Internet DRAFT - draft-ietf-trill-directory-assist-mechanisms
draft-ietf-trill-directory-assist-mechanisms
INTERNET-DRAFT Donald Eastlake
Intended status: Proposed Standard Linda Dunbar
Huawei
Radia Perlman
EMC
Yizhou Li
Huawei
Expires: September 1, 2017 March 2, 2017
TRILL: Edge Directory Assist Mechanisms
<draft-ietf-trill-directory-assist-mechanisms-12.txt>
Abstract
This document describes mechanisms for providing directory service to
TRILL (Transparent Interconnection of Lots of Links) edge switches.
The directory information provided can be used in reducing multi-
destination traffic, particularly ARP/ND and unknown unicast
flooding. It can also be used to detect traffic with forged source
addresses.
Status of This Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Distribution of this document is unlimited. Comments should be sent
to the TRILL working group mailing list.
Internet-Drafts are working documents of the Internet Engineering
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html. The list of Internet-Draft
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Table of Contents
1. Introduction............................................4
1.1 Uses of Directory Information..........................5
1.2 Terminology............................................5
2. Push Model Directory Assistance Mechanisms..............7
2.1 Requesting Push Service................................7
2.2 Push Directory Servers.................................7
2.3 Push Directory Server State Machine....................8
2.3.1 Push Directory States................................9
2.3.2 Push Directory Events and Conditions................11
2.3.3 State Transition Diagram and Table..................12
2.4 End Stations and Push Directories.....................13
2.5 Additional Push Details...............................14
2.6 Primary to Secondary Server Push Service..............15
2.7 Push Directory Configuration..........................16
3. Pull Model Directory Assistance Mechanisms.............17
3.1 Pull Directory Message Common Format..................18
3.1.1 Version Negotiation.................................19
3.2 Pull Directory Query and Response Messages............20
3.2.1 Pull Directory Query Message Format.................20
3.2.2 Pull Directory Responses............................23
3.2.2.1 Pull Directory Response Message Format............23
3.2.2.2 Pull Directory Forwarding.........................26
3.3 Cache Consistency.....................................27
3.3.1 Update Message Format...............................30
3.3.2 Acknowledge Message Format..........................31
3.4 Summary of Records Formats in Messages................32
3.5 End Stations and Pull Directories.....................32
3.5.1 Pull Directory Hosted on an End Station.............33
3.5.2 Use of Pull Directory by End Stations...............34
3.5.3 Native Pull Directory Messages......................35
3.6 Pull Directory Message Errors.........................35
3.6.1 Error Codes.........................................36
3.6.2 Sub-Errors Under Error Codes 1 and 3................37
3.6.3 Sub-Errors Under Error Codes 128 and 131............37
3.7 Additional Pull Details...............................38
3.8 The No Data Flag......................................38
3.9 Pull Directory Service Configuration..................39
4. Directory Use Strategies and Push-Pull Hybrids.........41
5. TRILL ES-IS............................................43
5.1 PDUs and System IDs...................................43
5.2 Adjacency, DRB Election, Hellos, TLVs, Etc............44
5.3 Link State............................................44
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Table of Contents Continued
6. Security Considerations................................45
6.1 Directory Information Security........................45
6.2 Directory Confidentiality and Privacy.................45
6.3 Directory Message Security Considerations.............45
7. IANA Considerations....................................47
7.1 ESADI-Parameter Data Extensions.......................47
7.2 RBridge Channel Protocol Numbers......................48
7.3 The Pull Directory (PUL) and No Data (NOD) Bits.......48
7.4 TRILL Pull Directory QTYPEs...........................49
7.5 Pull Directory Error Code Registries..................49
7.6 TRILL-ES-IS MAC Address...............................49
Normative References......................................50
Informational References..................................51
Acknowledgments...........................................53
Authors' Addresses........................................54
Copyright, Disclaimer, and Additional IPR Provisions......55
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1. Introduction
[RFC7067] gives a problem statement and high level design for using
directory servers to assist TRILL [RFC6325] [RFC7780] edge nodes in
reducing multi-destination ARP/ND [ARPND], reducing unknown unicast
flooding traffic, and improving security against address spoofing
within a TRILL campus. Because multi-destination traffic becomes an
increasing burden as a network scales up in number of nodes, reducing
ARP/ND and unknown unicast flooding improves TRILL network
scalability. This document describes specific mechanisms for TRILL
directory servers.
The information held by the Directory(s) is address mapping and
reachability information. Most commonly, what MAC (Media Access
Control) address [RFC7042] corresponds to an IP address within a Data
Label (VLAN or FGL (Fine Grained Label [RFC7172])) and the egress
TRILL switch (RBridge), and optionally what specific port on that
TRILL switch, from which that MAC address is reachable. But it could
be what IP address corresponds to a MAC address or possibly other
address mapping or reachability information.
The mechanism used to initially populate directory data in primary
servers is beyond the scope of this document. A primary server can
use the Push Directory service to provide directory data to secondary
servers as described in Section 2.6. In the data center environment,
it is common for orchestration software to know and control where all
the IP addresses, MAC addresses, and VLANs/tenants are in a data
center. Thus such orchestration software can be appropriate for
providing the directory function or for supplying the Directory(s)
with directory information.
Efficient routing of unicast traffic in a TRILL campus assumes that
the mapping of destination MAC addresses to edge RBridges is stable
enough that the default data plane learning of TRILL and/or the use
of directories reduces to an acceptable level the need to flood
packets where the location of the destination is unknown. Although
not prohibited, "Ephemeral" MAC addresses are unlikely to be used in
such an environment. Directories need not be complete and in the case
that any ephemeral MAC addresses were in use, they would probably not
be included in directory information.
Directory services can be offered in a Push Mode, Pull Mode, or both
[RFC7067] at the option of the server. Push Mode, in which a
directory server pushes information to TRILL switches indicating
interest, is specified in Section 2. Pull Mode, in which a TRILL
switch queries a server for the information it wants, is specified in
Section 3. More detail on modes of operation, including hybrid
Push/Pull, are provided in Section 4.
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1.1 Uses of Directory Information
A TRILL switch can consult Directory information whenever it wants,
by (1) searching through information that has been retained after
being pushed to it or pulled by it or (2) by requesting information
from a Pull Directory. However, the following are expected to be the
most common circumstances leading to directory information use. All
of these are cases of ingressing (or originating) a native frame.
1. ARP requests and replies [RFC826] are normally broadcast. But a
directory assisted edge TRILL switch could intercept ARP messages
and reply if the TRILL switch has the relevant information
[ARPND].
2. IPv6 ND (Neighbor Discovery [RFC4861]) requests and replies are
normally multicast. Except in the case of Secure ND [RFC3971],
where possession of the right keying material might be required, a
directory assisted edge TRILL switch could intercept ND messages
and reply if the TRILL switch has the relevant information.
[ARPND]
3. Unknown destination MAC addresses normally cause a native frame to
be flooded. An edge TRILL switch ingressing a native frame
necessarily has to determine if it knows the egress RBridge from
which the destination MAC address of the frame (in the frame's
VLAN or FGL) is reachable. It might have learned that information
from the directory or could query the directory if it does not
know it. Furthermore, if the edge TRILL switch has complete
directory information, it can detect a forged source MAC or IP
address in any native frame and discard the frame if it finds such
a forged address.
4. RARP [RFC903] (Reverse ARP) is similar to ARP as above.
1.2 Terminology
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].
The terminology and acronyms of [RFC6325] are used herein along with
the following:
AFN: Address Family Number, (http://www.iana.org/assignments/address-
family-numbers/)
CSNP Time: Complete Sequence Number PDU Time. See ESDADI [RFC7357]
and Section 7.1 below.
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Data Label: VLAN or FGL.
ESADI: End Station Address Distribution Information [RFC7357].
FGL: Fine Grained Label [RFC7172].
FR: Flood Record flag bit. See Section 3.2.1.
Host: A physical server or a virtual machine. A host must have a MAC
address and usually has at least one IP address.
Interested Labels sub-TLV: Short for "Interested Labels and Spanning
Tree Roots sub-TLV" [RFC7176].
Interested VLANs sub-TLV: Short for "Interested VLANs and Spanning
Tree Roots sub-TLV" [RFC7176].
IP: Internet Protocol. In this document, IP includes both IPv4 and
IPv6.
MAC: Media Access Control address [RFC7042]
MacDA: Destination MAC address.
MacSA: Source MAC address.
OV: Overflow flag bit. See Section 3.2.2.1.
PDSS: Push Directory Server Status. See Sections 2 and 7.1.
PUL: Pull Directory flag bit. See Sections 3 and 7.3.
primary server: A Directory server that obtains the information it is
serving up by a reliable mechanism outside the scope of this
document designed to assure the freshness of that information.
(See secondary server.)
RBridge: An alternative name for a TRILL switch.
secondary server: A Directory server that obtains the information it
is serving up from one or more primary servers.
TLV: Type, Length, Value
TRILL: Transparent Interconnection of Lots of Links or Tunneled
Routing in the Link Layer.
TRILL switch: A device that implements the TRILL protocol.
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2. Push Model Directory Assistance Mechanisms
In the Push Model [RFC7067], one or more Push Directory servers
reside at TRILL switches and push down the address mapping
information for the various addresses associated with end station
interfaces and the TRILL switches from which those interfaces are
reachable [RFC7961]. This service is scoped by Data Label (VLAN or
FGL [RFC7172]). A Push Directory advertises when, for a Data Label,
it both is configured to be a directory having complete information
and has actually pushed all the information it has. It might be
pushing only a subset of the mapping and/or reachability information
for a Data Label. The Push Model uses the ESADI [RFC7357] (End
Station Address Distribution Information) protocol as its
distribution mechanism.
With the Push Model, if complete address mapping information for a
Data Label is being pushed, a TRILL switch (RBridge) that has that
complete information and is ingressing a native frame can simply drop
the frame if the destination unicast MAC address can't be found in
the mapping information available, instead of flooding the frame
(ingressing it as an unknown MAC destination TRILL Data frame). But
this will result in lost traffic if ingress TRILL switch's directory
information is incomplete.
2.1 Requesting Push Service
In the Push Model, it is necessary to have a way for a TRILL switch
to subscribe to information from the directory server(s). TRILL
switches simply use the ESADI [RFC7357] protocol mechanism to
announce, in their core IS-IS LSPs, the Data Labels for which they
are participating in ESADI by using the Interested VLANs and/or
Interested Labels sub-TLVs [RFC7176]. This will cause the Directory
information to be pushed to them for all such Data Labels that are
being served by the one or more Push Directory servers.
2.2 Push Directory Servers
Push Directory servers advertise, through ESADI, their availability
to push the mapping information for a particular Data Label by
setting the PDSS (Push Directory Server Status) in their ESADI
Parameter APPsub-TLV for that ESADI instance (see [RFC7357] and
Section 7.1) to a non-zero value. This PDSS field setting is visible
to other ESADI participants, including other Push Directory servers,
for that Data Label. Each Push Directory server MUST participate in
ESADI for the Data Labels for which it will push mappings and set the
PDSS field in its ESADI-Parameters APPsub-TLV for that Data Label.
