <key>=<valuex>
The general format of text negotiation is:
Proposer-> <key>=<valuex>
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Acceptor-> <key>={<valuey>|NotUnderstood|Irrelevant|Reject}
Thus a declaration is a one-way textual exchange (unless the key
is not understood by the receiver) while a negotiation is a two-
way exchange.
The proposer or declarer can either be the initiator or the
target, and the acceptor can either be the target or initiator,
respectively. Targets are not limited to respond to key=value
pairs as proposed by the initiator. The target may propose
key=value pairs of its own.
All negotiations are explicit (i.e., the result MUST only be based
on newly exchanged or declared values). There are no implicit
proposals. If a proposal is not made, then a reply cannot be
expected. Conservative design also requires that default values
should not be relied upon when use of some other value has serious
consequences.
The value proposed or declared can be a numerical-value, a
numerical-range defined by lower and upper value with both
integers separated by tilde, a binary value, a text-value, an
iSCSI-name-value, an iSCSI-local-name-value, a boolean-value (Yes
or No), or a list of comma separated text-values. A range, a
large-numerical-value, an iSCSI-name-value and an iSCSI-local-
name-value MAY ONLY be used if it is explicitly allowed. An
accepted value can be a numerical-value, a large-numerical-value,
a text-value, or a boolean-value.
If a specific key is not relevant for the current negotiation, the
acceptor may answer with the constant "Irrelevant" for all types
of negotiation. However the negotiation is not considered as
failed if the answer is "Irrelevant". The "Irrelevant" answer is
meant for those cases in which several keys are presented by a
proposing party but the selection made by the acceptor for one of
the keys makes other keys irrelevant. The following example
illustrates the use of "Irrelevant":
I->T InitialR2T=No,ImmediateData=Yes,FirstBurstLength=4192
T->I InitialR2T=Yes,ImmediateData=No,FirstBurstLength=Irrelevant
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I->T X-rdname-vkey1=(bla,alb,None), X-rdname-vkey2=(bla,alb)
T->I X-rdname-vkey1=None, X-rdname-vkey2=Irrelevant
Any key not understood by the acceptor may be ignored by the
acceptor without affecting the basic function. However, the answer
for a key not understood MUST be key=NotUnderstood. Note that
NotUnderstood is a valid answer for both declarative and
negotiated keys. The general iSCSI philosophy is that
comprehension precedes processing for any iSCSI key. A proposer
of an iSCSI key, negotiated or declarative, in a text key exchange
MUST thus be able to properly handle a NotUnderstood response.
The proper way to handle a NotUnderstood response depends on where
the key is specified and whether the key is declarative vs.
negotiated. An iSCSI implementation MUST comprehend all text keys
defined in this document. Returning a NotUnderstood response on
any of these text keys therefore MUST be considered a protocol
error and handled accordingly. For all other "later" keys, i.e.
text keys defined in later specifications, a NotUnderstood answer
concludes the negotiation for a negotiated key whereas for a
declarative key, a NotUnderstood answer simply informs the
declarer of a lack of comprehension by the receiver.
In either case, a NotUnderstood answer always requires that the
protocol behavior associated with that key not be used within the
scope of the key (connection/session) by either side.
The constants "None", "Reject", "Irrelevant", and "NotUnderstood"
are reserved and MUST ONLY be used as described here. Violation of
this rule is a protocol error (in particular the use of "Reject",
"Irrelevant", and "NotUnderstood" as proposed values).
Reject or Irrelevant are legitimate negotiation options where
allowed but their excessive use is discouraged. A negotiation is
considered complete when the acceptor has sent the key value pair
even if the value is "Reject", "Irrelevant", or "NotUnderstood".
Sending the key again would be a re-negotiation and is forbidden
for many keys.
If the acceptor sends "Reject" as an answer the negotiated key is
left at its current value (or default if no value was set). If the
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current value is not acceptable to the proposer on the connection
or to the session it is sent, the proposer MAY choose to terminate
the connection or session.
All keys in this document MUST be supported by iSCSI initiators
and targets when used as specified here. If used as specified,
these keys MUST NOT be answered with NotUnderstood.
Implementers may introduce new private keys by prefixing them with
X- followed by their (reversed) domain name, or with new public
keys registered with IANA. For example, the entity owning the
domain example.com can issue:
X-com.example.bar.foo.do_something=3
Each new public key in the course of standardization MUST define
the acceptable responses to the key, including NotUnderstood as
appropriate. Unlike [RFC3720], note that this document prohibits
the X# prefix for new public keys. Based on iSCSI implementation
experience, we know that there is no longer a need for a standard
name prefix for keys that allow NotUnderstood response. Note that
NotUnderstood will generally have to be allowed for new public
keys for backwards compatibility, as well as for private X- keys.
Thus the name prefix "X#" in new public key names does not carry
any significance. New public key names MUST NOT begin with "X#"
prefix to avoid confusion.
Implementers MAY also introduce new values, but ONLY for new keys
or authentication methods (see Section 12), or digests (see
Section 13.1).
Whenever parameter action or acceptance are dependent on other
parameters, the dependency rules and parameter sequence must be
specified with the parameters.
In the Login Phase (see Section 6.3), every stage is a separate
negotiation. In the FullFeaturePhase, a Text Request Response
sequence is a negotiation. Negotiations MUST be handled as atomic
operations. For example, all negotiated values go into effect
after the negotiation concludes in agreement or are ignored if the
negotiation fails.
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Some parameters may be subject to integrity rules (e.g.,
parameter-x must not exceed parameter-y or parameter-u not 1
implies parameter-v be Yes). Whenever required, integrity rules
are specified with the keys. Checking for compliance with the
integrity rule must only be performed after all the parameters are
available (the existent and the newly negotiated). An iSCSI target
MUST perform integrity checking before the new parameters take
effect. An initiator MAY perform integrity checking.
An iSCSI initiator or target MAY terminate a negotiation that does
not terminate within an implementation-specific reasonable time or
number of exchanges, but SHOULD allow at least six (6) exchanges.
6.2.1. List negotiations
In list negotiation, the originator sends a list of values (which
may include "None") in its order of preference.
The responding party MUST respond with the same key and the first
value that it supports (and is allowed to use for the specific
originator) selected from the originator list.
The constant "None" MUST always be used to indicate a missing
function. However, "None" is only a valid selection if it is
explicitly proposed. When "None" is proposed as a selection item
in a negotiation for a key, it indicates to the responder that not
supporting any functionality related to that key is legal, and if
"None" is the negotiation result for such a key, it means that
key-specific semantics are not operational for the negotiation
scope (connection or session) of that key.
If an acceptor does not understand any particular value in a list,
it MUST ignore it. If an acceptor does not support, does not
understand, or is not allowed to use any of the proposed options
with a specific originator, it may use the constant "Reject" or
terminate the negotiation. The selection of a value not proposed
MUST be handled by the originator as a protocol error.
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6.2.2. Simple-value Negotiations
For simple-value negotiations, the accepting party MUST answer
with the same key. The value it selects becomes the negotiation
result.
Proposing a value not admissible (e.g., not within the specified
bounds) MAY be answered with the constant "Reject", otherwise the
acceptor MUST select an admissible value.
The selection, by the acceptor, of a value not admissible under
the selection rules is considered a protocol error. The selection
rules are key-specific.
For a numerical range the value selected MUST be an integer within
the proposed range or "Reject" (if the range is unacceptable).
For Boolean negotiations (i.e., keys taking the values Yes or No),
the accepting party MUST answer with the same key and the result
of the negotiation when the received value does not determine that
result by itself. The last value transmitted becomes the
negotiation result. The rules for selecting the value to answer
with are expressed as Boolean functions of the value received, and
the value that the accepting party would have selected if given a
choice.
Specifically, the two cases in which answers are OPTIONAL are:
- The Boolean function is "AND" and the value "No" is
received. The outcome of the negotiation is "No".
- The Boolean function is "OR" and the value "Yes" is
received. The outcome of the negotiation is "Yes".
Responses are REQUIRED in all other cases, and the value chosen
and sent by the acceptor becomes the outcome of the negotiation.
6.3. Login Phase
The Login Phase establishes an iSCSI connection between an
initiator and a target; it creates also a new session or
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associates the connection to an existing session. The Login Phase
sets the iSCSI protocol parameters, security parameters, and
authenticates the initiator and target to each other.
The Login Phase is only implemented via Login request and
responses. The whole Login Phase is considered as a single task
and has a single Initiator Task Tag (similar to the linked SCSI
commands).
There MUST NOT be more than one outstanding Login Request, or
Login Response on an iSCSI connection. An outstanding PDU in this
context is one that has not been acknowledged by the remote iSCSI
side.
The default MaxRecvDataSegmentLength is used during Login.
The Login Phase sequence of requests and responses proceeds as
follows:
- Login initial request
- Login partial response (optional)
- More Login requests and responses (optional)
- Login Final-Response (mandatory)
The initial login request of any connection MUST include the
InitiatorName key=value pair. The initial login request of the
first connection of a session MAY also include the SessionType
key=value pair. For any connection within a session whose type is
not "Discovery", the first login request MUST also include the
TargetName key=value pair.
The Login Final-response accepts or rejects the Login request.
The Login Phase MAY include a SecurityNegotiation stage and a
LoginOperationalNegotiation stage and MUST include at least one of
them, but the included stage MAY be empty except for the mandatory
names.
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The login requests and responses contain a field (CSG) that
indicates the current negotiation stage (SecurityNegotiation or
LoginOperationalNegotiation). If both stages are used, the
SecurityNegotiation MUST precede the LoginOperationalNegotiation.
Some operational parameters can be negotiated outside the login
through Text requests and responses.
Authentication-related security keys (Section 12 ) MUST be
completely negotiated within the Login Phase. The use of
underlying IPsec security is specified in Section 9.3, in
[RFC3723], and in [IPSEC-IPS}. iSCSI support for security within
the protocol only consists of authentication in the Login Phase.
In some environments, a target or an initiator is not interested
in authenticating its counterpart. It is possible to bypass
authentication through the Login request and response.
The initiator and target MAY want to negotiate iSCSI
authentication parameters. Once this negotiation is completed, the
channel is considered secure.
Most of the negotiation keys are only allowed in a specific stage.
The SecurityNegotiation keys appear in Section 12 and the
LoginOperationalNegotiation keys appear in Section 13. Only a
limited set of keys (marked as Any-Stage in Section 13) may be
used in any of the two stages.
Any given Login request or response belongs to a specific stage;
this determines the negotiation keys allowed with the request or
response. It is considered to be a protocol error to send a key
not allowed in the current stage.
Stage transition is performed through a command exchange
(request/response) that carries the T bit and the same CSG code.
During this exchange, the next stage is selected by the target
through the "next stage" code (NSG). The selected NSG MUST NOT
exceed the value stated by the initiator. The initiator can
request a transition whenever it is ready, but a target can only
respond with a transition after one is proposed by the initiator.
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In a negotiation sequence, the T bit settings in one pair of login
request-responses have no bearing on the T bit settings of the
next pair. An initiator that has a T bit set to 1 in one pair and
is answered with a T bit setting of 0 may issue the next request
with T bit set to 0.
When a transition is requested by the initiator and acknowledged
by the target, both the initiator and target switch to the
selected stage.
Targets MUST NOT submit parameters that require an additional
initiator login request in a login response with the T bit set to
1.
Stage transitions during login (including entering and exit) are
only possible as outlined in the following table:
+-----------------------------------------------------------+
|From To -> | Security | Operational | FullFeature |
| | | | | |
| V | | | |
+-----------------------------------------------------------+
| (start) | yes | yes | no |
+-----------------------------------------------------------+
| Security | no | yes | yes |
+-----------------------------------------------------------+
| Operational | no | no | yes |
+-----------------------------------------------------------+
The Login Final-Response that accepts a Login Request can only
come as a response to a Login request with the T bit set to 1, and
both the request and response MUST indicate FullFeaturePhase as
the next phase via the NSG field.
Neither the initiator nor the target should attempt to declare or
negotiate a parameter more than once during login except for
responses to specific keys that explicitly allow repeated key
declarations (e.g., TargetAddress). An attempt to
renegotiate/redeclare parameters not specifically allowed MUST be
detected by the initiator and target. If such an attempt is
detected by the target, the target MUST respond with Login reject
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(initiator error); if detected by the initiator, the initiator
MUST drop the connection.
6.3.1. Login Phase Start
The Login Phase starts with a login request from the initiator to
the target. The initial login request includes:
-Protocol version supported by the initiator.
-iSCSI Initiator Name and iSCSI Target Name
-ISID, TSIH, and connection Ids
-Negotiation stage that the initiator is ready to enter.
A login may create a new session or it may add a connection to an
existing session. Between a given iSCSI Initiator Node (selected
only by an InitiatorName) and a given iSCSI target defined by an
iSCSI TargetName and a Target Portal Group Tag, the login results
are defined by the following table:
+----------------------------------------------------------------+
|ISID | TSIH | CID | Target action |
+----------------------------------------------------------------+
|new | non-zero | any | fail the login |
| | | | ("session does not exist") |
+----------------------------------------------------------------+
|new | zero | any | instantiate a new session |
+----------------------------------------------------------------+
|existing| zero | any | do session reinstatement |
| | | | (see Section 6.3.5) |
+----------------------------------------------------------------+
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|existing| non-zero | new | add a new connection to |
| | existing | | the session |
+----------------------------------------------------------------+
|existing| non-zero |existing| do connection reinstatement|
| | existing | | (see Section 7.1.4.3) |
+----------------------------------------------------------------+
|existing| non-zero | any | fail the login |
| | new | | ("session does not exist") |
+----------------------------------------------------------------+
Determination of "existing" or "new" are made by the target.
Optionally, the login request may include:
-Security parameters
OR
-iSCSI operational parameters
AND/OR
-The next negotiation stage that the initiator is ready to
enter.
The target can answer the login in the following ways:
-Login Response with Login reject. This is an immediate
rejection from the target that causes the connection to
terminate and the session to terminate if this is the first
(or only) connection of a new session. The T bit and the CSG
and NSG fields are reserved.
-Login Response with Login accept as a final response (T bit
set to 1 and the NSG in both request and response are set to
FullFeaturePhase). The response includes the protocol
version supported by the target and the session ID, and may
include iSCSI operational or security parameters (that
depend on the current stage).
-Login Response with Login Accept as a partial response (NSG
not set to FullFeaturePhase in both request and response)
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that indicates the start of a negotiation sequence. The
response includes the protocol version supported by the
target and either security or iSCSI parameters (when no
security mechanism is chosen) supported by the target.
If the initiator decides to forego the SecurityNegotiation stage,
it issues the Login with the CSG set to
LoginOperationalNegotiation and the target may reply with a Login
Response that indicates that it is unwilling to accept the
connection (see Section 11.13) without SecurityNegotiation and
will terminate the connection with a response of Authentication
failure (see Section 11.13.5).
If the initiator is willing to negotiate iSCSI security, but is
unwilling to make the initial parameter proposal and may accept a
connection without iSCSI security, it issues the Login with the T
bit set to 1, the CSG set to SecurityNegotiation, and NSG set to
LoginOperationalNegotiation. If the target is also ready to skip
security, the login response only contains the
TargetPortalGroupTag key (see Section 13.9), the T bit set to 1,
the CSG set to SecurityNegotiation, and NSG set to
LoginOperationalNegotiation.
An initiator that chooses to operate without iSCSI security and
with all the operational parameters taking the default values
issues the Login with the T bit set to 1, the CSG set to
LoginOperationalNegotiation, and NSG set to FullFeaturePhase. If
the target is also ready to forego security and can finish its
LoginOperationalNegotiation, the Login response has T bit set to
1, the CSG set to LoginOperationalNegotiation, and NSG set to
FullFeaturePhase in the next stage.
During the Login Phase the iSCSI target MUST return the
TargetPortalGroupTag key with the first Login Response PDU with
which it is allowed to do so (i.e., the first Login Response
issued after the first Login Request with the C bit set to 0) for
all session types. The TargetPortalGroupTag key value indicates
the iSCSI portal group servicing the Login Request PDU. If the
reconfiguration of iSCSI portal groups is a concern in a given
environment, the iSCSI initiator should use this key to ascertain
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that it had indeed initiated the Login Phase with the intended
target portal group.
6.3.2. iSCSI Security Negotiation
The security exchange sets the security mechanism and
authenticates the initiator user and the target to each other. The
exchange proceeds according to the authentication method chosen in
the negotiation phase and is conducted using the login requests'
and responses' key=value parameters.
An initiator directed negotiation proceeds as follows:
-The initiator sends a login request with an ordered list of
the options it supports (authentication algorithm). The
options are listed in the initiator's order of preference.
The initiator MAY also send private or public extension
options.
-The target MUST reply with the first option in the list it
supports and is allowed to use for the specific initiator
unless it does not support any in which case it MUST answer
with "Reject" (see Section 6.2). The parameters are encoded
in UTF8 as key=value. For security parameters, see Section
12.
-When the initiator considers that it is ready to conclude the
SecurityNegotiation stage, it sets the T bit to 1 and the
NSG to what it would like the next stage to be. The target
will then set the T bit to 1 and set NSG to the next stage
in the Login response when it finishes sending its security
keys. The next stage selected will be the one the target
selected. If the next stage is FullFeaturePhase, the target
MUST respond with a Login Response with the TSIH value.
If the security negotiation fails at the target, then the target
MUST send the appropriate Login Response PDU. If the security
negotiation fails at the initiator, the initiator SHOULD close the
connection.
It should be noted that the negotiation might also be directed by
the target if the initiator does support security, but is not
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ready to direct the negotiation (propose options) - see Appendix B
for an example.
6.3.3. Operational Parameter Negotiation During the Login Phase
Operational parameter negotiation during the login MAY be done:
- Starting with the first Login request if the initiator does
not propose any security/ integrity option.
- Starting immediately after the security negotiation if the
initiator and target perform such a negotiation.
Operational parameter negotiation MAY involve several Login
request-response exchanges started and terminated by the
initiator. The initiator MUST indicate its intent to terminate the
negotiation by setting the T bit to 1; the target sets the T bit
to 1 on the last response.
Even when the initiator indicates its intent to switch stage by
setting the T bit to 1 in a Login request, the target MAY respond
with a Login response with the T bit set to 0. In that case, the
initiator SHOULD continue to set the T bit to 1 in subsequent
Login requests (even empty) that it sends, until target sends a
Login response with the T bit set to 1 or sends a key that
requires initiator to set the T bit to 0.
Some session specific parameters can only be specified during the
Login Phase of the first connection of a session (i.e., begun by a
login request that contains a zero-valued TSIH) - the leading
Login Phase (e.g., the maximum number of connections that can be
used for this session).
A session is operational once it has at least one connection in
FullFeaturePhase. New or replacement connections can only be added
to a session after the session is operational.
For operational parameters, see Section 13.
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6.3.4. Connection Reinstatement
Connection reinstatement is the process of an initiator logging in
with a ISID-TSIH-CID combination that is possibly active from the
target's perspective, which causes the implicit logging out of the
connection corresponding to the CID and reinstating a new Full
Feature Phase iSCSI connection in its place (with the same CID).
Thus, the TSIH in the Login Request PDU MUST be non-zero and CID
does not change during a connection reinstatement. The Login
request performs the logout function of the old connection if an
explicit logout was not performed earlier. In sessions with a
single connection, this may imply the opening of a second
connection with the sole purpose of cleaning up the first. Targets
MUST support opening a second connection even when they do not
support multiple connections in Full Feature Phase if
ErrorRecoveryLevel is 2 and SHOULD support opening a second
connection if ErrorRecoveryLevel is less than 2.
If the operational ErrorRecoveryLevel is 2, connection
reinstatement enables future task reassignment. If the operational
ErrorRecoveryLevel is less than 2, connection reinstatement is the
replacement of the old CID without enabling task reassignment. In
this case, all the tasks that were active on the old CID must be
immediately terminated without further notice to the initiator.
The initiator connection state MUST be CLEANUP_WAIT (Section
8.1.3) when the initiator attempts a connection reinstatement.
In practical terms, in addition to the implicit logout of the old
connection, reinstatement is equivalent to a new connection login.
6.3.5. Session Reinstatement, Closure, and Timeout
Session reinstatement is the process of the initiator logging in
with an ISID that is possibly active from the target's
perspective. Thus implicitly logging out the session that
corresponds to the ISID and reinstating a new iSCSI session in its
place (with the same ISID). Therefore, the TSIH in the Login PDU
MUST be zero to signal session reinstatement. Session
reinstatement causes all the tasks that were active on the old
session to be immediately terminated by the target without further
notice to the initiator.
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The initiator session state MUST be FAILED (Section 8.3) when the
initiator attempts a session reinstatement.
Session closure is an event defined to be one of the following:
- A successful "session close" logout.
- A successful "connection close" logout for the last Full
Feature Phase connection when no other connection in the
session is waiting for cleanup (Section 8.2) and no tasks in
the session are waiting for reassignment.
Session timeout is an event defined to occur when the last
connection state timeout expires and no tasks are waiting for
reassignment. This takes the session to the FREE state (N6
transition in the session state diagram).
6.3.5.1. Loss of Nexus Notification
The iSCSI layer provides the SCSI layer with the "I_T nexus loss"
notification when any one of the following events happens:
Successful completion of session reinstatement.
Session closure event.
Session timeout event.
Certain SCSI object clearing actions may result due to the
notification in the SCSI end nodes, as documented in Appendix E.
6.3.6. Session Continuation and Failure
Session continuation is the process by which the state of a
preexisting session continues to be used by connection
reinstatement (Section 6.3.4), or by adding a connection with a
new CID. Either of these actions associates the new transport
connection with the session state.
Session failure is an event where the last Full Feature Phase
connection reaches the CLEANUP_WAIT state (Section 8.2), or
completes a successful recovery logout thus causing all active
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tasks (that are formerly allegiant to the connection) to start
waiting for task reassignment.
6.4. Operational Parameter Negotiation Outside the Login Phase
Some operational parameters MAY be negotiated outside (after) the
Login Phase.
Parameter negotiation in Full Feature Phase is done through Text
requests and responses. Operational parameter negotiation MAY
involve several Text request-response exchanges, which the
initiator always starts, terminates, and uses the same Initiator
Task Tag. The initiator MUST indicate its intent to finish the
negotiation by setting the F bit to 1; the target sets the F bit
to 1 on the last response.
If the target responds to a Text request with the F bit set to 1
with a Text response with the F bit set to 0, the initiator should
keep sending the Text request (even empty) with the F bit set to
1, while it still wants to finish the negotiation, until it
receives the Text response with the F bit set to 1. Responding to
a Text request with the F bit set to 1 with an empty (no key=value
pairs) response with the F bit set to 0 is discouraged.
Even when the initiator indicates its intent to finish the
negotiation by setting the F bit to 1 in a Text request, the
target MAY respond with a Text response with the F bit set to 0.
In that case, the initiator SHOULD continue to set the F bit to 1
in subsequent Text requests (even empty) that it sends, until
target sends the final Text response with the F bit set to 1. Note
that in the same case of Text request with the F bit set to 1,
target SHOULD NOT respond with an empty (no key=value pairs) Text
response with the F bit set to 0, because such a response may
cause the initiator to abandon negotiation.
Targets MUST NOT submit parameters that require an additional
initiator Text request in a Text response with the F bit set to 1.
In a negotiation sequence, the F bit settings in one pair of Text
request-responses have no bearing on the F bit settings of the
next pair. An initiator that has the F bit set to 1 in a request
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and is being answered with an F bit setting of 0 may issue the
next request with the F bit set to 0.
Whenever the target responds with the F bit set to 0, it MUST set
the Target Transfer Tag to a value other than the default
0xffffffff.
An initiator MAY reset an operational parameter negotiation by
issuing a Text request with the Target Transfer Tag set to the
value 0xffffffff after receiving a response with the Target
Transfer Tag set to a value other than 0xffffffff. A target may
reset an operational parameter negotiation by answering a Text
request with a Reject PDU.
Neither the initiator nor the target should attempt to declare or
negotiate a parameter more than once during any negotiation
sequence, except for responses to specific keys that explicitly
allow repeated key declarations (e.g., TargetAddress). If detected
by the target, this MUST result in a Reject PDU with a reason of
"protocol error". The initiator MUST reset the negotiation as
outlined above.
Parameters negotiated by a text exchange negotiation sequence only
become effective after the negotiation sequence is completed.
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7. iSCSI Error Handling and Recovery
7.1. Overview
7.1.1. Background
The following two considerations prompted the design of much of
the error recovery functionality in iSCSI:
An iSCSI PDU may fail the digest check and be dropped, despite
being received by the TCP layer. The iSCSI layer must
optionally be allowed to recover such dropped PDUs.
A TCP connection may fail at any time during the data
transfer. All the active tasks must optionally be allowed
to be continued on a different TCP connection within the
same session.
Implementations have considerable flexibility in deciding what
degree of error recovery to support, when to use it and by which
mechanisms to achieve the required behavior. Only the externally
visible actions of the error recovery mechanisms must be
standardized to ensure interoperability.
This Section describes a general model for recovery in support of
interoperability. See Appendix D for further detail on how the
described model may be implemented. Compliant implementations do
not have to match the implementation details of this model as
presented, but the external behavior of such implementations must
correspond to the externally observable characteristics of the
presented model.
7.1.2. Goals
The major design goals of the iSCSI error recovery scheme are as
follows:
Allow iSCSI implementations to meet different requirements by
defining a collection of error recovery mechanisms that
implementations may choose from.
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Ensure interoperability between any two implementations
supporting different sets of error recovery capabilities.
Define the error recovery mechanisms to ensure command
ordering even in the face of errors, for initiators that
demand ordering.
Do not make additions in the fast path, but allow moderate
complexity in the error recovery path.
Prevent both the initiator and target from attempting to
recover the same set of PDUs at the same time. For example,
there must be a clear "error recovery functionality
distribution" between the initiator and target.
7.1.3. Protocol Features and State Expectations
The initiator mechanisms defined in connection with error recovery
are:
a) NOP-OUT to probe sequence numbers of the target (Section
11.18)
b) Command retry (Section 7.2.1)
c) Recovery R2T support (Section 7.8)
d) Requesting retransmission of status/data/R2T using the
SNACK facility (Section 11.16)
e) Acknowledging the receipt of the data (Section 11.16)
f) Reassigning the connection allegiance of a task to a
different TCP connection (Section 7.2.2)
g) Terminating the entire iSCSI session to start afresh
(Section 7.1.4.4)
The target mechanisms defined in connection with error recovery
are:
a) NOP-IN to probe sequence numbers of the initiator (Section
11.19)
b) Requesting retransmission of data using the recovery R2T
feature (Section 7)
c) SNACK support (Section 11.16)
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d) Requesting that parts of read data be acknowledged (Section
11.7.2)
e) Allegiance reassignment support (Section 7.2.2)
f) Terminating the entire iSCSI session to force the initiator
to start over (Section 7.1.4.4)
For any outstanding SCSI command, it is assumed that iSCSI, in
conjunction with SCSI at the initiator, is able to keep enough
information to be able to rebuild the command PDU, and that
outgoing data is available (in host memory) for retransmission
while the command is outstanding. It is also assumed that at the
target, incoming data (read data) MAY be kept for recovery or it
can be reread from a device server.
It is further assumed that a target will keep the "status & sense"
for a command it has executed if it supports status
retransmission.
A target that agrees to support data retransmission is expected to
be prepared to retransmit the outgoing data (i.e., Data-In) on
request until either the status for the completed command is
acknowledged, or the data in question has been separately
acknowledged.
7.1.4. Recovery Classes
iSCSI enables the following classes of recovery (in the order of
increasing scope of affected iSCSI tasks):
- Within a command (i.e., without requiring command restart).
- Within a connection (i.e., without requiring the connection
to be rebuilt, but perhaps requiring command restart).
- Connection recovery (i.e., perhaps requiring connections to
be rebuilt and commands to be reissued).
- Session recovery.
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The recovery scenarios detailed in the rest of this Section are
representative rather than exclusive. In every case, they detail
the lowest class recovery that MAY be attempted. The implementer
is left to decide under which circumstances to escalate to the
next recovery class and/or what recovery classes to implement.
Both the iSCSI target and initiator MAY escalate the error
handling to an error recovery class, which impacts a larger number
of iSCSI tasks in any of the cases identified in the following
discussion.
In all classes, the implementer has the choice of deferring errors
to the SCSI initiator (with an appropriate response code), in
which case the task, if any, has to be removed from the target and
all the side-effects, such as ACA, must be considered.
Use of within-connection and within-command recovery classes MUST
NOT be attempted before the connection is in Full Feature Phase.
In the detailed description of the recovery classes, the mandating
terms (MUST, SHOULD, MAY, etc.) indicate normative actions to be
executed if the recovery class is supported (see Section 7.1.5 for
the related negotiation semantics) and used.
7.1.4.1. Recovery Within-command
At the target, the following cases lend themselves to within-
command recovery:
a) Lost data PDU - realized through one of the following:
b) Data digest error - dealt with as specified in Section 7.8,
using the option of a recovery R2T.
c) Sequence reception timeout (no data or partial-data-and-no-F-
bit) - considered an implicit sequence error and dealt with
as specified in Section 7.9, using the option of a recovery
R2T.
d) Header digest error, which manifests as a sequence reception
timeout or a sequence error - dealt with as specified in
Section 7.9, using the option of a recovery R2T.
At the initiator, the following cases lend themselves to within-
command recovery:
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a) Lost data PDU or lost R2T - realized through one of the
following:
b) Data digest error - dealt with as specified in Section 7.8,
using the option of a SNACK.
c) Sequence reception timeout (no status) or response reception
timeout - dealt with as specified in Section 7.9, using the
option of a SNACK.
d) Header digest error, which manifests as a sequence reception
timeout or a sequence error - dealt with as specified in
Section 7.9, using the option of a SNACK.
To avoid a race with the target, which may already have a recovery
R2T or a termination response on its way, an initiator SHOULD NOT
originate a SNACK for an R2T based on its internal timeouts (if
any). Recovery in this case is better left to the target.
The timeout values used by the initiator and target are outside
the scope of this document. Sequence reception timeout is
generally a large enough value to allow the data sequence transfer
to be complete.
7.1.4.2. Recovery Within-connection
At the initiator, the following cases lend themselves to within-
connection recovery:
a) Requests not acknowledged for a long time. Requests are
acknowledged explicitly through ExpCmdSN or implicitly by
receiving data and/or status. The initiator MAY retry non-
acknowledged commands as specified in Section 7.2.
b) Lost iSCSI numbered Response. It is recognized by either
identifying a data digest error on a Response PDU or a Data-
In PDU carrying the status, or by receiving a Response PDU
with a higher StatSN than expected. In the first case, digest
error handling is done as specified in Section 7.8 using the
option of a SNACK. In the second case, sequence error
handling is done as specified in Section 7.9, using the
option of a SNACK.
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At the target, the following cases lend themselves to within-
connection recovery:
- Status/Response not acknowledged for a long time. The target
MAY issue a NOP-IN (with a valid Target Transfer Tag or
otherwise) that carries the next status sequence number it
is going to use in the StatSN field. This helps the
initiator detect any missing StatSN(s) and issue a SNACK for
the status.
The timeout values used by the initiator and the target are
outside the scope of this document.
7.1.4.3. Connection Recovery
At an iSCSI initiator, the following cases lend themselves to
connection recovery:
a) TCP connection failure: The initiator MUST close the
connection. It then MUST either implicitly or explicitly
logout the failed connection with the reason code "remove the
connection for recovery" and reassign connection allegiance
for all commands still in progress associated with the failed
connection on one or more connections (some or all of which
MAY be newly established connections) using the "Task
reassign" task management function (see Section 11.5.1). For
an initiator, a command is in progress as long as it has not
received a response or a Data-In PDU including status.
Note: The logout function is mandatory. However, a new
connection establishment is only mandatory if the failed
connection was the last or only connection in the session.
b) Receiving an Asynchronous Message that indicates one or all
connections in a session has been dropped. The initiator
MUST handle it as a TCP connection failure for the
connection(s) referred to in the Message.
At an iSCSI target, the following cases lend themselves to
connection recovery:
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- TCP connection failure. The target MUST close the connection
and, if more than one connection is available, the target
SHOULD send an Asynchronous Message that indicates it has
dropped the connection. Then, the target will wait for the
initiator to continue recovery.
7.1.4.4. Session Recovery
Session recovery should be performed when all other recovery
attempts have failed. Very simple initiators and targets MAY
perform session recovery on all iSCSI errors and rely on recovery
on the SCSI layer and above.
Session recovery implies the closing of all TCP connections,
internally aborting all executing and queued tasks for the given
initiator at the target, terminating all outstanding SCSI commands
with an appropriate SCSI service response at the initiator, and
restarting a session on a new set of connection(s) (TCP connection
establishment and login on all new connections).
For possible clearing effects of session recovery on SCSI and
iSCSI objects, refer to Appendix E.
7.1.5. Error Recovery Hierarchy
The error recovery classes described so far are organized into a
hierarchy for ease in understanding and to limit the
implementation complexity. With few and well defined recovery
levels interoperability is easier to achieve. The attributes of
this hierarchy are as follows:
a) Each level is a superset of the capabilities of the
previous level. For example, Level 1 support implies
supporting all capabilities of Level 0 and more.
b) As a corollary, supporting a higher error recovery level
means increased sophistication and possibly an increase
in resource requirements.
c) Supporting error recovery level "n" is advertised and
negotiated by each iSCSI entity by exchanging the text
key "ErrorRecoveryLevel=n". The lower of the two
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exchanged values is the operational ErrorRecoveryLevel
for the session.
The following diagram represents the error recovery hierarchy.
+
/ \
/ 2 \ <-- Connection recovery
+-----+
/ 1 \ <-- Digest failure recovery
+---------+
/ 0 \ <-- Session failure recovery
+-------------+
The following table lists the error recovery capabilities expected
from the implementations that support each error recovery level.
+-------------------+--------------------------------------------+
|ErrorRecoveryLevel | Associated Error recovery capabilities |
+-------------------+--------------------------------------------+
| 0 | Session recovery class |
| | (Session Recovery) |
+-------------------+--------------------------------------------+
| 1 | Digest failure recovery (See Note below.) |
| | plus the capabilities of ER Level 0 |
+-------------------+--------------------------------------------+
| 2 | Connection recovery class |
| | (Connection Recovery) |
| | plus the capabilities of ER Level 1 |
+-------------------+--------------------------------------------+
Note: Digest failure recovery is comprised of two recovery
classes: Within-Connection recovery class (Recovery Within-
connection) and Within-Command recovery class (Recovery Within-
command).
When a defined value of ErrorRecoveryLevel is proposed by an
originator in a text negotiation, the originator MUST support the
functionality defined for the proposed value and additionally,
functionality corresponding to any defined value numerically less
than the proposed. When a defined value of ErrorRecoveryLevel is
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returned by a responder in a text negotiation, the responder MUST
support the functionality corresponding to the ErrorRecoveryLevel
it is accepting.
When either party attempts to use error recovery functionality
beyond what is negotiated, the recovery attempts MAY fail unless
an apriori agreement outside the scope of this document exists
between the two parties to provide such support.
Implementations MUST support error recovery level "0", while the
rest are OPTIONAL to implement. In implementation terms, the
above striation means that the following incremental
sophistication with each level is required.
+-------------------+--------------------------------------------+
|Level transition | Incremental requirement |
+-------------------+--------------------------------------------+
| 0->1 | PDU retransmissions on the same connection|
+-------------------+--------------------------------------------+
| 1->2 | Retransmission across connections and |
| | allegiance reassignment |
+-------------------+--------------------------------------------+
7.2. Retry and Reassign in Recovery
This Section summarizes two important and somewhat related iSCSI
protocol features used in error recovery.
7.2.1. Usage of Retry
By resending the same iSCSI command PDU ("retry") in the absence
of a command acknowledgement (by way of an ExpCmdSN update) or a
response, an initiator attempts to "plug" (what it thinks are) the
discontinuities in CmdSN ordering on the target end. Discarded
command PDUs, due to digest errors, may have created these
discontinuities.
Retry MUST NOT be used for reasons other than plugging command
sequence gaps, and in particular, cannot be used for requesting
PDU retransmissions from a target. Any such PDU retransmission
requests for a currently allegiant command in progress may be made
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using the SNACK mechanism described in Section 11.16, although the
usage of SNACK is OPTIONAL.
If initiators, as part of plugging command sequence gaps as
described above, inadvertently issue retries for allegiant
commands already in progress (i.e., targets did not see the
discontinuities in CmdSN ordering), the duplicate commands are
silently ignored by targets as specified in Section 4.2.2.1.
When an iSCSI command is retried, the command PDU MUST carry the
original Initiator Task Tag and the original operational
attributes (e.g., flags, function names, LUN, CDB etc.) as well as
the original CmdSN. The command being retried MUST be sent on the
same connection as the original command unless the original
connection was already successfully logged out.
7.2.2. Allegiance Reassignment
By issuing a "task reassign" task management request (Section
11.5.1), the initiator signals its intent to continue an already
active command (but with no current connection allegiance) as part
of connection recovery. This means that a new connection
allegiance is requested for the command, which seeks to associate
it to the connection on which the task management request is being
issued. Before the allegiance reassignment is attempted for a
task, an implicit or explicit Logout with the reason code "remove
the connection for recovery" (see Section 11.14.1) MUST be
successfully completed for the previous connection to which the
task was allegiant.
In reassigning connection allegiance for a command, the targets
SHOULD continue the command from its current state. For example,
when reassigning read commands, the target SHOULD take advantage
of the ExpDataSN field provided by the Task Management function
request (which must be set to zero if there was no data transfer)
and bring the read command to completion by sending the remaining
data and sending (or resending) the status. ExpDataSN
acknowledges all data sent up to, but not including, the Data-In
PDU and or R2T with DataSN (or R2TSN) equal to ExpDataSN. However,
targets may choose to send/receive all unacknowledged data or all
of the data on a reassignment of connection allegiance if unable
to recover or maintain accurate state. Initiators MUST NOT
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subsequently request data retransmission through Data SNACK for
PDUs numbered less than ExpDataSN (i.e., prior to the acknowledged
sequence number). For all types of commands, a reassignment
request implies that the task is still considered in progress by
the initiator and the target must conclude the task appropriately
if the target returns the "Function Complete" response to the
reassignment request. This might possibly involve retransmission
of data/R2T/status PDUs as necessary, but MUST involve the
(re)transmission of the status PDU.
It is OPTIONAL for targets to support the allegiance reassignment.
This capability is negotiated via the ErrorRecoveryLevel text key
during the login time. When a target does not support allegiance
reassignment, it MUST respond with a Task Management response code
of "Allegiance reassignment not supported". If allegiance
reassignment is supported by the target, but the task is still
allegiant to a different connection, or a successful recovery
Logout of the previously allegiant connection was not performed,
the target MUST respond with a Task Management response code of
"Task still allegiant".
