Internet DRAFT - draft-ietf-pals-seamless-vccv
draft-ietf-pals-seamless-vccv
Internet Engineering Task Force V. Govindan
Internet-Draft C. Pignataro
Updates: 5885 (if approved) Cisco
Intended status: Standards Track April 28, 2016
Expires: October 30, 2016
Seamless BFD for VCCV
draft-ietf-pals-seamless-vccv-03
Abstract
This document extends the procedures and Connectivity Verification
(CV) types already defined for Bidirectional Forwarding Detection
(BFD) for Virtual Circuit Connectivity Verification (VCCV) to define
Seamless BFD (S-BFD) for VCCV. This document updates RFC 5885,
extending the CV Values and the Capability Selection.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on October 30, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
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include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Background . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. S-BFD Connectivity Verification . . . . . . . . . . . . . . . 3
2.1. Co-existence of S-BFD and BFD Capabilites . . . . . . . . 4
2.2. S-BFD CV Operation . . . . . . . . . . . . . . . . . . . 4
2.2.1. S-BFD Initiator Operation . . . . . . . . . . . . . . 4
2.2.2. S-BFD Reflector Operation . . . . . . . . . . . . . . 5
2.2.2.1. Demultiplexing . . . . . . . . . . . . . . . . . 5
2.2.2.2. Transmission of Control Packets . . . . . . . . . 5
2.2.2.3. Advertisement of Target Discriminators Using LDP 5
2.2.2.4. Advertisement of Target Discriminators Using L2TP 5
2.2.2.5. Provisioning of Target Discriminators . . . . . . 6
2.3. S-BFD Encapsulation . . . . . . . . . . . . . . . . . . . 6
2.4. S-BFD CV Types . . . . . . . . . . . . . . . . . . . . . 6
3. Capability Selection . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5.1. MPLS CV Types for the VCCV Interface Parameters Sub-TLV . 7
5.2. L2TPv3 CV Types for the VCCV Capability AVP . . . . . . . 8
5.3. PW Associated Channel Type . . . . . . . . . . . . . . . 8
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Background
BFD for VCCV [RFC5885] defines the CV types for BFD using VCCV,
protocol operation and the required packet encapsulation formats.
This document extends those procedures, CV type values to enable
S-BFD [I-D.ietf-bfd-seamless-base] operation for VCCV.
The new S-BFD CV Types are Pseudowire (PW) demultiplexer-agnostic,
and hence applicable for both MPLS and Layer Two Tunneling Protocol
version 3 (L2TPv3) pseudowire demultiplexers. This document concerns
itself with the S-BFD VCCV operation over single-segment pseudowires
(SS-PWs). The scope of this document is as follows:
This specification describes procedures only for S-BFD
asynchronous mode.
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S-BFD Echo mode is outside the scope of this specification.
S-BFD operation for fault detection and status signaling is
outside the scope of this specification.
This document specifies the use of a single S-BFD discriminator per
Pseudowire. There are cases where multiple S-BFD discriminators per
PW can be useful. One such cases is using different S-BFD
discriminators per Flow within a FAT PW [RFC6391]; however, the
mapping between Flows and discriminators is a prerequisite. FAT PWs
can be supported as described in Section 7 of [RFC6391].
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
2. S-BFD Connectivity Verification
S-BFD protocol provides continuity check services by monitoring the
S-BFD control packets sent and received over the VCCV channel of the
PW. The term "Connectivity Verification" is used throughout this
document to be consistent with [RFC5885].
This section defines the CV types to be used for S-BFD. It also
defines the procedures for the S-BFD reflector and S-BFD Initiator
operation.
Two CV Types are defined for S-BFD. Table 1 summarizes the S-BFD CV
Types, grouping them by encapsulation (i.e., with versus without IP/
UDP headers) for fault detection only. S-BFD for fault detection and
status signaling is outside the scope of this specification.
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+----------------------------------------+-----------+--------------+
| | Fault | Fault |
| | Detection | Detection |
| | Only | and Status |
| | | Signaling |
+----------------------------------------+-----------+--------------+
| S-BFD, IP/UDP Encapsulation (with | TBD1 | N/A |
| IP/UDP Headers) | | |
| | | |
| S-BFD, PW-ACH Encapsulation when using | TBD2 | N/A |
| MPLS PW or L2-Specific Sublayer (L2SS) | | |
| Encapsulation when using L2TP PW | | |
| (without IP/UDP Headers) | | |
+----------------------------------------+-----------+--------------+
Table 1: Bitmask Values for BFD CV Types
Two new bits are requested from IANA to indicate S-BFD operation.