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For increased robustness, increased bandwidth capability, and
improved locality, it is useful to have multiple Push Directory
Servers for each Data Label. Each Push Directory server is configured
with a number N in the range 1 to 8, which defaults to 2, for each
Data Label for which it can push directory information (see
PushDirServers, Section 2.7). If the Push Directory servers for a
Data Label are configured consistently with the same N and at least N
servers are available, then N copies of that directory will be
pushed.
Each Push Directory server also has a configurable 8-bit priority
(PushDirPriority) to be Active, which defaults to 0x3F (see Section
2.7). This priority is treated as an unsigned integer where larger
magnitude means higher priority. This priority appears in its ESADI
Parameter APPsub-TLV (see Section 7.1). In case of a tie in this
configurable priority, the System ID of the TRILL switch acting as
the server is used as an unsigned 6-byte integer where larger
magnitude indicates higher priority.
For each Data Label it can serve, each Push Directory server checks
to see if there appear to be enough higher priority servers to push
the desired number of copies. It does this by ordering, by priority,
the Push Directory servers whose advertisements are present in the
ESADI link state database for that Data Label and that are data
reachable [RFC7780] as indicated by its IS-IS link state database.
The Push Directory server then determines its own position in that
order. If a Push Directory server's configuration indicates that N
copies of the mappings for a Data Label should be pushed and the
server finds that it is number K in the priority ordering (where
number 1 in the ordered list is highest priority and the last is
lowest priority), then if K is less than or equal to N the Push
Directory server is Active. If K is greater than N it is Stand-By.
Active and Stand-By behavior are specified below in Section 2.3.
For a Push Directory to reside on an end station, one or more TRILL
switches locally connected to that end station must proxy for the
Push Directory server and advertise themselves in ESADI as Push
Directory servers. It appears to the rest of the TRILL campus that
these TRILL switches (that are proxying for the end station) are the
Push Directory server(s). The protocol between such a Push Directory
end station and the one or more proxying TRILL switches acting as
Push Directory servers is beyond the scope of this document.
2.3 Push Directory Server State Machine
The subsections below describe the states, events, and corresponding
actions for Push Directory servers.
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The meaning of the value of the PDSS field in a Push Directory's
ESADI Parameter APPsub-TLV is summarized in the table below.
PDSS Meaning
---- ----------
0 Not a Push Directory Server
1 Push Directory Server in Stand-By Mode
2 Push Directory Server in Active Mode but not complete
3 Push Directory Server in Active Mode that has pushed
complete data
2.3.1 Push Directory States
A Push Directory Server is in one of seven states, as listed below,
for each Data Label it can serve. The name of each state is followed
by a symbol that starts and ends with an angle bracket and represents
the state. The value that the Push Directory Server advertises in
PDSS is determined by the state. In addition, it has an internal
State-Transition-Time variable for each Data Label it serves that is
set at each state transition and which enables it to determine how
long it has been in its current state for that Data Label.
Down <S1>: A completely shut down virtual state defined for
convenience in specifying state diagrams. A Push Directory Server
in this state does not advertise any Push Directory data. It may
be participating in ESDADI [RFC7357] with the PDSS field zero in
its ESADI-Parameters or might be not participating in ESADI at
all. All states other than the Down state are considered to be Up
states and imply a non-zero PDSS field.
Stand-By <S2>: No Push Directory data is advertised. Any outstanding
EASDI-LSP fragments containing directory data are updated to
remove that data and, if the result is an empty fragment (contains
nothing except possibly an Authentication TLV), the fragment is
purged. The Push Directory participates in ESDADI [RFC7357] and
advertises its ESADI fragment zero that includes an ESADI-
Parameters APPsub-TLV with the PDSS field set to 1.
Active <S3>: The Push Directory participates in ESDADI [RFC7357] and
advertises its ESADI fragment zero that includes an ESADI-
Parameters APPsub-TLV with the PDSS field set to 2. It also
advertises its directory data and any changes through ESADI
[RFC7357] in its ESADI-LSPs using the Interface Addresses
[RFC7961] APPsub-TLV and updates that information as it changes.
Active Completing <S4>: Same behavior as the Active state except
that the server responds differently to events. The purpose of
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this state is to be sure there has been enough time for directory
information to propagate to subscribing edge TRILL switches (see
the Time Condition, Section 2.3.2) before the Directory Server
advertises that the information is complete.
Active Complete <S5>: The same behavior as Active except that the
PDSS field in the ESADI-Parameters APPsub-TLV is set to 3 and the
server responds differently to events.
Going Stand-By Was Complete <S6>: The same behavior as Active except
that the server responds differently to events. The purpose of
this state is to be sure that the information, that the directory
will no longer be complete, has enough time to propagate to edge
TRILL switches (see the Time Condition, Section 2.3.2) before the
Directory Server stops advertising updates to the information.
(See note below.)
Active Uncompleting <S7>: The same behavior as Active except that it
responds differently to events. The purpose of this state is to be
sure that the information, that the directory will no longer be
complete, has enough time to propagate to edge TRILL switches (see
the Time Condition, Section 2.3.2) before the Directory Server
might stop advertising updates to the information. (See note
below.)
Note: It might appear that a Push Directory could transition
directly from Active Complete to Active, since Active state
continues to advertise updates, eliminating the need for the
Active Uncompleting transition state. But consider the case of
the Push Directory that was complete being configured to be
incomplete and then the Stand-By Condition (see Section 2.3.2)
occurring shortly thereafter. If the first of these two events
caused the server to transition directly to the Active state
then, when the Stand-By Condition occurred, it would
immediately transition to Stand-By and stop advertising updates
even though there might not have been enough time for knowledge
of its incompleteness to have propagated to all edge TRILL
switches.
The following table summarizes PDSS value for each state:
State PDSS
---------- ------
Down <S1> 0
Stand-By <S2> 1
Active <S3> 2
Active Completing <S4> 2
Active Complete <S5> 3
Going Stand-By <S6> 2
Active Uncompleting <S7> 2
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2.3.2 Push Directory Events and Conditions
Three auxiliary conditions referenced later in this section are
defined as follows for convenience:
The Activate Condition: In order to have the desired number of Push
Directory servers pushing data for Data Label X, this Push
Directory server should be active. This is determined by the
server finding that (A) it is priority K among the data reachable
Push Directory servers (where highest priority server is 1) for
Data Label X, (B) it is configured that there should be N copies
pushed for Data Label X, and (C) K is less than or equal to N. For
example, if the Push Directory server is configured so that 2
copies should be pushed and finds that it is priority 1 or 2 among
the Push Directory servers that are visible in its ESADI link
state database and that are data reachable as indicated by its IS-
IS link state database.
The Stand-By Condition: In order to have the desired number of Push
Directory servers pushing data for Data Label X, this Push
Directory server should be stand-by (not active). This is
determined by the server finding that (A) it is priority K among
the data reachable Push Directory servers (where highest priority
server is 1) for Data Label X, (B) it is configured that there
should be N copies pushed for Data Label X, and (C) K is greater
than N. For example, the Push Directory server is configured that
2 copies should be pushed and finds that it is priority 3 or lower
priority (higher number) among the available Push directory
servers.
The Time Condition: The Push Directory server has been in its current
state for a configurable amount of time (PushDirTimer) that
defaults to twice its CSNP (Complete Sequence Number PDU) time
(see Sections 2.7 and 7.1).)
The events and conditions listed below cause state transitions in
Push Directory servers.
1. Push Directory server comes Up.
2. The Push Directory server or the TRILL switch on which it resides
is being shut down. This is a persistent condition unless the shut
down is canceled. So, for example, a Push Directory server in the
Going Stand-By Was Complete state does not transition out of that
state due to this condition but, after the Time Condition is met
and the directory transitions to Stand-By and performs the actions
required there (such as purging LSPs) continues to the Down state
if this condition is still true. Similar comments apply to
events/conditions 3, 4, and 5.
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3. The Activate Condition is met and the server's configuration
indicates it does not have complete data.
4. The Stand-By Condition is met.
5. The Activate Condition is met and the server's configuration
indicates it has complete data.
6. The server's configuration is changed to indicate it does not have
complete data.
7. The Time Condition is met.
2.3.3 State Transition Diagram and Table
The state transition table is as follows:
State|Down|Stand-By|Active| Active | Active | Going | Active
-----+ | | |Completing|Complete|Stand-By|Uncompleting
Event|<S1>| <S2> | <S3> | <S4> | <S5> | <S6> | <S7>
-----+----+--------+------+----------+--------+---------+------------
1 |<S2>| N/A | N/A | N/A | N/A | N/A | N/A
2 |<S1>| <S1> | <S2> | <S2> | <S6> | <S6> | <S7>
3 |<S1>| <S3> | <S3> | <S3> | <S7> | <S3> | <S7>
4 |<S1>| <S2> | <S2> | <S2> | <S6> | <S6> | <S6>
5 |<S1>| <S4> | <S4> | <S4> | <S5> | <S5> | <S5>
6 |<S1>| <S2> | <S3> | <S3> | <S7> | <S6> | <S7>
7 |<S1>| <S2> | <S3> | <S5> | <S5> | <S2> | <S3>
The above state table is equivalent to the following transition
diagram:
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+-----------+
| Down <S1> |<---------+
+-----------+ |
|1 ^ | 3,4,5,6,7 |
| | +------------+
V |2
+---------------+
| Stand-By <S2> |<--------------------------------------+
+---------------+ ^ ^ ^ |
|5 |3 |1,4,6,7 | | | |
| | +---------+ | | |
| V |2,4 | |
| +---------------------+ | |
| | Active <S3> |<---------|-------------+ |
| +---------------------+ ^ | | |
| |5 ^ |1,3,6,7 ^ | | | |
| | | | | | | | |
| | | +---------+ | | | |
| | | | | | |
V V |3,6 | | | |
+------------------------+ | | | |
| Active Completing <S4> |------------+ | |
+------------------------+ 2,4 | | |
|7 |1,5 ^ | | |
| | | | | |
| +-------+ | | |
| | | |
| +------------------------------------+ | |
| | | | | |
V V |7 |5 |3 |7
+-------------+ 3,6 +----------------+ 4 +----------------+
| Active |------->| Active |--->| Going Stand-By |
| Complete | | Uncompleting | | Was Complete |
| <S5> |<-------| <S7> | | <S6> |
+-------------+ 5 +----------------+ +----------------+
|1,5,7 ^ |2,4 |1,2,3,6 ^ ^ |1,2,4,6 ^
| | | | | | | |
+-------+ | +------------+ | +--------+
| |
+----------------------------------+
Figure 1. Push Server State Diagram
2.4 End Stations and Push Directories
End station hosting or use of Push Directories is outside of the
scope of this document. Push Directory information distribution is
accomplished using ESADI [RFC7357], which does not operate to end
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stations. In the future, ESADI might be extended to operate to end
stations or some other method, such as BGP, might be specified as a
way to support end station hosting or use of Push Directories.
2.5 Additional Push Details
Push Directory mappings can be distinguished from other data
distributed through ESADI because mappings are distributed only with
the Interface Addresses APPsub-TLV [RFC7961] and are flagged in that
APPsub-TLV as being Push Directory data.