If allegiance reassignment is supported by the target, the Task
Management response to the reassignment request MUST be issued
before the reassignment becomes effective.
If a SCSI Command that involves data input is reassigned, any
SNACK Tag it holds for a final response from the original
connection is deleted and the default value of 0 MUST be used
instead.
7.3. Usage Of Reject PDU in Recovery
Targets MUST NOT implicitly terminate an active task by sending a
Reject PDU for any PDU exchanged during the life of the task. If
the target decides to terminate the task, a Response PDU (SCSI,
Text, Task, etc.) must be returned by the target to conclude the
task. If the task had never been active before the Reject (i.e.,
the Reject is on the command PDU), targets should not send any
further responses because the command itself is being discarded.
The above rule means that the initiator can eventually expect a
response on receiving Rejects, if the received Reject is for a PDU
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other than the command PDU itself. The non-command Rejects only
have diagnostic value in logging the errors, and they can be used
for retransmission decisions by the initiators.
The CmdSN of the rejected command PDU (if it is a non-immediate
command) MUST NOT be considered received by the target (i.e., a
command sequence gap must be assumed for the CmdSN), even though
the CmdSN of the rejected command PDU may be reliably ascertained.
Upon receiving the Reject, the initiator MUST plug the CmdSN gap
in order to continue to use the session. The gap may be plugged
either by transmitting a command PDU with the same CmdSN, or by
aborting the task (see SCS on how an abort may plug a CmdSN gap).
When a data PDU is rejected and its DataSN can be ascertained, a
target MUST advance ExpDataSN for the current data burst if a
recovery R2T is being generated. The target MAY advance its
ExpDataSN if it does not attempt to recover the lost data PDU.
7.4. Error Recovery Considerations for Discovery Sessions
7.4.1. ErrorRecoveryLevel for Discovery Sessions
The negotiation of the key ErrorRecoveryLevel is not required for
Discovery sessions -- i.e., for sessions that negotiated
"SessionType=Discovery" -- because the default value of 0 is
necessary and sufficient for Discovery sessions. It is however
possible that some legacy iSCSI implementations might attempt to
negotiate the ErrorRecoveryLevel key on Discovery sessions. When
such a negotiation attempt is made by the remote side, a compliant
iSCSI implementation MUST propose a value of 0 (zero) in response.
The operational ErrorRecoveryLevel for Discovery sessions thus
MUST
be 0. This naturally follows from the functionality constraints
that Section 4.3 imposes on Discovery sessions.
7.4.2. Reinstatement Semantics for Discovery Sessions
Discovery sessions are intended to be relatively short-lived.
Initiators are not expected to establish multiple Discovery
sessions to the same iSCSI Network Portal. An initiator may use
the same iSCSI Initiator Name and ISID when establishing different
unique sessions with different targets and/or different portal
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groups. This behavior is discussed in Section 10.1.1 and is, in
fact, encouraged as conservative reuse of ISIDs.
The ISID RULE in Section 4.4.3 states that there must not be more
than one session with a matching 4-tuple: <InitiatorName, ISID,
TargetName, TargetPortalGroupTag>. While the spirit of the ISID
RULE applies to Discovery sessions the same as it does for Normal
sessions, note that some Discovery sessions differ from the Normal
sessions in two important aspects:
a) Because Appendix C allows a Discovery session to be
established without specifying a TargetName key in the
Login Request PDU (let us call such a session an "Unnamed"
Discovery session), there is no Target Node context to
enforce the ISID RULE.
b) Portal Groups are defined only in the context of a Target
Node. When the TargetName key is NULL-valued (i.e., not
specified), the TargetPortalGroupTag thus cannot be
ascertained to enforce the ISID RULE.
The following two sections describe each of the two scenarios --
Named Discovery sessions and Unnamed Discovery sessions.
7.4.2.1. Unnamed Discovery Sessions
For Unnamed Discovery sessions, neither the TargetName nor the
TargetPortalGroupTag is available to the targets in order to
enforce the ISID RULE. So the following rule applies.
UNNAMED ISID RULE: Targets MUST enforce the uniqueness of the
following 4-tuple for Unnamed Discovery sessions: <InitiatorName,
ISID, NULL, TargetAddress>. The following semantics are implied by
this uniqueness requirement.
Targets SHOULD allow concurrent establishment of one Discovery
session with each of its Network Portals by the same initiator
port with a given iSCSI Node Name and an ISID. Each of the
concurrent Discovery sessions, if established by the same
initiator port to other Network Portals, MUST be treated as
independent sessions -- i.e., one session MUST NOT reinstate the
other.
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A new Unnamed Discovery session that has a matching
<InitiatorName, ISID, NULL, TargetAddress> to an existing
Discovery session MUST reinstate the existing Unnamed Discovery
session. Note thus that only an Unnamed Discovery session may
reinstate an Unnamed Discovery session.
7.4.2.2. Named Discovery Session
For a Named Discovery session, the TargetName key is specified by
the initiator and thus the target can unambiguously ascertain the
TargetPortalGroupTag as well. Since all the four elements of the
4-tuple are known, the ISID RULE MUST be enforced by targets with
no changes from Section 4.4.3 semantics. A new session with a
matching <InitiatorName, ISID, TargetName, TargetPortalGroupTag>
thus will reinstate an existing session. Note in this case that
any new iSCSI session (Discovery or Normal) with the matching 4-
tuple may reinstate an existing Named Discovery iSCSI session.
7.4.3. Target PDUs During Discovery
Targets SHOULD NOT send any responses other than a Text Response
and Logout Response on a Discovery session, once in Full Feature
Phase.
Implementation Note: A target may simply drop the connection in a
Discovery session when it would have requested a Logout via an
Async Message on Normal sessions.
7.5. Connection Timeout Management
iSCSI defines two session-global timeout values (in seconds) -
Time2Wait and Time2Retain - that are applicable when an iSCSI Full
Feature Phase connection is taken out of service either
intentionally or by an exception. Time2Wait is the initial
"respite time" before attempting an explicit/implicit Logout for
the CID in question or task reassignment for the affected tasks
(if any). Time2Retain is the maximum time after the initial
respite interval that the task and/or connection state(s) is/are
guaranteed to be maintained on the target to cater to a possible
recovery attempt. Recovery attempts for the connection and/or
task(s) SHOULD NOT be made before Time2Wait seconds, but MUST be
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completed within Time2Retain seconds after that initial Time2Wait
waiting period.
7.5.1. Timeouts on Transport Exception Events
A transport connection shutdown or a transport reset without any
preceding iSCSI protocol interactions informing the end-points of
the fact causes a Full Feature Phase iSCSI connection to be
abruptly terminated. The timeout values to be used in this case
are the negotiated values of DefaultTime2Wait (Section 13.15) and
DefaultTime2Retain (Section 13.16) text keys for the session.
7.5.2. Timeouts on Planned Decommissioning
Any planned decommissioning of a Full Feature Phase iSCSI
connection is preceded by either a Logout Response PDU, or an
Async Message PDU. The Time2Wait and Time2Retain field values
(Section 11.15) in a Logout Response PDU, and the Parameter2 and
Parameter3 fields of an Async Message (AsyncEvent types "drop the
connection" or "drop all the connections"; Section 11.9.1) specify
the timeout values to be used in each of these cases.
These timeout values are only applicable for the affected
connection, and the tasks active on that connection. These
timeout values have no bearing on initiator timers (if any) that
are already running on connections or tasks associated with that
session.
7.6. Implicit Termination of Tasks
A target implicitly terminates the active tasks due to iSCSI
protocol dynamics in the following cases:
a) When a connection is implicitly or explicitly logged out
with the reason code of "Close the connection" and there
are active tasks allegiant to that connection.
b) When a connection fails and eventually the connection
state times out (state transition M1 in Section 8.2.2)
and there are active tasks allegiant to that connection.
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c) When a successful Logout with the reason code of "remove
the connection for recovery" is performed while there are
active tasks allegiant to that connection, and those
tasks eventually time out after the Time2Wait and
Time2Retain periods without allegiance reassignment.
d) When a connection is implicitly or explicitly logged out
with the reason code of "Close the session" and there are
active tasks in that session.
If the tasks terminated in the above cases a), b), c) and d)are
SCSI tasks, they must be internally terminated as if with CHECK
CONDITION status. This status is only meaningful for appropriately
handling the internal SCSI state and SCSI side effects with
respect to ordering because this status is never communicated back
as a terminating status to the initiator. However additional
actions may have to be taken at SCSI level depending on the SCSI
context as defined by the SCSI standards (e.g., queued commands
and ACA, UA for the next command on the I_T nexus in cases a), b),
and c) etc. - see [SAM2] and [SPC3]).
7.7. Format Errors
The following two explicit violations of PDU layout rules are
format errors:
a) Illegal contents of any PDU header field except the
Opcode (legal values are specified in Section 11).
b) Inconsistent field contents (consistent field contents
are specified in Section 11).
Format errors indicate a major implementation flaw in one of the
parties.
When a target or an initiator receives an iSCSI PDU with a format
error, it MUST immediately terminate all transport connections in
the session either with a connection close or with a connection
reset and escalate the format error to session recovery (see
Section 7.1.4.4).
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All initiator-detected PDU construction errors MUST be considered
as format errors. Some examples of such errors are:
- NOP-In with a valid TTT but an invalid LUN
- NOP-In with a valid ITT (i.e., a NOP-In response) and also a
valid TTT
- SCSI Response PDU with Status=CHECK CONDITION, but
DataSegmentLength = 0
7.8. Digest Errors
The discussion of the legal choices in handling digest errors
below excludes session recovery as an explicit option, but either
party detecting a digest error may choose to escalate the error to
session recovery.
When a target or an initiator receives any iSCSI PDU, with a
header digest error, it MUST either discard the header and all
data up to the beginning of a later PDU or close the connection.
Because the digest error indicates that the length field of the
header may have been corrupted, the location of the beginning of a
later PDU needs to be reliably ascertained by other means such as
the operation of a sync and steering layer.
When a target receives any iSCSI PDU with a payload digest error,
it MUST answer with a Reject PDU with a reason code of Data-
Digest-Error and discard the PDU.
- If the discarded PDU is a solicited or unsolicited iSCSI
data PDU (for immediate data in a command PDU, non-data PDU
rule below applies), the target MUST do one of the
following:
i) Request retransmission with a recovery R2T.
ii) Terminate the task with a response PDU with a CHECK
CONDITION Status and an iSCSI Condition of "protocol
service CRC error" (Section 11.4.7.2). If the target
chooses to implement this option, it MUST wait to
receive all the data (signaled by a Data PDU with the
final bit set for all outstanding R2Ts) before sending
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the response PDU. A task management command (such as an
abort task) from the initiator during this wait may
also conclude the task.
- No further action is necessary for targets if the discarded
PDU is a non-data PDU. In case of immediate data being
present on a discarded command, the immediate data is
implicitly recovered when the task is retried (see Section
7.2.1) followed by the entire data transfer for the task.
When an initiator receives any iSCSI PDU with a payload digest
error, it MUST discard the PDU.
- If the discarded PDU is an iSCSI data PDU, the initiator
MUST do one of the following:
a) Request the desired data PDU through SNACK. In
response to the SNACK, the target MUST either resend
the data PDU or reject the SNACK with a Reject PDU
with a reason code of "SNACK reject" in which case:
b) If the status has not already been sent for the
command, the target MUST terminate the command with a
CHECK CONDITION Status and an iSCSI Condition of
"SNACK rejected" (Section 11.4.7.2).
c) If the status was already sent, no further action is
necessary for the target. The initiator in this case
MUST wait for the status to be received and then
discard it, so as to internally signal the completion
with CHECK CONDITION Status and an iSCSI Condition of
"protocol service CRC error" (Section 11.4.7.2).
d) Abort the task and terminate the command with an
error.
- If the discarded PDU is a response PDU or an unsolicited PDU
(e.g. Async, Reject), the initiator MUST do one of the
following:
a) Request PDU retransmission with a status SNACK.
b) Logout the connection for recovery and continue the
tasks on a different connection instance as described
in Section 7.2.
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c) Logout to close the connection (abort all the
commands associated with the connection).
Note that an unsolicited PDU carries the next StatSN value on
an iSCSI connection, thereby advancing the StatSN. When an
initiator discards one of these PDUs due to a payload digest
error, the entire PDU including the header MUST be discarded.
Consequently, the initiator MUST treat the exception like a
loss of any other solicited response PDU.
7.9. Sequence Errors
When an initiator receives an iSCSI R2T/data PDU with an out of
order R2TSN/DataSN or a SCSI response PDU with an ExpDataSN that
implies missing data PDU(s), it means that the initiator must have
detected a header or payload digest error on one or more earlier
R2T/data PDUs. The initiator MUST address these implied digest
errors as described in Section 7.8. When a target receives a data
PDU with an out of order DataSN, it means that the target must
have hit a header or payload digest error on at least one of the
earlier data PDUs. The target MUST address these implied digest
errors as described in Section 7.8.
When an initiator receives an iSCSI status PDU with an out of
order StatSN that implies missing responses, it MUST address the
one or more missing status PDUs as described in Section 7.8. As a
side effect of receiving the missing responses, the initiator may
discover missing data PDUs. If the initiator wants to recover the
missing data for a command, it MUST NOT acknowledge the received
responses that start from the StatSN of the relevant command,
until it has completed receiving all the data PDUs of the command.
When an initiator receives duplicate R2TSNs (due to proactive
retransmission of R2Ts by the target) or duplicate DataSNs (due to
proactive SNACKs by the initiator), it MUST discard the
duplicates.
7.10. Message Error Checking
In the iSCSI implementations till date, there has been some
uncertainty on the extent to which incoming messages have to be
checked for protocol errors, beyond what is strictly required for
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processing the inbound message. This Section addresses this
question.
Unless this document requires it, an iSCSI implementation is not
required to do an exhaustive protocol conformance check on an
incoming iSCSI PDU. The iSCSI implementation especially is not
required to double-check the remote iSCSI implementation's
conformance to protocol requirements.
7.11. SCSI Timeouts
An iSCSI initiator MAY attempt to plug a command sequence gap on
the target end (in the absence of an acknowledgement of the
command by way of ExpCmdSN) before the ULP timeout by retrying the
unacknowledged command, as described in Section 7.2.
On a ULP timeout for a command (that carried a CmdSN of n), if the
iSCSI initiator intends to continue the session it MUST abort the
command by either using an appropriate Task Management function
request for the specific command, or a "close the connection"
Logout. When using an ABORT TASK, if the ExpCmdSN is still less
than (n+1), the target may see the abort request while missing the
original command itself due to one of the following reasons:
- Original command was dropped due to digest error.
- Connection on which the original command was sent was
successfully logged out. On logout, the unacknowledged
commands issued on the connection being logged out are
discarded.
If the abort request is received and the original command is
missing, targets MUST consider the original command with that
RefCmdSN to be received and issue a Task Management response with
the response code: "Function Complete". This response concludes
the task on both ends. If the abort request is received and the
target can determine (based on the Referenced Task Tag) that the
command was received and executed and also that the response was
sent prior to the abort, then the target MUST respond with the
response code of "Task Does Not Exist".
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7.12. Negotiation Failures
Text request and response sequences, when used to set/negotiate
operational parameters, constitute the negotiation/parameter
setting. A negotiation failure is considered to be one or more of
the following:
- None of the choices, or the stated value, is acceptable to
one of the sides in the negotiation.
- The text request timed out and possibly terminated.
- The text request was answered with a Reject PDU.
The following two rules should be used to address negotiation
failures:
a) During Login, any failure in negotiation MUST be
considered a login process failure and the Login Phase
MUST be terminated, and with it, the connection. If the
target detects the failure, it must terminate the login
with the appropriate login response code.
b) A failure in negotiation, while in the Full Feature
Phase, will terminate the entire negotiation sequence
that may consist of a series of text requests that use
the same Initiator Task Tag. The operational parameters
of the session or the connection MUST continue to be the
values agreed upon during an earlier successful
negotiation (i.e., any partial results of this
unsuccessful negotiation MUST NOT take effect and MUST be
discarded).
7.13. Protocol Errors
Mapping framed messages over a "stream" connection, such as TCP,
makes the proposed mechanisms vulnerable to simple software
framing errors. On the other hand, the introduction of framing
mechanisms to limit the effects of these errors may be onerous on
performance for simple implementations. Command Sequence Numbers
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and the above mechanisms for connection drop and reestablishment
help handle this type of mapping errors.
All violations of iSCSI PDU exchange sequences specified in this
draft are also protocol errors. This category of errors can only
be
addressed by fixing the implementations; iSCSI defines Reject and
response codes to enable this.
7.14. Connection Failures
iSCSI can keep a session in operation if it is able to
keep/establish at least one TCP connection between the initiator
and the target in a timely fashion. Targets and/or initiators may
recognize a failing connection by either transport level means
(TCP), a gap in the command sequence number, a response stream
that is not filled for a long time, or by a failing iSCSI NOP
(acting as a ping). The latter MAY be used periodically to
increase the speed and likelihood of detecting connection
failures. As an example for transport level means, initiators and
targets MAY also use the keep-alive option, see [RFC1122], on the
TCP connection to enable early link failure detection on otherwise
idle links.
On connection failure, the initiator and target MUST do one of the
following:
a) Attempt connection recovery within the session
(Connection Recovery).
b) Logout the connection with the reason code "closes the
connection" (Section 10.14.5), re-issue missing commands,
and implicitly terminate all active commands. This option
requires support for the within-connection recovery class
(Recovery Within-connection).
c) Perform session recovery (Session Recovery).
Either side may choose to escalate to session recovery (via the
initiator dropping all the connections, or via an Async Message
that announces the similar intent from a target), and the other
side MUST give it precedence. On a connection failure, a target
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MUST terminate and/or discard all of the active immediate commands
regardless of which of the above options is used (i.e., immediate
commands are not recoverable across connection failures).
7.15. Session Errors
If all of the connections of a session fail and cannot be
reestablished in a short time, or if initiators detect protocol
errors repeatedly, an initiator may choose to terminate a session
and establish a new session.
In this case, the initiator takes the following actions:
- Resets or closes all the transport connections.
- Terminates all outstanding requests with an appropriate
response before initiating a new session. If the same I_T
nexus is intended to be reestablished, the initiator MUST
employ session reinstatement (see Section 6.3.5).
When the session timeout (the connection state timeout for the
last failed connection) happens on the target, it takes the
following actions:
- Resets or closes the TCP connections (closes the session).
- Terminates all active tasks that were allegiant to the
connection(s) that constituted the session.
A target MUST also be prepared to handle a session reinstatement
request from the initiator that may be addressing session errors.
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8. State Transitions
iSCSI connections and iSCSI sessions go through several well-
defined states from the time they are created to the time they are
cleared.
The connection state transitions are described in two separate but
dependent state diagrams for ease in understanding. The first
diagram, "standard connection state diagram", describes the
connection state transitions when the iSCSI connection is not
waiting for, or undergoing, a cleanup by way of an explicit or
implicit Logout. The second diagram, "connection cleanup state
diagram", describes the connection state transitions while
performing the iSCSI connection cleanup.
The "session state diagram" describes the state transitions an
iSCSI session would go through during its lifetime, and it depends
on the states of possibly multiple iSCSI connections that
participate in the session.
States and transitions are described in text, tables and diagrams.
The diagrams are used for illustration. The text and the tables
are the governing specification.
8.1. Standard Connection State Diagrams
8.1.1. State Descriptions for Initiators and Targets
State descriptions for the standard connection state diagram are
as follows:
-S1: FREE
-initiator: State on instantiation, or after successful
connection closure.
-target: State on instantiation, or after successful
connection closure.
-S2: XPT_WAIT
-initiator: Waiting for a response to its transport
connection establishment request.
-target: Illegal
-S3: XPT_UP
-initiator: Illegal
-target: Waiting for the Login process to commence.
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-S4: IN_LOGIN
-initiator: Waiting for the Login process to conclude,
possibly involving several PDU exchanges.
-target: Waiting for the Login process to conclude,
possibly involving several PDU exchanges.
-S5: LOGGED_IN
-initiator: In Full Feature Phase, waiting for all
internal, iSCSI, and transport events.
-target: In Full Feature Phase, waiting for all internal,
iSCSI, and transport events.
-S6: IN_LOGOUT
-initiator: Waiting for a Logout response.
-target: Waiting for an internal event signaling completion
of logout processing.
-S7: LOGOUT_REQUESTED
-initiator: Waiting for an internal event signaling
readiness to proceed with Logout.
-target: Waiting for the Logout process to start after
having requested a Logout via an Async Message.
-S8: CLEANUP_WAIT
-initiator: Waiting for the context and/or resources to
initiate the cleanup processing for this CSM.
-target: Waiting for the cleanup process to start for this
CSM.
8.1.2. State Transition Descriptions for Initiators and Targets
-T1:
-initiator: Transport connect request was made (e.g., TCP
SYN sent).
-target: Illegal
-T2:
-initiator: Transport connection request timed out, a
transport reset was received, or an internal event of
receiving a Logout response (success) on another connection
for a "close the session" Logout request was received.
-target:Illegal
-T3:
-initiator: Illegal
-target: Received a valid transport connection request that
establishes the transport connection.
-T4:
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-initiator: Transport connection established, thus
prompting the initiator to start the iSCSI Login.
-target: Initial iSCSI Login request was received.
-T5:
-initiator: The final iSCSI Login response with a Status-
Class of zero was received.
-target: The final iSCSI Login request to conclude the
Login Phase was received, thus prompting the target to send
the final iSCSI Login response with a Status-Class of zero.
-T6:
-initiator: Illegal
-target: Timed out waiting for an iSCSI Login, transport
disconnect indication was received, transport reset was
received, or an internal event indicating a transport
timeout was received. In all these cases, the connection is
to be closed.
-T7:
-initiator - one of the following events caused the
transition:
a) The final iSCSI Login response was received with a
non-zero Status-Class.
b) Login timed out.
c) A transport disconnect indication was received.
d) A transport reset was received.
e) An internal event indicating a transport timeout was
received.
f) An internal event of receiving a Logout response
(success) on another connection for a "close the
session" Logout request was received.
In all these cases, the transport connection is closed.
-target - one of the following events caused the
transition:
a) The final iSCSI Login request to conclude the Login
Phase was received, prompting the target to send the
final iSCSI Login response with a non-zero Status-
Class.
b) Login timed out.
c) Transport disconnect indication was received.
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d) Transport reset was received.
e) An internal event indicating a transport timeout was
received.
f) On another connection, a "close the session" Logout
request was received.
In all these cases, the connection is to be closed.
-T8:
-initiator: An internal event of receiving a Logout
response (success) on another connection for a "close the
session" Logout request was received, thus closing this
connection requiring no further cleanup.
-target: An internal event of sending a Logout response
(success) on another connection for a "close the session"
Logout request was received, or an internal event of a
successful connection/session reinstatement is received,
thus prompting the target to close this connection cleanly.
-T9, T10:
-initiator: An internal event that indicates the readiness
to start the Logout process was received, thus prompting an
iSCSI Logout to be sent by the initiator.
-target: An iSCSI Logout request was received.
-T11, T12:
-initiator: Async PDU with AsyncEvent "Request Logout" was
received.
-target: An internal event that requires the
decommissioning of the connection is received, thus causing
an Async PDU with an AsyncEvent "Request Logout" to be
sent.
-T13:
-initiator: An iSCSI Logout response (success) was
received, or an internal event of receiving a Logout
response (success) on another connection for a "close the
session" Logout request was received.
-target: An internal event was received that indicates
successful processing of the Logout, which prompts an iSCSI
Logout response (success) to be sent; an internal event of
sending a Logout response (success) on another connection
for a "close the session" Logout request was received; or
an internal event of a successful connection/session
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reinstatement is received. In all these cases, the
transport connection is closed.
-T14:
-initiator: Async PDU with AsyncEvent "Request Logout" was
received again.
-target: Illegal
-T15, T16:
-initiator: One or more of the following events caused this
transition:
a) Internal event that indicates a transport connection
timeout was received thus prompting transport RESET
or transport connection closure.
b) A transport RESET.
c) A transport disconnect indication.
d) Async PDU with AsyncEvent "Drop connection" (for
this CID).
e) Async PDU with AsyncEvent "Drop all connections".
-target: One or more of the following events caused this
transition:
a) Internal event that indicates a transport connection
timeout was received, thus prompting transport RESET
or transport connection closure.
b) An internal event of a failed connection/session
reinstatement is received.
c) A transport RESET.
d) A transport disconnect indication.
e) Internal emergency cleanup event was received which
prompts an Async PDU with AsyncEvent "Drop
connection" (for this CID), or event "Drop all
connections".
-T17:
-initiator: One or more of the following events caused this
transition:
a) Logout response, (failure i.e., a non-zero status)
was received, or Logout timed out.
b) Any of the events specified for T15 and T16.
-target: One or more of the following events caused this
transition:
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a) Internal event that indicates a failure of the
Logout processing was received, which prompts a
Logout response (failure, i.e., a non-zero status)
to be sent.
b) Any of the events specified for T15 and T16.
-T18:
-initiator: An internal event of receiving a Logout
response (success) on another connection for a "close the
session" Logout request was received.
-target: An internal event of sending a Logout response
(success) on another connection for a "close the session"
Logout request was received, or an internal event of a
successful connection/session reinstatement is received.
In both these cases, the connection is closed.
The CLEANUP_WAIT state (S8) implies that there are possible iSCSI
tasks that have not reached conclusion and are still considered
busy.
8.1.3. Standard Connection State Diagram for an Initiator
Symbolic names for States:
S1: FREE
S2: XPT_WAIT
S4: IN_LOGIN
S5: LOGGED_IN
S6: IN_LOGOUT
S7: LOGOUT_REQUESTED
S8: CLEANUP_WAIT
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States S5, S6, and S7 constitute the Full Feature Phase operation
of the connection.
The state diagram is as follows:
-------<-------------+
+--------->/ S1 \<----+ |
T13| +->\ /<-+ \ |
| / ---+--- \ \ |
| / | T2 \ | |
| T8 | |T1 | | |
| | | / |T7 |
| | | / | |
| | | / | |
| | V / / |
| | ------- / / |
| | / S2 \ / |
| | \ / / |
| | ---+--- / |
| | |T4 / |
| | V / | T18
| | ------- / |
| | / S4 \ |
| | \ / |
| | ---+--- | T15
| | |T5 +--------+---------+
| | | /T16+-----+------+ |
| | | / -+-----+--+ | |
| | | / / S7 \ |T12| |
| | | / +->\ /<-+ V V
| | | / / -+----- -------
| | | / /T11 |T10 / S8 \
| | V / / V +----+ \ /
| | ---+-+- ----+-- | -------
| | / S5 \T9 / S6 \<+ ^
| +-----\ /--->\ / T14 |
| ------- --+----+------+T17
+---------------------------+
The following state transition table represents the above diagram.
Each row represents the starting state for a given transition,
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which after taking a transition marked in a table cell would end
in the state represented by the column of the cell. For example,
from state S1, the connection takes the T1 transition to arrive at
state S2. The fields marked "-" correspond to undefined
transitions.
+----+---+---+---+---+----+---+
|S1 |S2 |S4 |S5 |S6 |S7 |S8 |
---+----+---+---+---+---+----+---+
S1| - |T1 | - | - | - | - | - |
---+----+---+---+---+---+----+---+
S2|T2 |- |T4 | - | - | - | - |
---+----+---+---+---+---+----+---+
S4|T7 |- |- |T5 | - | - | - |
---+----+---+---+---+---+----+---+
S5|T8 |- |- | - |T9 |T11 |T15|
---+----+---+---+---+---+----+---+
S6|T13 |- |- | - |T14|- |T17|
---+----+---+---+---+---+----+---+
S7|T18 |- |- | - |T10|T12 |T16|
---+----+---+---+---+---+----+---+
S8| - |- |- | - | - | - | - |
---+----+---+---+---+---+----+---+
8.1.4. Standard Connection State Diagram for a Target
Symbolic names for States:
S1: FREE
S3: XPT_UP
S4: IN_LOGIN
S5: LOGGED_IN
S6: IN_LOGOUT
S7: LOGOUT_REQUESTED
S8: CLEANUP_WAIT
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States S5, S6, and S7 constitute the Full Feature Phase operation
of the connection.
The state diagram is as follows:
-------<-------------+
+--------->/ S1 \<----+ |
T13| +->\ /<-+ \ |
| / ---+--- \ \ |
| / | T6 \ | |
| T8 | |T3 | | |
| | | / |T7 |
| | | / | |
| | | / | |
| | V / / |
| | ------- / / |
| | / S3 \ / |
| | \ / / | T18
| | ---+--- / |
| | |T4 / |
| | V / |
| | ------- / |
| | / S4 \ |
| | \ / |
| | ---+--- T15 |
| | |T5 +--------+---------+
| | | /T16+-----+------+ |
| | | / -+-----+---+ | |
| | | / / S7 \ |T12| |
| | | / +->\ /<-+ V V
| | | / / -+----- -------
| | | / /T11 |T10 / S8 \
| | V / / V \ /
| | ---+-+- ------- -------
| | / S5 \T9 / S6 \ ^
| +-----\ /--->\ / |
| ------- --+----+--------+T17
+---------------------------+
The following state transition table represents the above diagram,
and follows the conventions described for the initiator diagram.
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+----+---+---+---+---+----+---+
|S1 |S3 |S4 |S5 |S6 |S7 |S8 |
---+----+---+---+---+---+----+---+
S1| - |T3 | - | - | - | - | - |
---+----+---+---+---+---+----+---+
S3|T6 |- |T4 | - | - | - | - |
---+----+---+---+---+---+----+---+
S4|T7 |- |- |T5 | - | - | - |
---+----+---+---+---+---+----+---+
S5|T8 |- |- | - |T9 |T11 |T15|
---+----+---+---+---+---+----+---+
S6|T13 |- |- | - |- |- |T17|
---+----+---+---+---+---+----+---+
S7|T18 |- |- | - |T10|T12 |T16|
---+----+---+---+---+---+----+---+
S8| - |- |- | - | - | - | - |
---+----+---+---+---+---+----+---+
8.2. Connection Cleanup State Diagram for Initiators and Targets
Symbolic names for states:
R1: CLEANUP_WAIT (same as S8)
R2: IN_CLEANUP
R3: FREE (same as S1)
Whenever a connection state machine in cleanup (let's call it CSM-
C) enters the CLEANUP_WAIT state (S8), it must go through the
state transitions described in the connection cleanup state
diagram either a) using a separate full-feature phase connection
(let's call it CSM-E, for explicit) in the LOGGED_IN state in the
same session, or b) using a new transport connection (let's call
it CSM-I, for implicit) in the FREE state that is to be added to
the same session. In the CSM-E case, an explicit logout for the
CID that corresponds to CSM-C (either as a connection or session
logout) needs to be performed to complete the cleanup. In the CSM-
I case, an implicit logout for the CID that corresponds to CSM-C
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needs to be performed by way of connection reinstatement (Section
6.3.4) for that CID. In either case, the protocol exchanges on
CSM-E or CSM-I determine the state transitions for CSM-C.
Therefore, this cleanup state diagram is only applicable to the
instance of the connection in cleanup (i.e., CSM-C). In the case
of an implicit logout for example, CSM-C reaches FREE (R3) at the
time CSM-I reaches LOGGED_IN. In the case of an explicit logout,
CSM-C reaches FREE (R3) when CSM-E receives a successful logout
response while continuing to be in the LOGGED_IN state.
An initiator must initiate an explicit or implicit connection
logout for a connection in the CLEANUP_WAIT state, if the
initiator intends to continue using the associated iSCSI session.
The following state diagram applies to both initiators and
targets.
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-------
/ R1 \
+--\ /<-+
/ ---+--- \
/ | \ M3
M1 | |M2 |
| | /
| | /
| | /
| V /
| ------- /
| / R2 \
| \ /
| -------
| |
| |M4
| |
| |
| |
| V
| -------
| / R3 \
+---->\ /
-------
The following state transition table represents the above diagram,
and follows the same conventions as in earlier sections.
+----+----+----+
|R1 |R2 |R3 |
-----+----+----+----+
R1 | - |M2 |M1 |
-----+----+----+----+
R2 |M3 | - |M4 |
-----+----+----+----+
R3 | - | - | - |
-----+----+----+----+
8.2.1. State Descriptions for Initiators and Targets
-R1: CLEANUP_WAIT (Same as S8)
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-initiator: Waiting for the internal event to initiate the
cleanup processing for CSM-C.
-target: Waiting for the cleanup process to start for CSM-
C.
-R2: IN_CLEANUP
-initiator: Waiting for the connection cleanup process to
conclude for CSM-C.
-target: Waiting for the connection cleanup process to
conclude for CSM-C.
-R3: FREE (Same as S1)
-initiator: End state for CSM-C.
-target: End state for CSM-C.
8.2.2. State Transition Descriptions for Initiators and Targets
-M1: One or more of the following events was received:
-initiator:
-An internal event that indicates connection state
timeout.
-An internal event of receiving a successful Logout
response on a different connection for a "close the
session" Logout.
-target:
-An internal event that indicates connection state
timeout.
-An internal event of sending a Logout response
(success) on a different connection for a "close the
session" Logout request.
-M2: An implicit/explicit logout process was initiated by the
initiator.
-In CSM-I usage:
-initiator: An internal event requesting the connection
(or session) reinstatement was received, thus prompting
a connection (or session) reinstatement Login to be
sent transitioning CSM-I to state IN_LOGIN.
-target: A connection/session reinstatement Login was
received while in state XPT_UP.
-In CSM-E usage:
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-initiator: An internal event that indicates that an
explicit logout was sent for this CID in state
LOGGED_IN.
-target: An explicit logout was received for this CID
in state LOGGED_IN.
-M3: Logout failure detected
-In CSM-I usage:
-initiator: CSM-I failed to reach LOGGED_IN and arrived
into FREE instead.
-target: CSM-I failed to reach LOGGED_IN and arrived
into FREE instead.
-In CSM-E usage:
-initiator: CSM-E either moved out of LOGGED_IN, or
Logout timed out and/or aborted, or Logout response
(failure) was received.
-target: CSM-E either moved out of LOGGED_IN, Logout
timed out and/or aborted, or an internal event that
indicates a failed Logout processing was received. A
Logout response (failure) was sent in the last case.
-M4: Successful implicit/explicit logout was performed.
- In CSM-I usage:
-initiator: CSM-I reached state LOGGED_IN, or an
internal event of receiving a Logout response (success)
on another connection for a "close the session" Logout
request was received.
-target: CSM-I reached state LOGGED_IN, or an internal
event of sending a Logout response (success) on a
different connection for a "close the session" Logout
request was received.
- In CSM-E usage:
-initiator: CSM-E stayed in LOGGED_IN and received a
Logout response (success), or an internal event of
receiving a Logout response (success) on another
connection for a "close the session" Logout request was
received.
-target: CSM-E stayed in LOGGED_IN and an internal
event indicating a successful Logout processing was
received, or an internal event of sending a Logout
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response (success) on a different connection for a
"close the session" Logout request was received.
8.3. Session State Diagrams
8.3.1. Session State Diagram for an Initiator
Symbolic Names for States:
Q1: FREE
Q3: LOGGED_IN
Q4: FAILED
State Q3 represents the Full Feature Phase operation of the
session.
The state diagram is as follows:
-------
/ Q1 \
+------>\ /<-+
/ ---+--- |
/ | |N3
N6 | |N1 |
| | |
| N4 | |
| +----------+ | /
| | | | /
| | | | /
| | V V /
-+--+-- -----+-
/ Q4 \ N5 / Q3 \
\ /<------\ /
------- -------
The state transition table is as follows:
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+---+---+---+
|Q1 |Q3 |Q4 |
-----+---+---+---+
Q1 | - |N1 | - |
-----+---+---+---+
Q3 |N3 | - |N5 |
-----+---+---+---+
Q4 |N6 |N4 | - |
-----+---+---+---+
8.3.2. Session State Diagram for a Target
Symbolic Names for States:
Q1: FREE
Q2: ACTIVE
Q3: LOGGED_IN
Q4: FAILED
Q5: IN_CONTINUE
State Q3 represents the Full Feature Phase operation of the
session.
The state diagram is as follows:
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-------
+------------------>/ Q1 \
/ +-------------->\ /<-+
| | ---+--- |
| | ^ | |N3
N 6 | |N11 N9| V N1 |
| | +------ |
| | / Q2 \ |
| | \ / |
| --+---- +--+--- |
| / Q5 \ | |
| \ / N10 | |
| +-+---+------------+ | N2 /
| ^ | | | /
| N7| |N8 | | /
| | | | V /
-+---+-V V------+-
/ Q4 \ N5 / Q3 \
\ /<-------------\ /
------- -------
The state transition table is as follows:
+----+----+----+----+----+
|Q1 |Q2 |Q3 |Q4 |Q5 |
-----+----+----+----+----+----+
Q1 | - |N1 | - | - | - |
-----+----+----+----+----+----+
Q2 |N9 | - |N2 | - | - |
-----+----+----+----+----+----+
Q3 |N3 | - | - |N5 | - |
-----+----+----+----+----+----+
Q4 |N6 | - | - | - |N7 |
-----+----+----+----+----+----+
Q5 |N11 | - |N10 |N8 | - |
-----+----+----+----+----+----+
8.3.3. State Descriptions for Initiators and Targets
-Q1: FREE
-initiator: State on instantiation or after cleanup.
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-target: State on instantiation or after cleanup.
-Q2: ACTIVE
-initiator: Illegal.
-target: The first iSCSI connection in the session
transitioned to IN_LOGIN, waiting for it to complete the
login process.
-Q3: LOGGED_IN
-initiator: Waiting for all session events.
-target: Waiting for all session events.
-Q4: FAILED
-initiator: Waiting for session recovery or session
continuation.
-target: Waiting for session recovery or session
continuation.
-Q5: IN_CONTINUE
-initiator: Illegal.
-target: Waiting for session continuation attempt to reach
a conclusion.
8.3.4. State Transition Descriptions for Initiators and Targets
-N1:
-initiator: At least one transport connection reached the
LOGGED_IN state.
-target: The first iSCSI connection in the session had
reached the IN_LOGIN state.
-N2:
-initiator: Illegal.
-target: At least one iSCSI connection reached the
LOGGED_IN state.
-N3:
-initiator: Graceful closing of the session via session
closure (Section 6.3.6).
-target: Graceful closing of the session via session
closure (Section 6.3.6) or a successful session
reinstatement cleanly closed the session.
-N4:
-initiator: A session continuation attempt succeeded.
-target: Illegal.
-N5:
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-initiator: Session failure (Section 6.3.6) occurred.