TRILL switches, whether or not they are Push Directory servers, MAY
continue to advertise any locally learned MAC attachment information
in ESADI [RFC7357] using the Reachable MAC Addresses TLV [RFC6165].
However, if a Data Label is being served by complete Push Directory
servers, advertising such locally learned MAC attachment generally
SHOULD NOT be done as it would not add anything and would just waste
bandwidth and ESADI link state space. An exception might be when a
TRILL switch learns local MAC connectivity and that information
appears to be missing from the directory mapping.
Because a Push Directory server needs to advertise interest in one or
more Data Labels even though it might not want to receive multi-
destination TRILL Data packets in those Data Labels, the No Data
(NOD) flag bit is provided as discussed in Section 3.8.
When a Push Directory server is no longer data reachable [RFC7780] as
indicated by the IS-IS link state database, other TRILL switches MUST
ignore any Push Directory data from that server because it is no
longer being updated and may be stale.
The nature of dynamic distributed asynchronous systems is such that
it is impossible for a TRILL switch receiving Push Directory
information to be absolutely certain that it has complete
information. However, it can obtain a reasonable assurance of
complete information by requiring two conditions to be met:
1. The PDSS field is 3 in the ESADI zero fragment from the server
for the relevant Data Label.
2. In so far as it can tell, it has had continuous data
connectivity to the server for a configurable amount of time
that defaults to twice the server's CSNP time (PushDirTimer,
see Section 2.7).
Condition 2 is necessary because a client TRILL switch might be just
coming up and receive an EASDI LSP meeting the requirement in
condition 1 above but has not yet received all of the ESADI LSP
fragments from the Push Directory server.
Likewise, due to various delays, when an end station connects to or
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disconnects from the campus there are timing differences between such
connection or disconnection, the update of directory information at
the directory, and the update of directory information at any
particular RBridge in the TRILL campus. Thus, there is commonly a
small window during which an RBridge using directory information
might either (1) drop or unnecessarily flood a frame as having an
unknown unicast destination or (2) encapsulate a frame to an edge
RBridge where the end station is not longer connected when the frame
arrives at that edge RBridge.
There may be conflicts between mapping information from different
Push Directory servers or conflicts between locally learned
information and information received from a Push Directory server. In
case of such conflicts, information with a higher confidence value
[RFC6325] [RFC7961] is preferred over information with a lower
confidence. In case of equal confidence, Push Directory information
is preferred to locally learned information and if information from
Push Directory servers conflicts, the information from the higher
priority Push Directory server is preferred.
2.6 Primary to Secondary Server Push Service
A secondary Push or Pull Directory server is one that obtains its
data from a primary directory server. Such mechanisms, where some
directory servers can be populated from others, have been found
useful for multiple-server directory applications, for example in the
DNS where it is the normal case that some authoritative servers
(secondary servers) are populated with data from other authoritative
servers (primary servers).
Other techniques MAY be used but, by default, this data transfer
occurs through the primary server acting as a Push Directory server
for the Data Labels involved while the secondary directory server
takes the pushed data it receives from the highest priority Push
Directory server and re-originates it. Such a secondary server may be
a Push Directory server or a Pull Directory server or both for any
particular Data Label. Because the data from a secondary server will
necessarily be at least a little less fresh than that from a primary
server, it is RECOMMENDED that the re-originated secondary server
data be given a confidence level at least one less than that of the
data as received from the primary (or unchanged if it is already of
minimum confidence).
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2.7 Push Directory Configuration
The following per Data Label configuration parameters are available
for controlling Push Directory behavior:
Name Range Default Section
--------------- -------- ------- -------
PushDirService T/F F 2.2
PushDirServers 1 - 8 2 2.2
PushDirPriority 0 - 255 0x3F 2.2
PushDirComplete T/F F 2.3.1, 2.3.2
PushDirTimer 1 - 511 2*CSNP 2.3.2, 2.5
PushDirService is a boolean. When false, Push Directory service is
not provided; when true, it is.
PushDirComplete is a boolean. When false, the server never indicates
that the information it has pushed is complete; when true, it does so
indicate after pushing all the information it knows.
PushDirTimer defaults to two times the ESADI CSNP configuration value
but not less than 1 second.
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3. Pull Model Directory Assistance Mechanisms
In the Pull Model [RFC7067], a TRILL switch (RBridge) pulls directory
information from an appropriate Directory Server when needed.
A TRILL switch that makes use of Pull Directory services must
implement appropriate connections between its directory utilization
and its link state database and link state updating. For example,
Pull Directory servers for a particular Data Label X are found by
looking in the core TRILL IS-IS link state database for data
reachable [RFC7780] TRILL switches that advertise themselves by
having the Pull Directory flag (PUL) on in their Interested VLANs or
Interested Labels sub-TLV (see Section 7.3) for that Data Label. The
set of such switches can change with configuration changes by network
management, such as starting up or shutting down of Pull Directory
servers, or changes in network topology, such the connection or
disconnection of TRILL switches that are Pull Directory servers, or
network partition or merger. As described in Section 3.7, a TRILL
switch MUST notice if a Pull Directory from which it has cached data
is no longer data reachable so it can discard such cached data.
If multiple data reachable TRILL switches indicate in the link state
database that they are Pull Directory Servers for a particular Data
Label, pull requests can be sent to any one or more of them but it is
RECOMMENDED that pull requests be preferentially sent to the server
or servers that are lowest cost from the requesting TRILL switch.
Pull Directory requests are sent by enclosing them in an RBridge
Channel [RFC7178] message using the Pull Directory channel protocol
number (see Section 7.2). Responses are returned in an RBridge
Channel message using the same channel protocol number. See Section
3.2 for Query and Response Message formats. For cache consistency or
notification purposes, Pull Directory servers, under certain
conditions, MUST send unsolicited Update Messages to client TRILL
switches they believe may be holding old data and those clients can
acknowledge such updates, as described in Section 3.3. All these
messages have a common header as described in Section 3.1. Errors are
returned as described in Section 3.6.
The requests to Pull Directory Servers are typically derived from
ingressed ARP [RFC826], ND [RFC4861], RARP [RFC903], or SEND
[RFC3971] messages, or data frames with unknown unicast destination
MAC addresses, intercepted by an ingress TRILL switch, as described
in Section 1.1.
Pull Directory responses include an amount of time for which the
response should be considered valid. This includes negative responses
that indicate no data is available. It is RECOMMENDED that both
positive responses with data and negative responses be cached and
used to locally handle ARP, ND, RARP, unknown destination MAC frames,
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or the like [ARPND], until the responses expire. If information
previously pulled is about to expire, a TRILL switch MAY try to
refresh it by issuing a new pull request but, to avoid unnecessary
requests, SHOULD NOT do so unless it has been recently used. The
validity timer of cached Pull Directory responses is NOT reset or
extended merely because that cache entry is used.
3.1 Pull Directory Message Common Format
All Pull Directory messages are transmitted as the Channel Protocol
specific payload of RBridge Channel messages [RFC7178]. Pull
Directory messages are formatted as described herein starting with
the following common 8-byte header:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver | Type | Flags | Count | Err | SubErr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type Specific Payload - variable length
+-+-+- ...
Ver: Version of the Pull Directory protocol as an unsigned
integer. Version zero is specified in this document. See
Section 3.1.1 for a discussion of version negotiation.
Type: The Pull Directory message type as follows:
Type Section Name
---- ------- --------
0 - Reserved
1 3.2.1 Query
2 3.2.2 Response
3 3.3.1 Update
4 3.3.2 Acknowledge
5-14 - Unassigned
15 - Reserved
Flags: Four flag bits whose meaning depends on the Pull Directory
message Type. Flags whose meanings are not specified are
reserved, MUST be sent as zero, and MUST be ignored on receipt.
Count: Some Pull Directory message types specified herein have
zero or more occurrences of a Record as part of the type
specific payload. The Count field is the number of occurrences
of that Record as an unsigned integer. For any Pull Directory
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messages not structured with such occurrences, this field MUST
be sent as zero and ignored on receipt.
Err, SubErr: The error and suberror fields are only used in
messages that are in the nature of replies. In messages that
are requests or updates, these fields MUST be sent as zero and
ignored on receipt. An Err field containing the value zero
means no error. The meaning of values in the SubErr field
depends on the value of the Err field but, in all cases, a zero
SubErr field is allowed and provides no additional information
beyond the value of the Err field.
Sequence Number: An identifying 32-bit quantity set by the TRILL
switch sending a request or other unsolicited message and
returned in every corresponding reply or acknowledgment. It is
used to match up responses with the message to which they
respond.
Type Specific Payload: Format depends on the Pull Directory
message Type.
3.1.1 Version Negotiation
The version number (Ver) in the Pull Directory message header is
incremented for a future version with changes such that TRILL
directory messages cannot be parsed correctly by an earlier version.
Ver is not incremented for minor changes such as defining a new field
value for an existing field.
Pull Directory messages come in pairs (Request-Response, Update-
Acknowledgment). The version number in the Request/Update (Ver1)
indicates the format of that message and of the corresponding
returned Response/Acknowledgment. The version number in the returned
Response/Acknowledgment (Ver2) indicates the highest version number
that the sender of that Response/Acknowledgment understands.
In the most common case of a well configured network, Ver1 and Ver2
will be equal.
If Ver2 is less than Ver1, the returned Response/Acknowledgment will
be an error message saying that the version is not understood.
If Ver2 is greater than Ver1 and the responder understands Ver1, it
responds normally in Ver1 format. However, if the responder does not
understand Ver1, it MUST send a version-not-understood error message
correctly formatted for Ver1. Thus all implementations that support
some version X MUST be able to send a version-not-understood error
message formatted correctly formatted for all lower versions down to
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version zero.
3.2 Pull Directory Query and Response Messages
The format of Pull Directory Query and Response Messages is specified
below.
3.2.1 Pull Directory Query Message Format
A Pull Directory Query Message is sent as the Channel Protocol
specific content of an RBridge Channel message [RFC7178] TRILL Data
packet or as a native RBridge Channel data frame (see Section 3.5).
The Data Label of the packet is the Data Label in which the query is
being made. The priority of the channel message is a mapping of the
priority of the ingressed frame that caused the query. The default
mapping depends, per Data Label, on the strategy (see Section 4) or a
configured priority (DirGenQPriority, Section 3.9) for generated
queries. (Generated queries are those not the result of a mapping.
For example, a query to refresh a cache entry.) The Channel Protocol
specific data is formatted as a header and a sequence of zero or more
QUERY Records as follows:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver | Type | Flags | Count | Err | SubErr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| QUERY 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
| QUERY 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
| ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
| QUERY K
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
Ver, Sequence Number: See Section 3.1.
Type: 1 for Query. Queries received by an TRILL switch that is not
a Pull Directory for the relevant Data Label result in an error
response (see Section 3.6) unless inhibited by rate limiting.
(See [RFC7178] for response if the Pull Directory RBridge
Channel protocol is not implemented or enabled.)
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Flags, Err, and SubErr: MUST be sent as zero and ignored on
receipt.
Count: Number of QUERY Records present. A Query Message Count of
zero is explicitly allowed, for the purpose of pinging a Pull
Directory server to see if it is responding. On receipt of such
an empty Query Message, a Response Message that also has a
Count of zero is returned unless inhibited by rate limiting.
QUERY: Each QUERY Record within a Pull Directory Query Message is
formatted as follows:
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| SIZE |FR| RESV | QTYPE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
If QTYPE = 1
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| AFN |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| Query address ...
+--+--+--+--+--+--+--+--+--+--+--...
If QTYPE = 2 or 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| Query frame ...
+--+--+--+--+--+--+--+--+--+--+--...
SIZE: Size of the QUERY Record in bytes as an unsigned integer
not including the SIZE field and following byte. A value of
SIZE so large that the material doesn't fit in the Query
Message indicates a malformed QUERY Record. The QUERY Record
with the illegal SIZE value and any subsequent QUERY Records
MUST be ignored and the entire Query Message MAY be ignored.
FR: The Flood Record flag that is ignored if QTYPE is zero. If
QTYPE is 2 or 5 and the directory information sought is not
found, the frame provided is flooded, otherwise it is not
forwarded. See Section 3.2.2.2. For QTYPEs other than 2 or
5, the FR flag has no effect.
RESV: A block of three reserved bits. MUST be sent as zero and
ignored on receipt.
QTYPE: There are several types of QUERY Records currently
defined in two classes as follows: (1) a QUERY Record that
provides an explicit address and asks for all addresses for
the interface specified by the query address and (2) a QUERY
Record that includes a frame. The fields of each are
specified below. Values of QTYPE are as follows:
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QTYPE Description
----- -----------
0 Reserved
1 Address query
2 Frame query
3-4 Unassigned
5 Unknown unicast MAC query frame
6-14 Unassigned
15 Reserved
AFN: Address Family Number of the query address.
Query Address: The query is asking for any other addresses,
and the nickname of the TRILL switch from which they are
reachable, that correspond to the same interface as this
address, within the Data Label of the query of the
address provided. A typically Query Address would be
something like the following:
(1) A 48-bit MAC address with the querying TRILL switch
primarily interested in either
(1a) the RBridge by which that MAC address is
reachable so that the querying RBridge can
forward an unknown (before the query)
destination MAC address native frame as a
unicast TRILL Data packet rather than flooding
it, or
(1b) the IP address corresponding to the MAC address
so that RBridge can locally respond to a RARP
[RFC903] native frame.
(2) An IPv4 or IPv6 address with the querying RBridge
interested in the corresponding MAC address so it can
locally respond to an ARP [RFC826] or ND [RFC4861]
native frame [ARPND].
But the query address could be some other address type
for which an AFN has been assigned, such as a 64-bit MAC
address [RFC7042] or a CLNS address [X.233].
Query Frame: Where a QUERY Record is the result of an ARP,
ND, RARP, SEND, or unknown unicast MAC destination
address, the ingress TRILL switch MAY send the frame to a
Pull Directory Server if the frame is small enough that
the resulting Query Message fits into a TRILL Data packet
within the campus MTU. The full frame is included,
starting with the destination and source MAC addresses
but does not include the FCS.
If no response is received to a Pull Directory Query Message within a
configurable timeout (DirQueryTimeout, see Section 3.9), then the
Query Message should be re-transmitted with the same Sequence Number
(up to a configurable number of times (DirQueryRetries, see Section
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3.9)). If there are multiple QUERY Records in a Query Message,
responses can be received to various subsets of these QUERY Records
before the timeout. In that case, the remaining unanswered QUERY
Records should be re-sent in a new Query Message with a new sequence
number. If a TRILL switch is not capable of handling partial
responses to queries with multiple QUERY Records, it MUST NOT send a
Request Message with more than one QUERY Record in it.
See Section 3.6 for a discussion of how Query Message errors are
handled.
3.2.2 Pull Directory Responses
A Pull Directory Query Message results in a Pull Directory Response
Message as described in Section 3.2.2.1.
In addition, if the QUERY Record QTYPE was 2 or 5, the frame included
in the Query may be modified and forwarded by the Pull Directory
server as described in Section 3.2.2.2.
3.2.2.1 Pull Directory Response Message Format
Pull Directory Response Messages are sent as the Channel Protocol
specific content of an RBridge Channel message [RFC7178] TRILL Data
packet or as a native RBridge Channel data frame (see Section 3.5).
Responses are sent with the same Data Label and priority as the Query
Message to which they correspond except that the Response Message
priority is limited to be not more than the configured value
DirRespMaxPriority (Section 3.9).
The RBridge Channel protocol specific data format is as follows:
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1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver | Type | Flags | Count | Err | SubErr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESPONSE 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
| RESPONSE 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
| ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
| RESPONSE K
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
Ver, Sequence Number: As specified in Section 3.1.
Type: 2 = Response.
Flags: MUST be sent as zero and ignored on receipt.
Count: Count is the number of RESPONSE Records present in the
Response Message.
Err, SubErr: A two-part error code. Zero unless there was an error
in the Query Message, for which case see Section 3.6.
RESPONSE: Each RESPONSE Record within a Pull Directory Response
Message is formatted as follows:
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| SIZE |OV| RESV | Index |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| Lifetime |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| Response Data ...
+--+--+--+--+--+--+--+--+--+--+--...
SIZE: The size of the RESPONSE Record is an unsigned integer
number of bytes not including the SIZE field and following
byte. A value of SIZE so large that the material doesn't fit
in the Query Message indicates a malformed RESPONSE Record.
The RESPONSE Record with such an excessive SIZE value and
any subsequent RESPONSE Records MUST be ignored and the
entire Response Message MAY be ignored.
OV: The overflow flag. Indicates, as described below, that
there was too much Response Data to include in one Response
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Message.
RESV: Three reserved bits that MUST be sent as zero and ignored
on receipt.
Index: The relative index of the QUERY Record in the Query
Message to which this RESPONSE Record corresponds. The index
will always be one for Query Messages containing a single
QUERY Record. If the Index is larger than the Count was in
the corresponding Query, that RESPONSE Record MUST be
ignored and subsequent RESPONSE Records or the entire
Response Message MAY be ignored.
Lifetime: The length of time for which the response should be
considered valid in units of 100 milliseconds except that
the values zero and 2**16-1 are special. If zero, the
response can only be used for the particular query from
which it resulted and MUST NOT be cached. If 2**16-1, the
response MAY be kept indefinitely but not after the Pull
Directory server goes down or becomes unreachable. (The
maximum definite time that can be expressed is a little over
1.8 hours.)
Response Data: There are three types of RESPONSE Records.
- If the Err field of the enclosing Response Message has a
message level error code in it, then the RESPONSE Records
are omitted and Count will be zero. See Section 3.6 for
additional information on errors.
- If the Err field of the enclosing Response Message has a
record level error code in it, then the RESPONSE Records
are those in error as further described in Section 3.6.
- If the Err field of the enclosing Response Message is
zero, then the Response Data in each RESPONSE Record is
formatted as the value part of an Interface Addresses
APPsub-TLV [RFC7961]. The maximum size of such contents
is 255 bytes, in which case the RESPONSE Record SIZE
field is 255.
Multiple RESPONSE Records can appear in a Response Message with the
same Index if an answer to the QUERY Record consists of multiple
Interface Address APPsub-TLV values. This would be necessary if, for
example, a MAC address within a Data Label appears to be reachable by
multiple TRILL switches. However, all RESPONSE Records to any
particular QUERY Record MUST occur in the same Response Message. If a
Pull Directory holds more mappings for a queried address than will
fit into one Response Message, it selects which to include by some
method outside the scope of this document and sets the overflow flag
(OV) in all of the RESPONSE Records responding to that query address.
See Section 3.6 for a discussion of how errors are handled.
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3.2.2.2 Pull Directory Forwarding
Query Messages with QTYPEs 2 and 5 are interpreted and handled as
described below. In these cases, if the information implicitly sought
is not in the directory and the FR flag in the query message was one,
the provided frame is forwarded by the Pull Directory server as a
multi-destination TRILL Data packet with the ingress nickname of the
Pull Directory server (or proxy if it is hosted on an end station) in
the TRILL header. If the FR flag is zero, the frame is not forwarded
in this case.
If there was no error in the handling of the enclosing Query Message,
the Pull Directory server forwards the frame inside that QUERY
Record, after modifying it in some cases, as described below:
ARP: When QTYPE is 2 and the Ethertype in the QUERY Record indicates
that an ARP [RFC826] frame is included in the Record: The ar$op
field MUST be ares_op$REQUEST and for the response described in
3.2.2.1, this is treated as a query for the target protocol
address where the AFN of that address is given by ar$pro. (ARP
field and value names with embedded dollar signs are specified in
[RFC826].) If ar$op is not ares_op$REQUEST or the ARP is malformed
or the query fails, an error is returned. Otherwise the ARP is
modified into the appropriate ARP response that is then sent by
the Pull Directory server as a TRILL Data packet.
ND/SEND: When QTYPE is 2 and the Ethertype in the QUERY Record
indicates an IPv6 Neighbor Discover (ND [RFC4861]) or Secure
Neighbor Discover (SEND [RFC3971]) frame is included in the
Record: Only Neighbor Solicitation ND frames (corresponding to an
ARP query) are allowed. An error is returned for other ND frames
or if the target address is not found. Otherwise, if the ND is not
a SEND, an ND Neighbor Advertisement response is returned by the
Pull Directory server as a TRILL Data packet. In the case of SEND
[RFC3971], an error is returned indicating that SEND was received
by the Pull Directory and the Pull Directory then either forwards
the SEND frame to the holder of the IPv6 address if that
information is in the directory or the directory multicasts the
SEND frame.
RARP: When QTYPE is 2 and the Ethertype in the QUERY Record indicates
that a RARP [RFC903] frame is included in the Record: If the ar$op
field is ares_op$REQUEST, the frame is handled as an ARP as
described above. Otherwise the ar$op field MUST be 'reverse
request' and for the response described in 3.2.2.1, this is
treated as a query for the target hardware address where the AFN
of that address is given by ar$hrd. (See [RFC826] for RARP
fields.) If ar$op is not one of these values or the RARP is
malformed or the query fails, an error is returned. Otherwise the
RARP is modified into the appropriate RARP response that is then
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unicast by the Pull Directory server as a TRILL Data packet to the
source hardware MAC address.
MacDA: When QTYPE is 5, indicating a frame is provided in the QUERY
Record whose destination MAC address TRILL switch attachment is
unknown, the only requirement is that this MAC address has to be
unicast. The Ethertype in the QUERY Record is ignored. If it is
group addressed an error is returned. For the response described
in 3.2.2.1, it is treated as a query for the MacDA. If the Pull
Directory contains TRILL switch attachment information for the MAC
address in the Data Label of the Query Message, it forwards the
frame to that switch in a unicast TRILL Data packet.
3.3 Cache Consistency
Unless it sends all responses with a Lifetime of zero, a Pull
Directory MUST take action, by sending Update Messages, to minimize
the amount of time that a TRILL switch will continue to use stale
information from that Pull Directory. The format of Update Messages
and the Acknowledge Messages used to respond to Update Messages are
given in Sections 3.3.1 and 3.3.2.