-target: Session failure (Section 6.3.6) occurred.
-N6:
-initiator: Session state timeout occurred, or a session
reinstatement cleared this session instance. This results
in the freeing of all associated resources and the session
state is discarded.
-target: Session state timeout occurred, or a session
reinstatement cleared this session instance. This results
in the freeing of all associated resources and the session
state is discarded.
-N7:
-initiator: Illegal.
-target: A session continuation attempt is initiated.
-N8:
-initiator: Illegal.
-target: The last session continuation attempt failed.
-N9:
-initiator: Illegal.
-target: Login attempt on the leading connection failed.
-N10:
-initiator: Illegal.
-target: A session continuation attempt succeeded.
-N11:
-initiator: Illegal.
-target: A successful session reinstatement cleanly closed
the session.
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9. Security Considerations
Historically, native storage systems have not had to consider
security because their environments offered minimal security
risks. That is, these environments consisted of storage devices
either directly attached to hosts or connected via a Storage Area
Network (SAN) distinctly separate from the communications network.
The use of storage protocols, such as SCSI, over IP-networks
requires that security concerns be addressed. iSCSI
implementations must provide means of protection against active
attacks (e.g., pretending to be another identity, message
insertion, deletion, modification, and replaying) and passive
attacks (e.g.,eavesdropping, gaining advantage by analyzing the
data sent over the line).
Although technically possible, iSCSI SHOULD NOT be configured
without security, specifically in-band authentication, see Section
9.2. iSCSI configured without security should be confined to
closed environments that have very limited and well controlled
security risks. [RFC3723] specifies the mechanisms that must be
used in order to mitigate risks fully described in that document.
The following Section describes the security mechanisms provided
by an iSCSI implementation.
9.1. iSCSI Security Mechanisms
The entities involved in iSCSI security are the initiator, target,
and the IP communication end points. iSCSI scenarios in which
multiple initiators or targets share a single communication end
point are expected. To accommodate such scenarios, iSCSI uses two
separate security mechanisms: In-band authentication between the
initiator and the target at the iSCSI connection level (carried
out by exchange of iSCSI Login PDUs), and packet protection
(integrity, authentication, and confidentiality) by IPsec at the
IP level. The two security mechanisms complement each other. The
in-band authentication provides end-to-end trust (at login time)
between the iSCSI initiator and the target while IPsec provides a
secure channel between the IP communication end points. iSCSI can
be used to access sensitive information for which significant
security protection is appropriate. As further specified in the
rest of this security considerations section, both iSCSI security
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mechanisms are mandatory to implement (MUST). Use of in-band
authentication is strongly recommended (SHOULD). In contrast, use
of IPsec is optional (MAY) as the security risks that it addresses
may only be present over a subset of the networks used by an iSCSI
connection or a session; a specific example is that when an iSCSI
session spans data centers, IPsec VPN gateways at the data center
boundaries to protect the WAN connectivity between data centers
may be appropriate in combination with in-band iSCSI
authentication.
Further details on typical iSCSI scenarios and the relation
between the initiators, targets, and the communication end points
can be found in [RFC3723].
9.2. In-band Initiator-Target Authentication
During login, the target MAY authenticate the initiator and the
initiator MAY authenticate the target. The authentication is
performed on every new iSCSI connection by an exchange of iSCSI
Login PDUs using a negotiated authentication method.
The authentication method cannot assume an underlying IPsec
protection, because IPsec is optional to use. An attacker should
gain as little advantage as possible by inspecting the
authentication phase PDUs. Therefore, a method using clear text
(or equivalent) passwords MUST NOT be used; on the other hand,
identity protection is not strictly required.
The authentication mechanism protects against an unauthorized
login to storage resources by using a false identity (spoofing).
Once the authentication phase is completed, if the underlying
IPsec is not used, all PDUs are sent and received in clear. The
authentication mechanism alone (without underlying IPsec) should
only be used when there is no risk of eavesdropping, message
insertion, deletion, modification, and replaying.
Section 11 defines several authentication methods and the exact
steps that must be followed in each of them, including the iSCSI-
text-keys and their allowed values in each step. Whenever an iSCSI
initiator gets a response whose keys, or their values, are not
according to the step definition, it MUST abort the connection.
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Whenever an iSCSI target gets a response whose keys, or their
values, are not according to the step definition, it MUST answer
with a Login reject with the "Initiator Error" or "Missing
Parameter" status. These statuses are not intended for
cryptographically incorrect values such as the CHAP response, for
which "Authentication Failure" status MUST be specified. The
importance of this rule can be illustrated in CHAP with target
authentication (see Section 12.1.3) where the initiator would have
been able to conduct a reflection attack by omitting his response
key (CHAP_R) using the same CHAP challenge as the target and
reflecting the target's response back to the target. In CHAP, this
is prevented because the target must answer the missing CHAP_R key
with a Login reject with the "Missing Parameter" status.
For some of the authentication methods, a key specifies the
identity of the iSCSI initiator or target for authentication
purposes. The value associated with that key MAY be different from
the iSCSI Name and SHOULD be configurable. (CHAP_N, see Section
12.1.3 and SRP_U, see Section 12.1.2). For this reason, iSCSI
implementations SHOULD manage authentication in a way that
impersonation across iSCSI Names via these authentication
identities is not possible. Specifically, implementations SHOULD
allow configuration of an authentication identity for a Name if
different, and authentication credentials for that identity.
During the login time, implementations SHOULD verify the Name-to-
identity relationship in addition to authenticating the identity
through the negotiated authentication method.
When an iSCSI session has multiple TCP connections, either
concurrently or sequentially, the authentication method and
identities should not vary among the connections. Therefore, all
connections in an iSCSI session SHOULD use the same authentication
method, iSCSI Name and authentication identity (for authentication
methods that use an authentication identity). Implementations
SHOULD check this and cause an authentication failure on a new
connection that uses a different authentication method, iSCSI
Name or authentication identity from those already used in the
session. In addition, implementations SHOULD NOT support both
authenticated and unauthenticated TCP connections in the same
iSCSI session, added either concurrently or sequentially to the
session.
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9.2.1. CHAP Considerations
Compliant iSCSI initiators and targets MUST implement the CHAP
authentication method [RFC1994] (according to Section 12.1.3
including the target authentication option).
When CHAP is performed over a non-encrypted channel, it is
vulnerable to an off-line dictionary attack. Implementations MUST
support use of up to 128 bit random CHAP secrets, including the
means to generate such secrets and to accept them from an external
generation source. Implementations MUST NOT provide secret
generation (or expansion) means other than random generation.
An administrative entity of an environment in which CHAP is used
with a secret that has less than 96 random bits MUST enforce IPsec
encryption (according to the implementation requirements in
Confidentiality) to protect the connection. Moreover, in this case
IKE authentication with group pre-shared cryptographic keys SHOULD
NOT be used unless it is not essential to protect group members
against off-line dictionary attacks by other members.
CHAP secrets MUST be an integral number of bytes (octets). A
compliant implementation SHOULD NOT continue with the login step
in which it should send a CHAP response (CHAP_R, Section 12.1.3)
unless it can verify that the CHAP secret is at least 96 bits, or
that IPsec encryption is being used to protect the connection.
Any CHAP secret used for initiator authentication MUST NOT be
configured for authentication of any target, and any CHAP secret
used for target authentication MUST NOT be configured for
authentication of any initiator. If the CHAP response received by
one end of an iSCSI connection is the same as the CHAP response
that the receiving endpoint would have generated for the same CHAP
challenge, the response MUST be treated as an authentication
failure and cause the connection to close (this ensures that the
same CHAP secret is not used for authentication in both
directions). Also, if an iSCSI implementation can function as
both initiator and target, different CHAP secrets and identities
MUST be configured for these two roles. The following is an
example of the attacks prevented by the above requirements:
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a) Rogue wants to impersonate Storage to Alice, and knows
that a single secret is used for both directions of
Storage-Alice authentication.
b) Rogue convinces Alice to open two connections to Rogue,
and Rogue identifies itself as Storage on both
connections.
c) Rogue issues a CHAP challenge on connection 1, waits for
Alice to respond, and then reflects Alice's challenge as
the initial challenge to Alice on connection 2.
d) If Alice doesn't check for the reflection across
connections, Alice's response on connection 2 enables
Rogue to impersonate Storage on connection 1, even though
Rogue does not know the Alice-Storage CHAP secret.
Originators MUST NOT reuse the CHAP challenge sent by the
Responder for the other direction of a bidirectional
authentication. Responders MUST check for this condition and close
the iSCSI TCP connection if it occurs.
The same CHAP secret SHOULD NOT be configured for authentication
of multiple initiators or multiple targets, as this enables any of
them to impersonate any other one of them, and compromising one of
them enables the attacker to impersonate any of them. It is
recommended that iSCSI implementations check for use of identical
CHAP secrets by different peers when this check is feasible, and
take appropriate measures to warn users and/or administrators when
this is detected.
When an iSCSI initiator or target authenticates itself to
counterparts in multiple administrative domains, it SHOULD use a
different CHAP secret for each administrative domain to avoid
propagating security compromises across domains.
Within a single administrative domain:
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- A single CHAP secret MAY be used for authentication of an
initiator to multiple targets.
- A single CHAP secret MAY be used for an authentication of a
target to multiple initiators when the initiators use an
external server (e.g., RADIUS, [RFC2865]) to verify the
target's CHAP responses and do not know the target's CHAP
secret.
If an external response verification server (e.g., RADIUS) is not
used, employing a single CHAP secret for authentication of a
target to multiple initiators requires that all such initiators
know that target secret. Any of these initiators can impersonate
the target to any other such initiator, and compromise of such an
initiator enables an attacker to impersonate the target to all
such initiators. Targets SHOULD use separate CHAP secrets for
authentication to each initiator when such risks are of concern;
in this situation it may be useful to configure a separate logical
iSCSI target with its own iSCSI Node Name for each initiator or
group of initiators among which such separation is desired.
The above requirements strengthen the security properties of CHAP
authentication for iSCSI by comparison to the basic CHAP
authentication mechanism [RFC1994]. It is very important to
adhere to these requirements, especially the requirements for
strong (large randomly generated) CHAP secrets, as iSCSI
implementations and deployments that fail to use strong CHAP
secrets are likely to be highly vulnerable to off-line dictionary
attacks on CHAP secrets.
Replacement of CHAP with a better authentication mechanism is
anticipated in a future version of iSCSI. The FC-SP-2 standard
[FC-SP-2] has specified the EAP-GPSK authentication mechanism
[RFC5433] as an alternative to (and possible future replacement
for) Fibre Channel's similar usage of strengthened CHAP. Another
possible replacement for CHAP is a secure password mechanism,
e.g., an updated version of iSCSI's current SRP authentication
mechanism.
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9.2.2. SRP Considerations
The strength of the SRP authentication method (specified in
[RFC2945]) is dependent on the characteristics of the group being
used (i.e., the prime modulus N and generator g). As described in
[RFC2945], N is required to be a Sophie-German prime (of the form
N = 2q + 1, where q is also prime) and the generator g is a
primitive root of GF(n). In iSCSI authentication, the prime
modulus N MUST be at least 768 bits.
The list of allowed SRP groups is provided in [RFC3723].
9.2.3. Kerberos Considerations
iSCSI uses raw Kerberos V5 [RFC4120] for authenticating a client
(iSCSI initiator) principal to a service (iSCSI target) principal.
Note that iSCSI does not use the Generic Security Services
Application Programming Interface (GSS-API) [RFC2743] nor the
Kerberos V5 GSS-API security mechanism [RFC4121]. This means that
iSCSI implementations supporting the KRB5 AuthMethod (Section
12.1) are directly involved in the Kerberos protocol. When
Kerberos V5 is used for authentication, the following actions MUST
be performed as specified in [RFC4120]:
Target MUST validate the KRB_AP_REQ to ensure that the
initiator can be trusted
When mutual authentication is selected, the initiator MUST
validate KRB_AP_REP to determine the outcome of mutual
authentication
As Kerberos V5 is capable of providing mutual authentication,
implementations SHOULD support mutual authentication by default
for login authentication.
Note however that Kerberos authentication only assures that the
server (iSCSI target) can be trusted by the Kerberos client
(initiator) and vice-versa; an initiator should employ
appropriately secured service discovery techniques (e.g. iSNS,
Section 4.2.7) to ensure that it is talking to the intended target
principal.
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iSCSI does not use Kerberos v5 for either integrity or
confidentiality protection of the iSCSI protocol. iSCSI uses IPsec
for those purposes as specified in Section 9.3.
9.3. IPsec
iSCSI uses the IPsec mechanism for packet protection
(cryptographic integrity, authentication, and confidentiality) at
the IP level between the iSCSI communicating end points. The
following sections describe the IPsec protocols that must be
implemented for data integrity and authentication,
confidentiality, and cryptographic key management.
An iSCSI initiator or target may provide the required IPsec
support fully integrated or in conjunction with an IPsec front-end
device. In the latter case, the compliance requirements with
regard to IPsec support apply to the "combined device". Only the
"combined device" is to be considered an iSCSI device.
Detailed considerations and recommendations for using IPsec for
iSCSI are provided in [RFC3723] as updated by [IPSEC-IPS]. The
IPsec requirements are reproduced here for convenience and are
intended to match those in [IPSEC-IPS]; in the event of a
discrepancy, the requirements in [IPSEC-IPS] apply.
9.3.1. Data Integrity and Authentication
Data authentication and integrity is provided by a cryptographic
keyed Message Authentication Code in every sent packet. This code
protects against message insertion, deletion, and modification.
Protection against message replay is realized by using a sequence
counter.
An iSCSI-compliant initiator or target MUST provide data integrity
and authentication by implementing IPsec v2 [RFC2401] with ESPv2
[RFC2406] in tunnel mode, SHOULD provide data integrity and
authentication by implementing IPsec v3 [RFC4301] with ESPv3
[RFC4303] in tunnel mode, and MAY provide data integrity and
authentication by implementing either IPsec v2 or v3 with the
appropriate version of ESP in transport mode. The IPsec
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implementation MUST fulfill the following iSCSI-specific
requirements:
- HMAC-SHA1 MUST be implemented in the specific form of HMAC-
SHA-1-96 [RFC2404].
- AES CBC MAC with XCBC extensions using 128-bit keys SHOULD
be implemented [RFC3566].
- Implementations that support IKEv2 [RFC5996] SHOULD also
implement AES GMAC [RFC4543] using 128-bit keys.
The ESP anti-replay service MUST also be implemented.
At the high speeds iSCSI is expected to operate, a single IPsec SA
could rapidly cycle through the ESP 32-bit sequence number space.
In view of this, an iSCSI implementation that is capable of
operating at speeds of 1 Gbps and that implements both IKEv2
[RFC5996] and ESPv3 [RFC4303] MUST also implement extended (64-
bit) sequence numbers for ESPv3 and SHOULD use ESPv3 extended
sequence numbers for all security associations that use ESPv3 to
protect iSCSI connections.
9.3.2. Confidentiality
Confidentiality is provided by encrypting the data in every
packet. When confidentiality is used it MUST be accompanied by
data integrity and authentication to provide comprehensive
protection against eavesdropping, message insertion, deletion,
modification, and replaying.
An iSCSI-compliant initiator or target MUST provide
confidentiality by implementing IPsec v2 [RFC2401] with ESPv2
[RFC2406] in tunnel mode, SHOULD provide confidentiality by
implementing IPsec v3 [RFC4301] with ESPv3 [RFC4303] in tunnel
mode and MAY provide confidentiality by implementing either IPsec
v2 or v3 with the appropriate version of ESP in transport mode,
with the following iSCSI specific requirements that apply to IPsec
v2 and IPsec v3:
- 3DES in CBC mode MAY be implemented [RFC2451].
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- AES in CBC mode with 128-bit keys MUST be implemented
[RFC3602]; other key sizes MAY be supported.
- AES in Counter mode MAY be implemented [RFC3686].
- Implementations that support IKEv2 [RFC5996] SHOULD also
implement AES GCM with 128-bit keys [RFC4106] ]; other key
sizes MAY be supported.
DES in CBC mode MUST NOT be used due to its inherent weakness.
The NULL encryption algorithm MUST also be implemented.
9.3.3. Policy, Security Associations, and Cryptographic Key
Management
A compliant iSCSI implementation MUST meet the cryptographic key
management requirements of the IPsec protocol suite.
Authentication, security association negotiation, and
cryptographic key management MUST be provided by implementing IKE
[RFC2409] using the IPsec DOI [RFC2407], and SHOULD be provided by
implementing IKEv2 [RFC5996], with the following iSCSI-specific
requirements:
a) Peer authentication using a pre-shared cryptographic key MUST
be supported. Certificate-based peer authentication using
digital signatures MAY be supported. For IKEv1 ([RFC2409]),
peer authentication using the public key encryption methods
outlined in IKE sections 5.2 and 5.3 of [RFC2409] SHOULD NOT
be used.
b) When digital signatures are used to achieve authentication,
an IKE negotiator SHOULD use IKE Certificate Request
Payload(s) to specify the certificate authority. IKE
negotiators SHOULD check the pertinent Certificate Revocation
List (CRL) before accepting a PKI certificate for use in IKE
authentication procedures. These checks may not be needed in
environments where a small number of certificates are
statically configured as trust anchors.
c) Conformant iSCSI implementations of IKEv1 MUST support Main
Mode and SHOULD support Aggressive Mode. Main Mode with pre-
shared key authentication method SHOULD NOT be used when
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either the initiator or the target uses dynamically assigned
addresses. While in many cases pre-shared keys offer good
security, situations in which dynamically assigned addresses
are used force the use of a group pre-shared key, which
creates vulnerability to a man-in-the-middle attack.
d) In the IKEv1 Phase 2 Quick Mode, exchanges for creating the
Phase 2 SA, the Identification Payload MUST be present.
e) The following identification type requirements apply to
IKEv1. ID_IPV4_ADDR, ID_IPV6_ADDR (if the protocol stack
supports IPv6) and ID_FQDN Identification Types MUST be
supported; ID_USER_FQDN SHOULD be supported. The IP Subnet,
IP Address Range, ID_DER_ASN1_DN, and ID_DER_ASN1_GN
Identification Types SHOULD NOT be used. The ID_KEY_ID
Identification Type MUST NOT be used.
f) If IKEv2 is supported, the following identification
requirements apply. ID_IPV4_ADDR, ID_IPV6_ADDR (if the
protocol stack supports IPv6) and ID_FQDN Identification
Types MUST be supported; ID_RFC822_ADDR SHOULD be supported.
The ID_DER_ASN1_DN, and ID_DER_ASN1_GN Identification Types
SHOULD NOT be used. The ID_KEY_ID Identification Type MUST
NOT be used.
The reasons for the "MUST NOT" and "SHOULD NOT" requirements for
identification type requirements in preceding bullets e) and f)
are:
- IP Subnet and IP Address Range are too broad to usefully
identify an iSCSI endpoint.
- The DN and GN types are X.500 identities; it is usually
better to use an identity from subjectAltName in a PKI
certificate.
- ID_KEY_ID is not interoperable as specified.
Manual cryptographic keying MUST NOT be used because it does not
provide the necessary re-keying support.
When DH groups are used, a DH group of at least 2048 bits SHOULD
be offered as a part of all proposals to create IPsec Security
Associations to protect iSCSI traffic, with both IKEv1 and IKEv2.
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When IPsec is used, the receipt of an IKEv1 Phase 2 delete message
or an IKEv2 INFORMATIONAL exchange that deletes the SA SHOULD NOT
be interpreted as a reason for tearing down the iSCSI TCP
connection. If additional traffic is sent on it, a new IKE SA will
be created to protect it.
The method used by the initiator to determine whether the target
should be connected using IPsec is regarded as an issue of IPsec
policy administration, and thus not defined in the iSCSI standard.
The method used by an initiator that supports both IPsec v2 and v3
to determine which versions of IPsec are supported by the target
is also regarded as an issue of IPsec policy administration, and
thus not defined in the iSCSI standard. If both IPsec v2 and v3
are supported by both the initiator and target, use of IPsec v3 is
recommended.
If an iSCSI target is discovered via a SendTargets request in a
discovery session not using IPsec, the initiator should assume
that it does not need IPsec to establish a session to that target.
If an iSCSI target is discovered using a discovery session that
does use IPsec, the initiator SHOULD use IPsec when establishing a
session to that target.
9.4. Security Considerations for the X#NodeArchitecture Key
The security considerations in this Section are specific to the
X#NodeArchitecture discussed in Section 13.26.
This extension key transmits specific implementation details about
the node that sends it; such details may be considered sensitive
in some environments. For example, if a certain software or
firmware version is known to contain security weaknesses,
announcing the presence of that version via this key may not be
desirable. The countermeasures for this security concern are:
a) sending less detailed information in the key values,
b) not sending the extension key, or
c) using IPsec ([RFC4303]) to provide confidentiality for the
iSCSI connection on which the key is sent
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To support the first and second countermeasures, all
implementations of this extension key MUST provide an
administrative mechanism to disable sending the key. In addition,
all implementations SHOULD provide an administrative mechanism to
configure a verbosity level of the key value, thereby controlling
the amount of information sent.
For example, a lower verbosity might enable transmission of node
architecture component names only, but no version numbers. The
choice of which countermeasure is most appropriate depends on the
environment. However, sending less detailed information in the key
values may be an acceptable countermeasure in many environments,
since it provides a compromise between sending too much
information and the other more complete countermeasures of not
sending the key at all or using IPsec.
In addition to security considerations involving transmission of
the key contents, any logging method(s) used for the key values
MUST keep the information secure from intruders. For all
implementations, the requirements to address this security concern
are:
a) Display of the log MUST only be possible with administrative
rights to the node.
b) Options to disable logging to disk and to keep logs for a
fixed duration SHOULD be provided.
Finally, it is important to note that different nodes may have
different levels of risk, and these differences may affect the
implementation. The components of risk include assets, threats,
and vulnerabilities. Consider the following example iSCSI nodes,
which demonstrate differences in assets and vulnerabilities of the
nodes, and as a result, differences in implementation:
a) One iSCSI target based on a special-purpose operating
system: Since the iSCSI target controls access to the
data storage containing company assets, the asset level
is seen as very high. Also, because of the special-
purpose operating system, in which vulnerabilities are
less well-known, the vulnerability level is viewed as
low.
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b) Multiple iSCSI initiators in a blade farm, each running a
general purpose operating system: The asset level of each
node is viewed as low, since blades are replaceable and
low cost. However, the vulnerability level is viewed as
high, since there may be many well-known vulnerabilities
to that general-purpose operating system. For this
target, an appropriate implementation might be logging of
received key values, but no transmission of the key. For
this initiator, an appropriate implementation might be
transmission of the key, but no logging of received key
values.
9.5. SCSI Access Control Considerations
iSCSI is a SCSI transport protocol and as such does not apply any
access controls on SCSI-level operations such as SCSI task
management functions (e.g. LU Reset, see Section 11.5.1). SCSI-
level access controls (e.g. ACCESS CONTROL OUT, see [SPC3]) have
to be appropriately deployed in practice to address SCSI-level
security considerations, in addition to security at iSCSI
connection and packet protection mechanisms that were already
discussed in preceding Sections.
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10. Notes to Implementers
This Section notes some of the performance and reliability
considerations of the iSCSI protocol. This protocol was designed
to allow efficient silicon and software implementations. The iSCSI
task tag mechanism was designed to enable Direct Data Placement
(DDP - a DMA form) at the iSCSI level or lower.
The guiding assumption made throughout the design of this protocol
is that targets are resource constrained relative to initiators.
Implementers are also advised to consider the implementation
consequences of the iSCSI to SCSI mapping model as outlined in
Section 4.4.3.
10.1. Multiple Network Adapters
The iSCSI protocol allows multiple connections, not all of which
need to go over the same network adapter. If multiple network
connections are to be utilized with hardware support, the iSCSI
protocol command-data-status allegiance to one TCP connection
ensures that there is no need to replicate information across
network adapters or otherwise require them to cooperate.
However, some task management commands may require some loose form
of cooperation or replication at least on the target.
10.1.1. Conservative Reuse of ISIDs
Historically, the SCSI model (and implementations and applications
based on that model) has assumed that SCSI ports are static,
physical entities. Recent extensions to the SCSI model have taken
advantage of persistent worldwide unique names for these ports. In
iSCSI however, the SCSI initiator ports are the endpoints of
dynamically created sessions, so the presumptions of "static and
physical" do not apply. In any case, the model clauses
(particularly, Section 4.4.1) provide for persistent, reusable
names for the iSCSI-type SCSI initiator ports even though there
does not need to be any physical entity bound to these names.
To both minimize the disruption of legacy applications and to
better facilitate the SCSI features that rely on persistent names
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for SCSI ports, iSCSI implementations SHOULD attempt to provide a
stable presentation of SCSI Initiator Ports (both to the upper OS-
layers and to the targets to which they connect). This can be
achieved in an initiator implementation by conservatively reusing
ISIDs. In other words, the same ISID should be used in the Login
process to multiple target portal groups (of the same iSCSI Target
or different iSCSI Targets). The ISID RULE (Section 4.4.3) only
prohibits reuse to the same target portal group. It does not
"preclude" reuse to other target portal groups.
The principle of conservative reuse "encourages" reuse to other
target portal groups. When a SCSI target device sees the same
(InitiatorName, ISID) pair in different sessions to different
target portal groups, it can identify the underlying SCSI
Initiator Port on each session as the same SCSI port. In effect,
it can recognize multiple paths from the same source.
10.1.2. iSCSI Name, ISID, and TPGT Use
The designers of the iSCSI protocol are aware that legacy SCSI
transports rely on initiator identity to assign access to storage
resources. Although newer techniques are available and simplify
access control, support for configuration and authentication
schemes that are based on initiator identity is deemed important
in order to support legacy systems and administration software.
iSCSI thus supports the notion that it should be possible to
assign access to storage resources based on "initiator device"
identity.
When there are multiple hardware or software components
coordinated as a single iSCSI Node, there must be some (logical)
entity that represents the iSCSI Node that makes the iSCSI Node
Name available to all components involved in session creation and
login. Similarly, this entity that represents the iSCSI Node must
be able to coordinate session identifier resources (ISID for
initiators) to enforce both the ISID and TSIH RULES (see Section
4.4.3).
For targets, because of the closed environment, implementation of
this entity should be straightforward. However, vendors of iSCSI
hardware (e.g., NICs or HBAs) intended for targets, SHOULD provide
mechanisms for configuration of the iSCSI Node Name across the
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portal groups instantiated by multiple instances of these
components within a target.
However, complex targets making use of multiple Target Portal
Group Tags may reconfigure them to achieve various quality goals.
The initiators have two mechanisms at their disposal to discover
and/or check reconfiguring targets - the discovery session type
and a key returned by the target during login to confirm the TPGT.
An initiator should attempt to "rediscover" the target
configuration anytime a session is terminated unexpectedly.
For initiators, in the long term, it is expected that operating
system vendors will take on the role of this entity and provide
standard APIs that can inform components of their iSCSI Node Name
and can configure and/or coordinate ISID allocation, use, and
reuse.
Recognizing that such initiator APIs are not available today,
other implementations of the role of this entity are possible. For
example, a human may instantiate the (common) Node name as part of
the installation process of each iSCSI component involved in
session creation and login. This may be done either by pointing
the component to a vendor-specific location for this datum or to a
system-wide location. The structure of the ISID namespace (see
Section 11.12.5 and [RFC3721]) facilitates implementation of the
ISID coordination by allowing each component vendor to
independently (of other vendor's components) coordinate
allocation, use, and reuse of its own partition of the ISID
namespace in a vendor-specific manner. Partitioning of the ISID
namespace within initiator portal groups managed by that vendor
allows each such initiator portal group to act independently of
all other portal groups when selecting an ISID for a login; this
facilitates enforcement of the ISID RULE (see Section 4.4.3) at
the initiator.
A vendor of iSCSI hardware (e.g., NICs or HBAs) intended for use
in initiators MUST implement a mechanism for configuring the iSCSI
Node Name. Vendors, and administrators must ensure that iSCSI Node
Names are unique worldwide. It is therefore important that when
one chooses to reuse the iSCSI Node Name of a disabled unit, not
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to re-assign that name to the original unit unless its worldwide
uniqueness can be ascertained again.
In addition, a vendor of iSCSI hardware must implement a mechanism
to configure and/or coordinate ISIDs for all sessions managed by
multiple instances of that hardware within a given iSCSI Node.
Such configuration might be either permanently pre-assigned at the
factory (in a necessarily globally unique way), statically
assigned (e.g., partitioned across all the NICs at initialization
in a locally unique way), or dynamically assigned (e.g., on-line
allocator, also in a locally unique way). In the latter two cases,
the configuration may be via public APIs (perhaps driven by an
independent vendor's software, such as the OS vendor) or via
private APIs driven by the vendor's own software.
The process of name assignment and coordination has to be as
encompassing and automated as possible as years of legacy usage
have shown it to be highly error-prone. It is to be mentioned
that SCSI has today alternative schemes of access control that can
be used by all transports and their security is not dependent on
strict naming coordination.
10.2. Autosense and Auto Contingent Allegiance (ACA)
Autosense refers to the automatic return of sense data to the
initiator in case a command did not complete successfully. iSCSI
initiators and targets MUST support and use autosense.
ACA helps preserve ordered command execution in the presence of
errors. As there can be many commands in-flight between an
initiator and a target, SCSI initiator functionality in some
operating systems depends on ACA to enforce ordered command
execution during error recovery, and hence iSCSI initiator
implementations for those operating systems need to support ACA.
In order to support error recovery for these operating systems and
iSCSI initiators, iSCSI targets SHOULD support ACA.
10.3. iSCSI Timeouts
iSCSI recovery actions are often dependent on iSCSI time-outs
being recognized and acted upon before SCSI time-outs. Determining
the right time-outs to use for various iSCSI actions (command
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acknowledgements expected, status acknowledgements, etc.) is very
much dependent on infrastructure (hardware, links, TCP/IP stack,
iSCSI driver). As a guide, the implementer may use an average Nop-
Out/Nop-In turnaround delay multiplied by a "safety factor" (e.g.,
4) as a good estimate for the basic delay of the iSCSI stack for a
given connection. The safety factor should account for the network
load variability. For connection teardown the implementer may
want to consider also TCP common practice for the given
infrastructure.
Text negotiations MAY also be subject to either time-limits or
limits in the number of exchanges. Those SHOULD be generous enough
to avoid affecting interoperability (e.g., allowing each key to be
negotiated on a separate exchange).
The relation between iSCSI timeouts and SCSI timeouts should also
be considered. SCSI timeouts should be longer than iSCSI timeouts
plus the time required for iSCSI recovery whenever iSCSI recovery
is planned. Alternatively, an implementer may choose to interlock
iSCSI timeouts and recovery with SCSI timeouts so that SCSI
recovery will become active only where iSCSI is not planned to, or
failed to, recover.
The implementer may also want to consider the interaction between
various iSCSI exception events - such as a digest failure - and
subsequent timeouts. When iSCSI error recovery is active, a digest
failure is likely to result in discovering a missing command or
data PDU. In these cases, an implementer may want to lower the
timeout values to enable faster initiation for recovery
procedures.
10.4. Command Retry and Cleaning Old Command Instances
To avoid having old, retried command instances appear in a valid
command window after a command sequence number wrap around, the
protocol requires (see Section 4.2.2.1) that on every connection
on which a retry has been issued, a non-immediate command be
issued and acknowledged within a 2**31-1 commands interval from
the CmdSN of the retried command. This requirement can be
fulfilled by an implementation in several ways.
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The simplest technique to use is to send a (non-retry) non-
immediate SCSI command (or a NOP if no SCSI command is available
for a while) after every command retry on the connection on which
the retry was attempted. As errors are deemed rare events, this
technique is probably the most effective, as it does not involve
additional checks at the initiator when issuing commands.
10.5. Synch and Steering Layer and Performance
While a synch and steering layer is optional, an initiator/target
that does not have it working against a target/initiator that
demands synch and steering may experience performance degradation
caused by packet reordering and loss. Providing a synch and
steering mechanism is recommended for all high-speed
implementations.
10.6. Considerations for State-dependent Devices and Long-lasting
SCSI Operations
Sequential access devices operate on the principle that the
position of the device is based on the last command processed. As
such, command processing order and knowledge of whether or not the
previous command was processed is of the utmost importance to
maintain data integrity. For example, inadvertent retries of SCSI
commands when it is not known if the previous SCSI command was
processed is a potential data integrity risk.
For a sequential access device, consider the scenario in which a
SCSI SPACE command to backspace one filemark is issued and then
re-issued due to no status received for the command. If the first
SPACE command was actually processed, the re-issued SPACE command,
if processed, will cause the position to change. Thus, a
subsequent write operation will write data to the wrong position
and any previous data at that position will be overwritten.
For a medium changer device, consider the scenario in which an
EXCHANGE MEDIUM command (the SOURCE ADDRESS and DESTINATION
ADDRESS are the same thus performing a swap) is issued and then
re-issued due to no status received for the command. If the first
EXCHANGE MEDIUM command was actually processed, the re-issued
EXCHANGE MEDIUM command, if processed, will perform the swap
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again. The net effect is no swap was performed thus leaving a data
integrity exposure.
All commands that change the state of the device (as in SPACE
commands for sequential access devices, and EXCHANGE MEDIUM for
medium changer device), MUST be issued as non-immediate commands
for deterministic and in order delivery to iSCSI targets.
For many of those state changing commands, the execution model
also assumes that the command is executed exactly once. Devices
implementing READ POSITION and LOCATE provide a means for SCSI
level command recovery and new tape-class devices should support
those commands. In their absence a retry at SCSI level is
difficult and error recovery at iSCSI level is advisable.
Devices operating on long latency delivery subsystems and
performing long lasting SCSI operations may need mechanisms that
enable connection replacement while commands are running (e.g.,
during an extended copy operation).
10.6.1. Determining the Proper ErrorRecoveryLevel
The implementation and use of a specific ErrorRecoveryLevel should
be determined based on the deployment scenarios of a given iSCSI
implementation. Generally, the following factors must be
considered before deciding on the proper level of recovery:
a) Application resilience to I/O failures.
b) Required level of availability in the face of transport
connection failures.
c) Probability of transport layer "checksum escape" (message
error undetected by TCP checksum - see [RFC3385] for
related discussion). This in turn decides the iSCSI
digest failure frequency, and thus the criticality of
iSCSI-level error recovery. The details of estimating
this probability are outside the scope of this document.
A consideration of the above factors for SCSI tape devices as an
example suggests that implementations SHOULD use
ErrorRecoveryLevel=1 when transport connection failure is not a
concern and SCSI level recovery is unavailable, and
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ErrorRecoveryLevel=2 when the connection failure is also of high
likelihood during a backup/retrieval.
For extended copy operations, implementations SHOULD use
ErrorRecoveryLevel=2 whenever there is a relatively high
likelihood of connection failure.
10.7. Multi-task Abort Implementation Considerations
Multi-task abort operations are typically issued in emergencies -
such as clearing a device lock-up, HA failover/failback etc. In
these circumstances, it is desirable to rapidly go through the
error handling process as opposed to the target waiting on
multiple third-party initiators who may not even be functional
anymore - especially if this emergency is triggered because of one
such initiator failure. Therefore, both iSCSI target and
initiator implementations SHOULD support FastAbort multi-task
abort semantics (Section 4.2.3.4).
Note that both in standard semantics (Section 4.2.3.3) and
FastAbort semantics (Section 4.2.3.4), there may be outstanding
data transfers even after the TMF completion is reported on the
issuing session. In the case of iSCSI/iSER [iSER], these would be
tagged data transfers for STags not owned by any active tasks.
Whether or not real buffers support these data transfers is
implementation-dependent. However, the data transfers logically
MUST be silently discarded by the target iSCSI layer in all cases.
A target MAY, on an implementation-defined internal timeout, also
choose to drop the connections on which it did not receive the
expected Data-Out sequences (Section 4.2.3.3) or NOP-Out
acknowledgements (Section 4.2.3.4) so as to reclaim the associated
buffer, STag, and TTT resources as appropriate.
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11. iSCSI PDU Formats
All multi-byte integers that are specified in formats defined in
this document are to be represented in network byte order (i.e.,
big endian). Any field that appears in this document assumes that
the most significant byte is the lowest numbered byte and the most
significant bit (within byte or field) is the lowest numbered bit
unless specified otherwise.
Any compliant sender MUST set all bits not defined and all
reserved fields to zero unless specified otherwise. Any compliant
receiver MUST ignore any bit not defined and all reserved fields
unless specified otherwise. Receipt of reserved code values in
defined fields MUST be reported as a protocol error.
Reserved fields are marked by the word "reserved", some
abbreviation of "reserved", or by "." for individual bits when no
other form of marking is technically feasible.
11.1. iSCSI PDU Length and Padding
iSCSI PDUs are padded to the closest integer number of four byte
words. The padding bytes SHOULD be sent as 0.
11.2. PDU Template, Header, and Opcodes
All iSCSI PDUs have one or more header segments and, optionally, a
data segment. After the entire header segment group a header-
digest MAY follow. The data segment MAY also be followed by a
data-digest.
The Basic Header Segment (BHS) is the first segment in all of the
iSCSI PDUs. The BHS is a fixed-length 48-byte header segment. It
MAY be followed by Additional Header Segments (AHS), a Header-
Digest, a Data Segment, and/or a Data-Digest.
The overall structure of an iSCSI PDU is as follows:
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0/ Basic Header Segment (BHS) /
+/ /
+---------------+---------------+---------------+--------------+
48/ Additional Header Segment 1 (AHS) (optional) /
+/ /
+---------------+---------------+---------------+--------------+
/ Additional Header Segment 2 (AHS) (optional) /
+/ /
+---------------+---------------+---------------+--------------+
+---------------+---------------+---------------+--------------+
/ Additional Header Segment n (AHS) (optional) /
+/ /
+---------------+---------------+---------------+--------------+
k/ Header-Digest (optional) /
+/ /
+---------------+---------------+---------------+--------------+
l/ Data Segment(optional) /
+/ /
+---------------+---------------+---------------+--------------+
m/ Data-Digest (optional) /
+/ /
+---------------+---------------+---------------+--------------+
All PDU segments and digests are padded to the closest integer
number of four byte words. For example, all PDU segments and
digests start at a four byte word boundary and the padding ranges
from 0 to 3 bytes. The padding bytes SHOULD be sent as 0.
iSCSI response PDUs do not have AH Segments.
11.2.1. Basic Header Segment (BHS)
The BHS is 48 bytes long. The Opcode and DataSegmentLength fields
appear in all iSCSI PDUs. In addition, when used, the Initiator
Task Tag and Logical Unit Number always appear in the same
location in the header.