A Pull Directory server MUST maintain one of three sets of records
concerning possible cached data at clients of that server. These are
numbered and listed below in order of increasing specificity:
Method 1, Least Specific. An overall record per Data Label of when
the last positive response data sent will expire and when the
last negative response sent will expire; the records are
retained until such expiration.
Pro: Minimizes the record keeping burden on the Pull
Directory server.
Con: Increases the volume of and overhead due to spontaneous
Update Messages and due to unnecessarily invalidating cached
information.
Method 2, Medium Specificity. For each unit of data (IA APPsub-TLV
Address Set [RFC7961]) held by the server, record when the last
response sent with that positive response data will expire. In
addition, record each address about which a negative response
was sent by the server and when the last such negative response
will expire. Each such record of a positive or negative response
is discarded upon expiration.
Pro/Con: An intermediate level of detail in server record
keeping and an intermediate volume of and overhead due to
spontaneous Update Messages with some unnecessary invalidation
of cached information.
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Method 3, Most Specific. For each unit of data held by the server
(IA APPsub-TLV Address Set [RFC7961]) and each address about
which a negative response was sent, a list of TRILL switches
that were sent that data as a positive response or sent a
negative response for the address, and the expected time to
expiration for that data or address at each such TRILL switch,
assuming the requester cached the response. Each list entry is
retained until such expiration time.
Pro: Minimizes spontaneous Update Messages sent to update
pull client TRILL switch caches and minimizes unnecessary
invalidation of cached information.
Con: Increased record keeping burden on the Pull Directory
server.
RESPONSE Records sent with a zero lifetime are considered to have
already expired and so do not need to be tracked. In all cases, there
may still be brief periods of time when directory information has
changed, but information a pull client has cached has not yet been
updated or expunged.
A Pull Directory server might have a limit as to how many TRILL
switches for which it can maintain detailed expiry information by
method 3 above or how many data units or addresses it can maintain
expiry information for by method 2 or the like. If such limits are
exceeded, it MUST transition to a lower numbered method but, in all
cases, MUST support, at a minimum, method 1, and SHOULD support
methods 2 and 3. Use of method 1 may be quite inefficient due to
large amounts of cached positive and negative information being
unnecessarily discarded.
When data at a Pull Directory is changed, deleted, or added and there
may be unexpired stale information at a requesting TRILL switch, the
Pull Directory MUST send an Update Message as discussed below. The
sending of such an Update Message MAY be delayed by a configurable
number of milliseconds (DirUpdateDelay, see Section 3.9) to await
other possible changes that could be included in the same Update.
1. If method 1, the least detailed method, is being followed, then
when any Pull Directory information in a Data Label is changed
or deleted and there are outstanding cached positive data
response(s), an all-addresses flush positive data Update Message
is flooded within that Data Label as an RBridge Channel Message.
Similarly if data is added and there are outstanding cached
negative responses, an all-addresses flush negative message is
similarly flooded. The Count field is zero in an Update Message
indicates "all-addresses". On receiving an all-addresses flooded
flush positive Update from a Pull Directory server it has used,
indicated by the F and P bits being one and the Count being
zero, a TRILL switch discards the cached data responses it has
for that Data Label. Similarly, on receiving an all addresses
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flush negative Update, indicated by the F and N bits being one
and the Count being zero, it discards all cached negative
replies for that Data Label. A combined flush positive and
negative can be flooded by having all of the F (flood), P
(positive), and N (negative) bits (see Section 3.3.1) set to one
and the Count field zero resulting in the discard of all
positive and negative cached information for the Data Label.
2. If method 2 is being followed, then a TRILL switch floods
address specific positive Update Messages when data that might
be cached by a querying TRILL switch is changed or deleted and
floods address specific negative Update Messages when such
information is added to. Such messages are sent as RBridge
Channel messages. The F bit will be one; however, the Count
field will be non-zero and either the P or N bit, but not both,
will be one. There are actually four possible message types
that can be flooded:
2.a If data that might still be cached is updated:
An unsolicited Update Message is sent with the P flag
set and the Err field zero. On receipt, the addresses in the
RESPONSE Records are compared to the addresses for which the
receiving TRILL switch is holding cached positive
information from that server. If they match, the cached
information is updated.
2.b If data that might still be cached is deleted:
An unsolicited Update Message is sent with the P flag
set and the Err field non-zero giving the error that would
now be encountered in attempting to pull information for the
relevant address from the Pull Directory server. In this
non-zero Err field case, the RESPONSE Record(s) differ from
non-zero Err Reply Message RESPONSE Records in that they do
include an interface address set. Any cached positive
information for the addresses given is deleted and the
negative response is cached as per the lifetime given.
2.c If data for an address for which a negative response was
sent is added, so that negative response that might still be
cached is now incorrect:
An unsolicited Update Message is sent with the N flag
set to one and the Err field zero. The addresses in the
RESPONSE Records are compared to the addresses for which the
receiving TRILL switch is holding cached negative
information from that server; if they match, the cached
negative information is deleted and the positive information
provided is cached as per the lifetime given.
2.d In the rare case where it is desired to change the lifetime
or error associated with negative information that might
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still be cached:
An unsolicited Update Message is sent with the N flag
set to one and the Err field non-zero. As in case 2.b above,
the RESPONSE Record(s) give the relevant addresses. Any
cached negative information for the address is updated.
3. If method 3 is being followed, the same sort of unsolicited
Update Messages are sent as with method 2 above except they are
not normally flooded but unicast only to the specific TRILL
switches the directory server believes may be holding the cached
positive or negative information that needs deletion or
updating. However, a Pull Directory server MAY flood unsolicited
updates under method 3, for example if it determines that a
sufficiently large fraction of the TRILL switches in some Data
Label are requesters that need to be updated so that flooding is
more efficient that unicast.
A Pull Directory server tracking cached information with method 3
MUST NOT clear the indication that it needs to update cached
information at a querying TRILL switch until it has either (a) sent
an Update Message and received a corresponding Acknowledge Message or
(b) it has sent a configurable number of updates at a configurable
interval that default to 3 updates 100 milliseconds apart (see
Section 3.9).
A Pull Directory server tracking cached information with methods 2 or
1 SHOULD NOT clear the indication that it needs to update cached
information until it has sent an Update Message and received a
corresponding Acknowledge Message from all of its ESADI neighbors or
it has sent a number of updates at an interval as in the paragraph
above.
3.3.1 Update Message Format
An Update Message is formatted as a Response Message with the
differences described in Section 3.3 above and the following:
o The Type field in the message header is set to 3.
o The Index field in the RESPONSE Record(s) is set to zero on
transmission and ignored on receipt (but the Count field in the
Update Message header MUST still correctly indicate the number of
RESPONSE Records present).
o The priority with which the message is sent, DirUpdatePriority, is
configurable and defaults to 5 (see Section 3.9).
Update Messages are initiated by a Pull Directory server. The
Sequence number space used is controlled by the originating Pull
Directory server. This update Sequence number space is different from
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the Sequence number space used in a Query and the corresponding
Response that are controlled by the querying TRILL switch.
The 4-bit Flags field of the message header for an Update Message is
as follows:
+---+---+---+---+
| F | P | N | R |
+---+---+---+---+
F: The Flood bit. If zero, the Update Message is unicast. If F=1, it
is multicast to All-Egress-RBridges.
P, N: Flags used to indicate positive or negative Update Messages.
P=1 indicates positive. N=1 indicates negative. Both may be 1 for
a flooded all addresses Update.
R: Reserved. MUST be sent as zero and ignored on receipt
For tracking methods 2 and 3 in Section 3.3.1, a particular Update
Message MUST have either the P flag or the N flag set but not both.
If both are set, the Update Message MUST be ignored as this
combination is only valid for method 1.
3.3.2 Acknowledge Message Format
An Acknowledge Message is sent in response to an Update Message to
confirm receipt or indicate an error, unless response is inhibited by
rate limiting. It is formatted as a Response Message but the Type is
set to 4.
If there are no errors in the processing of an Update Message or if
there is a message level overall or header error in an Update
Message, the message is echoed back with the Err and SubErr fields
set appropriately, the Type changed to Acknowledge, and a null
records section with the Count field set to zero.
If there is a record level error in an Update Message, one or more
Acknowledge Messages may be returned with the erroneous record(s)
indicated as discussed in Section 3.6.
The Acknowledge Messages is sent with the same priority as the Update
Message it acknowledges but not more than a configured priority
(DirAckMaxPriority) that defaults to 5 (see Section 3.9).
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3.4 Summary of Records Formats in Messages
As specified in Section 3.2 and 3.3, the Query, Response, Update, and
Acknowledge Messages can have zero or more repeating Record
structures under different circumstances, as summarized below. The
"Err" column abbreviations in this table have the meanings listed
below. "IA APPsub-TLV value" means the value part of the IA APPsub-
TLV specified in [RFC7961].
MBZ = MUST be zero
Z = zero
NZ = non-zero
NZM = non-zero message level error
NZR = non-zero record level error
Message Err Section Record Structure Response Data
----------- --- ------- ---------------- ------------------
Query MBZ 3.2.1 QUERY Record -
Response Z 3.2.2.1 RESPONSE Record IA APPsub-TLV value
Response NZM 3.2.2.1 null -
Response NZR 3.2.2.1 RESPONSE Record Records with error
Update MBZ 3.3.1 RESPONSE Record IA APPsub-TLV value
Acknowledge Z 3.3.2 null -
Acknowledge NZM 3.3.2 null -
Acknowledge NZR 3.3.2 RESPONSE Record Records with error
See Section 3.6 for further details on errors.
3.5 End Stations and Pull Directories
A Pull Directory can be hosted on an end station as specified in
Section 3.5.1.
A end station can use a Pull Directory as specified in Section 3.5.2.
This capability would be useful in supporting an end station that
performs directory assisted encapsulation [DirAsstEncap] or that is a
"smart end node" [SmartEN].
The native Pull Directory messages used in these cases are as
specified in Section 3.5.3. In these cases, the edge RBridge(s) and
end station(s) involved need to detect each other and exchange some
control information. This is accomplished with the TRILL ES-IS
mechanism specified in Section 5.
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3.5.1 Pull Directory Hosted on an End Station
Optionally, a Pull Directory actually hosted on an end station MAY be
supported. In that case, one or more TRILL switches must act as
indirect Pull Directory servers. That is, they host a Pull Directory
server, which is seen by other TRILL switches in the campus, and a
Pull Directory client, which fetches directory information from one
or more End Station Pull Directory servers, where at least some of
the information served up by the Pull Directory server may be
information fetched from an end station to which it is directly
connected by the co-located Pull Directory client. (Direct connection
means a connection not involving any intermediate TRILL switches.)
End stations hosting a Pull Directory server MUST support TRILL ES-IS
(see Section 5) and advertise the Data Labels for which they are
providing service in one or more Interested VLAN or Interested Label
sub-TLVs by setting the PUL flag (see Section 7.3).