The format of the BHS is:
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|I| Opcode |F| Opcode-specific fields |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8| LUN or Opcode-specific fields |
+ +
12| |
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+--------------+
20/ Opcode-specific fields /
+/ /
+---------------+---------------+---------------+--------------+
48
11.2.1.1. I
For request PDUs, the I bit set to 1 is an immediate delivery
marker.
11.2.1.2. Opcode
The Opcode indicates the type of iSCSI PDU the header
encapsulates.
The Opcodes are divided into two categories: initiator opcodes and
target opcodes. Initiator opcodes are in PDUs sent by the
initiator (request PDUs). Target opcodes are in PDUs sent by the
target (response PDUs).
Initiators MUST NOT use target opcodes and targets MUST NOT use
initiator opcodes.
Initiator opcodes defined in this specification are:
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0x00 NOP-Out
0x01 SCSI Command (encapsulates a SCSI Command Descriptor
Block)
0x02 SCSI Task Management function request
0x03 Login Request
0x04 Text Request
0x05 SCSI Data-out (for WRITE operations)
0x06 Logout Request
0x10 SNACK Request
0x1c-0x1e Vendor specific codes
Target opcodes are:
0x20 NOP-In
0x21 SCSI Response - contains SCSI status and possibly sense
information or other response information.
0x22 SCSI Task Management function response
0x23 Login Response
0x24 Text Response
0x25 SCSI Data-in - for READ operations.
0x26 Logout Response
0x31 Ready To Transfer (R2T) - sent by target when it is ready
to receive data.
0x32 Asynchronous Message - sent by target to indicate certain
special conditions.
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0x3c-0x3e Vendor specific codes
0x3f Reject
All other opcodes are reserved.
11.2.1.3. Final (F) bit
When set to 1 it indicates the final (or only) PDU of a sequence.
11.2.1.4. Opcode-specific Fields
These fields have different meanings for different opcode types.
11.2.1.5. TotalAHSLength
Total length of all AHS header segments in units of four byte
words including padding, if any.
The TotalAHSLength is only used in PDUs that have an AHS and MUST
be 0 in all other PDUs.
11.2.1.6. DataSegmentLength
This is the data segment payload length in bytes (excluding
padding). The DataSegmentLength MUST be 0 whenever the PDU has no
data segment.
11.2.1.7. LUN
Some opcodes operate on a specific Logical Unit. The Logical Unit
Number (LUN) field identifies which Logical Unit. If the opcode
does not relate to a Logical Unit, this field is either ignored or
may be used in an opcode specific way. The LUN field is 64-bits
and should be formatted in accordance with [SAM2]. For example,
LUN[0] from [SAM2] is BHS byte 8 and so on up to LUN[7] from
[SAM2], which is BHS byte 15.
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11.2.1.8. Initiator Task Tag
The initiator assigns a Task Tag to each iSCSI task it issues.
While a task exists, this tag MUST uniquely identify the task
session-wide. SCSI may also use the initiator task tag as part of
the SCSI task identifier when the timespan during which an iSCSI
initiator task tag must be unique extends over the timespan during
which a SCSI task tag must be unique. However, the iSCSI Initiator
Task Tag must exist and be unique even for untagged SCSI commands.
An ITT value of 0xffffffff is reserved and MUST NOT be assigned
for a task by the initiator. The only instance in which it may be
seen on the wire is in a target-initiated NOP-In PDU (Section
11.19) and in the initiator response to that PDU, if necessary.
11.2.2. Additional Header Segment (AHS)
The general format of an AHS is:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0| AHSLength | AHSType | AHS-Specific |
+---------------+---------------+---------------+--------------+
4/ AHS-Specific /
+/ /
+---------------+---------------+---------------+--------------+
x
11.2.2.1. AHSType
The AHSType field is coded as follows:
bit 0-1 - Reserved
bit 2-7 - AHS code
0 - Reserved
1 - Extended CDB
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2 - Expected Bidirectional Read Data Length
3 - 63 Reserved
11.2.2.2. AHSLength
This field contains the effective length in bytes of the AHS
excluding AHSType and AHSLength and padding, if any. The AHS is
padded to the smallest integer number of 4 byte words (i.e., from
0 up to 3 padding bytes).
11.2.2.3. Extended CDB AHS
The format of the Extended CDB AHS is:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0| AHSLength (CDBLength-15) | 0x01 | Reserved |
+---------------+---------------+---------------+--------------+
4/ ExtendedCDB...+padding /
+/ /
+---------------+---------------+---------------+--------------+
x
This type of AHS MUST NOT be used if the CDBLength is less than
17.
The length includes the reserved byte 3.
11.2.2.4. Bidirectional Expected Read-Data Length AHS
The format of the Bidirectional Read Expected Data Transfer Length
AHS is:
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0| AHSLength (0x0005) | 0x02 | Reserved |
+---------------+---------------+---------------+--------------+
4| Expected Read-Data Length |
+---------------+---------------+---------------+--------------+
8
11.2.3. Header Digest and Data Digest
Optional header and data digests protect the integrity of the
header and data, respectively. The digests, if present, are
located, respectively, after the header and PDU-specific data, and
cover respectively the header and the PDU data, each including
the padding bytes, if any.
The existence and type of digests are negotiated during the Login
Phase.
The separation of the header and data digests is useful in iSCSI
routing applications, in which only the header changes when a
message is forwarded. In this case, only the header digest should
be recalculated.
Digests are not included in data or header length fields.
A zero-length Data Segment also implies a zero-length data-digest.
11.2.4. Data Segment
The (optional) Data Segment contains PDU associated data. Its
payload effective length is provided in the BHS field -
DataSegmentLength. The Data Segment is also padded to an integer
number of 4 byte words.
11.3. SCSI Command
The format of the SCSI Command PDU is:
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|I| 0x01 |F|R|W|. .|ATTR | Reserved |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8| Logical Unit Number (LUN) |
+ +
12| |
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+--------------+
20| Expected Data Transfer Length |
+---------------+---------------+---------------+--------------+
24| CmdSN |
+---------------+---------------+---------------+--------------+
28| ExpStatSN |
+---------------+---------------+---------------+--------------+
32/ SCSI Command Descriptor Block (CDB) /
+/ /
+---------------+---------------+---------------+--------------+
48/ AHS (Optional) /
+---------------+---------------+---------------+--------------+
x/ Header Digest (Optional) /
+---------------+---------------+---------------+--------------+
y/ (DataSegment, Command Data) (Optional) /
+/ /
+---------------+---------------+---------------+--------------+
z/ Data Digest (Optional) /
+---------------+---------------+---------------+--------------+
11.3.1. Flags and Task Attributes (byte 1)
The flags for a SCSI Command are:
bit 0 (F) is set to 1 when no unsolicited SCSI Data-Out PDUs
follow this PDU. When F=1 for a write and if Expected Data
Transfer Length is larger than the DataSegmentLength, the
target may solicit additional data through R2T.
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bit 1 (R) is set to 1 when the command is expected to input
data.
bit 2 (W) is set to 1 when the command is expected to output
data.
bit 3-4 Reserved.
bit 5-7 contains Task Attributes.
Task Attributes (ATTR) have one of the following integer values
(see [SAM2] for details):
0 - Untagged
1 - Simple
2 - Ordered
3 - Head of Queue
4 - ACA
5-7 - Reserved
At least one of the W and F bits MUST be set to 1.
Either or both of R and W MAY be 1 when either the Expected Data
Transfer Length and/or Bidirectional Read Expected Data Transfer
Length are 0, but they MUST NOT both be 0 when the Expected Data
Transfer Length and/or Bidirectional Read Expected Data Transfer
Length are not 0 (i.e., when some data transfer is expected the
transfer direction is indicated by the R and/or W bit).
11.3.2. CmdSN - Command Sequence Number
Enables ordered delivery across multiple connections in a single
session.
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11.3.3. ExpStatSN
Command responses up to ExpStatSN-1 (mod 2**32) have been received
(acknowledges status) on the connection.
11.3.4. Expected Data Transfer Length
For unidirectional operations, the Expected Data Transfer Length
field contains the number of bytes of data involved in this SCSI
operation. For a unidirectional write operation (W flag set to 1
and R flag set to 0), the initiator uses this field to specify the
number of bytes of data it expects to transfer for this operation.
For a unidirectional read operation (W flag set to 0 and R flag
set to 1), the initiator uses this field to specify the number of
bytes of data it expects the target to transfer to the initiator.
It corresponds to the SAM2 byte count.
For bidirectional operations (both R and W flags are set to 1),
this field contains the number of data bytes involved in the write
transfer. For bidirectional operations, an additional header
segment MUST be present in the header sequence that indicates the
Bidirectional Read Expected Data Transfer Length. The Expected
Data Transfer Length field and the Bidirectional Read Expected
Data Transfer Length field correspond to the SAM2 byte count.
If the Expected Data Transfer Length for a write and the length of
the immediate data part that follows the command (if any) are the
same, then no more data PDUs are expected to follow. In this
case, the F bit MUST be set to 1.
If the Expected Data Transfer Length is higher than the
FirstBurstLength (the negotiated maximum amount of unsolicited
data the target will accept), the initiator MUST send the maximum
amount of unsolicited data OR ONLY the immediate data, if any.
Upon completion of a data transfer, the target informs the
initiator (through residual counts) of how many bytes were
actually processed (sent and/or received) by the target.
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11.3.5. CDB - SCSI Command Descriptor Block
There are 16 bytes in the CDB field to accommodate the commonly
used CDBs. Whenever the CDB is larger than 16 bytes, an Extended
CDB AHS MUST be used to contain the CDB spillover.
11.3.6. Data Segment - Command Data
Some SCSI commands require additional parameter data to accompany
the SCSI command. This data may be placed beyond the boundary of
the iSCSI header in a data segment. Alternatively, user data
(e.g., from a WRITE operation) can be placed in the data segment
(both cases are referred to as immediate data). These data are
governed by the rules for solicited vs. unsolicited data outlined
in Section 4.2.5.2.
11.4. SCSI Response
The format of the SCSI Response PDU is:
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|.| 0x21 |1|. .|o|u|O|U|.| Response | Status |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8| Reserved |
+ +
12| |
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+--------------+
20| SNACK Tag or Reserved |
+---------------+---------------+---------------+--------------+
24| StatSN |
+---------------+---------------+---------------+--------------+
28| ExpCmdSN |
+---------------+---------------+---------------+--------------+
32| MaxCmdSN |
+---------------+---------------+---------------+--------------+
36| ExpDataSN or Reserved |
+---------------+---------------+---------------+--------------+
40| Bidirectional Read Residual Count or Reserved |
+---------------+---------------+---------------+--------------+
44| Residual Count or Reserved |
+---------------+---------------+---------------+--------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+--------------+
/ Data Segment (Optional) /
+/ /
+---------------+---------------+---------------+--------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+--------------+
11.4.1. Flags (byte 1)
bit 1-2 Reserved.
bit 3 - (o) set for Bidirectional Read Residual Overflow. In
this case, the Bidirectional Read Residual Count indicates
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the number of bytes that were not transferred to the
initiator because the initiator's Expected Bidirectional
Read Data Transfer Length was not sufficient.
bit 4 - (u) set for Bidirectional Read Residual Underflow. In
this case, the Bidirectional Read Residual Count indicates
the number of bytes that were not transferred to the
initiator out of the number of bytes expected to be
transferred.
bit 5 - (O) set for Residual Overflow. In this case, the
Residual Count indicates the number of bytes that were not
transferred because the initiator's Expected Data Transfer
Length was not sufficient. For a bidirectional operation,
the Residual Count contains the residual for the write
operation.
bit 6 - (U) set for Residual Underflow. In this case, the
Residual Count indicates the number of bytes that were not
transferred out of the number of bytes that were expected to
be transferred. For a bidirectional operation, the Residual
Count contains the residual for the write operation.
bit 7 - (0) Reserved.
Bits O and U and bits o and u are mutually exclusive (i.e., having
both o and u or O and U set to 1 is a protocol error).
For a response other than "Command Completed at Target", bits 3-6
MUST be 0.
11.4.2. Status
The Status field is used to report the SCSI status of the command
(as specified in [SAM2]) and is only valid if the Response Code is
Command Completed at target.
Some of the status codes defined in [SAM2] are:
0x00 GOOD
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0x02 CHECK CONDITION
0x08 BUSY
0x18 RESERVATION CONFLICT
0x28 TASK SET FULL
0x30 ACA ACTIVE
0x40 TASK ABORTED
See [SAM2] for the complete list and definitions.
If a SCSI device error is detected while data from the initiator
is still expected (the command PDU did not contain all the data
and the target has not received a Data PDU with the final bit
Set), the target MUST wait until it receives a Data PDU with the F
bit set in the last expected sequence before sending the Response
PDU.
11.4.3. Response
This field contains the iSCSI service response.
iSCSI service response codes defined in this specification are:
0x00 - Command Completed at Target
0x01 - Target Failure
0x80-0xff - Vendor specific
All other response codes are reserved.
The Response is used to report a Service Response. The mapping of
the response code into a SCSI service response code value, if
needed, is outside the scope of this document. However, in
symbolic terms response value 0x00 maps to the SCSI service
response (see [SAM2] and [SPC3]) of TASK COMPLETE or LINKED
COMMAND COMPLETE. All other Response values map to the SCSI
service response of SERVICE DELIVERY OR TARGET FAILURE.
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If a SCSI Response PDU does not arrive before the session is
terminated, the SCSI service response is SERVICE DELIVERY OR
TARGET FAILURE.
A non-zero response field indicates a failure to execute the
command in which case the Status and Flag fields are undefined and
MUST be ignored on reception.
11.4.4. SNACK Tag
This field contains a copy of the SNACK Tag of the last SNACK Tag
accepted by the target on the same connection and for the command
for which the response is issued. Otherwise it is reserved and
should be set to 0.
After issuing a R-Data SNACK the initiator must discard any SCSI
status unless contained in an SCSI Response PDU carrying the same
SNACK Tag as the last issued R-Data SNACK for the SCSI command on
the current connection.
For a detailed discussion on R-Data SNACK see 11.16.3.
11.4.5. Residual Count
11.4.5.1. Field Semantics
The Residual Count field MUST be valid in the case where either
the U bit or the O bit is set. If neither bit is set, the Residual
Count field MUST be ignored on reception and SHOULD be set to 0
when sending. Targets may set the residual count and initiators
may use it when the response code is "completed at target" (even
if the status returned is not GOOD). If the O bit is set, the
Residual Count indicates the number of bytes that were not
transferred because the initiator's Expected Data Transfer Length
was not sufficient. If the U bit is set, the Residual Count
indicates the number of bytes that were not transferred out of the
number of bytes expected to be transferred.
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11.4.5.2. Residuals Concepts Overview
SCSI-Presented Data Transfer Length (SPDTL) is the term this
document uses (see Section 2.1 for definition) to represent the
aggregate data length that the target SCSI layer attempts to
transfer using the local iSCSI layer for a task. Expected Data
Transfer Length (EDTL) is the iSCSI term that represents the
length of data that the iSCSI layer expects to transfer for a
task. EDTL is specified in the SCSI Command PDU.
When SPDTL = EDTL for a task, the target iSCSI layer completes the
task with no residuals. Whenever SPDTL differs from EDTL for a
task, that task is said to have a residual.
If SPDTL > EDTL for a task, iSCSI Overflow MUST be signaled in the
SCSI Response PDU as specified in Section 11.4.5.1. The Residual
Count MUST be set to the numerical value of (SPDTL - EDTL).
If SPDTL < EDTL for a task, iSCSI Underflow MUST be signaled in
the SCSI Response PDU as specified in Section 11.4.5.1. The
Residual Count MUST be set to the numerical value of (EDTL -
SPDTL).
Note that the Overflow and Underflow scenarios are independent of
Data-In and Data-Out. Either scenario is logically possible in
either direction of data transfer.
11.4.5.3. SCSI REPORT LUNS and Residual Overflow
This Section discusses the residual overflow issues citing the
example of the SCSI REPORT LUNS command. Note however that there
are several SCSI commands (e.g., INQUIRY) with ALLOCATION LENGTH
fields following the same underlying rules. The semantics in the
rest of the Section apply to all such SCSI commands.
The specification of the SCSI REPORT LUNS command requires that
the SCSI target limit the amount of data transferred to a maximum
size (ALLOCATION LENGTH) provided by the initiator in the REPORT
LUNS CDB.
If the Expected Data Transfer Length (EDTL) in the iSCSI header of
the SCSI Command PDU for a REPORT LUNS command is set to at least
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as large as that ALLOCATION LENGTH, the SCSI layer truncation
prevents an iSCSI Residual Overflow from occurring. A SCSI
initiator can detect that such truncation has occurred via other
information at the SCSI layer. The rest of the Section elaborates
this required behavior.
The SCSI REPORT LUNS command requests a target SCSI layer to
return a logical unit inventory (LUN list) to the initiator SCSI
layer (see Section 6.21 of [SPC3]). The size of this LUN list may
not be known to the initiator SCSI layer when it issues the REPORT
LUNS command; to avoid transferring more LUN list data than the
initiator is prepared for, the REPORT LUNS CDB contains an
ALLOCATION LENGTH field to specify the maximum amount of data to
be transferred to the initiator for this command. If the initiator
SCSI layer has underestimated the number of logical units at the
target, it is possible that the complete logical unit inventory
does not fit in the specified ALLOCATION LENGTH. In this
situation, Section 4.3.3.6 in [SPC3] requires that the target SCSI
layer "shall terminate transfers to the Data-In Buffer" when the
number of bytes specified by the ALLOCATION LENGTH field have been
transferred.
Therefore, in response to a REPORT LUNS command, the SCSI layer at
the target presents at most ALLOCATION LENGTH bytes of data
(logical unit inventory) to iSCSI for transfer to the initiator.
For a REPORT LUNS command, if the iSCSI EDTL is at least as large
as the ALLOCATION LENGTH, the SCSI truncation ensures that the
EDTL will accommodate all of the data to be transferred. If all of
the logical unit inventory data presented to the iSCSI layer --
i.e., the data remaining after any SCSI truncation -- is
transferred to the initiator by the iSCSI layer, an iSCSI Residual
Overflow has not occurred and the iSCSI (O) bit MUST NOT be set in
the SCSI Response or final SCSI Data-Out PDU. Note that this
behavior is implied by the combination of Section 11.4.5.1 along
with the specification of the REPORT LUNS command in [SPC3].
However, if the iSCSI EDTL is larger than the ALLOCATION LENGTH in
this scenario, note that the iSCSI Underflow MUST be signaled in
the SCSI Response PDU. An iSCSI Underflow MUST also be signaled
when the iSCSI EDTL is equal to the ALLOCATION LENGTH but the
logical unit inventory data presented to the iSCSI layer is
smaller than the ALLOCATION LENGTH.
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The LUN LIST LENGTH field in the logical unit inventory (the first
field in the inventory) is not affected by truncation of the
inventory to fit in ALLOCATION LENGTH; this enables a SCSI
initiator to determine that the received inventory is incomplete
by noticing that the LUN LIST LENGTH in the inventory is larger
than the ALLOCATION LENGTH that was sent in the REPORT LUNS CDB. A
common initiator behavior in this situation is to re-issue the
REPORT LUNS command with a larger ALLOCATION LENGTH.
11.4.6. Bidirectional Read Residual Count
The Bidirectional Read Residual Count field MUST be valid in the
case where either the u bit or the o bit is set. If neither bit is
set, the Bidirectional Read Residual Count field is reserved.
Targets may set the Bidirectional Read Residual Count and
initiators may use it when the response code is "completed at
target". If the o bit is set, the Bidirectional Read Residual
Count indicates the number of bytes that were not transferred to
the initiator because the initiator's Expected Bidirectional Read
Transfer Length was not sufficient. If the u bit is set, the
Bidirectional Read Residual Count indicates the number of bytes
that were not transferred to the initiator out of the number of
bytes expected to be transferred.
11.4.7. Data Segment - Sense and Response Data Segment
iSCSI targets MUST support and enable autosense. If Status is
CHECK CONDITION (0x02), then the Data Segment MUST contain sense
data for the failed command.
For some iSCSI responses, the response data segment MAY contain
some response related information, (e.g., for a target failure, it
may contain a vendor specific detailed description of the
failure).
If the DataSegmentLength is not 0, the format of the Data Segment
is as follows:
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|SenseLength | Sense Data |
+---------------+---------------+---------------+--------------+
x/ Sense Data /
+---------------+---------------+---------------+--------------+
y/ Response Data /
/ /
+---------------+---------------+---------------+--------------+
11.4.7.1. SenseLength
Length of Sense Data.
11.4.7.2. Sense Data
The Sense Data contains detailed information about a check
condition and [SPC3] specifies the format and content of the Sense
Data.
Certain iSCSI conditions result in the command being terminated at
the target (response Command Completed at Target) with a SCSI
Check Condition Status as outlined in the next table:
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+--------------------------+----------+--------------------------+
| iSCSI Condition |Sense | Additional Sense Code & |
| |Key | Qualifier |
+--------------------------+----------+--------------------------+
| Unexpected unsolicited |Aborted | ASC = 0x0c ASCQ = 0x0c |
| data |Command-0B| Write Error |
+--------------------------+----------+--------------------------+
| Incorrect amount of data |Aborted | ASC = 0x0c ASCQ = 0x0d |
| |Command-0B| Write Error |
+--------------------------+----------+--------------------------+
| Protocol Service CRC |Aborted | ASC = 0x47 ASCQ = 0x05 |
| error |Command-0B| CRC Error Detected |
+--------------------------+----------+--------------------------+
| SNACK rejected |Aborted | ASC = 0x11 ASCQ = 0x13 |
| |Command-0B| Read Error |
+--------------------------+----------+--------------------------+
The target reports the "Incorrect amount of data" condition if
during data output the total data length to output is greater than
FirstBurstLength and the initiator sent unsolicited non-immediate
data but the total amount of unsolicited data is different than
FirstBurstLength. The target reports the same error when the
amount of data sent as a reply to an R2T does not match the amount
requested.
11.4.8. ExpDataSN
The number of Data-In (read) PDUs the target has sent for the
command.
This field MUST be 0 if the response code is not Command Completed
at Target or the target sent no Data-In PDUs for the command.
11.4.9. StatSN - Status Sequence Number
StatSN is a Sequence Number that the target iSCSI layer generates
per connection and that in turn, enables the initiator to
acknowledge status reception. StatSN is incremented by 1 for every
response/status sent on a connection except for responses sent as
a result of a retry or SNACK. In the case of responses sent due to
a retransmission request, the StatSN MUST be the same as the first
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time the PDU was sent unless the connection has since been
restarted.
11.4.10. ExpCmdSN - Next Expected CmdSN from this Initiator
ExpCmdSN is a Sequence Number that the target iSCSI returns to the
initiator to acknowledge command reception. It is used to update a
local variable with the same name. An ExpCmdSN equal to MaxCmdSN+1
indicates that the target cannot accept new commands.
11.4.11. MaxCmdSN - Maximum CmdSN from this Initiator
MaxCmdSN is a Sequence Number that the target iSCSI returns to the
initiator to indicate the maximum CmdSN the initiator can send. It
is used to update a local variable with the same name. If MaxCmdSN
is equal to ExpCmdSN-1, this indicates to the initiator that the
target cannot receive any additional commands. When MaxCmdSN
changes at the target while the target has no pending PDUs to
convey this information to the initiator, it MUST generate a NOP-
IN to carry the new MaxCmdSN.
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11.5. Task Management Function Request
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|I| 0x02 |1| Function | Reserved |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8| Logical Unit Number (LUN) or Reserved |
+ +
12| |
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+--------------+
20| Referenced Task Tag or 0xffffffff |
+---------------+---------------+---------------+--------------+
24| CmdSN |
+---------------+---------------+---------------+--------------+
28| ExpStatSN |
+---------------+---------------+---------------+--------------+
32| RefCmdSN or Reserved |
+---------------+---------------+---------------+--------------+
36| ExpDataSN or Reserved |
+---------------+---------------+---------------+--------------+
40/ Reserved /
+/ /
+---------------+---------------+---------------+--------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+--------------+
11.5.1. Function
The Task Management functions provide an initiator with a way to
explicitly control the execution of one or more Tasks (SCSI and
iSCSI tasks). The Task Management function codes are listed below.
For a more detailed description of SCSI task management, see
[SAM2].
1 - ABORT TASK - aborts the task identified by the
Referenced Task Tag field.
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2 - ABORT TASK SET - aborts all Tasks issued via this
session on the logical unit.
3 - CLEAR ACA - clears the Auto Contingent Allegiance
condition.
4 - CLEAR TASK SET - aborts all Tasks in the appropriate
task set as defined by the TST field in the Control mode
page (see [SPC3]).
5 - LOGICAL UNIT RESET
6 - TARGET WARM RESET
7 - TARGET COLD RESET
8 - TASK REASSIGN - reassigns connection allegiance for the
task identified by the Initiator Task Tag field to this
connection, thus resuming the iSCSI exchanges for the task.
All other possible values for Function field are reserved.
For all these functions, the Task Management function response
MUST be returned as detailed in Section 11.6. All these functions
apply to the referenced tasks regardless of whether they are
proper SCSI tasks or tagged iSCSI operations. Task management
requests must act on all the commands from the same session having
a CmdSN lower than the task management CmdSN. LOGICAL UNIT RESET,
TARGET WARM RESET and TARGET COLD RESET may affect commands from
other sessions or commands from the same session regardless of
their CmdSN value.
If the task management request is marked for immediate delivery,
it must be considered immediately for execution, but the
operations involved (all or part of them) may be postponed to
allow the target to receive all relevant tasks. According to
[SAM2], for all the tasks covered by the Task Management response
(i.e., with CmdSN lower than the task management command CmdSN)
but except the Task Management response to a TASK REASSIGN,
additional responses MUST NOT be delivered to the SCSI layer after
the Task Management response. The iSCSI initiator MAY deliver to
the SCSI layer all responses received before the Task Management
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response (i.e., it is a matter of implementation if the SCSI
responses, received before the Task Management response but after
the task management request was issued, are delivered to the SCSI
layer by the iSCSI layer in the initiator). The iSCSI target MUST
ensure that no responses for the tasks covered by a task
management function are delivered to the iSCSI initiator after the
Task Management response except for a task covered by a TASK
REASSIGN.
For ABORT TASK SET and CLEAR TASK SET, the issuing initiator MUST
continue to respond to all valid target transfer tags (received
via R2T, Text Response, NOP-In, or SCSI Data-in PDUs) related to
the affected task set, even after issuing the task management
request. The issuing initiator SHOULD however terminate (i.e., by
setting the F-bit to 1) these response sequences as quickly as
possible. The target on its part MUST wait for responses on all
affected target transfer tags before acting on either of these two
task management requests. In case all or part of the response
sequence is not received (due to digest errors) for a valid TTT,
the target MAY treat it as a case of within-command error recovery
class (see Section 7.1.4.1) if it is supporting ErrorRecoveryLevel
>= 1, or alternatively may drop the connection to complete the
requested task set function.
If an ABORT TASK is issued for a task created by an immediate
command then RefCmdSN MUST be that of the Task Management request
itself (i.e. CmdSN and RefCmdSN are equal); otherwise RefCmdSN
MUST be set to the CmdSN of the task to be aborted (lower than
CmdSN).
If the connection is still active (it is not undergoing an
implicit or explicit logout), ABORT TASK MUST be issued on the
same connection to which the task to be aborted is allegiant at
the time the Task Management Request is issued. If the connection
is implicitly or explicitly logged out (i.e., no other request
will be issued on the failing connection and no other response
will be received on the failing connection), then an ABORT TASK
function request may be issued on another connection. This Task
Management request will then establish a new allegiance for the
command to be aborted as well as abort it (i.e., the task to be
aborted will not have to be retried or reassigned, and its status,
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if sent but not acknowledged, will be resent followed by the Task
Management response).
At the target an ABORT TASK function MUST NOT be executed on a
Task Management request; such a request MUST result in Task
Management response of "Function rejected".
For the LOGICAL UNIT RESET function, the target MUST behave as
dictated by the Logical Unit Reset function in [SAM2].
The implementation of the TARGET WARM RESET function and the
TARGET COLD RESET function is OPTIONAL and when implemented,
should act as described below. The TARGET WARM RESET is also
subject to SCSI access controls on the requesting initiator as
defined in [SPC3]. When authorization fails at the target, the
appropriate response as described in Section 11.6.1 MUST be
returned by the target. The TARGET COLD RESET function is not
subject to SCSI access controls, but its execution privileges may
be managed by iSCSI mechanisms such as login authentication.
When executing the TARGET WARM RESET and TARGET COLD RESET
functions, the target cancels all pending operations on all
Logical Units known by the issuing initiator. Both functions are
equivalent to the Target Reset function specified by [SAM2]. They
can affect many other initiators logged in with the servicing SCSI
target port.
The target MUST treat the TARGET COLD RESET function additionally
as a power on event, thus terminating all of its TCP connections
to all initiators (all sessions are terminated). For this reason,
the Service Response (defined by [SAM2]) for this SCSI task
management function may not be reliably delivered to the issuing
initiator port.
For the TASK REASSIGN function, the target should reassign the
connection allegiance to this new connection (and thus resume
iSCSI exchanges for the task). TASK REASSIGN MUST ONLY be received
by the target after the connection on which the command was
previously executing has been successfully logged-out. The Task
Management response MUST be issued before the reassignment becomes
effective.
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For additional usage semantics see Section 7.2.
At the target a TASK REASSIGN function request MUST NOT be
executed to reassign the connection allegiance of a Task
Management function request, an active text negotiation task, or a
Logout task; such a request MUST result in Task Management
response of "Function rejected".
TASK REASSIGN MUST be issued as an immediate command.
11.5.2. TotalAHSLength and DataSegmentLength
For this PDU, TotalAHSLength and DataSegmentLength MUST be 0.
11.5.3. LUN
This field is required for functions that address a specific LU
(ABORT TASK, CLEAR TASK SET, ABORT TASK SET, CLEAR ACA, LOGICAL
UNIT RESET) and is reserved in all others.
11.5.4. Referenced Task Tag
The Initiator Task Tag of the task to be aborted for the ABORT
TASK function or reassigned for the TASK REASSIGN function. For
all the other functions this field MUST be set to the reserved
value 0xffffffff.
11.5.5. RefCmdSN
If an ABORT TASK is issued for a task created by an immediate
command then RefCmdSN MUST be that of the Task Management request
itself (i.e. CmdSN and RefCmdSN are equal).
For an ABORT TASK of a task created by non-immediate command
RefCmdSN MUST be set to the CmdSN of the task identified by the
Referenced Task Tag field. Targets must use this field as
described in Section 11.6.1 when the task identified by the
Referenced Task Tag field is not with the target.
Otherwise, this field is reserved.
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11.5.6. ExpDataSN
For recovery purposes, the iSCSI target and initiator maintain a
data acknowledgement reference number - the first input DataSN
number unacknowledged by the initiator. When issuing a new
command, this number is set to 0. If the function is TASK
REASSIGN, which establishes a new connection allegiance for a
previously issued Read or Bidirectional command, ExpDataSN will
contain an updated data acknowledgement reference number or the
value 0; the latter indicating that the data acknowledgement
reference number is unchanged. The initiator MUST discard any data
PDUs from the previous execution that it did not acknowledge and
the target MUST transmit all Data-in PDUs (if any) starting with
the data acknowledgement reference number. The number of
retransmitted PDUs may or may not be the same as the original
transmission depending on if there was a change in
MaxRecvDataSegmentLength in the reassignment. The target MAY also
send no more Data-In PDUs if all data has been acknowledged.
The value of ExpDataSN MUST be 0 or higher than the DataSN of the
last acknowledged Data-In PDU, but not larger than DataSN+1 of the
last Data-IN PDU sent by the target. Any other value MUST be
ignored by the target.
For other functions this field is reserved.
11.6. Task Management Function Response
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|.| 0x22 |1| Reserved | Response | Reserved |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+--------------------------------------------------------------+
8/ Reserved /
/ /
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+--------------+
20| Reserved |
+---------------+---------------+---------------+--------------+
24| StatSN |
+---------------+---------------+---------------+--------------+
28| ExpCmdSN |
+---------------+---------------+---------------+--------------+
32| MaxCmdSN |
+---------------+---------------+---------------+--------------+
36/ Reserved /
+/ /
+---------------+---------------+---------------+--------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+--------------+
For the functions ABORT TASK, ABORT TASK SET, CLEAR ACA, CLEAR
TASK SET, LOGICAL UNIT RESET, TARGET COLD RESET, TARGET WARM RESET
and TASK REASSIGN, the target performs the requested Task
Management function and sends a Task Management response back to
the initiator. For TASK REASSIGN, the new connection allegiance
MUST ONLY become effective at the target after the target issues
the Task Management Response.
11.6.1. Response
The target provides a Response, which may take on the following
values:
0 - Function complete.
1 - Task does not exist.
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2 - LUN does not exist.
3 - Task still allegiant.
4 - Task allegiance reassignment not supported.
5 - Task management function not supported.
6 - Function authorization failed.
255 - Function rejected.
All other values are reserved.
For a discussion on usage of response codes 3 and 4, see Section
7.2.2.
For the TARGET COLD RESET and TARGET WARM RESET functions, the
target cancels all pending operations across all Logical Units
known to the issuing initiator. For the TARGET COLD RESET
function, the target MUST then close all of its TCP connections to
all initiators (terminates all sessions).
The mapping of the response code into a SCSI service response code
value, if needed, is outside the scope of this document. However,
in symbolic terms, Response values 0 and 1 map to the SCSI service
response of FUNCTION COMPLETE. Response value 2 maps to SCSI
service response of INCORRECT LOGICAL UNIT NUMBER. All other
Response values map to the SCSI service response of FUNCTION
REJECTED. If a Task Management function response PDU does not
arrive before the session is terminated, the SCSI service response
is SERVICE DELIVERY OR TARGET FAILURE.
The response to ABORT TASK SET and CLEAR TASK SET MUST only be
issued by the target after all of the commands affected have been
received by the target, the corresponding task management
functions have been executed by the SCSI target, and the delivery
of all responses delivered until the task management function
completion have been confirmed (acknowledged through ExpStatSN) by
the initiator on all connections of this session. For the exact
timeline of events, refer to Section 4.2.3.3 and Section 4.2.3.4.
For the ABORT TASK function,
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a) If the Referenced Task Tag identifies a valid task leading
to a successful termination, then targets must return the
"Function complete" response.
b) If the Referenced Task Tag does not identify an existing
task, but if the CmdSN indicated by the RefCmdSN field in
the Task Management function request is within the valid
CmdSN window and less than the CmdSN of the Task Management
function request itself, then targets must consider the
CmdSN received and return the "Function complete" response.
c) If the Referenced Task Tag does not identify an existing
task and if the CmdSN indicated by the RefCmdSN field in
the Task Management function request is outside the valid
CmdSN window, then targets must return the "Task does not
exist" response.
For response semantics on function types that can potentially
impact multiple active tasks on the target, see Section 4.2.3.
11.6.2. TotalAHSLength and DataSegmentLength
For this PDU TotalAHSLength and DataSegmentLength MUST be 0.
11.7. SCSI Data-out & SCSI Data-in
The SCSI Data-out PDU for WRITE operations has the following
format:
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|.| 0x05 |F| Reserved |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+--------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+--------------+
24| Reserved |
+---------------+---------------+---------------+--------------+
28| ExpStatSN |
+---------------+---------------+---------------+--------------+
32| Reserved |
+---------------+---------------+---------------+--------------+
36| DataSN |
+---------------+---------------+---------------+--------------+
40| Buffer Offset |
+---------------+---------------+---------------+--------------+
44| Reserved |
+---------------+---------------+---------------+--------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+--------------+
/ DataSegment /
+/ /
+---------------+---------------+---------------+--------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+--------------+
The SCSI Data-in PDU for READ operations has the following format:
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|.| 0x25 |F|A|0 0 0|O|U|S| Reserved |Status or Rsvd|
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+--------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+--------------+
24| StatSN or Reserved |
+---------------+---------------+---------------+--------------+
28| ExpCmdSN |
+---------------+---------------+---------------+--------------+
32| MaxCmdSN |
+---------------+---------------+---------------+--------------+
36| DataSN |
+---------------+---------------+---------------+--------------+
40| Buffer Offset |
+---------------+---------------+---------------+--------------+
44| Residual Count |
+---------------+---------------+---------------+--------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+--------------+
/ DataSegment /
+/ /
+---------------+---------------+---------------+--------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+--------------+
Status can accompany the last Data-in PDU if the command did not
end with an exception (i.e., the status is "good status" - GOOD,
CONDITION MET or INTERMEDIATE CONDITION MET). The presence of
status (and of a residual count) is signaled though the S flag
bit. Although targets MAY choose to send even non-exception
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status in separate responses, initiators MUST support non-
exception status in Data-In PDUs.
11.7.1. F (Final) Bit
For outgoing data, this bit is 1 for the last PDU of unsolicited
data or the last PDU of a sequence that answers an R2T.
For incoming data, this bit is 1 for the last input (read) data
PDU of a sequence. Input can be split into several sequences,
each having its own F bit. Splitting the data stream into
sequences does not affect DataSN counting on Data-In PDUs. It MAY
be used as a "change direction" indication for Bidirectional
operations that need such a change.
DataSegmentLength MUST NOT exceed MaxRecvDataSegmentLength for the
direction it is sent and the total of all the DataSegmentLength of
all PDUs in a sequence MUST NOT exceed MaxBurstLength (or
FirstBurstLength for unsolicited data). However the number of
individual PDUs in a sequence (or in total) may be higher than the
MaxBurstLength (or FirstBurstLength) to MaxRecvDataSegmentLength
ratio (as PDUs may be limited in length by the sender
capabilities). Using DataSegmentLength of 0 may increase beyond
what is reasonable for the number of PDUs and should therefore be
avoided.
For Bidirectional operations, the F bit is 1 for both the end of
the input sequences and the end of the output sequences.
11.7.2. A (Acknowledge) bit
For sessions with ErrorRecoveryLevel 1 or higher, the target sets
this bit to 1 to indicate that it requests a positive
acknowledgement from the initiator for the data received. The
target should use the A bit moderately; it MAY only set the A bit
to 1 once every MaxBurstLength bytes, or on the last Data-In PDU
that concludes the entire requested read data transfer for the
task from the target's perspective, and it MUST NOT do so more
frequently. The target MUST NOT set to 1 the A bit for sessions
with ErrorRecoveryLevel=0. The initiator MUST ignore the A bit set
to 1 for sessions with ErrorRecoveryLevel=0.