* * * * * * *
+---------------+ * *
| End Station 1 | +---------------+ *
| Pull Directory+--------------+ RB1, Pull | *
| Server | | Directory| *
+---------------+ +-------+ Client|Server | +----+
| +---------------+ |RB99|
+---------------+ | * +----+
| End Station 2 | +--+---+ +---------------+ *
| Pull Directory+---+Bridge+---+ RB2, Pull | *
| Server | +--+---+ | Directory| *
+---------------+ | | Client|Server | *
| +---------------+ *
| * TRILL *
. * Campus *
. * *
. * * * * * * *
Figure 2. End Station Pull Directory Example
The figure above gives an example where RB1 and RB2 advertise
themselves to the rest of the TRILL campus, such as RB99, as Pull
Directory servers and obtain at least some of the information they
are serving up by issuing Pull Directory queries to end stations 1
and/or 2. This example is specific but many variations are possible.
The Bridge shown might be a complex bridged LAN, a LAN without a
bridge (as shown for End Station 1), or connected via point-to-point
links (as shown for End Station 2 that is connected through a bridge
with point-to-point Ethernet links to RB1 and RB2). There could be
one or more than two RBridges having such indirect Pull Directory
servers. Furthermore, there could be one or more than two end
stations with Pull Directory servers on them. Each TRILL switch
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server could then be differently configured as to the Data Labels for
which it is providing indirect service selected from the union of the
Data Labels supported by the End Station hosted servers and could
select from among those End Station hosted servers supporting each
Data Label the indirect server is configured to serve up.
When an indirect Pull Directory server receives a Query Message from
another TRILL switch, it answers from information it has cached or
issues Pull Directory request to End Station Pull Directory servers
with which it has TRILL ES-IS adjacency to obtain the information.
Any Response sent by an indirect Pull Directory server MUST NOT have
a validity time longer that the valid of the data on which it is
based. When an indirect Pull Directory server receives Update
Messages, it updates its cached information and MUST originate Update
messages to any clients that may have mirrors of the cached
information so updated.
Since an indirect Pull Directory server discards information it has
cached from queries to an end station Pull Directory server if it
loses adjacency to the server (Section 3.7), if it detects that such
information may be cached at RBridge clients and has no other source
for the information, it MUST send Update Messages to those clients
withdrawing the information. For this reason, indirect Pull Directory
servers may wish to query multiple sources, if available, and cache
multiple copies of returned information from those multiple sources.
Then if one end station source becomes inaccessible or withdraws the
information but the indirect Pull Directory server has the
information from another source, it need not originate Updates.
3.5.2 Use of Pull Directory by End Stations
Some special end stations, such as those discussed in [DirAsstEncap]
and [SmartEN], may need to access directory information. How edge
RBridges provide this optional service is specified below.
When Pull Directory support is provided by an edge RBridge to end
stations, the messages used are as specified in Section 3.5.3 below.
The edge RBridge MUST support TRILL ES-IS (Section 5) and advertises
the Data Labels for which it offers this service to end stations by
setting the Pull Directory flag (PUL) to one in its Interested VLANs
or Interested Labels sub-TLV (see Section 7.3) for that Data Label
advertised through TRILL ES-IS.
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3.5.3 Native Pull Directory Messages
The Pull Directory messages used between TRILL switches and end
stations are native RBridge Channel messages [RFC7178]. These
RBridge Channel messages use the same Channel protocol number as the
inter-RBridge Pull Directory RBridge Channel messages. The Outer.VLAN
ID used is the TRILL ES-IS Designated VLAN (see Section 5) on the
link to the end station. Since there is no TRILL Header or inner Data
Label for native RBridge Channel messages, that information is added
to the Pull Directory message header as specified below.
The native RBridge Channel message Pull Directory message protocol
dependent data part is the same as for inter-RBridge Channel messages
except that the 8-byte header described in Section 3.1 is expanded to
12 or 16 bytes as follows:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver | Type | Flags | Count | Err | SubErr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Label ... (4 or 8 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+
| Type Specific Payload - variable length
+-+-+- ...
Fields other than Data Label are as in Section 3.1. The Data Label
that normally appears right after the Inner.MacSA of the an RBridge
Channel Pull Directory message appears in the Data Label field of the
Pull Directory message header in the native RBridge Channel message
version. This Data Label appears in a native Query Message, to be
reflected in a Response Message, or it might appear in a native
Update to be reflected in an Acknowledge Message. Since the
appropriate VLAN or FGL [RFC7172] Ethertype is included, the length
of the Data Label can be determined from the first two bytes.
3.6 Pull Directory Message Errors
A non-zero Err field in the Pull Directory Response or Acknowledge
Message header indicates an error message.
If there is an error that applies to an entire Query or Update
Message or its header, as indicated by the range of the value of the
Err field, then the QUERY Records probably were not even looked at by
the Pull Directory Server and would provide no additional information
in the Response or Acknowledge Message. Therefore, the Records
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section of the Query Response or Update Message is omitted and the
Count field is set to zero in the Response or Acknowledgment Message.
If errors occur at the QUERY Record level for a Query Message, they
MUST be reported in a Response Message separate from the results of
any successful non-erroneous QUERY Records. If multiple QUERY Records
in a Query Message have different errors, they MUST be reported in
separate Response Messages. If multiple QUERY Records in a Query
Message have the same error, this error response MAY be reported in
one or multiple Response Messages. In an error Response Message, the
QUERY Record or Records being responded to appear, expanded by the
Lifetime for which the server thinks the error might persist (usually
2**16-1 which indicates indefinitely) and with their Index inserted,
as the RESPONSE Record or Records.
If errors occur at the RESPONSE Record level for an Update Message,
they MUST be reported in an Acknowledge Message separate from the
acknowledgment of any non-erroneous RESPONSE Records. If multiple
RESPONSE Records in an Update have different errors, they MUST be
reported in separate Acknowledge Messages. If multiple RESPONSE
Records in an Update Message have the same error, this error response
MAY be reported in one or multiple Acknowledge Messages. In an error
Acknowledge Message, the RESPONSE Record or Records being responded
to appear, expanded by the time for which the server thinks the error
might persist and with their Index inserted, as a RESPONSE Record or
Records.
Err values 1 through 126 are available for encoding Request or Update
Message level errors. Err values 128 through 254 are available for
encoding QUERY or RESPONSE Record level errors. The SubErr field is
available for providing more detail on errors. The meaning of a
SubErr field value depends on the value of the Err field.
3.6.1 Error Codes
The following table lists error code values for the Err field, their
meaning, and whether they apply at the Message or Record level.
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Err Level Meaning
------ ------- -------
0 - No Error
1 Message Unknown or reserved Query Message field value
2 Message Request Message/data too short
3 Message Unknown or reserved Update Message field value
4 Message Update Message/data too short
5-126 Message Unassigned
127 - Reserved
128 Record Unknown or reserved QUERY Record field value
129 Record QUERY Record truncated
130 Record Address not found
131 Record Unknown or reserved RESPONSE Record field value
132 Record RESPONSE Record truncated
133-254 Record Unassigned
255 - Reserved
Note that some error codes are for overall message level errors while
some are for errors in the repeating records that occur in messages.
3.6.2 Sub-Errors Under Error Codes 1 and 3
The following sub-errors are specified under error codes 1 and 3:
SubErr Field with Error
------ ----------------
0 Unspecified
1 Version not understood (see Section 3.1.1)
2 Unknown Type field value
3 Specified Data Label not being served
4-254 Unassigned
255 Reserved
3.6.3 Sub-Errors Under Error Codes 128 and 131
The following sub-errors are specified under error code 128 and 131:
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SubErr Field with Error
------ ----------------
0 Unspecified
1 Unknown AFN field value
2 Unknown or Reserved QTYPE field value
3 Invalid or inconsistent SIZE field value
4 Invalid frame for QTYPE 2 (other than SEND)
5 SEND frame sent as QTYPE 2
6 Invalid frame for QTYPE 5 (such as multicast MacDA)
7-254 Unassigned
255 Reserved
3.7 Additional Pull Details
A Pull Directory client MUST notice, by tracking link state changes,
when a Pull Directory server is no longer accessible (data reachable
[RFC7780] for the inter-RBridge case or TRILL ES-IS (Section 5)
adjacent for end station to RBridge case), and MUST promptly discard
all pull responses it is retaining from that server as it can no
longer receive cache consistency Update Messages from the server.
A secondary Pull Directory server is one that obtains its data from a
primary directory server. See discussion of primary to secondary
directory information transfer in Section 2.6.
3.8 The No Data Flag
In the TRILL base protocol [RFC6325] as extended for FGL [RFC7172],
the mere presence of an Interested VLANs or Interested Labels sub-
TLVs in the LSP of a TRILL switch indicates connection to end
stations in the VLAN(s) or FGL(s) listed and thus a need to receive
multi-destination traffic in those Data Labels. However, with Pull
Directories, advertising that you are a directory server requires
using these sub-TLVs to indicate the Data Label(s) you are serving.
If a directory server does not wish to received multi-destination
TRILL Data packets for the Data Labels it lists in one of the
Interested VLAN or Interested FGL [RFC7172] sub-TLVs, it sets the "No
Data" (NOD) bit to one (see Section 7.3). This means that data on a
distribution tree may be pruned so as not to reach the "No Data"
TRILL switch as long as there are no TRILL switches interested in the
Data Label that are beyond the "No Data" TRILL switch on that
distribution tree. The NOD bit is backwards compatible as TRILL
switches ignorant of it will simply not prune when they could, which
is safe although it may cause increased link utilization by some
sending multi-destination traffic where it is not needed.
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Push Directories advertise themselves inside ESADI which normally
requires the ability to send and receive multi-destination TRILL Data
packets but can be implemented with serial unicast.
Examples of a TRILL switch serving as a directory that might not want
multi-destination traffic in some Data Labels would be a TRILL switch
that does not offer end station service for any of the Data Labels
for which it is serving as a directory and is either
- a Pull Directory and/or
- a Push Directory for one or more Data Labels where all of the
ESADI traffic for those Data Labels will be handled by unicast
ESADI [RFC7357].
A Push Directory MUST NOT set the NOD bit for a Data Label if it
needs to communicate via multi-destination ESADI or RBridge Channel
PDUs in that Data Label since such PDUs look like TRILL Data packets
to transit TRILL switches and are likely to be incorrectly pruned if
NOD was set.
3.9 Pull Directory Service Configuration
The following per RBridge scalar configuration parameters are
available for controlling Pull Directory service behavior. In
addition, there is a configurable per Data Label mapping from the
priority of a native frame being ingress to the priority of any Pull
Directory query it causes. The default such mapping depends on the
client strategy as described in Section 4.
Name Default Section Note Below
------------------ ------- ------- ----------
DirQueryTimeout 100 milliseconds 3.2.1 1
DirQueryRetries 3 3.2.1 1
DirGenQPriority 5 3.2.1 2
DirRespMaxPriority 6 3.2.2.1 3
DirUpdateDelay 50 milliseconds 3.3
DirUpdatePriority 5 3.3.1
DirUpdateTimeout 100 milliseconds 3.3.3
DirUpdateRetries 3 3.3.3
DirAckMaxPriority 5 3.3.2 4
Note 1: Pull Directory Query client timeout waiting for response and
maximum number of retries
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Note 2: Priority for client generated requests (such as a query to
refresh cached information).