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On receiving a Data-In PDU with the A bit set to 1 on a session
with ErrorRecoveryLevel greater than 0, if there are no holes in
the read data until that Data-In PDU, the initiator MUST issue a
SNACK of type DataACK except when it is able to acknowledge the
status for the task immediately via ExpStatSN on other outbound
PDUs if the status for the task is also received. In the latter
case (acknowledgement through ExpStatSN), sending a SNACK of type
DataACK in response to the A bit is OPTIONAL, but if it is done,
it must not be sent after the status acknowledgement through
ExpStatSN. If the initiator has detected holes in the read data
prior to that Data-In PDU, it MUST postpone issuing the SNACK of
type DataACK until the holes are filled. An initiator also MUST
NOT acknowledge the status for the task before those holes are
filled. A status acknowledgement for a task that generated the
Data-In PDUs is considered by the target as an implicit
acknowledgement of the Data-In PDUs if such an acknowledgement was
requested by the target.
11.7.3. Flags (byte 1)
The last SCSI Data packet sent from a target to an initiator for a
SCSI command that completed successfully (with a status of GOOD,
CONDITION MET, INTERMEDIATE or INTERMEDIATE CONDITION MET) may
also optionally contain the Status for the data transfer. In this
case, Sense Data cannot be sent together with the Command Status.
If the command is completed with an error, then the response and
sense data MUST be sent in a SCSI Response PDU (i.e., MUST NOT be
sent in a SCSI Data packet). For Bidirectional commands, the
status MUST be sent in a SCSI Response PDU.
bit 2-4 - Reserved.
bit 5-6 - used the same as in a SCSI Response. These bits are
only valid when S is set to 1. For details see SNACK .
bit 7 S (status)- set to indicate that the Command Status
field contains status. If this bit is set to 1, the F bit
MUST also be set to 1.
The fields StatSN, Status, and Residual Count only have meaningful
content if the S bit is set to 1 and their values are defined in
SNACK .
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11.7.4. Target Transfer Tag and LUN
On outgoing data, the Target Transfer Tag is provided to the
target if the transfer is honoring an R2T. In this case, the
Target Transfer Tag field is a replica of the Target Transfer Tag
provided with the R2T.
On incoming data, the Target Transfer Tag and LUN MUST be provided
by the target if the A bit is set to 1; otherwise they are
reserved. The Target Transfer Tag and LUN are copied by the
initiator into the SNACK of type DataACK that it issues as a
result of receiving a SCSI Data-in PDU with the A bit set to 1.
The Target Transfer Tag values are not specified by this protocol
except that the value 0xffffffff is reserved and means that the
Target Transfer Tag is not supplied. If the Target Transfer Tag
is provided, then the LUN field MUST hold a valid value and be
consistent with whatever was specified with the command;
otherwise, the LUN field is reserved.
11.7.5. DataSN
For input (read) or bidirectional Data-In PDUs, the DataSN is the
input PDU number within the data transfer for the command
identified by the Initiator Task Tag.
R2T and Data-In PDUs, in the context of bidirectional commands,
share the numbering sequence (see Section 4.2.2.4).
For output (write) data PDUs, the DataSN is the Data-Out PDU
number within the current output sequence. The current output
sequence is either identified by the Initiator Task Tag (for
unsolicited data) or is a data sequence generated for one R2T (for
data solicited through R2T).
11.7.6. Buffer Offset
The Buffer Offset field contains the offset of this PDU payload
data within the complete data transfer. The sum of the buffer
offset and length should not exceed the expected transfer length
for the command.
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The order of data PDUs within a sequence is determined by
DataPDUInOrder. When set to Yes, it means that PDUs have to be in
increasing Buffer Offset order and overlays are forbidden.
The ordering between sequences is determined by
DataSequenceInOrder. When set to Yes, it means that sequences have
to be in increasing Buffer Offset order and overlays are
forbidden.
11.7.7. DataSegmentLength
This is the data payload length of a SCSI Data-In or SCSI Data-Out
PDU. The sending of 0 length data segments should be avoided, but
initiators and targets MUST be able to properly receive 0 length
data segments.
The Data Segments of Data-in and Data-out PDUs SHOULD be filled to
the integer number of 4 byte words (real payload) unless the F bit
is set to 1.
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11.8. Ready To Transfer (R2T)
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|.| 0x31 |1| Reserved |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8| LUN |
+ +
12| |
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+--------------+
20| Target Transfer Tag |
+---------------+---------------+---------------+--------------+
24| StatSN |
+---------------+---------------+---------------+--------------+
28| ExpCmdSN |
+---------------+---------------+---------------+--------------+
32| MaxCmdSN |
+---------------+---------------+---------------+--------------+
36| R2TSN |
+---------------+---------------+---------------+--------------+
40| Buffer Offset |
+---------------+---------------+---------------+--------------+
44| Desired Data Transfer Length |
+--------------------------------------------------------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+--------------+
When an initiator has submitted a SCSI Command with data that
passes from the initiator to the target (WRITE), the target may
specify which blocks of data it is ready to receive. The target
may request that the data blocks be delivered in whichever order
is convenient for the target at that particular instant. This
information is passed from the target to the initiator in the
Ready To Transfer (R2T) PDU.
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In order to allow write operations without an explicit initial
R2T, the initiator and target MUST have negotiated the key
InitialR2T to No during Login.
An R2T MAY be answered with one or more SCSI Data-out PDUs with a
matching Target Transfer Tag. If an R2T is answered with a single
Data-out PDU, the Buffer Offset in the Data PDU MUST be the same
as the one specified by the R2T, and the data length of the Data
PDU MUST be the same as the Desired Data Transfer Length specified
in the R2T. If the R2T is answered with a sequence of Data PDUs,
the Buffer Offset and Length MUST be within the range of those
specified by R2T, and the last PDU MUST have the F bit set to 1.
If the last PDU (marked with the F bit) is received before the
Desired Data Transfer Length is transferred, a target MAY choose
to Reject that PDU with "Protocol error" reason code.
DataPDUInOrder governs the Data-Out PDU ordering. If
DataPDUInOrder is set to Yes, the Buffer Offsets and Lengths for
consecutive PDUs MUST form a continuous non-overlapping range and
the PDUs MUST be sent in increasing offset order.
The target may send several R2T PDUs. It, therefore, can have a
number of pending data transfers. The number of outstanding R2T
PDUs are limited by the value of the negotiated key
MaxOutstandingR2T. Within a task, outstanding R2Ts MUST be
fulfilled by the initiator in the order in which they were
received.
R2T PDUs MAY also be used to recover Data Out PDUs. Such an R2T
(Recovery-R2T) is generated by a target upon detecting the loss of
one or more Data-Out PDUs due to:
- Digest error
- Sequence error
- Sequence reception timeout
A Recovery-R2T carries the next unused R2TSN, but requests part of
or the entire data burst that an earlier R2T (with a lower R2TSN)
had already requested.
DataSequenceInOrder governs the buffer offset ordering in
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consecutive R2Ts. If DataSequenceInOrder is Yes, then consecutive
R2Ts MUST refer to continuous non-overlapping ranges except for
Recovery-R2Ts.
11.8.1. TotalAHSLength and DataSegmentLength
For this PDU TotalAHSLength and DataSegmentLength MUST be 0.
11.8.2. R2TSN
R2TSN is the R2T PDU input PDU number within the command
identified by the Initiator Task Tag.
For bidirectional commands R2T and Data-In PDUs share the input
PDU numbering sequence (see Section 4.2.2.4).
11.8.3. StatSN
The StatSN field will contain the next StatSN. The StatSN for this
connection is not advanced after this PDU is sent.
11.8.4. Desired Data Transfer Length and Buffer Offset
The target specifies how many bytes it wants the initiator to send
because of this R2T PDU. The target may request the data from the
initiator in several chunks, not necessarily in the original order
of the data. The target, therefore, also specifies a Buffer Offset
that indicates the point at which the data transfer should begin,
relative to the beginning of the total data transfer. The Desired
Data Transfer Length MUST NOT be 0 and MUST NOT exceed
MaxBurstLength.
11.8.5. Target Transfer Tag
The target assigns its own tag to each R2T request that it sends
to the initiator. This tag can be used by the target to easily
identify the data it receives. The Target Transfer Tag and LUN are
copied in the outgoing data PDUs and are only used by the target.
There is no protocol rule about the Target Transfer Tag except
that the value 0xffffffff is reserved and MUST NOT be sent by a
target in an R2T.
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11.9. Asynchronous Message
An Asynchronous Message may be sent from the target to the
initiator without correspondence to a particular command. The
target specifies the reason for the event and sense data.
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|.| 0x32 |1| Reserved |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+--------------+
16| 0xffffffff |
+---------------+---------------+---------------+--------------+
20| Reserved |
+---------------+---------------+---------------+--------------+
24| StatSN |
+---------------+---------------+---------------+--------------+
28| ExpCmdSN |
+---------------+---------------+---------------+--------------+
32| MaxCmdSN |
+---------------+---------------+---------------+--------------+
36| AsyncEvent | AsyncVCode | Parameter1 or Reserved |
+---------------+---------------+---------------+--------------+
40| Parameter2 or Reserved | Parameter3 or Reserved |
+---------------+---------------+---------------+--------------+
44| Reserved |
+---------------+---------------+---------------+--------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+--------------+
/ DataSegment - Sense Data and iSCSI Event Data /
+/ /
+---------------+---------------+---------------+--------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+--------------+
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Some Asynchronous Messages are strictly related to iSCSI while
others are related to SCSI [SAM2].
StatSN counts this PDU as an acknowledgeable event (StatSN is
advanced), which allows for initiator and target state
synchronization.
11.9.1. AsyncEvent
The codes used for iSCSI Asynchronous Messages (events) are:
0 (SCSI_ASYNC) - a SCSI Asynchronous Event is reported in the
sense data. Sense Data that accompanies the report, in the
data segment, identifies the condition. The sending of a
SCSI Event (Asynchronous Event Reporting in SCSI
terminology) is dependent on the target support for SCSI
asynchronous event reporting (see [SAM2]) as indicated in
the standard INQUIRY data (see [SPC3]). Its use may be
enabled by parameters in the SCSI Control mode page (see
[SPC3]).
1 (REQUEST_LOGOUT) - target requests Logout. This Async
Message MUST be sent on the same connection as the one
requesting to be logged out. The initiator MUST honor this
request by issuing a Logout as early as possible, but no
later than Parameter3 seconds. Initiator MUST send a
Logout with a reason code of "Close the connection" OR
"Close the session" to close all the connections. Once this
message is received, the initiator SHOULD NOT issue new
iSCSI commands on the connection to be logged out. The
target MAY reject any new I/O requests that it receives
after this Message with the reason code "Waiting for
Logout". If the initiator does not Logout in Parameter3
seconds, the target should send an Async PDU with iSCSI
event code "Dropped the connection" if possible, or simply
terminate the transport connection. Parameter1 and
Parameter2 are reserved.
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2 (CONNECTION_DROP) - target indicates it will drop the
connection.
The Parameter1 field indicates the CID of the connection
going to be dropped.
The Parameter2 field (Time2Wait) indicates, in seconds, the
minimum time to wait before attempting to reconnect or
reassign.
The Parameter3 field (Time2Retain) indicates the maximum
time allowed to reassign commands after the initial wait (in
Parameter2).
If the initiator does not attempt to reconnect and/or
reassign the outstanding commands within the time specified
by Parameter3, or if Parameter3 is 0, the target will
terminate all outstanding commands on this connection. In
this case, no other responses should be expected from the
target for the outstanding commands on this connection.
A value of 0 for Parameter2 indicates that reconnect can be
attempted immediately.
3 (SESSION_DROP) - target indicates it will drop all the
connections of this session.
Parameter1 field is reserved.
The Parameter2 field (Time2Wait) indicates, in seconds, the
minimum time to wait before attempting to reconnect.
The Parameter3 field (Time2Retain) indicates the maximum
time allowed to reassign commands after the initial wait (in
Parameter2).
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If the initiator does not attempt to reconnect and/or
reassign the outstanding commands within the time specified
by Parameter3, or if Parameter3 is 0, the session is
terminated. In this case, the target will terminate all
outstanding commands in this session; no other responses
should be expected from the target for the outstanding
commands in this session. A value of 0 for Parameter2
indicates that reconnect can be attempted immediately.
4 (RENEGOTIATE) - target requests parameter negotiation on
this connection. The initiator MUST honor this request by
issuing a Text Request (that can be empty) on the same
connection as early as possible, but no later than
Parameter3 seconds, unless a Text Request is already pending
on the connection, or by issuing a Logout Request. If the
initiator does not issue a Text Request the target may
reissue the Asynchronous Message requesting parameter
negotiation.
5 (FAST_ABORT) - all active tasks for LU with a matching LUN
field in the Async Message PDU are being terminated. The
receiving initiator iSCSI layer MUST respond to this Message
by taking the following steps in order.
- Stop Data-Out transfers on that connection for all active
TTTs for the affected LUN quoted in the Async Message
PDU.
- Acknowledge the StatSN of the Async Message PDU via a NOP-
Out PDU with ITT=0xffffffff (i.e., non-ping flavor),
while copying the LUN field from the Async Message to
NOP-Out.
This value of AsyncEvent however MUST NOT be used on an
iSCSI session unless the new TaskReporting text key defined
in Section 13.23 was negotiated to FastAbort on the session.
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255 - vendor-specific iSCSI Event. The AsyncVCode details the
vendor code, and data MAY accompany the report.
All other event codes are reserved.
11.9.2. AsyncVCode
AsyncVCode is a vendor specific detail code that is only valid if
the AsyncEvent field indicates a vendor specific event. Otherwise,
it is reserved.
11.9.3. LUN
The LUN field MUST be valid if AsyncEvent is 0. Otherwise, this
field is reserved.
11.9.4. Sense Data and iSCSI Event Data
For a SCSI event, this data accompanies the report in the data
segment and identifies the condition.
For an iSCSI event, additional vendor-unique data MAY accompany
the Async event. Initiators MAY ignore the data when not
understood while processing the rest of the PDU.
If the DataSegmentLength is not 0, the format of the DataSegment
is as follows:
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|SenseLength | Sense Data |
+---------------+---------------+---------------+--------------+
x/ Sense Data /
+---------------+---------------+---------------+--------------+
y/ iSCSI Event Data /
/ /
+---------------+---------------+---------------+--------------+
z|
11.9.4.1. SenseLength
This is the length of Sense Data. When the Sense Data field is
empty (e.g., the event is not a SCSI event) SenseLength is 0.
11.10. Text Request
The Text Request is provided to allow for the exchange of
information and for future extensions. It permits the initiator to
inform a target of its capabilities or to request some special
operations.
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|I| 0x04 |F|C| Reserved |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+--------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+--------------+
24| CmdSN |
+---------------+---------------+---------------+--------------+
28| ExpStatSN |
+---------------+---------------+---------------+--------------+
32/ Reserved /
+/ /
+---------------+---------------+---------------+--------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+--------------+
/ DataSegment (Text) /
+/ /
+---------------+---------------+---------------+--------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+--------------+
An initiator MUST NOT have more than one outstanding Text Request
on a connection at any given time.
On a connection failure, an initiator must either explicitly abort
any active allegiant text negotiation task or must cause such a
task to be implicitly terminated by the target.
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11.10.1. F (Final) Bit
When set to 1, indicates that this is the last or only text
request in a sequence of Text Requests; otherwise, it indicates
that more Text Requests will follow.
11.10.2. C (Continue) Bit
When set to 1, indicates that the text (set of key=value pairs) in
this Text Request is not complete (it will be continued on
subsequent Text Requests); otherwise, it indicates that this Text
Request ends a set of key=value pairs. A Text Request with the C
bit set to 1 MUST have the F bit set to 0.
11.10.3. Initiator Task Tag
The initiator assigned identifier for this Text Request. If the
command is sent as part of a sequence of text requests and
responses, the Initiator Task Tag MUST be the same for all the
requests within the sequence (similar to linked SCSI commands).
The I bit for all requests in a sequence also MUST be the same.
11.10.4. Target Transfer Tag
When the Target Transfer Tag is set to the reserved value
0xffffffff, it tells the target that this is a new request and the
target resets any internal state associated with the Initiator
Task Tag (resets the current negotiation state).
The target sets the Target Transfer Tag in a text response to a
value other than the reserved value 0xffffffff whenever it
indicates that it has more data to send or more operations to
perform that are associated with the specified Initiator Task Tag.
It MUST do so whenever it sets the F bit to 0 in the response. By
copying the Target Transfer Tag from the response to the next Text
Request, the initiator tells the target to continue the operation
for the specific Initiator Task Tag. The initiator MUST ignore the
Target Transfer Tag in the Text Response when the F bit is set to
1.
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This mechanism allows the initiator and target to transfer a large
amount of textual data over a sequence of text-command/text-
response exchanges, or to perform extended negotiation sequences.
If the Target Transfer Tag is not 0xffffffff, the LUN field MUST
be sent by the target in the Text Response.
A target MAY reset its internal negotiation state if an exchange
is stalled by the initiator for a long time or if it is running
out of resources.
Long text responses are handled as in the following example:
I->T Text SendTargets=All (F=1,TTT=0xffffffff)
T->I Text <part 1> (F=0,TTT=0x12345678)
I->T Text <empty> (F=1, TTT=0x12345678)
T->I Text <part 2> (F=0, TTT=0x12345678)
I->T Text <empty> (F=1, TTT=0x12345678)
...
T->I Text <part n> (F=1, TTT=0xffffffff)
11.10.5. Text
The data lengths of a text request MUST NOT exceed the iSCSI
target MaxRecvDataSegmentLength (a per connection and per
direction negotiated parameter). The text format is specified in
Section 6.2.
Section 12 and Section 13 list some basic Text key=value pairs,
some of which can be used in Login Request/Response and some in
Text Request/Response.
A key=value pair can span Text request or response boundaries. A
key=value pair can start in one PDU and continue on the next. In
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other words the end of a PDU does not necessarily signal the end
of a key=value pair.
The target responds by sending its response back to the initiator.
The response text format is similar to the request text format.
The text response MAY refer to key=value pairs presented in an
earlier text request and the text in the request may refer to
earlier responses.
Section 6.2 details the rules for the Text Requests and Responses.
Text operations are usually meant for parameter
setting/negotiations, but can also be used to perform some long
lasting operations.
Text operations that take a long time should be placed in their
own Text request.
11.11. Text Response
The Text Response PDU contains the target's responses to the
initiator's Text request. The format of the Text field matches
that of the Text request.
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|.| 0x24 |F|C| Reserved |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+--------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+--------------+
24| StatSN |
+---------------+---------------+---------------+--------------+
28| ExpCmdSN |
+---------------+---------------+---------------+--------------+
32| MaxCmdSN |
+---------------+---------------+---------------+--------------+
36/ Reserved /
+/ /
+---------------+---------------+---------------+--------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+--------------+
/ DataSegment (Text) /
+/ /
+---------------+---------------+---------------+--------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+--------------+
11.11.1. F (Final) Bit
When set to 1, in response to a Text Request with the Final bit
set to 1, the F bit indicates that the target has finished the
whole operation. Otherwise, if set to 0 in response to a Text
Request with the Final Bit set to 1, it indicates that the target
has more work to do (invites a follow-on text request). A Text
Response with the F bit set to 1 in response to a Text Request
with the F bit set to 0 is a protocol error.
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A Text Response with the F bit set to 1 MUST NOT contain key=value
pairs that may require additional answers from the initiator.
A Text Response with the F bit set to 1 MUST have a Target
Transfer Tag field set to the reserved value of 0xffffffff.
A Text Response with the F bit set to 0 MUST have a Target
Transfer Tag field set to a value other than the reserved
0xffffffff.
11.11.2. C (Continue) Bit
When set to 1, indicates that the text (set of key=value pairs) in
this Text Response is not complete (it will be continued on
subsequent Text Responses); otherwise, it indicates that this Text
Response ends a set of key=value pairs. A Text Response with the C
bit set to 1 MUST have the F bit set to 0.
11.11.3. Initiator Task Tag
The Initiator Task Tag matches the tag used in the initial Text
Request.
11.11.4. Target Transfer Tag
When a target has more work to do (e.g., cannot transfer all the
remaining text data in a single Text Response or has to continue
the negotiation) and has enough resources to proceed, it MUST set
the Target Transfer Tag to a value other than the reserved value
of 0xffffffff. Otherwise, the Target Transfer Tag MUST be set to
0xffffffff.
When the Target Transfer Tag is not 0xffffffff, the LUN field may
be significant.
The initiator MUST copy the Target Transfer Tag and LUN in its
next request to indicate that it wants the rest of the data.
When the target receives a Text Request with the Target Transfer
Tag set to the reserved value of 0xffffffff, it resets its
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internal information (resets state) associated with the given
Initiator Task Tag (restarts the negotiation).
When a target cannot finish the operation in a single Text
Response, and does not have enough resources to continue, it
rejects the Text Request with the appropriate Reject code.
A target may reset its internal state associated with an Initiator
Task Tag (the current negotiation state), state expressed through
the Target Transfer Tag if the initiator fails to continue the
exchange for some time. The target may reject subsequent Text
Requests with the Target Transfer Tag set to the "stale" value.
11.11.5. StatSN
The target StatSN variable is advanced by each Text Response sent.
11.11.6. Text Response Data
The data lengths of a text response MUST NOT exceed the iSCSI
initiator MaxRecvDataSegmentLength (a per connection and per
direction negotiated parameter).
The text in the Text Response Data is governed by the same rules
as the text in the Text Request Data (see Section 11.11.2).
Although the initiator is the requesting party and controls the
request-response initiation and termination, the target can offer
key=value pairs of its own as part of a sequence and not only in
response to the initiator.
11.12. Login Request
After establishing a TCP connection between an initiator and a
target, the initiator MUST start a Login Phase to gain further
access to the target's resources.
The Login Phase (see Section 6.3) consists of a sequence of Login
requests and responses that carry the same Initiator Task Tag.
Login requests are always considered as immediate.
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|1| 0x03 |T|C|.|.|CSG|NSG| Version-max | Version-min |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8| ISID |
+ +---------------+--------------+
12| | TSIH |
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+--------------+
20| CID | Reserved |
+---------------+---------------+---------------+--------------+
24| CmdSN |
+---------------+---------------+---------------+--------------+
28| ExpStatSN or Reserved |
+---------------+---------------+---------------+--------------+
32| Reserved |
+---------------+---------------+---------------+--------------+
36| Reserved |
+---------------+---------------+---------------+--------------+
40/ Reserved /
+/ /
+---------------+---------------+---------------+--------------+
48/ DataSegment - Login Parameters in Text request Format /
+/ /
+---------------+---------------+---------------+--------------+
11.12.1. T (Transit) Bit
If set to 1, indicates that the initiator is ready to transit to
the next stage.
If the T bit is set to 1 and NSG is FullFeaturePhase, then this
also indicates that the initiator is ready for the Final Login
Response (see Section 6.3).
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11.12.2. C (Continue) Bit
When set to 1, this bit indicates that the text (set of key=value
pairs) in this Login Request is not complete (it will be continued
on subsequent Login Requests); otherwise, it indicates that this
Login Request ends a set of key=value pairs. A Login Request with
the C bit set to 1 MUST have the T bit set to 0.
11.12.3. CSG and NSG
Through these fields, Current Stage (CSG) and Next Stage (NSG),
the Login negotiation requests and responses are associated with a
specific stage in the session (SecurityNegotiation,
LoginOperationalNegotiation, FullFeaturePhase) and may indicate
the next stage to which they want to move (see Section 6.3). The
next stage value is only valid when the T bit is 1; otherwise, it
is reserved.
The stage codes are:
- 0 - SecurityNegotiation
- 1 - LoginOperationalNegotiation
- 3 - FullFeaturePhase
All other codes are reserved.
11.12.4. Version
The version number of the current draft is 0x00. As such, all
devices MUST carry version 0x00 for both Version-min and Version-
max.
11.12.4.1. Version-max
Maximum Version number supported.
All Login requests within the Login Phase MUST carry the same
Version-max.
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The target MUST use the value presented with the first login
request.
11.12.4.2. Version-min
All Login requests within the Login Phase MUST carry the same
Version-min. The target MUST use the value presented with the
first login request.
11.12.5. ISID
This is an initiator-defined component of the session identifier
and is structured as follows (see Section 10.1.1 for details):
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
8| T | A | B | C |
+---------------+---------------+---------------+--------------+
12| D |
+---------------+---------------+
The T field identifies the format and usage of A, B, C, and D as
indicated below:
T
00b OUI-Format
A&B are a 22 bit OUI
(the I/G & U/L bits are omitted)
C&D 24 bit qualifier
01b EN - Format (IANA Enterprise Number)
A - Reserved
B&C EN (IANA Enterprise Number)
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D - Qualifier
10b "Random"
A - Reserved
B&C Random
D - Qualifier
11b A,B,C&D Reserved
For the T field values 00b and 01b, a combination of A and B (for
00b) or B and C (for 01b) identifies the vendor or organization
whose component (software or hardware) generates this ISID. A
vendor or organization with one or more OUIs, or one or more
Enterprise Numbers, MUST use at least one of these numbers and
select the appropriate value for the T field when its components
generate ISIDs. An OUI or EN MUST be set in the corresponding
fields in network byte order (byte big-endian).
If the T field is 10b, B and C are set to a random 24-bit unsigned
integer value in network byte order (byte big-endian). See
[RFC3721] for how this affects the principle of "conservative
reuse".
The Qualifier field is a 16 or 24-bit unsigned integer value that
provides a range of possible values for the ISID within the
selected namespace. It may be set to any value within the
constraints specified in the iSCSI protocol (see Section 4.4.3 and
Section 10.1.1).
The T field value of 11b is reserved.
If the ISID is derived from something assigned to a hardware
adapter or interface by a vendor, as a preset default value, it
MUST be configurable to a value assigned according to the SCSI
port behavior desired by the system in which it is installed (see
Section 10.1.1 and Section 10.1.2). The resultant ISID MUST also
be persistent over power cycles, reboot, card swap, etc.
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11.12.6. TSIH
TSIH must be set in the first Login Request. The reserved value 0
MUST be used on the first connection for a new session. Otherwise,
the TSIH sent by the target at the conclusion of the successful
login of the first connection for this session MUST be used. The
TSIH identifies to the target the associated existing session for
this new connection.
All Login requests within a Login Phase MUST carry the same TSIH.
The target MUST check the value presented with the first login
request and act as specified in Section 5.3.1.
11.12.7. Connection ID - CID
A unique ID for this connection within the session.
All Login requests within the Login Phase MUST carry the same CID.
The target MUST use the value presented with the first login
request.
A Login request with a non-zero TSIH and a CID equal to that of an
existing connection implies a logout of the connection followed by
a Login (see Section 6.3.4). For the details of the implicit
Logout Request, see Section 11.14.
11.12.8. CmdSN
CmdSN is either the initial command sequence number of a session
(for the first Login request of a session - the "leading" login),
or the command sequence number in the command stream if the login
is for a new connection in an existing session.
Examples:
- Login on a leading connection - if the leading login carries
the CmdSN 123, all other login requests in the same login
phase carry the CmdSN 123 and the first non-immediate
command in FullFeaturePhase also carries the CmdSN 123.
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- Login on other than a leading connection - if the current
CmdSN at the time the first login on the connection is
issued is 500, then that PDU carries CmdSN=500. Subsequent
login requests that are needed to complete this login phase
may carry a CmdSN higher than 500 if non-immediate requests
that were issued on other connections in the same session
advance CmdSN.
If the login request is a leading login request, the target MUST
use the value presented in CmdSN as the target value for ExpCmdSN.
11.12.9. ExpStatSN
For the first Login Request on a connection this is ExpStatSN for
the old connection and this field is only valid if the Login
request restarts a connection (see Section 6.3.4).
For subsequent Login Requests it is used to acknowledge the Login
Responses with their increasing StatSN values.
11.12.10. Login Parameters
The initiator MUST provide some basic parameters in order to
enable the target to determine if the initiator may use the
target's resources and the initial text parameters for the
security exchange.
All the rules specified in Section 11.10.5 for text requests also
hold for login requests. Keys and their explanations are listed
in Section 12 (security negotiation keys) and Section 13
(operational parameter negotiation keys). All keys in Section 13,
except for the X extension formats, MUST be supported by iSCSI
initiators and targets. Keys in Section 12 only need to be
supported when the function to which they refer is mandatory to
implement.
11.13. Login Response
The Login Response indicates the progress and/or end of the Login
Phase.
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|.| 0x23 |T|C|.|.|CSG|NSG| Version-max |Version-active|
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8| ISID |
+ +---------------+--------------+
12| | TSIH |
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+--------------+
20| Reserved |
+---------------+---------------+---------------+--------------+
24| StatSN |
+---------------+---------------+---------------+--------------+
28| ExpCmdSN |
+---------------+---------------+---------------+--------------+
32| MaxCmdSN |
+---------------+---------------+---------------+--------------+
36| Status-Class | Status-Detail | Reserved |
+---------------+---------------+---------------+--------------+
40/ Reserved /
+/ /
+---------------+---------------+---------------+--------------+
48/ DataSegment - Login Parameters in Text request Format /
+/ /
+---------------+---------------+---------------+--------------+
11.13.1. Version-max
This is the highest version number supported by the target.
All Login responses within the Login Phase MUST carry the same
Version-max.
The initiator MUST use the value presented as a response to the
first login request.
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11.13.2. Version-active
Indicates the highest version supported by the target and
initiator. If the target does not support a version within the
range specified by the initiator, the target rejects the login and
this field indicates the lowest version supported by the target.
All Login responses within the Login Phase MUST carry the same
Version-active.
The initiator MUST use the value presented as a response to the
first login request.
11.13.3. TSIH
The TSIH is the target assigned session identifying handle. Its
internal format and content are not defined by this protocol
except for the value 0 that is reserved. With the exception of the
Login Final-Response in a new session, this field should be set to
the TSIH provided by the initiator in the Login Request. For a
new session, the target MUST generate a non-zero TSIH and ONLY
return it in the Login Final-Response (see Section 6.3).
11.13.4. StatSN
For the first Login Response (the response to the first Login
Request), this is the starting status Sequence Number for the
connection. The next response of any kind, including the next
login response, if any, in the same Login Phase, will carry this
number + 1. This field is only valid if the Status-Class is 0.
11.13.5. Status-Class and Status-Detail
The Status returned in a Login Response indicates the execution
status of the Login Phase. The status includes:
Status-Class
Status-Detail
0 Status-Class indicates success.
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A non-zero Status-Class indicates an exception. In this case,
Status-Class is sufficient for a simple initiator to use when
handling exceptions, without having to look at the Status-Detail.
The Status-Detail allows finer-grained exception handling for more
sophisticated initiators and for better information for logging.
The status classes are as follows:
0 - Success - indicates that the iSCSI target successfully
received, understood, and accepted the request. The
numbering fields (StatSN, ExpCmdSN, MaxCmdSN) are only valid
if Status-Class is 0.
1 - Redirection - indicates that the initiator must take
further action to complete the request. This is usually due
to the target moving to a different address. All of the
redirection status class responses MUST return one or more
text key parameters of the type "TargetAddress", which
indicates the target's new address. A redirection response
MAY be issued by a target prior or after completing a
security negotiation if a security negotiation is required.
A redirection SHOULD be accepted by an initiator even
without having the target complete a security negotiation if
any security negotiation is required, and MUST be accepted
by the initiator after the completion of the security
negotiation if any security negotiation is required.
2 - Initiator Error (not a format error) - indicates that the
initiator most likely caused the error. This MAY be due to a
request for a resource for which the initiator does not have
permission. The request should not be tried again.
3 - Target Error - indicates that the target sees no errors in
the initiator's login request, but is currently incapable of
fulfilling the request. The initiator may re-try the same
login request later.
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The table below shows all of the currently allocated status codes.
The codes are in hexadecimal; the first byte is the status class
and the second byte is the status detail.
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-----------------------------------------------------------------
Status | Code | Description
|(hex) |
-----------------------------------------------------------------
Success | 0000 | Login is proceeding OK (*1).
-----------------------------------------------------------------
Target moved | 0101 | The requested iSCSI Target Name (ITN)
temporarily | | has temporarily moved
| | to the address provided.
-----------------------------------------------------------------
Target moved | 0102 | The requested ITN has permanently moved
permanently | | to the address provided.
-----------------------------------------------------------------
Initiator | 0200 | Miscellaneous iSCSI initiator
error | | errors.
----------------------------------------------------------------
Authentication| 0201 | The initiator could not be
failure | | successfully authenticated or target
| | authentication is not supported.
-----------------------------------------------------------------
Authorization | 0202 | The initiator is not allowed access
failure | | to the given target.
-----------------------------------------------------------------
Not found | 0203 | The requested ITN does not
| | exist at this address.
-----------------------------------------------------------------
Target removed| 0204 | The requested ITN has been removed and
| | no forwarding address is provided.
-----------------------------------------------------------------
Unsupported | 0205 | The requested iSCSI version range is
version | | not supported by the target.
-----------------------------------------------------------------
Too many | 0206 | Too many connections on this SSID.
connections | |
-----------------------------------------------------------------
Missing | 0207 | Missing parameters (e.g., iSCSI
parameter | | Initiator and/or Target Name).
-----------------------------------------------------------------
Can't include | 0208 | Target does not support session
in session | | spanning to this connection (address).
-----------------------------------------------------------------
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Session type | 0209 | Target does not support this type of
not supported | | of session or not from this Initiator.
-----------------------------------------------------------------
Session does | 020a | Attempt to add a connection
not exist | | to a non-existent session.
-----------------------------------------------------------------
Invalid during| 020b | Invalid Request type during Login.
login | |
-----------------------------------------------------------------
Target error | 0300 | Target hardware or software error.
-----------------------------------------------------------------
Service | 0301 | The iSCSI service or target is not
unavailable | | currently operational.
-----------------------------------------------------------------
Out of | 0302 | The target has insufficient session,
resources | | connection, or other resources.
-----------------------------------------------------------------
(*1)If the response T bit is 1 in both the request and the
matching response, and the NSG is FullFeaturePhase in both the
request and the matching response, the Login Phase is finished and
the initiator may proceed to issue SCSI commands.
If the Status Class is not 0, the initiator and target MUST close
the TCP connection.
If the target wishes to reject the login request for more than one
reason, it should return the primary reason for the rejection.
11.13.6. T (Transit) bit
The T bit is set to 1 as an indicator of the end of the stage. If
the T bit is set to 1 and NSG is FullFeaturePhase, then this is
also the Final Login Response (see Section 6.3). A T bit of 0
indicates a "partial" response, which means "more negotiation
needed".
A login response with a T bit set to 1 MUST NOT contain key=value
pairs that may require additional answers from the initiator
within the same stage.
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If the status class is 0, the T bit MUST NOT be set to 1 if the T
bit in the request was set to 0.
11.13.7. C (Continue) Bit
When set to 1, indicates that the text (set of key=value pairs) in
this Login Response is not complete (it will be continued on
subsequent Login Responses); otherwise, it indicates that this
Login Response ends a set of key=value pairs. A Login Response
with the C bit set to 1 MUST have the T bit set to 0.
11.13.8. Login Parameters
The target MUST provide some basic parameters in order to enable
the initiator to determine if it is connected to the correct port
and the initial text parameters for the security exchange.
All the rules specified in Section 11.11.6 for text responses also
hold for login responses. Keys and their explanations are listed
in Section 12(security negotiation keys) and Section 13
(operational parameter negotiation keys). All keys in Section 13,
except for the X extension formats, MUST be supported by iSCSI
initiators and targets. Keys in Section 12, only need to be
supported when the function to which they refer is mandatory to
implement.
11.14. Logout Request
The Logout request is used to perform a controlled closing of a
connection.
An initiator MAY use a logout request to remove a connection from
a session or to close an entire session.
After sending the Logout request PDU, an initiator MUST NOT send
any new iSCSI requests on the closing connection. If the Logout
request is intended to close the session, new iSCSI requests MUST
NOT be sent on any of the connections participating in the
session.
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When receiving a Logout request with the reason code of "close the
connection" or "close the session", the target MUST terminate all
pending commands, whether acknowledged via ExpCmdSN or not, on
that connection or session respectively.
When receiving a Logout request with the reason code "remove
connection for recovery", the target MUST discard all requests not
yet acknowledged via ExpCmdSN that were issued on the specified
connection, and suspend all data/status/R2T transfers on behalf of
pending commands on the specified connection.
The target then issues the Logout response and half-closes the TCP
connection (sends FIN). After receiving the Logout response and
attempting to receive the FIN (if still possible), the initiator
MUST completely close the logging-out connection. For the
terminated commands, no additional responses should be expected.
A Logout for a CID may be performed on a different transport
connection when the TCP connection for the CID has already been
terminated. In such a case, only a logical "closing" of the iSCSI
connection for the CID is implied with a Logout.
All commands that were not terminated or not completed (with
status) and acknowledged when the connection is closed completely
can be reassigned to a new connection if the target supports
connection recovery.
If an initiator intends to start recovery for a failing
connection, it MUST use the Logout request to "clean-up" the
target end of a failing connection and enable recovery to start,
or the Login request with a non-zero TSIH and the same CID on a
new connection for the same effect. In sessions with a single
connection, the connection can be closed and then a new connection
reopened. A connection reinstatement login can be used for
recovery (see Section 6.3.4).
A successful completion of a logout request with the reason code
of "close the connection" or "remove the connection for recovery"
results at the target in the discarding of unacknowledged commands
received on the connection being logged out. These are commands
that have arrived on the connection being logged out, but have not
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been delivered to SCSI because one or more commands with a smaller
CmdSN has not been received by iSCSI. See Section 4.2.2.1. The
resulting holes in the command sequence numbers will have to be
handled by appropriate recovery (see Section 7) unless the session
is also closed.
The entire logout discussion in this Section is also applicable
for an implicit Logout realized by way of a connection
reinstatement or session reinstatement. When a Login Request
performs an implicit Logout, the implicit Logout is performed as
if having the reason codes specified below:
Reason code Type of implicit Logout
-------------------------------------------
0 session reinstatement
1 connection reinstatement when the operational
ErrorRecoveryLevel < 2
2 connection reinstatement when the operational
ErrorRecoveryLevel = 2
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|I| 0x06 |1| Reason Code | Reserved |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+--------------------------------------------------------------+
8/ Reserved /
+/ /
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+--------------+
20| CID or Reserved | Reserved |
+---------------+---------------+---------------+--------------+
24| CmdSN |
+---------------+---------------+---------------+--------------+
28| ExpStatSN |
+---------------+---------------+---------------+--------------+
32/ Reserved /
+/ /
+---------------+---------------+---------------+--------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+--------------+
11.14.1. Reason Code
Reason Code indicates the reason for Logout as follows:
0 - close the session. All commands associated with the
session (if any) are terminated.
1 - close the connection. All commands associated with
connection (if any) are terminated.