Note 3: Pull Directory Response Messages SHOULD NOT be sent with
priority 7 as that priority SHOULD be reserved for messages critical
to network connectivity.
Note 4: Pull Directory Acknowledge Messages SHOULD NOT be sent with
priority 7 as that priority SHOULD be reserved for messages critical
to network connectivity.
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4. Directory Use Strategies and Push-Pull Hybrids
For some edge nodes that have a great number of Data Labels enabled,
managing the MAC and Data Label <-> Edge RBridge mapping for hosts
under all those Data Labels can be a challenge. This is especially
true for Data Center gateway nodes, which need to communicate with
many, if not all, Data Labels.
For those edge TRILL switch nodes, a hybrid model should be
considered. That is, the Push Model is used for some Data Labels or
addresses within a Data Label while the Pull Model is used for other
Data Labels or addresses within a Data Label. It is the network
operator's decision by configuration as to which Data Labels' mapping
entries are pushed down from directories and which Data Labels'
mapping entries are pulled.
For example, assume a data center where hosts in specific Data
Labels, say VLANs 1 through 100, communicate regularly with external
peers. Probably, the mapping entries for those 100 VLANs should be
pushed down to the data center gateway routers. For hosts in other
Data Labels that only communicate with external peers occasionally
for management interfacing, the mapping entries for those VLANs
should be pulled down from directory when the need comes up.
Similarly, it could be that within a Data Label that some addresses,
such as the addresses of gateways, file, DNS, or database server
hosts are commonly referenced by most other hosts but those other
hosts, perhaps compute engines, are typically only referenced by a
few hosts in that Data Label. In that case, the address information
for the commonly referenced hosts could be pushed as an incomplete
directory while the addresses of the others are pulled when needed.
The mechanisms described in this document for Push and Pull Directory
services make it easy to use Push for some Data Labels or addresses
and Pull for others. In fact, different TRILL switches can even be
configured so that some use Push Directory services and some use Pull
Directory services for the same Data Label if both Push and Pull
Directory services are available for that Data Label. And there can
be Data Labels for which directory services are not used at all.
There are a wide variety of strategies that a TRILL switch can adopt
for making use of directory assistance. A few suggestions are given
below.
- Even if a TRILL switch will normally be operating with
information from a complete Push Directory server, there will be a
period of time when it first comes up before the information it
holds is complete. Or, it could be that the only Push Directories
that can push information to it are incomplete or that they are
just starting and may not yet have pushed the entire directory.
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Thus, it is RECOMMENDED that all TRILL switches have a strategy
for dealing with the situation where they do not have complete
directory information. Examples are to send a Pull Directory query
or to revert to [RFC6325] behavior.
- If a TRILL switch receives a native frame X resulting in
seeking directory information, a choice needs to be made as to
what to do if it does not already have the directory information
it needs. In particular, it could (1) immediately flood the TRILL
Data packet resulting from ingressing X in parallel with seeking
the directory information, (2) flood that TRILL Data packet after
a delay, if it fails to obtain the directory information, or (3)
discard X if it fails to obtain the information. The choice might
depend on the priority of frame X since the higher that priority
typically the more urgent the frame is and the greater the
probability of harm in delaying it. If a Pull Directory request is
sent, it is RECOMMENDED that its priority be derived from the
priority of the frame X with the derived priority configurable and
having the following defaults:
Ingressed If Flooded If Flooded
Priority Immediately After Delay
-------- ----------- -----------
7 5 6
6 5 6
5 4 5
4 3 4
3 2 3
2 0 2
0 1 0
1 1 1
NOTE: The odd looking numbers towards the bottom of the columns
above are because priority 1 is lower than priority zero. That is
to say, the values in the first column are in priority order. They
will look more logical if you think of "0" as being "1 1/2".
Priority 7 is normally only used for urgent messages critical to
adjacency and so SHOULD NOT be the default for directory traffic.
Unsolicited updates are sent with a priority that is configured per
Data Label that defaults to priority 5.
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5. TRILL ES-IS
TRILL ES-IS (End System to Intermediate System) is a variation of
TRILL IS-IS [RFC7176] [RFC7177] [RFC7780] designed to operate on a
TRILL link among and between one or more TRILL switches and end
stations on that link. Support of TRILL ES-IS is generally optional
for both the TRILL switches and the end stations on a link but may be
required to support certain features. As of the date of this
document, the only features requiring TRILL ES-IS are those listed in
this Section 5.
TRILL ES-IS is useful in supporting Pull Directory hosting on or use
from end stations (see Section 3.5) and supporting specialized end
stations [DirAsstEncap] [SmartEN] and may have additional future
uses. The advantages of TRILL ES-IS over simply making an "end
station" be a TRILL Switch include relieving the end station of
having to maintain a copy of the core link state database (LSPs) and
of having to perform routing calculations or having the ability to
forward traffic.
Except as provided below in this Section 5, TRILL ES-IS PDUs and TLVs
are the same TRILL IS-IS PDUs and TLVs.
5.1 PDUs and System IDs
All TRILL ES-IS PDUs (except some MTU-probe and MTU-ack PDUs which
may be unicast) are multicast using the TRILL-ES-IS multicast MAC
address (see Section 7.6). This use of a different multicast address
assures that TRILL ES-IS and TRILL IS-IS PDUs will not be confused
for one another.
Because end stations do not have IS-IS System IDs, TRILL ES-IS uses
port MAC addresses in their place. This is convenient since MAC
addresses are 48-bit and almost all IS-IS implementations use 48-bit
System IDs. Logically TRILL IS-IS operates between the TRILL switches
in a TRILL campus as identified by System ID while TRILL ES-IS
operates between Ethernet ports on an Ethernet link (which may be a
bridged LAN) as identified by MAC address [RFC6325].
As System IDs of TRILL Switches in a campus are required to be
unique, so the MAC addresses of TRILL ES-IS ports on a link MUST be
unique.
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5.2 Adjacency, DRB Election, Hellos, TLVs, Etc.
TRILL ES-IS Adjacency formation and DRB election operate between the
ports on the link as specified in [RFC7177] for a broadcast link.
The DRB specifies an ES-IS Designated VLAN for the link. This
adjacency determination, DRB election, and Designated VLAM are
distinct from TRILL IS-IS adjacency, DRB election, and Designated
VLAN.
Although the "Report State" [RFC7177] exists for TRILL ES-IS
adjacencies, such adjacencies are only reported in TRILL ES-IS LSPs,
not in any TRILL IS-IS LSPs.
End stations supporting TRILL ES-IS MUST assign a unique Port ID to
each of their TRILL ES-IS ports which appears in the TRILL ES-IS
Hellos they send.
TRILL ES-IS has nothing to do with Appointed Forwarders and the
Appointed Forwarders sub-TLV and VLANs Appointed sub-TLV [RFC7176]
are not used and SHOULD NOT be sent in TRILL ES-IS; if such a sub-TLV
is received in TRILL ES-IS it is ignored. (The Appointed Forwarders
on a link are determined as specified in [rfc6439bis] using TRILL IS-
IS.)
Although some of the ports sending TRILL ES-IS PDUs are on end
stations and thus not on routers (TRILL switches), they nevertheless
may make use of the Router Capability (#242) and MT-Capability (#222)
IS-IS TLVs to indicate capabilities as specified in [RFC7176].
TRILL ES-IS Hellos are like TRILL IS-IS Hellos but note the
following: In the Special VLANs and Flags Sub-TLV, any TRILL switches
advertise a nickname they own but for end stations that field MUST be
sent as zero and ignored on receipt. In addition, the AF and TR flag
bits MUST be sent as zero and the AC flag bit MUST be sent as one and
all three are ignored on receipt.
5.3 Link State
The only link state transmission and synchronization that occurs in
TRILL ES-IS is for E-L1CS PDUs (Extended Level 1 Circuit Scoped
[RFC7356]). In particular, the end station Ethernet ports supporting
TRILL ES-IS do not support the core TRILL IS-IS LSPs and do not
support E-L1FS LSPs (or the CSNPs or PSNPs corresponding to either of
them). TLVs and sub-TLVs that would otherwise be sent in TRILL IS-IS
LSPs or E-L1FS SPs are instead sent in E-L1CS LSPs.
D. Eastlake, et al [Page 44]
INTERNET-DRAFT TRILL: Directory Service Mechanisms
6. Security Considerations
For general TRILL security considerations, see [RFC6325].
6.1 Directory Information Security
Incorrect directory information can result in a variety of security
threats including those below. Directory servers therefore need to
take care to implement and enforce access control policies that are
not overly permissive.
Incorrect directory mappings can result in data being delivered to
the wrong end stations, or set of end stations in the case of
multi-destination packets, violating security policy.
Missing, incorrect, or inaccessible directory data can result in
denial of service due to sending data packets to black holes or
discarding data on ingress due to incorrect information that their
destinations are not reachable or that their source addresses are
forged.
For these reasons directory information needs to be protected from
unauthorized modification whatever server or end station it resides
on. Parties authorized to modify directory data can violate
availability and integrity policies.
6.2 Directory Confidentiality and Privacy
In implementations of the base TRILL protocol [RFC6325] [RFC7780],
RBridges deal almost exclusively with MAC addresses. Use of
directories to map to/from IP addresses means that RBridges deal more
actively with IP addresses as well. But RBridges in any case would be
exposed to plain text ARP/ND/SEND/IP traffic and so can see all this
addressing meta-data. So this more explicit dealing with IP addresses
has little effect on the privacy of end station traffic.
Parties authorized to read directory data can violate privacy polices
for such data.
6.3 Directory Message Security Considerations
Push Directory data is distributed through ESADI-LSPs [RFC7357].
ESADI is built on IS-IS and such data can thus be authenticated with
the widely implemented and deployed IS-IS PDU security. This
D. Eastlake, et al [Page 45]
INTERNET-DRAFT TRILL: Directory Service Mechanisms
mechanism provides authentication and integrity protection. See
[RFC5304] [RFC5310] and the Security Considerations section of
[RFC7357].
Pull Directory queries and responses are transmitted as RBridge-to-
RBridge or native RBridge Channel messages [RFC7178]. Such messages
can be secured by the mechanisms specified in [RFC7978]. These
mechanisms can provide authentication and confidentiality
protections. At the time of this RFC, these security mechanisms are
believed to be less widely implemented than IS-IS security.
D. Eastlake, et al [Page 46]
INTERNET-DRAFT TRILL: Directory Service Mechanisms
7. IANA Considerations
This section gives IANA assignment and registry considerations.
7.1 ESADI-Parameter Data Extensions
Action 1: IANA is requested to create a sub-registry in the TRILL
Parameters Registry as follows:
Sub-Registry: ESADI-Parameter APPsub-TLV Flag Bits
Registration Procedures: Standards Action
References: [RFC7357] [This document]
Bit Mnemonic Description Reference
--- -------- ----------- ---------
0 UN Supports Unicast ESADI ESADI [RFC7357]
1-2 PDSS Push Directory Server Status [this document]
3-7 - Available for assignment
Action 2: In addition, the ESADI-Parameter APPsub-TLV is optionally
extended, as provided in its original specification in ESADI
[RFC7357], by one byte as show below. Therefore [this document]
should be added as a second reference to the ESADI-Parameter APPsub-
TLV in the "TRILL APPsub-TLV Types under IS-IS TLV 251 Application
Identifier 1" Registry.