2 - remove the connection for recovery. Connection is closed
and all commands associated with it, if any, are to be
prepared for a new allegiance.
All other values are reserved.
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11.14.2. TotalAHSLength and DataSegmentLength
For this PDU TotalAHSLength and DataSegmentLength MUST be 0.
11.14.3. CID
This is the connection ID of the connection to be closed
(including closing the TCP stream). This field is only valid if
the reason code is not "close the session".
11.14.4. ExpStatSN
This is the last ExpStatSN value for the connection to be closed.
11.14.5. Implicit termination of tasks
A target implicitly terminates the active tasks due to the iSCSI
protocol in the following cases:
a) When a connection is implicitly or explicitly logged out
with the reason code of "Close the connection" and there
are active tasks allegiant to that connection.
b) When a connection fails and eventually the connection state
times out (state transition M1 in Section 8.2.2) and there
are active tasks allegiant to that connection.
c) When a successful recovery Logout is performed while there
are active tasks allegiant to that connection, and those
tasks eventually time out after the Time2Wait and
Time2Retain periods without allegiance reassignment.
d) When a connection is implicitly or explicitly logged out
with the reason code of "Close the session" and there are
active tasks in that session.
If the tasks terminated in any of the above cases are SCSI tasks,
they must be internally terminated as if with CHECK CONDITION
status. This status is only meaningful for appropriately handling
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the internal SCSI state and SCSI side effects with respect to
ordering because this status is never communicated back as a
terminating status to the initiator. However additional actions
may have to be taken at SCSI level depending on the SCSI context
as defined by the SCSI standards (e.g., queued commands and ACA,
UA for the next command on the I_T nexus in cases a), b), and c),
after the tasks are terminated, the target MUST report a Unit
Attention condition on the next command processed on any
connection for each affected I_T_L nexus with the status of CHECK
CONDITION, and the ASC/ASCQ value of 47h/7Fh - "SOME COMMANDS
CLEARED BY ISCSI PROTOCOL EVENT" - etc. - see [SPC3]).
11.15. Logout Response
The logout response is used by the target to indicate if the
cleanup operation for the connection(s) has completed.
After Logout, the TCP connection referred by the CID MUST be
closed at both ends (or all connections must be closed if the
logout reason was session close).
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|.| 0x26 |1| Reserved | Response | Reserved |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+--------------------------------------------------------------+
8/ Reserved /
+/ /
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+--------------+
20| Reserved |
+---------------+---------------+---------------+--------------+
24| StatSN |
+---------------+---------------+---------------+--------------+
28| ExpCmdSN |
+---------------+---------------+---------------+--------------+
32| MaxCmdSN |
+---------------+---------------+---------------+--------------+
36| Reserved |
+--------------------------------------------------------------+
40| Time2Wait | Time2Retain |
+---------------+---------------+---------------+--------------+
44| Reserved |
+---------------+---------------+---------------+--------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+--------------+
11.15.1. Response
Logout response:
0 - connection or session closed successfully.
1 - CID not found.
2 - connection recovery is not supported. If Logout reason
code was recovery and target does not support it as
indicated by the ErrorRecoveryLevel.
3 - cleanup failed for various reasons.
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11.15.2. TotalAHSLength and DataSegmentLength
For this PDU TotalAHSLength and DataSegmentLength MUST be 0.
11.15.3. Time2Wait
If the Logout response code is 0 and if the operational
ErrorRecoveryLevel is 2, this is the minimum amount of time, in
seconds, to wait before attempting task reassignment. If the
Logout response code is 0 and if the operational
ErrorRecoveryLevel is less than 2, this field is to be ignored.
This field is invalid if the Logout response code is 1.
If the Logout response code is 2 or 3, this field specifies the
minimum time to wait before attempting a new implicit or explicit
logout.
If Time2Wait is 0, the reassignment or a new Logout may be
attempted immediately.
11.15.4. Time2Retain
If the Logout response code is 0 and if the operational
ErrorRecoveryLevel is 2, this is the maximum amount of time, in
seconds, after the initial wait (Time2Wait), the target waits for
the allegiance reassignment for any active task after which the
task state is discarded. If the Logout response code is 0 and if
the operational ErrorRecoveryLevel is less than 2, this field is
to be ignored.
This field is invalid if the Logout response code is 1.
If the Logout response code is 2 or 3, this field specifies the
maximum amount of time, in seconds, after the initial wait
(Time2Wait), the target waits for a new implicit or explicit
logout.
If it is the last connection of a session, the whole session state
is discarded after Time2Retain.
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If Time2Retain is 0, the target has already discarded the
connection (and possibly the session) state along with the task
states. No reassignment or Logout is required in this case.
11.16. SNACK Request
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|.| 0x10 |1|.|.|.| Type | Reserved |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag or 0xffffffff |
+---------------+---------------+---------------+--------------+
20| Target Transfer Tag or SNACK Tag or 0xffffffff |
+---------------+---------------+---------------+--------------+
24| Reserved |
+---------------+---------------+---------------+--------------+
28| ExpStatSN |
+---------------+---------------+---------------+--------------+
32/ Reserved /
+/ /
+---------------+---------------+---------------+--------------+
40| BegRun |
+--------------------------------------------------------------+
44| RunLength |
+--------------------------------------------------------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+--------------+
If the implementation supports ErrorRecoveryLevel greater than
zero, it MUST support all SNACK types.
The SNACK is used by the initiator to request the retransmission
of numbered-responses, data, or R2T PDUs from the target. The
SNACK request indicates the numbered-responses or data "runs"
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whose retransmission is requested by the target, where the run
starts with the first StatSN, DataSN, or R2TSN whose
retransmission is requested and indicates the number of Status,
Data, or R2T PDUs requested including the first. 0 has special
meaning when used as a starting number and length:
- When used in RunLength, it means all PDUs starting with the
initial.
- When used in both BegRun and RunLength, it means all
unacknowledged PDUs.
The numbered-response(s) or R2T(s), requested by a SNACK, MUST be
delivered as exact replicas of the ones that the target
transmitted originally except for the fields ExpCmdSN, MaxCmdSN,
and ExpDataSN, which MUST carry the current values.
R2T(s)requested by SNACK MUST also carry the current value of
StatSN.
The numbered Data-In PDUs, requested by a Data SNACK MUST be
delivered as exact replicas of the ones that the target
transmitted originally except for the fields ExpCmdSN and
MaxCmdSN, which MUST carry the current values and except for
resegmentation (see Section 11.16.3).
Any SNACK that requests a numbered-response, Data, or R2T that was
not sent by the target or was already acknowledged by the
initiator, MUST be rejected with a reason code of "Protocol
error".
11.16.1. Type
This field encodes the SNACK function as follows:
0-Data/R2T SNACK - requesting retransmission of one or more
Data-In or R2T PDUs.
1-Status SNACK - requesting retransmission of one or more
numbered responses.
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2-DataACK - positively acknowledges Data-In PDUs.
3-R-Data SNACK - requesting retransmission of Data-In PDUs
with possible resegmentation and status tagging.
All other values are reserved.
Data/R2T SNACK, Status SNACK, or R-Data SNACK for a command MUST
precede status acknowledgement for the given command.
11.16.2. Data Acknowledgement
If an initiator operates at ErrorRecoveryLevel 1 or higher, it
MUST issue a SNACK of type DataACK after receiving a Data-In PDU
with the A bit set to 1. However, if the initiator has detected
holes in the input sequence, it MUST postpone issuing the SNACK of
type DataACK until the holes are filled. An initiator MAY ignore
the A bit if it deems that the bit is being set aggressively by
the target (i.e., before the MaxBurstLength limit is
reached).
The DataACK is used to free resources at the target and not to
request or imply data retransmission.
An initiator MUST NOT request retransmission for any data it had
already acknowledged.
11.16.3. Resegmentation
If the initiator MaxRecvDataSegmentLength changed between the
original transmission and the time the initiator requests
retransmission, the initiator MUST issue a R-Data SNACK (see
Section 11.16.1). With R-Data SNACK, the initiator indicates that
it discards all the unacknowledged data and expects the target to
resend it. It also expects resegmentation. In this case, the
retransmitted Data-In PDUs MAY be different from the ones
originally sent in order to reflect changes in
MaxRecvDataSegmentLength. Their DataSN starts with the BegRun of
the last DataACK received by the target if any was received;
otherwise it starts with 0 and is increased by 1 for each resent
Data-In PDU.
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A target that has received a R-Data SNACK MUST return a SCSI
Response that contains a copy of the SNACK Tag field from the R-
Data SNACK in the SCSI Response SNACK Tag field as its last or
only Response. For example, if it has already sent a response
containing another value in the SNACK Tag field or had the status
included in the last Data-In PDU, it must send a new SCSI Response
PDU. If a target sends more than one SCSI Response PDU due to this
rule, all SCSI responses must carry the same StatSN (see Section
11.4.4). If an initiator attempts to recover a lost SCSI Response
(with a Status-SNACK, see Section 11.16.1) when more than one
response has been sent, the target will send the SCSI Response
with the latest content known to the target, including the last
SNACK Tag for the command.
For considerations in allegiance reassignment of a task to a
connection with a different MaxRecvDataSegmentLength, refer to
Section 7.2.2.
11.16.4. Initiator Task Tag
For Status SNACK and DataACK, the Initiator Task Tag MUST be set
to the reserved value 0xffffffff. In all other cases, the
Initiator Task Tag field MUST be set to the Initiator Task Tag of
the referenced command.
11.16.5. Target Transfer Tag or SNACK Tag
For an R-Data SNACK, this field MUST contain a value that is
different from 0 or 0xffffffff and is unique for the task
(identified by the Initiator Task Tag). This value MUST be copied
by the iSCSI target in the last or only SCSI Response PDU it
issues for the command.
For DataACK, the Target Transfer Tag MUST contain a copy of the
Target Transfer Tag and LUN provided with the SCSI Data-In PDU
with the A bit set to 1.
In all other cases, the Target Transfer Tag field MUST be set to
the reserved value of 0xffffffff.
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11.16.6. BegRun
The DataSN, R2TSN, or StatSN of the first PDU whose retransmission
is requested (Data/R2T and Status SNACK), or the next expected
DataSN (DataACK SNACK).
BegRun 0 when used in conjunction with RunLength 0 means resend
all unacknowledged Data-In, R2T or Response PDUs.
BegRun MUST be 0 for a R-Data SNACK.
11.16.7. RunLength
The number of PDUs whose retransmission is requested.
RunLength 0 signals that all Data-In, R2T, or Response PDUs
carrying the numbers equal to or greater than BegRun have to be
resent.
The RunLength MUST also be 0 for a DataACK SNACK in addition to R-
Data SNACK.
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11.17. Reject
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|.| 0x3f |1| Reserved | Reason | Reserved |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8/ Reserved /
+/ /
+---------------+---------------+---------------+--------------+
16| 0xffffffff |
+---------------+---------------+---------------+--------------+
20| Reserved |
+---------------+---------------+---------------+--------------+
24| StatSN |
+---------------+---------------+---------------+--------------+
28| ExpCmdSN |
+---------------+---------------+---------------+--------------+
32| MaxCmdSN |
+---------------+---------------+---------------+--------------+
36| DataSN/R2TSN or Reserved |
+---------------+---------------+---------------+--------------+
40| Reserved |
+---------------+---------------+---------------+--------------+
44| Reserved |
+---------------+---------------+---------------+--------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+--------------+
xx/ Complete Header of Bad PDU /
+/ /
+---------------+---------------+---------------+--------------+
yy/Vendor specific data (if any) /
/ /
+---------------+---------------+---------------+--------------+
zz| Data-Digest (Optional) |
+---------------+---------------+---------------+--------------+
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Reject is used to indicate an iSCSI error condition (protocol,
unsupported option, etc.).
11.17.1. Reason
The reject Reason is coded as follows:
+------+----------------------------------------+----------------+
| Code | Explanation |Can the original|
| (hex)| |PDU be re-sent? |
+------+----------------------------------------+----------------+
| 0x01 | Reserved | no |
| | | |
| 0x02 | Data (payload) Digest Error | yes (Note 1) |
| | | |
| 0x03 | SNACK Reject | yes |
| | | |
| 0x04 | Protocol Error (e.g., SNACK request for| no |
| | a status that was already acknowledged)| |
| | | |
| 0x05 | Command not supported | no |
| | | |
| 0x06 | Immediate Command Reject - too many | yes |
| | immediate commands | |
| | | |
| 0x07 | Task in progress | no |
| | | |
| 0x08 | Invalid Data ACK | no |
| | | |
| 0x09 | Invalid PDU field | no (Note 2) |
| | | |
| 0x0a | Long Operation Reject - Can't generate | yes |
| | Target Transfer Tag - out of resources | |
| | | |
| 0x0c | Waiting for Logout | no |
+------+----------------------------------------+----------------+
Note 1: For iSCSI, Data-Out PDU retransmission is only done if the
target requests retransmission with a recovery R2T. However, if
this is the data digest error on immediate data, the initiator may
choose to retransmit the whole PDU including the immediate data.
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Note 2: A target should use this reason code for all invalid
values of PDU fields that are meant to describe a task, a
response, or a data transfer. Some examples are invalid TTT/ITT,
buffer offset, LUN qualifying a TTT, and an invalid sequence
number in a SNACK.
Note 3: Reason code 0x0b ("Negotiation reset") defined in
[RFC3720] is deprecated and MUST NOT be used by implementations.
An implementation receiving reason code 0x0b MUST treat it as a
negotiation failure that terminates the Login Phase and the TCP
connection, as specified in Section 7.12.
All other values for Reason are reserved.
In all the cases in which a pre-instantiated SCSI task is
terminated because of the reject, the target MUST issue a proper
SCSI command response with CHECK CONDITION as described in Section
11.4.3. In these cases in which a status for the SCSI task was
already sent before the reject, no additional status is required.
If the error is detected while data from the initiator is still
expected (i.e., the command PDU did not contain all the data and
the target has not received a Data-out PDU with the Final bit set
to 1 for the unsolicited data, if any, and all outstanding R2Ts,
if any), the target MUST wait until it receives the last expected
Data-out PDUs with the F bit set to 1 before sending the Response
PDU.
For additional usage semantics of Reject PDU, see Section 7.3.
11.17.2. DataSN/R2TSN
This field is only valid if the rejected PDU is a Data/R2T SNACK
and the Reject reason code is "Protocol error" (see Section
11.16). The DataSN/R2TSN is the next Data/R2T sequence number
that the target would send for the task, if any.
11.17.3. StatSN, ExpCmdSN and MaxCmdSN
These fields carry their usual values and are not related to the
rejected command. StatSN is advanced after a Reject.
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11.17.4. Complete Header of Bad PDU
The target returns the header (not including digest) of the PDU in
error as the data of the response.
11.18. NOP-Out
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|I| 0x00 |1| Reserved |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag or 0xffffffff |
+---------------+---------------+---------------+--------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+--------------+
24| CmdSN |
+---------------+---------------+---------------+--------------+
28| ExpStatSN |
+---------------+---------------+---------------+--------------+
32/ Reserved /
+/ /
+---------------+---------------+---------------+--------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+--------------+
/ DataSegment - Ping Data (optional) /
+/ /
+---------------+---------------+---------------+--------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+--------------+
A NOP-Out may be used by an initiator as a "ping request" to
verify that a connection/session is still active and all its
components are operational. The NOP-In response is the "ping
echo".
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A NOP-Out is also sent by an initiator in response to a NOP-In.
A NOP-Out may also be used to confirm a changed ExpStatSN if
another PDU will not be available for a long time.
Upon receipt of a NOP-In with the Target Transfer Tag set to a
valid value (not the reserved 0xffffffff), the initiator MUST
respond with a NOP-Out. In this case, the NOP-Out Target Transfer
Tag MUST contain a copy of the NOP-In Target Transfer Tag. The
initiator SHOULD NOT send a NOP-Out in response to any other
received NOP-In in order to avoid lengthy sequences of NOP-In and
NOP-Out PDUs sent in response to each other.
11.18.1. Initiator Task Tag
The NOP-Out MUST have the Initiator Task Tag set to a valid value
only if a response in the form of NOP-In is requested (i.e., the
NOP-Out is used as a ping request). Otherwise, the Initiator Task
Tag MUST be set to 0xffffffff.
When a target receives the NOP-Out with a valid Initiator Task
Tag, it MUST respond with a Nop-In Response (see Section 6).
If the Initiator Task Tag contains 0xffffffff, the I bit MUST be
set to 1 and the CmdSN is not advanced after this PDU is sent.
11.18.2. Target Transfer Tag
A target assigned identifier for the operation.
The NOP-Out MUST only have the Target Transfer Tag set if it is
issued in response to a NOP-In with a valid Target Transfer Tag.
In this case, it copies the Target Transfer Tag from the NOP-In
PDU. Otherwise, the Target Transfer Tag MUST be set to 0xffffffff.
When the Target Transfer Tag is set to a value other than
0xffffffff, the LUN field MUST also be copied from the NOP-In.
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11.18.3. Ping Data
Ping data is reflected in the NOP-In Response. The length of the
reflected data is limited to MaxRecvDataSegmentLength. The length
of ping data is indicated by the DataSegmentLength. 0 is a valid
value for the DataSegmentLength and indicates the absence of ping
data.
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11.19. NOP-In
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 67|
+---------------+---------------+---------------+--------------+
0|.|.| 0x20 |1| Reserved |
+---------------+---------------+---------------+--------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+--------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+--------------+
16| Initiator Task Tag or 0xffffffff |
+---------------+---------------+---------------+--------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+--------------+
24| StatSN |
+---------------+---------------+---------------+--------------+
28| ExpCmdSN |
+---------------+---------------+---------------+--------------+
32| MaxCmdSN |
+---------------+---------------+---------------+--------------+
36/ Reserved /
+/ /
+---------------+---------------+---------------+--------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+--------------+
/ DataSegment - Return Ping Data /
+/ /
+---------------+---------------+---------------+--------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+--------------+
NOP-In is either sent by a target as a response to a NOP-Out, as a
"ping" to an initiator, or as a means to carry a changed ExpCmdSN
and/or MaxCmdSN if another PDU will not be available for a long
time (as determined by the target).
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When a target receives the NOP-Out with a valid Initiator Task Tag
(not the reserved value 0xffffffff), it MUST respond with a NOP-In
with the same Initiator Task Tag that was provided in the NOP-Out
request. It MUST also duplicate up to the first
MaxRecvDataSegmentLength bytes of the initiator provided Ping
Data. For such a response, the Target Transfer Tag MUST be
0xffffffff. The target SHOULD NOT send a NOP-In in response to any
other received NOP-Out in order to avoid lengthy sequences of NOP-
In and NOP-Out PDUs sent in response to each other.
Otherwise, when a target sends a NOP-In that is not a response to
a Nop-Out received from the initiator, the Initiator Task Tag MUST
be set to 0xffffffff and the Data Segment MUST NOT contain any
data (DataSegmentLength MUST be 0).
11.19.1. Target Transfer Tag
If the target is responding to a NOP-Out, this is set to the
reserved value 0xffffffff.
If the target is sending a NOP-In as a Ping (intending to receive
a corresponding NOP-Out), this field is set to a valid value (not
the reserved 0xffffffff).
If the target is initiating a NOP-In without wanting to receive a
corresponding NOP-Out, this field MUST hold the reserved value of
0xffffffff.
11.19.2. StatSN
The StatSN field will always contain the next StatSN. However,
when the Initiator Task Tag is set to 0xffffffff StatSN for the
connection is not advanced after this PDU is sent.
11.19.3. LUN
A LUN MUST be set to a correct value when the Target Transfer Tag
is valid (not the reserved value 0xffffffff).
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12. iSCSI Security Text Keys and Authentication Methods
Only the following keys are used during the SecurityNegotiation
stage of the Login Phase:
SessionType
InitiatorName
TargetName
TargetAddress
InitiatorAlias
TargetAlias
TargetPortalGroupTag
AuthMethod and the keys used by the authentication methods
specified under Section 12.1 along with all of their
associated keys as well as Vendor-Specific Authentication
Methods.
Other keys MUST NOT be used.
SessionType, InitiatorName, TargetName, InitiatorAlias,
TargetAlias, and TargetPortalGroupTag are described in Section 13
as they can be used also in the OperationalNegotiation stage.
All security keys have connection-wide applicability.
12.1. AuthMethod
Use: During Login - Security Negotiation
Senders: Initiator and Target
Scope: connection
AuthMethod = <list-of-values>
The main item of security negotiation is the authentication method
(AuthMethod).
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The authentication methods that can be used (appear in the list-
of-values) are either those listed in the following table or are
vendor-unique methods:
+------------------------------------------------------------+
| Name | Description |
+------------------------------------------------------------+
| KRB5 | Kerberos V5 - defined in [RFC4120] |
+------------------------------------------------------------+
| SRP | Secure Remote Password |
| | defined in [RFC2945] |
+------------------------------------------------------------+
| CHAP | Challenge Handshake Authentication Protocol|
| | defined in [RFC1994] |
+------------------------------------------------------------+
| None | No authentication |
+------------------------------------------------------------+
The AuthMethod selection is followed by an "authentication
exchange" specific to the authentication method selected.
The authentication method proposal may be made by either the
initiator or the target. However the initiator MUST make the first
step specific to the selected authentication method as soon as it
is selected. It follows that if the target makes the
authentication method proposal the initiator sends the first
key(s) of the exchange together with its authentication method
selection.
The authentication exchange authenticates the initiator to the
target, and optionally, the target to the initiator.
Authentication is OPTIONAL to use but MUST be supported by the
target and initiator.
The initiator and target MUST implement CHAP. All other
authentication methods are OPTIONAL.
Private or public extension algorithms MAY also be negotiated for
authentication methods. Whenever a private or public extension
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algorithm is part of the default offer (the offer made in absence
of explicit administrative action) the implementer MUST ensure
that CHAP is listed as an alternative in the default offer and
"None" is not part of the default offer.
Extension authentication methods MUST be named using one of the
following two formats:
i) Z-reversed.vendor.dns_name.do_something=
ii) New public key with no name prefix constraints
Authentication methods named using the Z- format are used as
private extensions. New public keys must be registered with IANA
using IETF Review process ([RFC5226]). New public extensions for
authentication methods MUST NOT use the Z# name prefix.
For all of the public or private extension authentication methods,
the method specific keys MUST conform to the format specified in
Section 6.1 for standard-label.
To identify the vendor for private extension authentication
methods, we suggest you use the reversed DNS-name as a prefix to
the proper digest names.
The part of digest-name following Z- MUST conform to the format
for standard-label specified in Section 6.1.
Support for public or private extension authentication methods is
OPTIONAL.
The following subsections define the specific exchanges for each
of the standardized authentication methods. As mentioned earlier
the first step is always done by the initiator.
12.1.1. Kerberos
For KRB5 (Kerberos V5) [RFC4120] and [RFC1964], the initiator MUST
use:
KRB_AP_REQ=<KRB_AP_REQ>
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where KRB_AP_REQ is the client message as defined in [RFC4120].
The default principal name assumed by an iSCSI initiator or target
(prior to any administrative configuration action) MUST be the
iSCSI Initiator Name or iSCSI Target Name respectively, prefixed
by the string "iscsi/".
If the initiator authentication fails, the target MUST respond
with a Login reject with "Authentication Failure" status.
Otherwise, if the initiator has selected the mutual authentication
option (by setting MUTUAL-REQUIRED in the ap-options field of the
KRB_AP_REQ), the target MUST reply with:
KRB_AP_REP=<KRB_AP_REP>
where KRB_AP_REP is the server's response message as defined in
[RFC4120].
If mutual authentication was selected and target authentication
fails, the initiator MUST close the connection.
KRB_AP_REQ and KRB_AP_REP are binary-values and their binary
length (not the length of the character string that represents
them in encoded form) MUST NOT exceed 65536 bytes. Hex or Base64
encoding may be used for KRB_AP_REQ and KRB_AP_REP, see Section
6.1.
12.1.2. Secure Remote Password (SRP)
For SRP [RFC2945], the initiator MUST use:
SRP_U=<U> TargetAuth=Yes /* or TargetAuth=No */
The target MUST answer with a Login reject with the "Authorization
Failure" status or reply with:
SRP_GROUP=<G1,G2...> SRP_s=<s>
Where G1,G2... are proposed groups, in order of preference.
The initiator MUST either close the connection or continue with:
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SRP_A=<A> SRP_GROUP=<G>
Where G is one of G1,G2... that were proposed by the target.
The target MUST answer with a Login reject with the
"Authentication Failure" status or reply with:
SRP_B=<B>
The initiator MUST close the connection or continue with:
SRP_M=<M>
If the initiator authentication fails, the target MUST answer with
a Login reject with "Authentication Failure" status. Otherwise, if
the initiator sent TargetAuth=Yes in the first message (requiring
target authentication), the target MUST reply with:
SRP_HM=<H(A | M | K)>
If the target authentication fails, the initiator MUST close the
connection.
Where U, s, A, B, M, and H(A | M | K) are defined in [RFC2945]
(using the SHA1 hash function, such as SRP-SHA1) and G,Gn (Gn
stands for G1,G2...) are identifiers of SRP groups specified in
[RFC3723]. G, Gn, and U are text strings, s,A,B,M, and H(A | M |
K) are binary-values. The length of s,A,B,M and H(A | M | K) in
binary form (not the length of the character string that
represents them in encoded form) MUST NOT exceed 1024 bytes. Hex
or Base64 encoding may be used for s,A,B,M and H(A | M | K), see
Section 6.1.
See Appendix B for the related login example.
For the SRP_GROUP, all the groups specified in [RFC3723] up to
1536 bits (i.e., SRP-768, SRP-1024, SRP-1280, SRP-1536) must be
supported by initiators and targets. To guarantee
interoperability, targets MUST always offer "SRP-1536" as one of
the proposed groups.
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12.1.3. Challenge Handshake Authentication Protocol (CHAP)
For CHAP [RFC1994], the initiator MUST use:
CHAP_A=<A1,A2...>
Where A1,A2... are proposed algorithms, in order of preference.
The target MUST answer with a Login reject with the
"Authentication Failure" status or reply with:
CHAP_A=<A> CHAP_I=<I> CHAP_C=<C>
Where A is one of A1,A2... that were proposed by the initiator.
The initiator MUST continue with:
CHAP_N=<N> CHAP_R=<R>
or, if it requires target authentication, with:
CHAP_N=<N> CHAP_R=<R> CHAP_I=<I> CHAP_C=<C>
If the initiator authentication fails, the target MUST answer with
a Login reject with "Authentication Failure" status. Otherwise, if
the initiator required target authentication, the target MUST
either answer with a Login reject with "Authentication Failure" or
reply with:
CHAP_N=<N> CHAP_R=<R>
If target authentication fails, the initiator MUST close the
connection.
Where N, (A,A1,A2), I, C, and R are (correspondingly) the Name,
Algorithm, Identifier, Challenge, and Response as defined in
[RFC1994], N is a text string, A,A1,A2, and I are numbers, and C
and R are binary-values and their binary length (not the length of
the character string that represents them in encoded form) MUST
NOT exceed 1024 bytes. Hex or Base64 encoding may be used for C
and R, see Section 6.1.
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See Appendix B for the related login example.
For the Algorithm, as stated in [RFC1994], one value is required
to be implemented:
5 (CHAP with MD5)
To guarantee interoperability, initiators MUST always offer it as
one of the proposed algorithms.
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13. Login/Text Operational Text Keys
Some session specific parameters MUST only be carried on the
leading connection and cannot be changed after the leading
connection login (e.g., MaxConnections, the maximum number of
connections). This holds for a single connection session with
regard to connection restart. The keys that fall into this
category have the use: LO (Leading Only).
Keys that can only be used during login have the use: IO
(initialize only), while those that can be used in both the Login
Phase and Full Feature Phase have the use: ALL.
Keys that can only be used during Full Feature Phase use FFPO
(Full Feature Phase only).
Keys marked as Any-Stage may also appear in the
SecurityNegotiation stage while all other keys described in this
Section are operational keys.
Keys that do not require an answer are marked as Declarative.
Key scope is indicated as session-wide (SW) or connection-only
(CO).
Result function, wherever mentioned, states the function that can
be applied to check the validity of the responder selection.
Minimum means that the selected value cannot exceed the offered
value. Maximum means that the selected value cannot be lower than
the offered value. AND means that the selected value must be a
possible result of a Boolean "and" function with an arbitrary
Boolean value (e.g., if the offered value is No the selected value
must be No). OR means that the selected value must be a possible
result of a Boolean "or" function with an arbitrary Boolean value
(e.g., if the offered value is Yes the selected value must be
Yes).
13.1. HeaderDigest and DataDigest
Use: IO
Senders: Initiator and Target
Scope: CO
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HeaderDigest = <list-of-values>
DataDigest = <list-of-values>
Default is None for both HeaderDigest and DataDigest.
Digests enable the checking of end-to-end, non-cryptographic data
integrity beyond the integrity checks provided by the link layers
and the covering of the whole communication path including all
elements that may change the network level PDUs such as routers,
switches, and proxies.
The following table lists cyclic integrity checksums that can be
negotiated for the digests and that MUST be implemented by every
iSCSI initiator and target. These digest options only have error
detection significance.
+---------------------------------------------+
| Name | Description | Generator |
+---------------------------------------------+
| CRC32C | 32 bit CRC |0x11edc6f41|
+---------------------------------------------+
| None | no digest |
+---------------------------------------------+
The generator polynomial for this digest is given in hex-notation
(e.g., 0x3b stands for 0011 1011 and the polynomial is
x**5+X**4+x**3+x+1).
When the Initiator and Target agree on a digest, this digest MUST
be used for every PDU in Full Feature Phase.
Padding bytes, when present in a segment covered by a CRC, SHOULD
be set to 0 and are included in the CRC.
The CRC MUST be calculated by a method that produces the same
results as the following process:
- The PDU bits are considered as the coefficients of a
polynomial M(x) of degree n-1; bit 7 of the lowest numbered
byte is considered the most significant bit (x^n-1),
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followed by bit 6 of the lowest numbered byte through bit 0
of the highest numbered byte (x^0).
- The most significant 32 bits are complemented.
- The polynomial is multiplied by x^32 then divided by G(x).
The generator polynomial produces a remainder R(x) of degree
<= 31.
- The coefficients of R(x) are considered a 32 bit sequence.
- The bit sequence is complemented and the result is the CRC.
- The CRC bits are mapped into the digest word. The x^31
coefficient in bit 7 of the lowest numbered byte of the
digest continuing through to the byte up to the x^24
coefficient in bit 0 of the lowest numbered byte, continuing
with the x^23 coefficient in bit 7 of next byte through x^0
in bit 0 of the highest numbered byte.
- Computing the CRC over any segment (data or header) extended
to include the CRC built using the generator 0x11edc6f41
will always get the value 0x1c2d19ed as its final remainder
(R(x)). This value is given here in its polynomial form
(i.e., not mapped as the digest word).
For a discussion about selection criteria for the CRC, see
[RFC3385]. For a detailed analysis of the iSCSI polynomial, see
[Castagnoli93].
Private or public extension algorithms MAY also be negotiated for
digests. Whenever a private or public digest extension algorithm
is part of the default offer (the offer made in absence of
explicit administrative action) the implementer MUST ensure that
CRC32C is listed as an alternative in the default offer and "None"
is not part of the default offer.
Extension digest algorithms MUST be named using one of the
following two formats:
i) Y-reversed.vendor.dns_name.do_something=
ii) New public key with no name prefix constraints
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Digests named using the Y- format are used for private purposes
(unregistered). New public keys must be registered with IANA using
IETF Review process ([RFC5226]). New public extensions for digests
MUST NOT use the Y# name prefix.
For private extension digests, to identify the vendor, we suggest
you use the reversed DNS-name as a prefix to the proper digest
names.
The part of digest-name following Y- MUST conform to the format
for standard-label specified in Section 6.1.
Support for public or private extension digests is OPTIONAL.
13.2. MaxConnections
Use: LO
Senders: Initiator and Target
Scope: SW
Irrelevant when: SessionType=Discovery
MaxConnections=<numerical-value-from-1-to-65535>
Default is 1.
Result function is Minimum.
Initiator and target negotiate the maximum number of connections
requested/acceptable.
13.3. SendTargets
Use: FFPO
Senders: Initiator
Scope: SW
For a complete description, see Appendix C.
13.4. TargetName
Use: IO by initiator, FFPO by target - only as response to a
SendTargets, Declarative, Any-Stage
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Senders: Initiator and Target
Scope: SW
TargetName=<iSCSI-name-value>
Examples:
TargetName=iqn.1993-11.com.disk-vendor:diskarrays.sn.45678
TargetName=eui.020000023B040506
TargetName=naa.62004567BA64678D0123456789ABCDEF
The initiator of the TCP connection MUST provide this key to the
remote endpoint in the first login request if the initiator is not
establishing a discovery session. The iSCSI Target Name specifies
the worldwide unique name of the target.
The TargetName key may also be returned by the "SendTargets" text
request (which is its only use when issued by a target).
TargetName MUST NOT be redeclared within the login phase.
13.5. InitiatorName
Use: IO, Declarative, Any-Stage
Senders: Initiator
Scope: SW
InitiatorName=<iSCSI-name-value>
Examples:
InitiatorName=iqn.1992-04.com.os-vendor.plan9:cdrom.12345
InitiatorName=iqn.2001-02.com.ssp.users:customer235.host90
InitiatorName=naa.52004567BA64678D
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The initiator of the TCP connection MUST provide this key to the
remote endpoint at the first Login of the Login Phase for every
connection. The InitiatorName key enables the initiator to
identify itself to the remote endpoint.
InitiatorName MUST NOT be redeclared within the login phase.
13.6. TargetAlias
Use: ALL, Declarative, Any-Stage
Senders: Target
Scope: SW
TargetAlias=<iSCSI-local-name-value>
Examples:
TargetAlias=Bob-s Disk
TargetAlias=Database Server 1 Log Disk
TargetAlias=Web Server 3 Disk 20
If a target has been configured with a human-readable name or
description, this name SHOULD be communicated to the initiator
during a Login Response PDU if SessionType=Normal (see 13.21).
This string is not used as an identifier, nor is it meant to be
used for authentication or authorization decisions. It can be
displayed by the initiator's user interface in a list of targets
to which it is connected.
13.7. InitiatorAlias
Use: ALL, Declarative, Any-Stage
Senders: Initiator
Scope: SW
InitiatorAlias=<iSCSI-local-name-value>
Examples:
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InitiatorAlias=Web Server 4
InitiatorAlias=spyalley.nsa.gov
InitiatorAlias=Exchange Server
If an initiator has been configured with a human-readable name or
description, it SHOULD be communicated to the target during a
Login Request PDU. If not, the host name can be used instead. This
string is not used as an identifier, nor is meant to be used for
authentication or authorization decisions. It can be displayed by
the target's user interface in a list of initiators to which it is
connected.
13.8. TargetAddress
Use: ALL, Declarative, Any-Stage
Senders: Target
Scope: SW
TargetAddress=domainname[:port][,portal-group-tag]
The domainname can be specified as either a DNS host name, a
dotted-decimal IPv4 address, or a bracketed IPv6 address as
specified in [RFC3986].
If the TCP port is not specified, it is assumed to be the IANA-
assigned default port for iSCSI (see Section 14).
If the TargetAddress is returned as the result of a redirect
status in a login response, the comma and portal group tag MUST be
omitted.
If the TargetAddress is returned within a SendTargets response,
the portal group tag MUST be included.
Examples:
TargetAddress=10.0.0.1:5003,1
TargetAddress=[1080:0:0:0:8:800:200C:417A],65
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TargetAddress=[1080::8:800:200C:417A]:5003,1
TargetAddress=computingcenter.example.com,23
Use of the portal-group-tag is described in Appendix C. The
formats for the port and portal-group-tag are the same as the one
specified in TargetPortalGroupTag.
13.9. TargetPortalGroupTag
Use: IO by target, Declarative, Any-Stage
Senders: Target
Scope: SW
TargetPortalGroupTag=<16-bit-binary-value>
Examples:
TargetPortalGroupTag=1
The target portal group tag is a 16-bit binary-value that uniquely
identifies a portal group within an iSCSI target node. This key
carries the value of the tag of the portal group that is servicing
the Login request. The iSCSI target returns this key to the
initiator in the Login Response PDU to the first Login Request PDU
that has the C bit set to 0 when TargetName is given by the
initiator.
[SAM2] notes in its informative text that TPGT value should be
non-zero, note that it is incorrect. A zero value is allowed as a
legal value for TPGT. This discrepancy currently stands corrected
in [SAM4].
For the complete usage expectations of this key see Section 6.3.
13.10. InitialR2T
Use: LO
Senders: Initiator and Target
Scope: SW
Irrelevant when: SessionType=Discovery
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InitialR2T=<boolean-value>
Examples:
I->InitialR2T=No
T->InitialR2T=No
Default is Yes.
Result function is OR.
The InitialR2T key is used to turn off the default use of R2T for
unidirectional and the output part of bidirectional commands, thus
allowing an initiator to start sending data to a target as if it
has received an initial R2T with Buffer Offset=Immediate Data
Length and Desired Data Transfer Length=(min(FirstBurstLength,
Expected Data Transfer Length) - Received Immediate Data Length).
The default action is that R2T is required, unless both the
initiator and the target send this key-pair attribute specifying
InitialR2T=No. Only the first outgoing data burst (immediate data
and/or separate PDUs) can be sent unsolicited (i.e., not requiring
an explicit R2T).
13.11. ImmediateData
Use: LO
Senders: Initiator and Target
Scope: SW
Irrelevant when: SessionType=Discovery
ImmediateData=<boolean-value>
Default is Yes.
Result function is AND.
The initiator and target negotiate support for immediate data. To
turn immediate data off, the initiator or target must state its
desire to do so. ImmediateData can be turned on if both the
initiator and target have ImmediateData=Yes.
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If ImmediateData is set to Yes and InitialR2T is set to Yes
(default), then only immediate data are accepted in the first
burst.
If ImmediateData is set to No and InitialR2T is set to Yes, then
the initiator MUST NOT send unsolicited data and the target MUST
reject unsolicited data with the corresponding response code.
If ImmediateData is set to No and InitialR2T is set to No, then
the initiator MUST NOT send unsolicited immediate data, but MAY
send one unsolicited burst of Data-OUT PDUs.
If ImmediateData is set to Yes and InitialR2T is set to No, then
the initiator MAY send unsolicited immediate data and/or one
unsolicited burst of Data-OUT PDUs.
The following table is a summary of unsolicited data options:
+----------+-------------+------------------+--------------+
|InitialR2T|ImmediateData| Unsolicited |Immediate Data|
| | | Data Out PDUs | |
+----------+-------------+------------------+--------------+
| No | No | Yes | No |
+----------+-------------+------------------+--------------+
| No | Yes | Yes | Yes |
+----------+-------------+------------------+--------------+
| Yes | No | No | No |
+----------+-------------+------------------+--------------+
| Yes | Yes | No | Yes |
+----------+-------------+------------------+--------------+
13.12. MaxRecvDataSegmentLength
Use: ALL, Declarative
Senders: Initiator and Target
Scope: CO
MaxRecvDataSegmentLength=<numerical-value-512-to-(2**24-1)>
Default is 8192 bytes.
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The initiator or target declares the maximum data segment length
in bytes it can receive in an iSCSI PDU.
The transmitter (initiator or target) is required to send PDUs
with a data segment that does not exceed MaxRecvDataSegmentLength
of the receiver.
A target receiver is additionally limited by MaxBurstLength for
solicited data and FirstBurstLength for unsolicited data. An
initiator MUST NOT send solicited PDUs exceeding MaxBurstLength
nor unsolicited PDUs exceeding FirstBurstLength (or
FirstBurstLength-Immediate Data Length if immediate data were
sent).
13.13. MaxBurstLength
Use: LO
Senders: Initiator and Target
Scope: SW
Irrelevant when: SessionType=Discovery
MaxBurstLength=<numerical-value-512-to-(2**24-1)>
Default is 262144 (256 Kbytes).
Result function is Minimum.
The initiator and target negotiate maximum SCSI data payload in
bytes in a Data-In or a solicited Data-Out iSCSI sequence. A
sequence consists of one or more consecutive Data-In or Data-Out
PDUs that end with a Data-In or Data-Out PDU with the F bit set to
one.
13.14. FirstBurstLength
Use: LO
Senders: Initiator and Target
Scope: SW
Irrelevant when: SessionType=Discovery
Irrelevant when: ( InitialR2T=Yes and ImmediateData=No )
FirstBurstLength=<numerical-value-512-to-(2**24-1)>
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Default is 65536 (64 Kbytes).
Result function is Minimum.
The initiator and target negotiate the maximum amount in bytes of
unsolicited data an iSCSI initiator may send to the target during
the execution of a single SCSI command. This covers the immediate
data (if any) and the sequence of unsolicited Data-Out PDUs (if
any) that follow the command.
FirstBurstLength MUST NOT exceed MaxBurstLength.
13.15. DefaultTime2Wait
Use: LO
Senders: Initiator and Target
Scope: SW
DefaultTime2Wait=<numerical-value-0-to-3600>
Default is 2.
Result function is Maximum.
The initiator and target negotiate the minimum time, in seconds,
to wait before attempting an explicit/implicit logout or an active
task reassignment after an unexpected connection termination or a
connection reset.
A value of 0 indicates that logout or active task reassignment can
be attempted immediately.
13.16. DefaultTime2Retain
Use: LO
Senders: Initiator and Target
Scope: SW
DefaultTime2Retain=<numerical-value-0-to-3600>
Default is 20.
Result function is Minimum.
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The initiator and target negotiate the maximum time, in seconds
after an initial wait (Time2Wait), before which an active task
reassignment is still possible after an unexpected connection
termination or a connection reset.
This value is also the session state timeout if the connection in
question is the last LOGGED_IN connection in the session.
A value of 0 indicates that connection/task state is immediately
discarded by the target.
13.17. MaxOutstandingR2T
Use: LO
Senders: Initiator and Target
Scope: SW
MaxOutstandingR2T=<numerical-value-from-1-to-65535>
Irrelevant when: SessionType=Discovery
Default is 1.
Result function is Minimum.
Initiator and target negotiate the maximum number of outstanding
R2Ts per task, excluding any implied initial R2T that might be
part of that task. An R2T is considered outstanding until the last
data PDU (with the F bit set to 1) is transferred, or a sequence
reception timeout (Section 7.1.4.1) is encountered for that data
sequence.
13.18. DataPDUInOrder
Use: LO
Senders: Initiator and Target
Scope: SW
Irrelevant when: SessionType=Discovery
DataPDUInOrder=<boolean-value>
Default is Yes.
Result function is OR.
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No is used by iSCSI to indicate that the data PDUs within
sequences can be in any order. Yes is used to indicate that data
PDUs within sequences have to be at continuously increasing
addresses and overlays are forbidden.
13.19. DataSequenceInOrder
Use: LO
Senders: Initiator and Target
Scope: SW
Irrelevant when: SessionType=Discovery
DataSequenceInOrder=<boolean-value>
Default is Yes.
Result function is OR.
A Data Sequence is a sequence of Data-In or Data-Out PDUs that end
with a Data-In or Data-Out PDU with the F bit set to one. A Data-
out sequence is sent either unsolicited or in response to an R2T.
Sequences cover an offset-range.
If DataSequenceInOrder is set to No, Data PDU sequences may be
transferred in any order.
If DataSequenceInOrder is set to Yes, Data Sequences MUST be
transferred using continuously non-decreasing sequence offsets
(R2T buffer offset for writes, or the smallest SCSI Data-In buffer
offset within a read data sequence).
If DataSequenceInOrder is set to Yes, a target may retry at most
the last R2T, and an initiator may at most request retransmission
for the last read data sequence. For this reason, if
ErrorRecoveryLevel is not 0 and DataSequenceInOrder is set to Yes
then MaxOustandingR2T MUST be set to 1.
13.20. ErrorRecoveryLevel
Use: LO
Senders: Initiator and Target
Scope: SW
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ErrorRecoveryLevel=<numerical-value-0-to-2>
Default is 0.
Result function is Minimum.
The initiator and target negotiate the recovery level supported.
Recovery levels represent a combination of recovery capabilities.
Each recovery level includes all the capabilities of the lower
recovery levels and adds some new ones to them.
In the description of recovery mechanisms, certain recovery
classes are specified. Section 7.1.5 describes the mapping between
the classes and the levels.
13.21. SessionType
Use: LO, Declarative, Any-Stage
Senders: Initiator
Scope: SW
SessionType= <Discovery|Normal>
Default is Normal.
The Initiator indicates the type of session it wants to create.
The target can either accept it or reject it.
A Discovery session indicates to the Target that the only purpose
of this Session is discovery. The only requests a target accepts
in this type of session are a text request with a SendTargets key
and a logout request with reason "close the session".
The Discovery session implies MaxConnections = 1 and overrides
both the default and an explicit setting. As Section 7.4.1
states, ErrorRecoveryLevel MUST be 0 (zero) for Discovery
sessions.
Depending on the type of the session, a target may decide on
resources to allocate and the security to enforce, etc. for thion.
If the SessionType key is thus going to be offered as "Discovery",
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it SHOULD be offered in the initial Login request by the
initiator.
13.22. The Private Extension Key Format
Use: ALL
Senders: Initiator and Target
Scope: specific key dependent
X-reversed.vendor.dns_name.do_something=
Keys with this format are used for private extension purposes.
These keys always start with X- if unregistered with IANA
(private). New public keys (if registered with IANA via an IETF
Review, [RFC5226]) no longer have an X# name prefix requirement,
implementers may propose any intuitive unique name.
For unregistered keys, to identify the vendor, we suggest you use
the reversed DNS-name as a prefix to the key-proper.
The part of key-name following X- MUST conform to the format for
key-name specified in Section 6.1.
Vendor specific keys MUST ONLY be used in normal sessions.
Support for public or private extension keys is OPTIONAL.
13.23. TaskReporting
Use: LO
Senders: Initiator and Target
Scope: SW
Irrelevant when: SessionType=Discovery
TaskReporting=<list-of-values>
Default is RFC3720.
Result function is AND.
This key is used to negotiate the task completion reporting
semantics from the SCSI target. The following table describes the
semantics that an iSCSI target MUST support for respective
negotiated key values. Whenever this key is negotiated, at least
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the RFC3720 and ResponseFence values MUST be offered as options by
the negotiation originator.
+--------------+------------------------------------------+
| Name | Description |
+--------------+------------------------------------------+
| RFC3720 | RFC 3720-compliant semantics. Response |
| | fencing is not guaranteed and fast |
| | completion of multi-task aborting is not |
| | supported |
+--------------+------------------------------------------+
| ResponseFence| Response Fence (Section 4.2.2.3.3) |
| | semantics MUST be supported in reporting |
| | task completions |
+--------------+------------------------------------------+
| FastAbort | Updated fast multi-task abort semantics |
| | defined in Section 4.2.3.4 MUST be |
| | supported. Support for Response Fence is |
| | implied -- i.e., (Section 4.2.2.3.3) |
| | semantics MUST be supported as well |
+--------------+------------------------------------------+
When TaskReporting is not negotiated to FastAbort, the standard
multi-task abort semantics in Section 4.2.3.3 MUST be used.
13.24. iSCSIProtocolLevel Negotiation
The iSCSIProtocolLevel associated with this document is "1". As a
responder or an originator in a negotiation of this key, an iSCSI
implementation compliant to this document alone, without any
future protocol extensions, MUST use this value as defined by the
[iSCSI-SAM] document.
13.25. Obsoleted Keys
This document obsoletes the following keys defined in [RFC3720]:
IFMarker, OFMarker, OFMarkInt, IFMarkInt. However, iSCSI
implementations compliant to this document may still receive these
obsoleted keys - i.e. in a responder role - in a text negotiation.
When IFMarker or OFMarker key is received, a compliant iSCSI
implementation SHOULD respond with the constant "Reject" value.
The implementation MAY alternatively respond with a "No" value.
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However, the implementation MUST NOT respond with a
"NotUnderstood" value for either of these keys.
When IFMarkInt or OFMarkInt key is received, a compliant iSCSI
implementation MUST respond with the constant "Reject" value.
The implementation MUST NOT respond with a "NotUnderstood" value
for either of these keys.
13.26. X#NodeArchitecture
13.26.1. Definition
Use: LO, Declarative
Senders: Initiator and Target
Scope: SW
X#NodeArchitecture=<list-of-values>
Default is none.
Examples:
X#NodeArchitecture=ExampleOS/v1234,ExampleInc_SW_Initiator/1.05a
X#NodeArchitecture=ExampleInc_HW_Initiator/4010,Firmware/2.0.0.5
X#NodeArchitecture=ExampleInc_SW_Initiator/2.1,CPU_Arch/i686
This document does not define the structure or content of the list
of values.
The initiator or target declares the details of its iSCSI node
architecture to the remote endpoint. These details may include,
but are not limited to, iSCSI vendor software, firmware, or
hardware versions, the OS version, or hardware architecture. This
key may be declared on a Discovery session or a Normal session.
The length of the key value (total length of the list-of-values)
MUST NOT be greater than 255 bytes.
X#NodeArchitecture MUST NOT be redeclared during the login phase.
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13.26.2. Implementation Requirements
Functional behavior of the iSCSI node (this includes the iSCSI
protocol logic -- the SCSI, iSCSI, and TCP/IP protocols) MUST NOT
depend on the presence, absence, or content of the
X#NodeArchitecture key. The key MUST NOT be used by iSCSI nodes
for interoperability, or exclusion of other nodes. To ensure
proper use, key values SHOULD be set by the node itself, and there
SHOULD NOT be provisions for the key values to contain user-
defined text.
Nodes implementing this key MUST choose one of the following
implementation options:
- only transmit the key,
- only log the key values received from other nodes, or
- both transmit and log the key values.
Each node choosing to implement transmission of the key values
MUST be prepared to handle the response of iSCSI Nodes that do not
understand the key.
Nodes that implement transmission and/or logging of the key values
may also implement administrative mechanisms that disable and/or
change the logging and key transmission detail (see Section 9.4).
Thus, a valid behavior for this key may be that a node is
completely silent (the node does not transmit any key value, and
simply discards any key values it receives without issuing a
NotUnderstood response).
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14. Rationale for revised IANA Considerations
This document makes rather significant changes in this area, and
this Section outlines the reasons behind the changes. As
previously specified in [RFC3720], iSCSI had used text string
prefixes, such as X- and X#, to distinguish extended login/text
keys, digest algorithms and authentication methods from their
standardized counterparts. Based on experience with other
protocols, [RFC6648] however strongly recommends against this
practice, in large part because extensions that use such prefixes
may become standard over time at which point it can be infeasible
to change their text string names due to widespread usage under
the existing text string name.
iSCSI's experience with public extensions supports the
recommendations in [RFC6648], as the only extension item ever
registered with IANA, the X#NodeArchitecture key, was specified as
a standard key in a standards-track RFC [RFC4850], and hence did
not require the X# prefix. In addition, that key is the only
public iSCSI extension that has been registered with IANA since
RFC 3720 was originally published, so there has been effectively
no use of the X#, Y# and Z# public extension formats.
Therefore, this document makes the following changes to the IANA
registration procedures for iSCSI:
(1) The separate registries for X#, Y# and Z# public
extensions are removed. The single entry in the registry for
X# login/text keys(X#NodeArchitecture) is transferred to the
main login/text key registry. IANA has never created the
latter two registries because there have been no
registration requests for them. These public extension
formats (X#, Y#, Z#) MUST NOT be used with the exception of
the existing X#NodeArchitecture key.
(2) The Registration Procedures for the main login/text key,
digest algorithm and authentication method IANA registries
are changed to IETF Review [RFC5226] for possible future
extensions to iSCSI. This change includes a deliberate
decision to remove the possibility of specifying an IANA-
registered iSCSI extension in an RFC published via an RFC
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Editor independent submission, as the level of review in
that process is insufficient for iSCSI extensions.
(3) The restriction against registering items using the
private extension formats (X-, Y-, Z-) in the main IANA
registries is removed. Extensions using these formats MAY be
registered under the IETF Review registration procedures,
but each format is restricted to the type of extension for
which it is specified in this RFC and MUST NOT be used for
other types. For example, the X- extension format for
extension login/text keys MUST NOT be used for digest
algorithms or authentication methods.
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15. IANA Considerations
The well-known TCP port number for iSCSI connections assigned by
IANA is 3260 and this is the default iSCSI port. Implementations
needing a system TCP port number may use port 860, the port
assigned by IANA as the iSCSI system port; however in order to use
port 860, it MUST be explicitly specified - implementations MUST
NOT default to use of port 860, as 3260 is the only allowed
default.
IANA is requested to update all references to RFC 3720, RFC 4850
and RFC 5048 to instead reference this RFC in all of the iSCSI
registries that are part of the "Internet Small Computer System
Interface (iSCSI) Parameters" set of registries. This change
reflects the fact that those three RFCs are obsoleted by this RFC.
References to other RFCs that are not being obsoleted (e.g., RFC
3723, RFC 5046) should not be changed.
IANA is requested to perform the following actions on the iSCSI
Login/Text Keys registry:
- Change the registration procedure to IETF Review from
Standard Required.
- Change the RFC 5048 reference for the registry to reference
this RFC.
- Add the X#NodeArchitecture Key from the iSCSI extended key
registry and change its reference to this RFC.
- Change all references of RFC 3720 and RFC 5048 to reference
this RFC.
IANA is requested to change the Registration Procedures for the
iSCSI authentication methods and iSCSI digests registries to IETF
Review from RFC Required.
IANA is requested to remove the iSCSI extended key registry, as
its one entry is to be added to the iSCSI login/text keys
registry.
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IANA is requested to mark obsolete the values 4 and 5, for SPKM1
and SPKM2 respectively, in the iSCSI authentication methods
subregistry of the Internet Small Computer System Interface
(iSCSI) Parameters registries.
All the other IANA considerations stated in [RFC3720] and
[RFC5048] remain unchanged.
This document obsoletes the SPKM1 and SPKM2 key values for the
AuthMethod text key. Consequently, the SPKM_ text key prefix MUST
be treated as obsolete and be not reused.
References
Normative References
[EUI] "Guidelines for 64-bit Global Identifier (EUI-64)",
http://standards.ieee.org/regauth/oui/tutorials/EUI64.html
[FC-FS3] INCITS 470-2011, Fibre Channel - Framing and
Signaling - 3 (FC-FS-3).
[IPSEC-IPS] Black, D., Koning, P., "Securing Block Storage
Protocols over IP: RFC 3723 Requirements Update for IPsec
v3", draft-ietf-storm-ipsec-ips-update-03.txt (work in
progress), July 2013
[iSCSI-SAM] Knight, F., Chadalapaka, M., "Internet Small
Computer Systems Interface (iSCSI) SCSI Architecture
Features Update", draft-ietf-storm-iscsi-sam-07.txt (work in
progress), July 2013
[OUI] "IEEE OUI and Company_Id Assignments",
http://standards.ieee.org/regauth/oui
[RFC1122] R.Braden, "Requirements for Internet Hosts --
Communication Layers", October 1989.
[RFC1964] J. Linn, "The Kerberos Version 5 GSS-API Mechanism",
June 1996.
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[RFC1982] Elz, R., Bush, R., "Serial Number Arithmetic",
August 1996.
[RFC1994] W. Simpson, "PPP Challenge Handshake Authentication
Protocol (CHAP)", August 1996.
[RFC2119] Bradner, S. "Key Words for use in RFCs to Indicate
Requirement Levels", BCP 14, March 1997.
[RFC2404] C. Madson, R. Glenn, "The Use of HMAC-SHA-1-96
within ESP and AH", November 1998.
[RFC2451] R. Pereira, R. Adams "The ESP CBC-Mode Cipher
Algorithms".
[RFC2945] Wu, T., "The SRP Authentication and Key Exchange
System", September 2000.
[RFC3454] Hoffman, P. and M. Blanchet, "Preparation of
Internationalized Strings ("stringprep")", RFC 3454,
December 2002.
[RFC3566] Frankel, S. and H. Herbert, "The AES-XCBC-MAC-96
Algorithm and Its Use With IPsec", RFC 3566, September 2003.
[RFC3629] Yergeau, F., "UTF-8, a Transformation Format of ISO
10646", RFC 3629, November 2003
[RFC3686] Housley, R., "Using Advanced Encryption Standard
(AES) Counter Mode with IPsec Encapsulating Security Payload
(ESP)", RFC 3686, January 2004.
[RFC3722] Bakke, M., "String Profile for Internet Small
Computer Systems Interface (iSCSI) Names", RFC 3722, March
2004.
[RFC3723] Aboba, B., Tseng, J., Walker, J., Rangan, V. and F.
Travostino, "Securing Block Storage Protocols over IP", RFC
3723, March 2004.
[RFC3986] T. Berners-Lee, R. Fielding, L. Masinter "Uniform
Resource Identifier (URI): Generic Syntax", January 2005.
Chadalapaka et al. Expires January 31, 2014 [Page 290]
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[RFC4106] J. Viega, D. McGrew, "The Use of Galois/Counter Mode
(GCM) in IPsec Encapsulating Security Payload (ESP)", RFC
4106, June 2005.
[RFC4120] Neuman, C., Yu, T., Hartman, S., Raeburn, K, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
[RFC4171] J. Tseng, K. Gibbons, F. Travostino, C. Du Laney, J.
Souza, "Internet Storage Name Service (iSNS)", September
2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", February 2006.
[RFC4301] S. Kent, K.Seo, "Security Architecture for the
Internet Protocol", December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005
[RFC4543] D. McGrew, J. Viega, "The Use of Galois Message
Authentication Code (GMAC) in IPsec ESP and AH", RFC 4543,
May 2006
[RFC4648] S. Josefsson, "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006
[RFC5226] H. Alvestrand, T. Narten, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226, May 2008
[RFC5996] C. Kaufman, P. Hoffman, Y. Nir, P. Eronen, "Internet
Key Exchange Protocol Version 2 (IKEv2) ", RFC 5996,
September 2010.
[SAM2] T10/1157-D, SCSI Architecture Model - 2 (SAM-2).
[SAM4] T10/1683-D, SCSI Architecture Model - 4 (SAM-4).
[SPC2] T10/1236-D, SCSI Primary Commands-2.
[SPC3] T10/1416-D, SCSI Primary Commands-3.
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[UML] ISO/IEC 19501, Unified Modeling Language
Specification Version 1.4.2.
[UNICODE] Unicode Standard Annex #15, "Unicode Normalization
Forms", http://www.unicode.org/unicode/reports/tr15
Informative References
[FC-SP-2] T11/1835-D, Fibre Channel Security Protocols- 2 (FC-
SP-2).
[RFC1737] K. Sollins, L. Masinter "Functional Requirements for
Uniform Resource Names".
[RFC5433] T. Clancy, H. Tschofenig "Extensible Authentication
Protocol - Generalized Pre-Shared Key (EAP-GPSK) Method",
RFC 5433, February 2009.
[IB] InfiniBand{tm} Architecture Specification, Vol. 1,
Rel.1.0.a, InfiniBand Trade
Association(http://www.infinibandta.org).
[Castagnoli93] G. Castagnoli, S. Braeuer and M. Herrman
"Optimization of Cyclic Redundancy-Check Codes with 24 and
32 Parity Bits", IEEE Transact. on Communications, Vol. 41,
No. 6, June 1993.
[CRC] ISO 3309, High-Level Data Link Control (CRC 32).
[RFC2401] S. Kent, R. Atkinson, "Security Architecture for the
Internet Protocol ", November 1998.
[RFC2406] S. Kent, R. Atkinson, "IP Encapsulating Security
Payload (ESP)", November 1998.
[RFC2407] D. Piper, "The Internet IP Security Domain of
Interpretation for ISAKMP", November 1998.
[RFC2409] D. Harkins, D. Carrel, "The Internet Key Exchange
(IKE)", November 1998.
Chadalapaka et al. Expires January 31, 2014 [Page 292]
iSCSI (Consolidated) 7/13/2013
[RFC2608] E. Guttman, C. Perkins, J. Veizades, M. Day,
"Service Location Protocol, Version 2", June 1999.
[RFC2743] J.Linn, "Generic Security Service Application
Program Interface Version 2, Update 1", January 2000
[RFC2865] C. Rigney, S. Willens, A. Rubens, W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", June
2000.
[RFC3385] Sheinwald, D., Satran, J., Thaler, P. and V.
Cavanna, "Internet Protocol Small Computer System Interface
(iSCSI) Cyclic Redundancy Check (CRC)/Checksum
Considerations", RFC 3385, September 2002.
[RFC3602] S. Frankel, R. Glenn, S. Kelly, "The AES-CBC Cipher
Algorithm and Its Use with IPsec", RFC 3602, September 2003.
[RFC3720] Satran, J., Meth, K., Sapuntzakis, C., Chadalapaka,
M., and E. Zeidner, "Internet Small Computer Systems
Interface (iSCSI)", RFC 3720, April 2004.
[RFC3721] Bakke, M., Hafner, J., Hufferd, J., Voruganti, K.
and M. Krueger, "Internet Small Computer Systems Interface
(iSCSI) Naming and Discovery", RFC 3721, March 2004
[RFC3783] M. Chadalapaka, R. Elliott, "Small Computer Systems
Interface (SCSI) Command Ordering Considerations with
iSCSI", RFC 3783, May 2004.
[RFC4121] L. Zhu, K. Jaganathan, S. Hartman, "The Kerberos
Version 5 Generic Security Service Application Program
Interface (GSS-API) Mechanism: Version 2", RFC 4121, July
2005.
[RFC4297] Romanow, A., Mogul, J., Talpey, T., and S. Bailey,
"Remote Direct Memory Access (RDMA) over IP Problem
Statement", RFC 4297, October 2004
[RFC4850] Wysochanski, D., "Declarative Public Extension Key
for Internet Small Computer Systems Interface (iSCSI) Node
Architecture", RFC 4850, April 2007.
Chadalapaka et al. Expires January 31, 2014 [Page 293]
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[RFC5046] Ko, M., Chadalapaka, M., Hufferd, J., Elzur, U.,
Shah, H., and P. Thaler, "Internet Small Computer System
Interface (iSCSI) Extensions for Remote Direct Memory Access
(RDMA)", RFC 5046, October 2007
[RFC5048] Chadalapaka, M., "Internet Small Computer Systems
Interface (iSCSI) Corrections and Clarifications", RFC 5048,
October 2007.
[RFC6648] P. Saint-Andre, D. Crocker, M. Nottingham,
"Deprecating the X- Prefix and Similar Constructs in
Application Protocols", RFC 6648, June 2012
[SAS] T10/2125-D, Serial Attached SCSI - 2.1 (SAS-2.1);
T10/2124-D, SAS Protocol Layer (SPL); T10/2124-M, SAS
Protocol Layer (SPL) Amendment #1 (SPL AM1).
[SBC2] NCITS.405-205, SCSI Block Commands - 2 (SBC-2).
[SPC4] T10/1731-D, SCSI Primary Commands-4.
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Appendix A. Examples
Read Operation Example
+------------------+-----------------------+---------------------+
|Initiator Function| PDU Type | Target Function |
+------------------+-----------------------+---------------------+
| Command request |SCSI Command (READ)>>> | |
| (read) | | |
+------------------+-----------------------+---------------------+
| | |Prepare Data Transfer|
+------------------+-----------------------+---------------------+
| Receive Data | <<< SCSI Data-in | Send Data |
+------------------+-----------------------+---------------------+
| Receive Data | <<< SCSI Data-in | Send Data |
+------------------+-----------------------+---------------------+
| Receive Data | <<< SCSI Data-in | Send Data |
+------------------+-----------------------+---------------------+
| | <<< SCSI Response |Send Status and Sense|
+------------------+-----------------------+---------------------+
| Command Complete | | |
+------------------+-----------------------+---------------------+
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Write Operation Example
+------------------+-----------------------+---------------------+
|Initiator Function| PDU Type | Target Function |
+------------------+-----------------------+---------------------+
| Command request |SCSI Command (WRITE)>>>| Receive command |
| (write) | | and queue it |
+------------------+-----------------------+---------------------+
| | | Process old commands|
+------------------+-----------------------+---------------------+
| | | Ready to process |
| | <<< R2T | WRITE command |
+------------------+-----------------------+---------------------+
| Send Data | SCSI Data-out >>> | Receive Data |
+------------------+-----------------------+---------------------+
| | <<< R2T | Ready for data |
+------------------+-----------------------+---------------------+
| | <<< R2T | Ready for data |
+------------------+-----------------------+---------------------+
| Send Data | SCSI Data-out >>> | Receive Data |
+------------------+-----------------------+---------------------+
| Send Data | SCSI Data-out >>> | Receive Data |
+------------------+-----------------------+---------------------+
| | <<< SCSI Response |Send Status and Sense|
+------------------+-----------------------+---------------------+
| Command Complete | | |
+------------------+-----------------------+---------------------+
R2TSN/DataSN Use Examples
Output (write) data DataSN/R2TSN Example
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+------------------+-----------------------+---------------------+
|Initiator Function| PDU Type & Content | Target Function |
+------------------+-----------------------+---------------------+
| Command request |SCSI Command (WRITE)>>>| Receive command |
| (write) | | and queue it |
+------------------+-----------------------+---------------------+
| | | Process old commands|
+------------------+-----------------------+---------------------+
| | <<< R2T | Ready for data |
| | R2TSN = 0 | |
+------------------+-----------------------+---------------------+
| | <<< R2T | Ready for more data |
| | R2TSN = 1 | |
+------------------+-----------------------+---------------------+
| Send Data | SCSI Data-out >>> | Receive Data |
| for R2TSN 0 | DataSN = 0, F=0 | |
+------------------+-----------------------+---------------------+
| Send Data | SCSI Data-out >>> | Receive Data |
| for R2TSN 0 | DataSN = 1, F=1 | |
+------------------+-----------------------+---------------------+
| Send Data | SCSI Data >>> | Receive Data |
| for R2TSN 1 | DataSN = 0, F=1 | |
+------------------+-----------------------+---------------------+
| | <<< SCSI Response |Send Status and Sense|
| | ExpDataSN = 0 | |
+------------------+-----------------------+---------------------+
| Command Complete | | |
+------------------+-----------------------+---------------------+
Input (read) data DataSN Example
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+------------------+-----------------------+---------------------+
|Initiator Function| PDU Type | Target Function |
+------------------+-----------------------+---------------------+
| Command request |SCSI Command (READ)>>> | |
| (read) | | |
+------------------+-----------------------+---------------------+
| | |Prepare Data Transfer|
+------------------+-----------------------+---------------------+
| Receive Data | <<< SCSI Data-in | Send Data |
| | DataSN = 0, F=0 | |
+------------------+-----------------------+---------------------+
| Receive Data | <<< SCSI Data-in | Send Data |
| | DataSN = 1, F=0 | |
+------------------+-----------------------+---------------------+
| Receive Data | <<< SCSI Data-in | Send Data |
| | DataSN = 2, F=1 | |
+------------------+-----------------------+---------------------+
| | <<< SCSI Response |Send Status and Sense|
| | ExpDataSN = 3 | |
+------------------+-----------------------+---------------------+
| Command Complete | | |
+------------------+-----------------------+---------------------+
Bidirectional DataSN Example
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+------------------+-----------------------+---------------------+
|Initiator Function| PDU Type | Target Function |
+------------------+-----------------------+---------------------+
| Command request |SCSI Command >>> | |
| (Read-Write) | Read-Write | |
+------------------+-----------------------+---------------------+
| | | Process old commands|
+------------------+-----------------------+---------------------+
| | <<< R2T | Ready to process |
| | R2TSN = 0 | WRITE command |
+------------------+-----------------------+---------------------+
| * Receive Data | <<< SCSI Data-in | Send Data |
| | DataSN = 0, F=0 | |
+------------------+-----------------------+---------------------+
| * Receive Data | <<< SCSI Data-in | Send Data |
| | DataSN = 1, F=1 | |
+------------------+-----------------------+---------------------+
| * Send Data | SCSI Data-out >>> | Receive Data |
| for R2TSN 0 | DataSN = 0, F=1 | |
+------------------+-----------------------+---------------------+
| | <<< SCSI Response |Send Status and Sense|
| | ExpDataSN = 2 | |
+------------------+-----------------------+---------------------+
| Command Complete | | |
+------------------+-----------------------+---------------------+
*) Send data and Receive Data may be transferred simultaneously as
in an atomic Read-Old-Write-New or sequentially as in an atomic
Read-Update-Write (in the latter case the R2T may follow the
received data).
Unsolicited and immediate output (write) data with DataSN Example
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+------------------+-----------------------+---------------------+
|Initiator Function| PDU Type & Content | Target Function |
+------------------+-----------------------+---------------------+
| Command request |SCSI Command (WRITE)>>>| Receive command |
| (write) |F=0 | and data |
|+ immediate data | | and queue it |
+------------------+-----------------------+---------------------+
| Send Unsolicited | SCSI Write Data >>> | Receive more Data |
| Data | DataSN = 0, F=1 | |
+------------------+-----------------------+---------------------+
| | | Process old commands|
+------------------+-----------------------+---------------------+
| | <<< R2T | Ready for more data |
| | R2TSN = 0 | |
+------------------+-----------------------+---------------------+
| Send Data | SCSI Write Data >>> | Receive Data |
| for R2TSN 0 | DataSN = 0, F=1 | |
+------------------+-----------------------+---------------------+
| | <<< SCSI Response |Send Status and Sense|
| | | |
+------------------+-----------------------+---------------------+
| Command Complete | | |
+------------------+-----------------------+---------------------+
CRC Examples
N.B. all Values are Hexadecimal
32 bytes of zeroes:
Byte: 0 1 2 3
0: 00 00 00 00
...
28: 00 00 00 00
CRC: aa 36 91 8a
32 bytes of ones:
Byte: 0 1 2 3
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0: ff ff ff ff
...
28: ff ff ff ff
CRC: 43 ab a8 62
32 bytes of incrementing 00..1f:
Byte: 0 1 2 3
0: 00 01 02 03
...
28: 1c 1d 1e 1f
CRC: 4e 79 dd 46
32 bytes of decrementing 1f..00:
Byte: 0 1 2 3
0: 1f 1e 1d 1c
...
28: 03 02 01 00
CRC: 5c db 3f 11
An iSCSI - SCSI Read (10) Command PDU
Byte: 0 1 2 3
0: 01 c0 00 00
4: 00 00 00 00
8: 00 00 00 00
12: 00 00 00 00
16: 14 00 00 00
20: 00 00 04 00
24: 00 00 00 14
28: 00 00 00 18
32: 28 00 00 00
36: 00 00 00 00
40: 02 00 00 00
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44: 00 00 00 00
CRC: 56 3a 96 d9
Appendix B. Login Phase Examples
In the first example, the initiator and target authenticate each
other via Kerberos:
I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=KRB5,SRP,None
T-> Login (CSG,NSG=0,0 T=0)
AuthMethod=KRB5
I-> Login (CSG,NSG=0,1 T=1)
KRB_AP_REQ=<krb_ap_req>
(krb_ap_req contains the Kerberos V5 ticket and authenticator with
MUTUAL-REQUIRED set in the ap-options field)
If the authentication is successful, the target proceeds with:
T-> Login (CSG,NSG=0,1 T=1)
KRB_AP_REP=<krb_ap_rep>
(krb_ap_rep is the Kerberos V5 mutual authentication reply)
If the authentication is successful, the initiator may proceed
with:
I-> Login (CSG,NSG=1,0 T=0) FirstBurstLength=8192
T-> Login (CSG,NSG=1,0 T=0) FirstBurstLength=4096
MaxBurstLength=8192
I-> Login (CSG,NSG=1,0 T=0) MaxBurstLength=8192
... more iSCSI Operational Parameters
T-> Login (CSG,NSG=1,0 T=0)
... more iSCSI Operational Parameters
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And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
If the initiator's authentication by the target is not successful,
the target responds with:
T-> Login "login reject"
instead of the Login KRB_AP_REP message, and terminates the
connection.
If the target's authentication by the initiator is not successful,
the initiator terminates the connection (without responding to the
Login KRB_AP_REP message).
In the next example only the initiator is authenticated by the
target via Kerberos:
I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=SRP,KRB5,None
T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=KRB5
I-> Login (CSG,NSG=0,1 T=1)
KRB_AP_REQ=krb_ap_req
(MUTUAL-REQUIRED not set in the ap-options field of krb_ap_req)
If the authentication is successful, the target proceeds with:
T-> Login (CSG,NSG=0,1 T=1)
I-> Login (CSG,NSG=1,0 T=0)
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... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
. . .
T-> Login (CSG,NSG=1,3 T=1)"login accept"
In the next example, the initiator and target authenticate each
other via SRP:
I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=KRB5,SRP,None
T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=SRP
I-> Login (CSG,NSG=0,0 T=0)
SRP_U=<user>
TargetAuth=Yes
T-> Login (CSG,NSG=0,0 T=0)
SRP_N=<N>
SRP_g=<g>
SRP_s=<s>
I-> Login (CSG,NSG=0,0 T=0)
SRP_A=<A>
T-> Login (CSG,NSG=0,0 T=0)
SRP_B=<B>
I-> Login (CSG,NSG=0,1 T=1)
SRP_M=<M>
If the initiator authentication is successful, the target
proceeds:
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T-> Login (CSG,NSG=0,1 T=1)
SRP_HM=<H(A | M | K)>
Where N, g, s, A, B, M, and H(A | M | K) are defined in
[RFC2945].
If the target authentication is not successful, the initiator
terminates the connection; otherwise, it proceeds.
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
If the initiator authentication is not successful, the target
responds with:
T-> Login "login reject"
Instead of the T-> Login SRP_HM=<H(A | M | K)> message and
terminates the connection.
In the next example, only the initiator is authenticated by the
target via SRP:
I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=KRB5,SRP,None
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T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=SRP
I-> Login (CSG,NSG=0,0 T=0)
SRP_U=<user>
TargetAuth=No
T-> Login (CSG,NSG=0,0 T=0)
SRP_N=<N>
SRP_g=<g>
SRP_s=<s>
I-> Login (CSG,NSG=0,0 T=0)
SRP_A=<A>
T-> Login (CSG,NSG=0,0 T=0)
SRP_B=<B>
I-> Login (CSG,NSG=0,1 T=1)
SRP_M=<M>
If the initiator authentication is successful, the target
proceeds:
T-> Login (CSG,NSG=0,1 T=1)
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
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And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
In the next example the initiator and target authenticate each
other via CHAP:
I-> Login (CSG,NSG=0,0 T=0)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=KRB5,CHAP,None
T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=CHAP
I-> Login (CSG,NSG=0,0 T=0)
CHAP_A=<A1,A2>
T-> Login (CSG,NSG=0,0 T=0)
CHAP_A=<A1>
CHAP_I=<I>
CHAP_C=<C>
I-> Login (CSG,NSG=0,1 T=1)
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CHAP_N=<N>
CHAP_R=<R>
CHAP_I=<I>
CHAP_C=<C>
If the initiator authentication is successful, the target
proceeds:
T-> Login (CSG,NSG=0,1 T=1)
CHAP_N=<N>
CHAP_R=<R>
If the target authentication is not successful, the initiator
aborts the connection; otherwise, it proceeds.
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
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T-> Login (CSG,NSG=1,3 T=1) "login accept"
If the initiator authentication is not successful, the target
responds with:
T-> Login "login reject"
Instead of the Login CHAP_R=<response> "proceed and change
stage" message and terminates the connection.
In the next example, only the initiator is authenticated by the
target via CHAP:
I-> Login (CSG,NSG=0,1 T=0)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=KRB5,CHAP,None
T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=CHAP
I-> Login (CSG,NSG=0,0 T=0)
CHAP_A=<A1,A2>
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T-> Login (CSG,NSG=0,0 T=0)
CHAP_A=<A1>
CHAP_I=<I>
CHAP_C=<C>
I-> Login (CSG,NSG=0,1 T=1)
CHAP_N=<N>
CHAP_R=<R>
If the initiator authentication is successful, the target
proceeds:
T-> Login (CSG,NSG=0,1 T=1)
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
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T-> Login (CSG,NSG=1,3 T=1) "login accept"
In the next example, the initiator does not offer any security
parameters. It therefore may offer iSCSI parameters on the Login
PDU with the T bit set to 1, and the target may respond with a
final Login Response PDU immediately:
I-> Login (CSG,NSG=1,3 T=1)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
... iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
... ISCSI parameters
In the next example, the initiator does offer security
parameters on the Login PDU, but the target does not choose
any (i.e., chooses the "None" values):
I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=KRB5,SRP,None
T-> Login-PR (CSG,NSG=0,1 T=1)
AuthMethod=None
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I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
Appendix C. SendTargets Operation
The text in this Appendix is a normative part of this document.
To reduce the amount of configuration required on an initiator,
iSCSI provides the SendTargets text request. The initiator uses
the SendTargets request to get a list of targets to which it may
have access, as well as the list of addresses (IP address and TCP
port) on which these targets may be accessed.
To make use of SendTargets, an initiator must first establish one
of two types of sessions. If the initiator establishes
the session using the key "SessionType=Discovery", the session is
a discovery session, and a target name does not need to be
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specified. Otherwise, the session is a normal, operational
session. The SendTargets command MUST only be sent during the
Full Feature Phase of a normal or discovery session.