+-+-+-+-+-+-+-+-+
| Type | (1 byte)
+-+-+-+-+-+-+-+-+
| Length | (1 byte)
+-+-+-+-+-+-+-+-+
|R| Priority | (1 byte)
+-+-+-+-+-+-+-+-+
| CSNP Time | (1 byte)
+-+-+-+-+-+-+-+-+
| Flags | (1 byte)
+---------------+
|PushDirPriority| (optional, 1 byte)
+---------------+
| Reserved for (variable)
| expansion
+-+-+-+-...
The meanings of all the fields are as specified in ESDADI [RFC7357]
except that the added PushDirPriority is the priority of the
advertising ESADI instance to be a Push Directory as described in
Section 2.3. If the PushDirPriority field is not present (Length = 3)
it is treated as if it were 0x3F. 0x3F is also the value used and
D. Eastlake, et al [Page 47]
INTERNET-DRAFT TRILL: Directory Service Mechanisms
placed here by an TRILL switch whose priority to be a Push Directory
has not been configured.
7.2 RBridge Channel Protocol Numbers
Action 3: IANA is requested to assign a new RBridge Channel protocol
number from the range assignable by Standards Action and update the
subregistry of such protocol number in the TRILL Parameters Registry.
Description is "Pull Directory Services". Reference is [this
document].
7.3 The Pull Directory (PUL) and No Data (NOD) Bits
Actions 4 and 5: IANA is requested to assign a currently reserved
bits in the Interested VLANs field of the Interested VLANs sub-TLV
and the Interested Labels field of the Interested Labels sub-TLV
[RFC7176] to indicate Pull Directory server (PUL). This bit is to be
added, with this document as reference, to the "Interested VLANs Flag
Bits" and "Interested Labels Flag Bits" subregistries created by
[RFC7357] as shown below after Action 7.
Actions 6 and 7: IANA is requested to assign a currently reserved bit
in the Interested VLANs field of the Interested VLANs sub-TLV and the
Interested Labels field of the Interested Labels sub-TLV [RFC7176] to
indicate No Data (NOD, see Section 3.8). This bit is to be added,
with this document as reference, to the "Interested VLANs Flag Bits"
and "Interested Labels Flag Bits" subregistries created by [RFC7357]
as shown below.
Bits and format suggested for above actions 4 through 7 are shown
below:
Registry: Interested BLANs Flag Bits
Bit Mnemonic Description Reference
--- -------- -------------- ---------------
18 PUL Pull Directory [this document]
19 NOD No Data [this document]
Registry: Interested Labels Flag Bits
Bit Mnemonic Description Reference
--- -------- -------------- ---------------
6 PUL Pull Directory [this document]
7 NOD No Data [this document]
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INTERNET-DRAFT TRILL: Directory Service Mechanisms
7.4 TRILL Pull Directory QTYPEs
Action 8: IANA is requested to create a new Registry on the
"Transparent Interconnection of Lots of Links (TRILL) Parameters" web
page as follows:
Name: TRILL Pull Directory Query Types (QTYPEs)
Registration Procedure: IETF Review
Reference: [this document]
Initial contents as in Section 3.2.1.
7.5 Pull Directory Error Code Registries
Actions 9, 10, and 11: IANA is requested to create a new Registry and
two new indented SubRegistries under that Registry on the
"Transparent Interconnection of Lots of Links (TRILL) Parameters" web
page as follows:
Registry
Name: TRILL Pull Directory Errors
Registration Procedure: IETF Review
Reference: [this document]
Initial contents as in Section 3.6.1.
Sub-Registry
Name: Sub-codes for TRILL Pull Directory Errors 1 and 3
Registration Procedure: Expert Review
Reference: [this document]
Initial contents as in Section 3.6.2.
Sub-Registry
Name: Sub-codes for TRILL Pull Directory Errors 128 and 131
Registration Procedure: Expert Review
Reference: [this document]
Initial contents as in Section 3.6.3.
7.6 TRILL-ES-IS MAC Address
Action 12: IANA is requested to assign a TRILL multicast MAC address
from the "TRILL Multicast Addresses" registry on the TRILL Parameters
IANA web page [value 01-80-C2-00-00-47 recommended]. Description is
"TRILL-ES-IS". Reference is [this document].
D. Eastlake, et al [Page 49]
INTERNET-DRAFT TRILL: Directory Service Mechanisms
Normative References
[RFC826] - Plummer, D., "An Ethernet Address Resolution Protocol",
RFC 826, November 1982.
[RFC903] - Finlayson, R., Mann, T., Mogul, J., and M. Theimer, "A
Reverse Address Resolution Protocol", STD 38, RFC 903, June
1984
[RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997
[RFC3971] - Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC4861] - Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, October 2008.
[RFC5310] - Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic Authentication", RFC
5310, February 2009.
[RFC6165] - Banerjee, A. and D. Ward, "Extensions to IS-IS for
Layer-2 Systems", RFC 6165, April 2011.
[RFC6325] - Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, July 2011.
[RFC7042] - Eastlake 3rd, D. and J. Abley, "IANA Considerations and
IETF Protocol and Documentation Usage for IEEE 802 Parameters",
BCP 141, RFC 7042, October 2013.
[RFC7172] - Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R.,
and D. Dutt, "Transparent Interconnection of Lots of Links
(TRILL): Fine-Grained Labeling", RFC 7172, May 2014,
<http://www.rfc-editor.org/info/rfc7172>.
[RFC7176] - Eastlake 3rd, D., Senevirathne, T., Ghanwani, A., Dutt,
D., and A. Banerjee, "Transparent Interconnection of Lots of
Links (TRILL) Use of IS-IS", RFC 7176, May 2014,
<http://www.rfc-editor.org/info/rfc7176>.
[RFC7177] - Eastlake 3rd, D., Perlman, R., Ghanwani, A., Yang, H.,
and V. Manral, "Transparent Interconnection of Lots of Links
(TRILL): Adjacency", RFC 7177, DOI 10.17487/RFC7177, May 2014,
D. Eastlake, et al [Page 50]
INTERNET-DRAFT TRILL: Directory Service Mechanisms
<http://www.rfc-editor.org/info/rfc7177>.
[RFC7178] - Eastlake 3rd, D., Manral, V., Li, Y., Aldrin, S., and D.
Ward, "Transparent Interconnection of Lots of Links (TRILL):
RBridge Channel Support", RFC 7178, May 2014, <http://www.rfc-
editor.org/info/rfc7178>.
[RFC7356] - Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
Scope Link State PDUs (LSPs)", RFC 7356, DOI 10.17487/RFC7356,
September 2014, <http://www.rfc-editor.org/info/rfc7356>.
[RFC7357] - Zhai, H., Hu, F., Perlman, R., Eastlake 3rd, D., and O.
Stokes, "Transparent Interconnection of Lots of Links (TRILL):
End Station Address Distribution Information (ESADI) Protocol",
RFC 7357, September 2014, <http://www.rfc-
editor.org/info/rfc7357>.
[RFC7780] - Eastlake 3rd, D., Zhang, M., Perlman, R., Banerjee, A.,
Ghanwani, A., and S. Gupta, "Transparent Interconnection of
Lots of Links (TRILL): Clarifications, Corrections, and
Updates", RFC 7780, DOI 10.17487/RFC7780, February 2016,
<http://www.rfc-editor.org/info/rfc7780>.
[RFC7961] - Eastlake 3rd, D. and L. Yizhou, "Transparent
Interconnection of Lots of Links (TRILL): Interface Addresses
APPsub-TLV", RFC 7961, DOI 10.17487/RFC7961, August 2016,
<http://www.rfc-editor.org/info/rfc7961>.
[rfc6439bis] - D. Eastlake, Y. Li, M. Umair, A. Banerjee, and F. Hu,
"Routing Bridges (RBridges): Appointed Forwarders", draft-ietf-
trill-rfc6439bis, work in progress.
Informational References
[RFC7067] - Dunbar, L., Eastlake 3rd, D., Perlman, R., and I.
Gashinsky, "Directory Assistance Problem and High-Level Design
Proposal", RFC 7067, November 2013.
[RFC7978] - Eastlake 3rd, D., Umair, M., and Y. Li, "Transparent
Interconnection of Lots of Links (TRILL): RBridge Channel
Header Extension", RFC 7978, DOI 10.17487/RFC7978, September
2016, <http://www.rfc-editor.org/info/rfc7978>.
[ARPND] - Y. Li, D. Eastlake, L. Dunbar, R. Perlman, I. Gashinsky,
"TRILL: ARP/ND Optimization", draft-ietf-trill-arp-
optimization, work in progress.
[DirAsstEncap] L. Dunbar, D. Eastlake, R. Perlman, I. Gashingksy,
D. Eastlake, et al [Page 51]
INTERNET-DRAFT TRILL: Directory Service Mechanisms
"Directory Assisted TRILL Encapsulation", draft-ietf-trill-
directory-assisted-encap, work in progress.
[SmartEN] R. Perlman, F. Hu, D. Eastlake, K. Krupakaran, T. Liao,
"TRILL Smart Endnodes", draft-ietf-trill-smart-endnodes",
draft-ietf-trill-smart-endnodes, work in progress.
[X.233] - ITU-T Recommendation X.233: Protocol for providing the
connectionless-mode network service: Protocol specification,
International Telecommunications Union, August 1997
D. Eastlake, et al [Page 52]
INTERNET-DRAFT TRILL: Directory Service Mechanisms
Acknowledgments
The contributions of the following persons are gratefully
acknowledged:
Amanda Barber, Matthew Bocci, Alissa Cooper, Stephen Farrell,
Daniel Franke, Igor Gashinski, Joel Halpern, Susan Hares, Alexey
Melnikov, Gsyle Noble, Tianran Zhou
The document was prepared in raw nroff. All macros used were defined
within the source file.
D. Eastlake, et al [Page 53]
INTERNET-DRAFT TRILL: Directory Service Mechanisms
Authors' Addresses
Donald Eastlake
Huawei Technologies
155 Beaver Street
Milford, MA 01757, USA
Phone: +1-508-333-2270
Email: d3e3e3@gmail.com
Linda Dunbar
Huawei Technologies
5430 Legacy Drive, Suite #175
Plano, TX 75024, USA
Phone: +1-469-277-5840
Email: ldunbar@huawei.com
Radia Perlman
EMC
2010 256th Avenue NE, #200
Bellevue, WA 98007, USA
Email: Radia@alum.mit.edu
Yizhou Li
Huawei Technologies
101 Software Avenue,
Nanjing 210012, China
Phone: +86-25-56622310
Email: liyizhou@huawei.com
D. Eastlake, et al [Page 54]
INTERNET-DRAFT TRILL: Directory Service Mechanisms
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D. Eastlake, et al [Page 55]