A system that contains targets MUST support discovery sessions on
each of its iSCSI IP address-port pairs, and MUST support the
SendTargets command on the discovery session. In a discovery
session, a target MUST return all path information (IP address-
port pairs and portal group tags) for the targets on the target
network entity which the requesting initiator is authorized to
access.
A target MUST support the SendTargets command on operational
sessions; these will only return path information about the target
to which the session is connected, and do not need to return
information about other target names that may be defined in the
responding system.
An initiator MAY make use of the SendTargets as it sees fit.
A SendTargets command consists of a single Text request PDU.
This PDU contains exactly one text key and value. The text key
MUST be SendTargets. The expected response depends upon the
value, as well as whether the session is a discovery or
operational session.
The value must be one of:
All
The initiator is requesting that information on all relevant
targets known to the implementation be returned. This value
MUST be supported on a discovery session, and MUST NOT be
supported on an operational session.
<iSCSI-target-name>
If an iSCSI target name is specified, the session should
respond with addresses for only the named target, if
possible. This value MUST be supported on discovery
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sessions. A discovery session MUST be capable of returning
addresses for those targets that would have been returned
had value=All been designated.
<nothing>
The session should only respond with addresses for the target
to which the session is logged in. This MUST be supported
on operational sessions, and MUST NOT return targets other
than the one to which the session is logged in.
The response to this command is a text response that contains a
list of zero or more targets and, optionally, their addresses.
Each target is returned as a target record. A target record
begins with the TargetName text key, followed by a list of
TargetAddress text keys, and bounded by the end of the text
response or the next TargetName key, which begins a new record.
No text keys other than TargetName and TargetAddress are permitted
within a SendTargets response.
For the format of the TargetName, see Section 13.4.
A discovery session MAY respond to a SendTargets request with its
complete list of targets, or with a list of targets that is based
on the name of the initiator logged in to the session.
A SendTargets response MUST NOT contain target names if there are
no targets for the requesting initiator to access.
Each target record returned includes zero or more TargetAddress
fields.
Each target record starts with one text key of the form:
TargetName=<target-name-goes-here>
Followed by zero or more address keys of the form:
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TargetAddress=<hostname-or-ipaddress>[:<tcp-port>],<portal-
group-tag>
The hostname-or-ipaddress contains a domain name, IPv4 address, or
IPv6 address ([RFC4291]), as specified for the TargetAddress key.
A hostname-or-ipaddress duplicated in TargetAddress responses for
a given node (the port is absent or equal) would probably indicate
that multiple address families are in use at once (IPv6 and IPv4).
Each TargetAddress belongs to a portal group, identified by its
numeric portal group tag (as in Section 13.9). The iSCSI target
name, together with this tag, constitutes the SCSI port
identifier; the tag only needs to be unique within a given
target's name list of addresses.
Multiple-connection sessions can span iSCSI addresses that belong
to the same portal group.
Multiple-connection sessions cannot span iSCSI addresses that
belong to different portal groups.
If a SendTargets response reports an iSCSI address for a target,
it SHOULD also report all other addresses in its portal group in
the same response.
A SendTargets text response can be longer than a single Text
Response PDU, and makes use of the long text responses as
specified.
After obtaining a list of targets from the discovery target
session,
an iSCSI initiator may initiate new sessions to log in to the
discovered targets for full operation. The initiator MAY keep the
discovery session open, and MAY send subsequent SendTargets
commands to discover new targets.
Examples:
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This example is the SendTargets response from a single target that
has no other interface ports.
Initiator sends text request that contains:
SendTargets=All
Target sends a text response that contains:
TargetName=iqn.1993-11.com.example:diskarray.sn.8675309
All the target had to return in the simple case was the target
name. It is assumed by the initiator that the IP address and TCP
port for this target are the same as used on the current
connection to the default iSCSI target.
The next example has two internal iSCSI targets, each accessible
via two different ports with different IP addresses. The
following is the text response:
TargetName=iqn.1993-11.com.example:diskarray.sn.8675309
TargetAddress=10.1.0.45:3000,1
TargetAddress=10.1.1.45:3000,2
TargetName=iqn.1993-11.com.example:diskarray.sn.1234567
TargetAddress=10.1.0.45:3000,1
TargetAddress=10.1.1.45:3000,2
Both targets share both addresses; the multiple addresses are
likely used to provide multi-path support. The initiator may
connect to either target name on either address. Each of the
addresses has its own portal group tag; they do not support
spanning multiple-connection sessions with each other. Keep in
mind that the portal group tags for the two named targets are
independent of one another; portal group "1" on the first target
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is not necessarily the same as portal group "1" on the second
target.
In the above example, a DNS host name or an IPv6 address could
have been returned instead of an IPv4 address.
The next text response shows a target that supports spanning
sessions across multiple addresses, and further illustrates the
use of the portal group tags:
TargetName=iqn.1993-11.com.example:diskarray.sn.8675309
TargetAddress=10.1.0.45:3000,1
TargetAddress=10.1.1.46:3000,1
TargetAddress=10.1.0.47:3000,2
TargetAddress=10.1.1.48:3000,2
TargetAddress=10.1.1.49:3000,3
In this example, any of the target addresses can be used to reach
the same target. A single-connection session can be established
to any of these TCP addresses. A multiple-connection session
could span addresses .45 and .46 or .47 and .48, but cannot span
any other combination. A TargetAddress with its own tag (.49)
cannot be combined with any other address within the same session.
This SendTargets response does not indicate whether .49 supports
multiple connections per session; it is communicated via the
MaxConnections text key upon login to the target.
Appendix D. Algorithmic Presentation of Error Recovery Classes
This Appendix illustrates the error recovery classes using a
pseudo-programming-language. The procedure names are chosen to be
obvious to most implementers. Each of the recovery classes
described has initiator procedures as well as target procedures.
These algorithms focus on outlining the mechanics of error
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recovery classes, and do not exhaustively describe all other
aspects/cases. Examples of this approach are:
- Handling for only certain Opcode types is shown.
- Only certain reason codes (e.g., Recovery in Logout command)
are outlined.
- Resultant cases, such as recovery of Synchronization on a
header digest error are considered out-of-scope in these
algorithms. In this particular example, a header digest
error may lead to connection recovery if some type of sync
and steering layer is not implemented.
These algorithms strive to convey the iSCSI error recovery
concepts in the simplest terms, and are not designed to be
optimal.
D.1. General Data Structure and Procedure Description
This Section defines the procedures and data structures that are
commonly used by all the error recovery algorithms. The structures
may not be the exhaustive representations of what is required for
a typical implementation.
Data structure definitions -
struct TransferContext {
int TargetTransferTag;
int ExpectedDataSN;
};
struct TCB { /* task control block */
Boolean SoFarInOrder;
int ExpectedDataSN; /* used for both R2Ts, and Data */
int MissingDataSNList[MaxMissingDPDU];
Boolean FbitReceived;
Boolean StatusXferd;
Boolean CurrentlyAllegiant;
int ActiveR2Ts;
int Response;
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char *Reason;
struct TransferContext
TransferContextList[MaxOutStandingR2T];
int InitiatorTaskTag;
int CmdSN;
int SNACK_Tag;
};
struct Connection {
struct Session SessionReference;
Boolean SoFarInOrder;
int CID;
int State;
int CurrentTimeout;
int ExpectedStatSN;
int MissingStatSNList[MaxMissingSPDU];
Boolean PerformConnectionCleanup;
};
struct Session {
int NumConnections;
int CmdSN;
int Maxconnections;
int ErrorRecoveryLevel;
struct iSCSIEndpoint OtherEndInfo;
struct Connection ConnectionList[MaxSupportedConns];
};
Procedure descriptions -
Receive-a-In-PDU(transport connection, inbound PDU);
check-basic-validity(inbound PDU);
Start-Timer(timeout handler, argument, timeout value);
Build-And-Send-Reject(transport connection, bad PDU, reason
code);
D.2. Within-command Error Recovery Algorithms
D.2.1. Procedure Descriptions
Recover-Data-if-Possible(last required DataSN, task control
block);
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Build-And-Send-DSnack(task control block);
Build-And-Send-RDSnack(task control block);
Build-And-Send-Abort(task control block);
SCSI-Task-Completion(task control block);
Build-And-Send-A-Data-Burst(transport connection, data-
descriptor,
task control
block);
Build-And-Send-R2T(transport connection, data-descriptor,
task control
block);
Build-And-Send-Status(transport connection, task control block);
Transfer-Context-Timeout-Handler(transfer context);
Notes:
- One procedure used in this Section: Handle-Status-SNACK-
request is defined in Within-connection recovery algorithms.
- The Response processing pseudo-code, shown in the target
algorithms, applies to all solicited PDUs that carry StatSN
- SCSI Response, Text Response etc.
D.2.2. Initiator Algorithms
Recover-Data-if-Possible(LastRequiredDataSN, TCB)
{
if (operational ErrorRecoveryLevel > 0) {
if (# of missing PDUs is trackable) {
Note the missing DataSNs in TCB.
if (the task spanned a change in
MaxRecvDataSegmentLength) {
if (TCB.StatusXferd is TRUE)
drop the status PDU;
Build-And-Send-RDSnack(TCB);
} else {
Build-And-Send-DSnack(TCB);
}
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} else {
TCB.Reason = "Protocol service CRC error";
}
} else {
TCB.Reason = "Protocol service CRC error";
}
if (TCB.Reason == "Protocol service CRC error") {
Clear the missing PDU list in the TCB.
if (TCB.StatusXferd is not TRUE)
Build-And-Send-Abort(TCB);
}
}
Receive-a-In-PDU(Connection, CurrentPDU)
{
check-basic-validity(CurrentPDU);
if (Header-Digest-Bad) discard, return;
Retrieve TCB for CurrentPDU.InitiatorTaskTag.
if ((CurrentPDU.type == Data)
or (CurrentPDU.type = R2T)) {
if (Data-Digest-Bad for Data) {
send-data-SNACK = TRUE;
LastRequiredDataSN = CurrentPDU.DataSN;
} else {
if (TCB.SoFarInOrder = TRUE) {
if (current DataSN is expected) {
Increment TCB.ExpectedDataSN.
} else {
TCB.SoFarInOrder = FALSE;
send-data-SNACK = TRUE;
}
} else {
if (current DataSN was considered
missing) {
remove current DataSN from missing
PDU list.
} else if (current DataSN is higher than
expected) {
send-data-SNACK = TRUE;
} else {
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discard, return;
}
Adjust TCB.ExpectedDataSN if
appropriate.
}
LastRequiredDataSN = CurrentPDU.DataSN - 1;
}
if (send-data-SNACK is TRUE and
task is not already considered failed) {
Recover-Data-if-Possible(LastRequiredDataSN, TCB);
}
if (missing data PDU list is empty) {
TCB.SoFarInOrder = TRUE;
}
if (CurrentPDU.type == R2T) {
Increment ActiveR2Ts for this task.
Create a data-descriptor for the data burst.
Build-And-Send-A-Data-Burst(Connection, data-
descriptor,
TCB);
}
} else if (CurrentPDU.type == Response) {
if (Data-Digest-Bad) {
send-status-SNACK = TRUE;
} else {
TCB.StatusXferd = TRUE;
Store the status information in TCB.
if (ExpDataSN does not match) {
TCB.SoFarInOrder = FALSE;
Recover-Data-if-Possible(current DataSN, TCB);
}
if (missing data PDU list is empty) {
TCB.SoFarInOrder = TRUE;
}
}
} else { /* REST UNRELATED TO WITHIN-COMMAND-RECOVERY, NOT
SHOWN */
}
if ((TCB.SoFarInOrder == TRUE) and
(TCB.StatusXferd == TRUE)) {
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SCSI-Task-Completion(TCB);
}
}
D.2.3. Target Algorithms
Receive-a-In-PDU(Connection, CurrentPDU)
{
check-basic-validity(CurrentPDU);
if (Header-Digest-Bad) discard, return;
Retrieve TCB for CurrentPDU.InitiatorTaskTag.
if (CurrentPDU.type == Data) {
Retrieve TContext from CurrentPDU.TargetTransferTag;
if (Data-Digest-Bad) {
Build-And-Send-Reject(Connection, CurrentPDU,
Payload-Digest-Error);
Note the missing data PDUs in MissingDataRange[].
send-recovery-R2T = TRUE;
} else {
if (current DataSN is not expected) {
Note the missing data PDUs in MissingDataRange[].
send-recovery-R2T = TRUE;
}
if (CurrentPDU.Fbit == TRUE) {
if (current PDU is solicited) {
Decrement TCB.ActiveR2Ts.
}
if ((current PDU is unsolicited and
data received is less than I/O length and
data received is less than
FirstBurstLength)
or (current PDU is solicited and the length of
this burst is less than expected)) {
send-recovery-R2T = TRUE;
Note the missing data in MissingDataRange[].
}
}
}
Increment TContext.ExpectedDataSN.
if (send-recovery-R2T is TRUE and
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task is not already considered failed) {
if (operational ErrorRecoveryLevel > 0) {
Increment TCB.ActiveR2Ts.
Create a data-descriptor for the data burst
from MissingDataRange.
Build-And-Send-R2T(Connection, data-descriptor,
TCB);
} else {
if (current PDU is the last unsolicited)
TCB.Reason = "Not enough unsolicited data";
else
TCB.Reason = "Protocol service CRC error";
}
}
if (TCB.ActiveR2Ts == 0) {
Build-And-Send-Status(Connection, TCB);
}
} else if (CurrentPDU.type == SNACK) {
snack-failure = FALSE;
if (operational ErrorRecoveryLevel > 0) {
if (CurrentPDU.type == Data/R2T) {
if (the request is satisfiable) {
if (request for Data) {
Create a data-descriptor for the data burst
from BegRun and RunLength.
Build-And-Send-A-Data-Burst(Connection,
data-descriptor, TCB);
} else { /* R2T */
Create a data-descriptor for the data burst
from BegRun and RunLength.
Build-And-Send-R2T(Connection, data-
descriptor,
TCB);
}
} else {
snack-failure = TRUE;
}
} else if (CurrentPDU.type == status) {
Handle-Status-SNACK-request(Connection,
CurrentPDU);
} else if (CurrentPDU.type == DataACK) {
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Consider all data upto CurrentPDU.BegRun as
acknowledged.
Free up the retransmission resources for that data.
} else if (CurrentPDU.type == R-Data SNACK) {
Create a data descriptor for a data burst
covering
all unacknowledged data.
Build-And-Send-A-Data-Burst(Connection,
data-descriptor, TCB);
TCB.SNACK_Tag = CurrentPDU.SNACK_Tag;
if (there's no more data to send) {
Build-And-Send-Status(Connection, TCB);
}
}
} else { /* operational ErrorRecoveryLevel = 0 */
snack-failure = TRUE;
}
if (snack-failure == TRUE) {
Build-And-Send-Reject(Connection, CurrentPDU,
SNACK-Reject);
if (TCB.StatusXferd != TRUE) {
TCB.Reason = "SNACK Rejected";
Build-And-Send-Status(Connection, TCB);
}
}
} else { /* REST UNRELATED TO WITHIN-COMMAND-RECOVERY, NOT
SHOWN */
}
}
Transfer-Context-Timeout-Handler(TContext)
{
Retrieve TCB and Connection from TContext.
Decrement TCB.ActiveR2Ts.
if (operational ErrorRecoveryLevel > 0 and
task is not already considered failed) {
Note the missing data PDUs in MissingDataRange[].
Create a data-descriptor for the data burst
from MissingDataRange[].
Build-And-Send-R2T(Connection, data-descriptor, TCB);
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} else {
TCB.Reason = "Protocol service CRC error";
if (TCB.ActiveR2Ts = 0) {
Build-And-Send-Status(Connection, TCB);
}
}
}
D.3. Within-connection Recovery Algorithms
D.3.1. Procedure Descriptions
Procedure descriptions:
Recover-Status-if-Possible(transport connection,
currently received PDU);
Evaluate-a-StatSN(transport connection, currently received PDU);
Retransmit-Command-if-Possible(transport connection, CmdSN);
Build-And-Send-SSnack(transport connection);
Build-And-Send-Command(transport connection, task control
block);
Command-Acknowledge-Timeout-Handler(task control block);
Status-Expect-Timeout-Handler(transport connection);
Build-And-Send-Nop-Out(transport connection);
Handle-Status-SNACK-request(transport connection, status SNACK
PDU);
Retransmit-Status-Burst(status SNACK, task control block);
Is-Acknowledged(beginning StatSN, run length);
Implementation-specific tunables:
InitiatorProactiveSNACKEnabled
Notes:
- The initiator algorithms only deal with unsolicited Nop-In
PDUs for generating status SNACKs. A solicited Nop-In PDU
has an assigned StatSN, which, when out of order, could
trigger the out of order StatSN handling in Within-command
algorithms, again leading to Recover-Status-if-Possible.
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- The pseudo-code shown may result in the retransmission of
unacknowledged commands in more cases than necessary. This
will not, however, affect the correctness of the operation
because the target is required to discard the duplicate
CmdSNs.
- The procedure Build-And-Send-Async is defined in the
Connection recovery algorithms.
- The procedure Status-Expect-Timeout-Handler describes how
initiators may proactively attempt to retrieve the Status if
they so choose. This procedure is assumed to be triggered
much before the standard ULP timeout.
D.3.2. Initiator Algorithms
Recover-Status-if-Possible(Connection, CurrentPDU)
{
if ((Connection.state == LOGGED_IN) and
connection is not already considered
failed) {
if (operational ErrorRecoveryLevel > 0) {
if (# of missing PDUs is trackable) {
Note the missing StatSNs in Connection
that were not already requested with SNACK;
Build-And-Send-SSnack(Connection);
} else {
Connection.PerformConnectionCleanup = TRUE;
}
} else {
Connection.PerformConnectionCleanup = TRUE;
}
if (Connection.PerformConnectionCleanup == TRUE) {
Start-Timer(Connection-Cleanup-Handler, Connection,
0);
}
}
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}
Retransmit-Command-if-Possible(Connection, CmdSN)
{
if (operational ErrorRecoveryLevel > 0) {
Retrieve the InitiatorTaskTag, and thus TCB for the
CmdSN.
Build-And-Send-Command(Connection, TCB);
}
}
Evaluate-a-StatSN(Connection, CurrentPDU)
{
send-status-SNACK = FALSE;
if (Connection.SoFarInOrder == TRUE) {
if (current StatSN is the expected) {
Increment Connection.ExpectedStatSN.
} else {
Connection.SoFarInOrder = FALSE;
send-status-SNACK = TRUE;
}
} else {
if (current StatSN was considered missing) {
remove current StatSN from the missing list.
} else {
if (current StatSN is higher than expected){
send-status-SNACK = TRUE;
} else {
send-status-SNACK = FALSE;
discard the PDU;
}
}
Adjust Connection.ExpectedStatSN if appropriate.
if (missing StatSN list is empty) {
Connection.SoFarInOrder = TRUE;
}
}
return send-status-SNACK;
}
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Receive-a-In-PDU(Connection, CurrentPDU)
{
check-basic-validity(CurrentPDU);
if (Header-Digest-Bad) discard, return;
Retrieve TCB for CurrentPDU.InitiatorTaskTag.
if (CurrentPDU.type == Nop-In) {
if (the PDU is unsolicited) {
if (current StatSN is not expected) {
Recover-Status-if-Possible(Connection,
CurrentPDU);
}
if (current ExpCmdSN is not Session.CmdSN) {
Retransmit-Command-if-Possible(Connection,
CurrentPDU.ExpCmdSN);
}
}
} else if (CurrentPDU.type == Reject) {
if (it is a data digest error on immediate data) {
Retransmit-Command-if-Possible(Connection,
CurrentPDU.BadPDUHeader.CmdSN);
}
} else if (CurrentPDU.type == Response) {
send-status-SNACK = Evaluate-a-StatSN(Connection,
CurrentPDU);
if (send-status-SNACK == TRUE)
Recover-Status-if-Possible(Connection, CurrentPDU);
} else { /* REST UNRELATED TO WITHIN-CONNECTION-RECOVERY,
* NOT SHOWN */
}
}
Command-Acknowledge-Timeout-Handler(TCB)
{
Retrieve the Connection for TCB.
Retransmit-Command-if-Possible(Connection, TCB.CmdSN);
}
Status-Expect-Timeout-Handler(Connection)
{
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if (operational ErrorRecoveryLevel > 0) {
Build-And-Send-Nop-Out(Connection);
} else if (InitiatorProactiveSNACKEnabled){
if ((Connection.state == LOGGED_IN) and
connection is not already considered
failed) {
Build-And-Send-SSnack(Connection);
}
}
}
D.3.3.Target Algorithms
Handle-Status-SNACK-request(Connection, CurrentPDU)
{
if (operational ErrorRecoveryLevel > 0) {
if (request for an acknowledged run) {
Build-And-Send-Reject(Connection, CurrentPDU,
Protocol-Error);
} else if (request for an untransmitted run) {
discard, return;
} else {
Retransmit-Status-Burst(CurrentPDU, TCB);
}
} else {
Build-And-Send-Async(Connection, DroppedConnection,
DefaultTime2Wait,
DefaultTime2Retain);
}
}
D.4. Connection Recovery Algorithms
D.4.1. Procedure Descriptions
Build-And-Send-Async(transport connection, reason code,
minimum time, maximum time);
Pick-A-Logged-In-Connection(session);
Build-And-Send-Logout(transport connection, logout connection
identifier, reason code);
PerformImplicitLogout(transport connection, logout connection
identifier, target information);
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PerformLogin(transport connection, target information);
CreateNewTransportConnection(target information);
Build-And-Send-Command(transport connection, task control
block);
Connection-Cleanup-Handler(transport connection);
Connection-Resource-Timeout-Handler(transport connection);
Quiesce-And-Prepare-for-New-Allegiance(session, task control
block);
Build-And-Send-Logout-Response(transport connection,
CID of connection in recovery, reason
code);
Build-And-Send-TaskMgmt-Response(transport connection,
task mgmt command PDU, response code);
Establish-New-Allegiance(task control block, transport
connection);
Schedule-Command-To-Continue(task control block);
Notes:
- Transport exception conditions, such as unexpected
connection termination, connection reset, and hung
connection while the connection is in the full-feature
phase, are all assumed to be asynchronously signaled to the
iSCSI layer using the Transport_Exception_Handler procedure.
D.4.2. Initiator Algorithms
Receive-a-In-PDU(Connection, CurrentPDU)
{
check-basic-validity(CurrentPDU);
if (Header-Digest-Bad) discard, return;
Retrieve TCB from CurrentPDU.InitiatorTaskTag.
if (CurrentPDU.type == Async) {
if (CurrentPDU.AsyncEvent == ConnectionDropped) {
Retrieve the AffectedConnection for
CurrentPDU.Parameter1.
AffectedConnection.CurrentTimeout =
CurrentPDU.Parameter3;
AffectedConnection.State = CLEANUP_WAIT;
Start-Timer(Connection-Cleanup-Handler,
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AffectedConnection,
CurrentPDU.Parameter2);
} else if (CurrentPDU.AsyncEvent == LogoutRequest)) {
AffectedConnection = Connection;
AffectedConnection.State = LOGOUT_REQUESTED;
AffectedConnection.PerformConnectionCleanup = TRUE;
AffectedConnection.CurrentTimeout =
CurrentPDU.Parameter3;
Start-Timer(Connection-Cleanup-Handler,
AffectedConnection, 0);
} else if (CurrentPDU.AsyncEvent == SessionDropped)) {
for (each Connection) {
Connection.State = CLEANUP_WAIT;
Connection.CurrentTimeout = CurrentPDU.Parameter3;
Start-Timer(Connection-Cleanup-Handler,
Connection, CurrentPDU.Parameter2);
}
Session.state = FAILED;
}
} else if (CurrentPDU.type == LogoutResponse) {
Retrieve the CleanupConnection for CurrentPDU.CID.
if (CurrentPDU.Response = failure) {
CleanupConnection.State = CLEANUP_WAIT;
} else {
CleanupConnection.State = FREE;
}
} else if (CurrentPDU.type == LoginResponse) {
if (this is a response to an implicit Logout) {
Retrieve the CleanupConnection.
if (successful) {
CleanupConnection.State = FREE;
Connection.State = LOGGED_IN;
} else {
CleanupConnection.State = CLEANUP_WAIT;
DestroyTransportConnection(Connection);
}
}
} else { /* REST UNRELATED TO CONNECTION-RECOVERY,
* NOT SHOWN */
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}
if (CleanupConnection.State == FREE) {
for (each command that was active on CleanupConnection) {
/* Establish new connection allegiance */
NewConnection = Pick-A-Logged-In-
Connection(Session);
Build-And-Send-Command(NewConnection, TCB);
}
}
}
Connection-Cleanup-Handler(Connection)
{
Retrieve Session from Connection.
if (Connection can still exchange iSCSI PDUs) {
NewConnection = Connection;
} else {
Start-Timer(Connection-Resource-Timeout-Handler,
Connection, Connection.CurrentTimeout);
if (there are other logged-in connections) {
NewConnection = Pick-A-Logged-In-
Connection(Session);
} else {
NewConnection =
CreateTransportConnection(Session.OtherEndInfo);
Initiate an implicit Logout on NewConnection for
Connection.CID.
return;
}
}
Build-And-Send-Logout(NewConnection, Connection.CID,
RecoveryRemove);
}
Transport_Exception_Handler(Connection)
{
Connection.PerformConnectionCleanup = TRUE;
if (the event is an unexpected transport disconnect) {
Connection.State = CLEANUP_WAIT;
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Connection.CurrentTimeout = DefaultTime2Retain;
Start-Timer(Connection-Cleanup-Handler, Connection,
DefaultTime2Wait);
} else {
Connection.State = FREE;
}
}
D.4.3. Target Algorithms
Receive-a-In-PDU(Connection, CurrentPDU)
{
check-basic-validity(CurrentPDU);
if (Header-Digest-Bad) discard, return;
else if (Data-Digest-Bad) {
Build-And-Send-Reject(Connection, CurrentPDU,
Payload-Digest-Error);
discard, return;
}
Retrieve TCB and Session.
if (CurrentPDU.type == Logout) {
if (CurrentPDU.ReasonCode = RecoveryRemove) {
Retrieve the CleanupConnection from CurrentPDU.CID).
for (each command active on CleanupConnection) {
Quiesce-And-Prepare-for-New-Allegiance(Session,
TCB);
TCB.CurrentlyAllegiant = FALSE;
}
Cleanup-Connection-State(CleanupConnection);
if ((quiescing successful) and (cleanup successful))
{
Build-And-Send-Logout-Response(Connection,
CleanupConnection.CID,
Success);
} else {
Build-And-Send-Logout-Response(Connection,
CleanupConnection.CID,
Failure);
}
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}
} else if ((CurrentPDU.type == Login) and
operational ErrorRecoveryLevel == 2) {
Retrieve the CleanupConnection from CurrentPDU.CID).
for (each command active on CleanupConnection) {
Quiesce-And-Prepare-for-New-Allegiance(Session,
TCB);
TCB.CurrentlyAllegiant = FALSE;
}
Cleanup-Connection-State(CleanupConnection);
if ((quiescing successful) and (cleanup successful))
{
Continue with the rest of the Login processing;
} else {
Build-And-Send-Login-Response(Connection,
CleanupConnection.CID, Target
Error);
}
}
} else if (CurrentPDU.type == TaskManagement) {
if (CurrentPDU.function == "TaskReassign") {
if (Session.ErrorRecoveryLevel < 2) {
Build-And-Send-TaskMgmt-Response(Connection,
CurrentPDU, "Allegiance reassignment
not supported");
} else if (task is not found) {
Build-And-Send-TaskMgmt-Response(Connection,
CurrentPDU, "Task not in task set");
} else if (task is currently allegiant) {
Build-And-Send-TaskMgmt-Response(Connection,
CurrentPDU, "Task still allegiant");
} else {
Establish-New-Allegiance(TCB, Connection);
TCB.CurrentlyAllegiant = TRUE;
Schedule-Command-To-Continue(TCB);
}
}
} else { /* REST UNRELATED TO CONNECTION-RECOVERY,
* NOT SHOWN */
}
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}
Transport_Exception_Handler(Connection)
{
Connection.PerformConnectionCleanup = TRUE;
if (the event is an unexpected transport disconnect) {
Connection.State = CLEANUP_WAIT;
Start-Timer(Connection-Resource-Timeout-Handler,
Connection,
(DefaultTime2Wait+DefaultTime2Retain));
if (this Session has full-feature phase connections
left) {
DifferentConnection =
Pick-A-Logged-In-Connection(Session);
Build-And-Send-Async(DifferentConnection,
DroppedConnection, DefaultTime2Wait,
DefaultTime2Retain);
}
} else {
Connection.State = FREE;
}
}
Appendix E. Clearing Effects of Various Events on Targets
E.1. Clearing Effects on iSCSI Objects
The following tables describe the target behavior on receiving the
events specified in the rows of the table. The second table is
an extension of the first table and defines clearing actions for
more objects on the same events. The legend is:
Y = Yes (cleared/discarded/reset on the event specified in
the row). Unless otherwise noted, the clearing action is
only applicable for the issuing initiator port.
N = No (not affected on the event specified in the row,
i.e., stays at previous value).
NA = Not Applicable or Not Defined.
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+-----+-----+-----+-----+-----+
|IT(1)|IC(2)|CT(5)|ST(6)|PP(7)|
+---------------------+-----+-----+-----+-----+-----+
|connection failure(8)|Y |Y |N |N |Y |
+---------------------+-----+-----+-----+-----+-----+
|connection state |NA |NA |Y |N |NA |
|timeout (9) | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|session timeout/ |Y |Y |Y |Y |Y(14)|
|closure/reinstatement| | | | | |
|(10) | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|session continuation |NA |NA |N(11)|N |NA |
|(12) | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|successful connection|Y |Y |Y |N |Y(13)|
|close logout | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|session failure (18) |Y |Y |N |N |Y |
+---------------------+-----+-----+-----+-----+-----+
|successful recovery |Y |Y |N |N |Y(13)|
|Logout | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|failed Logout |Y |Y |N |N |Y |
+---------------------+-----+-----+-----+-----+-----+
|connection Login |NA |NA |NA |Y(15)|NA |
|(leading) | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|connection Login |NA |NA |N(11)|N |Y |
|(non-leading) | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|target cold reset(16)|Y(20)|Y |Y |Y |Y |
+---------------------+-----+-----+-----+-----+-----+
|target warm reset(16)|Y(20)|Y |Y |Y |Y |
+---------------------+-----+-----+-----+-----+-----+
|LU reset(19) |Y(20)|Y |Y |Y |Y |
+---------------------+-----+-----+-----+-----+-----+
|powercycle(16) |Y |Y |Y |Y |Y |
+---------------------+-----+-----+-----+-----+-----+
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1. Incomplete TTTs - Target Transfer Tags on which the target is
still expecting PDUs to be received. Examples include TTTs
received via R2T, NOP-IN, etc.
2. Immediate Commands - immediate commands, but waiting for
execution on a target. For example, Abort Task Set.
5. Connection Tasks - tasks that are active on the iSCSI connection
in question.
6. Session Tasks - tasks that are active on the entire iSCSI
session. A union of "connection tasks" on all participating
connections.
7. Partial PDUs (if any) - PDUs that are partially sent and waiting
for transport window credit to complete the transmission.
8. Connection failure is a connection exception condition - one of
the transport connections shutdown, transport connections
reset, or transport connections timed out, which abruptly
terminated the iSCSI full-feature phase connection. A
connection failure always takes the connection state machine to
the CLEANUP_WAIT state.
9. Connection state timeout happens if a connection spends more
time than agreed upon during Login negotiation in the
CLEANUP_WAIT state, and this takes the connection to the FREE
state (M1 transition in connection cleanup state diagram).
10.These are defined in Section 6.3.5.
11.This clearing effect is "Y" only if it is a connection
reinstatement and the operational ErrorRecoveryLevel is less
than 2.
12.Session continuation is defined in Section 6.3.5.
13.This clearing effect is only valid if the connection is being
logged out on a different connection and when the connection
being logged out on the target may have some partial PDUs
pending to be sent. In all other cases, the effect is "NA".
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14.This clearing effect is only valid for a "close the session"
logout in a multi-connection session. In all other cases, the
effect is "NA".
15.Only applicable if this leading connection login is a session
reinstatement. If this is not the case, it is "NA".
16.This operation affects all logged-in initiators.
18.Session failure is defined in Section 6.3.5.
19.This operation affects all logged-in initiators and the clearing
effects are only applicable to the LU being reset.
20.With Standard multi-task abort semantics (Section 4.2.3.3), a
target warm reset or a target cold reset or an LU reset would
clear the active TTTs upon completion. However, the FastAbort
multi-task abort semantics defined by Section 4.2.3.4 do not
guarantee that the active TTTs are cleared by the end of the
reset operations. In fact, the FastAbort semantics are designed
to allow clearing the TTTs in a "lazy" fashion after the TMF
Response is delivered. Thus, when TaskReporting=FastAbort
(Section 13.23) is operational on a session, the clearing
effects of reset operations on "Incomplete TTTs" is "N".
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+-----+-----+-----+-----+-----+
|DC(1)|DD(2)|SS(3)|CS(4)|DS(5)|
+---------------------+-----+-----+-----+-----+-----+
|connection failure |N |Y |N |N |N |
+---------------------+-----+-----+-----+-----+-----+
|connection state |Y |NA |Y |N |NA |
|timeout | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|session timeout/ |Y |Y |Y(7) |Y |NA |
|closure/reinstatement| | | | | |
+---------------------+-----+-----+-----+-----+-----+
|session continuation |N(11)|NA*12|NA |N |NA*13|
+---------------------+-----+-----+-----+-----+-----+
|successful connection|Y |Y |Y |N |NA |
|close Logout | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|session failure |N |Y |N |N |N |
+---------------------+-----+-----+-----+-----+-----+
|successful recovery |Y |Y |Y |N |N |
|Logout | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|failed Logout |N |Y(9) |N |N |N |
+---------------------+-----+-----+-----+-----+-----+
|connection Login |NA |NA |N(8) |N(8) |NA |
|(leading | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|connection Login |N(11)|NA*12|N(8) |N |NA*13|
|(non-leading) | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|target cold reset |Y |Y |Y |Y(10)|NA |
+---------------------+-----+-----+-----+-----+-----+
|target warm reset |Y |Y |N |N |NA |
+---------------------+-----+-----+-----+-----+-----+
|LU reset |N |Y |N |N |N |
+---------------------+-----+-----+-----+-----+-----+
|powercycle |Y |Y |Y |Y(10)|NA |
+---------------------+-----+-----+-----+-----+-----+
1. Discontiguous Commands - commands allegiant to the connection
in question and waiting to be reordered in the iSCSI layer. All
"Y"s in this column assume that the task causing the event (if
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indeed the event is the result of a task) is issued as an
immediate command, because the discontiguities can be ahead of the
task.
2. Discontiguous Data - data PDUs received for the task in
question and waiting to be reordered due to prior discontiguities
in DataSN.
3. StatSN
4. CmdSN
5. DataSN
7. It clears the StatSN on all the connections.
8. This sequence number is instantiated on this event.
9. A logout failure drives the connection state machine to the
CLEANUP_WAIT state, similar to the connection failure event.
Hence, it has a similar effect on this and several other protocol
aspects.
10. This is cleared by virtue of the fact that all sessions with
all initiators are terminated.
11. This clearing effect is "Y" if it is a connection
reinstatement.
12. This clearing effect is "Y" only if it is a connection
reinstatement and the operational ErrorRecoveryLevel is 2.
13. This clearing effect is "N" only if it is a connection
reinstatement and the operational ErrorRecoveryLevel is 2.
E.2. Clearing Effects on SCSI Objects
The only iSCSI protocol action that can effect clearing actions on
SCSI objects is the "I_T nexus loss" notification (Section 6.3.5.1
Loss of Nexus notification). [SPC3] describes the clearing effects
of this notification on a variety of SCSI attributes. In addition,
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SCSI standards documents (such as [SAM2] and [SBC2]) define
additional clearing actions that may take place for several SCSI
objects on SCSI events such as LU resets and power-on resets.
Since iSCSI defines a target cold reset as a protocol-equivalent
to a target power-cycle, the iSCSI target cold reset must also be
considered as the power-on reset event in interpreting the actions
defined in the SCSI standards.
When the iSCSI session is reconstructed (between the same SCSI
ports with the same nexus identifier) reestablishing the same I_T
nexus, all SCSI objects that are defined to not clear on the "I_T
nexus loss" notification event, such as persistent reservations,
are automatically associated to this new session.
Acknowledgments
Several individuals on the original IPS Working Group made
significant contributions to the original RFCs 3720, 3980, 4850
and 5048.
Specifically, the authors of the original RFCs - which this draft
consolidates into a single document - were the following:
RFC 3720: Julian Satran, Kalman Meth, Costa Sapuntzakis,
Mallikarjun Chadalapaka, Efri Zeidner
RFC 3980: Marjorie Krueger, Mallikarjun Chadalapaka, Rob Elliott
RFC 4850: David Wysochanski
RFC 5048: Mallikarjun Chadalapaka
Many thanks to Fred Knight for contributing to the UML notations
and drawings in this draft.
We would in addition like to acknowledge the following individuals
who contributed to this revised draft: David Harrington, Paul
Koning, Mark Edwards, Rob Elliott, Martin Stiemerling.
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Thanks to Yi Zeng and Nico Williams for suggesting and/or
reviewing Kerberos-related security considerations text.
The authors gratefully acknowledge the valuable feedback during
the Last call review process from a number of individuals, which
had significantly improved this draft. The individuals were:
Stephen Farrell, Brian Haberman, Barry Leiba, Pete Resnick, Sean
Turner, Alexey Melnikov, Kathleen Moriarty, Fred Knight, Mike
Christie, Qiang Wang, Shiv Rajpal and Andy Banta.
Finally, this draft also benefited from significant review
contributions from the Storm Working Group at large.
Authors' Addresses
Mallikarjun Chadalapaka
Microsoft
One Microsoft Way
Redmond WA 98052 USA
E-mail: cbm@chadalapaka.com
Julian Satran
Infinidat Ltd.
E-mail: julians@infinidat.com, julian@satran.net
Kalman Meth
IBM Haifa Research Lab
Haifa University Campus - Mount Carmel
Haifa 31905, Israel
Phone +972.4.829.6341
E-mail: meth@il.ibm.com
David L. Black,
EMC Corporation,
176 South St., Hopkinton, MA 01748
Phone +1 (508) 293-7953
Email: david.black@emc.com
Comments may be sent to Mallikarjun Chadalapaka
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society
Chadalapaka et al. Expires January 31, 2014 [Page 344]