2.1. Co-existence of S-BFD and BFD Capabilites
Since the CV types for S-BFD and BFD are unique, BFD and S-BFD
capabilities can be advertised concurrently.
2.2. S-BFD CV Operation
2.2.1. S-BFD Initiator Operation
The S-BFD Initiator SHOULD bootstrap S-BFD sessions after it learns
the discriminator of the remote target identifier. This can be
achieved, for example but not limited to, through one or more of the
following methods:
1. Advertisements of S-BFD discriminators made through a PW
signaling protocol, for example AVP/TLVs defined in L2TP/LDP.
2. Provisioning of S-BFD discriminators by manual configuration of
the PE/LCCEs.
3. Assignment of S-BFD discriminators by a controller.
4. Probing remote S-BFD discriminators through a mechanism such as
S-BFD Alert discriminators [I-D.akiya-bfd-seamless-alert-discrim]
S-BFD Initiator operation MUST be according to the specifications in
Section 7.2 of [I-D.ietf-bfd-seamless-base].
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2.2.2. S-BFD Reflector Operation
When a pseudowire signaling protocol such as LDP or L2TPv3 is in
use, the S-BFD Reflector can advertise its target discriminators
using that signaling protocol. When static PWs are in use the
target discriminator of S-BFD needs to be provisioned on the S-BFD
Initiator nodes.
All point to point pseudowires are bidirectional, the S-BFD
Reflector therefore reflects the S-BFD packet back to the
Initiator using the VCCV channel of the reverse direction of the
PW on which it was received.
It is observed that the reflector has enough information to
reflect the S-BFD Async packet received by it back to the S-BFD
initiator using the PW context (e.g., fields of the L2TPv3
headers).
S-BFD Reflector operation for BFD protocol fields MUST be
according to the specifications of [I-D.ietf-bfd-seamless-base].
2.2.2.1. Demultiplexing
Demultiplexing of S-BFD is achieved using the PW context, following
the procedures in Section 7.1 of [I-D.ietf-bfd-seamless-base].
2.2.2.2. Transmission of Control Packets
The procedures of S-BFD Reflector described in
[I-D.ietf-bfd-seamless-base] apply for S-BFD using VCCV.
2.2.2.3. Advertisement of Target Discriminators Using LDP
The advertisement of the target discriminator using LDP is left for
further study. It should be noted that S-BFD can still be used with
signaled PWs over an MPLS PSN, by provisioning of the S-BFD
discriminators or by learning the S-BFD discriminators by other
means.
2.2.2.4. Advertisement of Target Discriminators Using L2TP
The S-BFD Reflector MUST use the AVP
[I-D.ietf-l2tpext-sbfd-discriminator] defined for advertising its
target discriminators using L2TP.
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2.2.2.5. Provisioning of Target Discriminators
S-BFD target discriminators MAY be provisioned when static PWs are
used.
2.3. S-BFD Encapsulation
Unless specified differently below, the encapsulation of S-BFD
packets is identical to the method specified in Section 3.2 [RFC5885]
and in [RFC5880] for the encapsulation of BFD packets.
o IP/UDP BFD Encapsulation (BFD with IP/UDP Headers)
* The destination UDP port for the IP encapsulated S-BFD packet
MUST be 7784 [I-D.ietf-bfd-seamless-ip].
* The encapsulation of the S-BFD header fields MUST be according
to Section 7.3.2 of [I-D.ietf-bfd-seamless-base].
* The Time to Live (TTL) (IPv4) or Hop Limit (IPv6) is set to
255.
o PW-ACH/ L2SS BFD Encapsulation (BFD without IP/UDP Headers)
* The encapsulation of S-BFD packets using this format MUST be
according to Section 3.2 of [RFC5885] with the exception of the
value for the PW-ACH/L2SS type.
* When VCCV carries PW-ACH/ L2SS-encapsulated S-BFD (i.e., "raw"
S-BFD), the PW-ACH (pseudowire CW's) or L2SS' Channel Type MUST
be set to TBD3 to indicate "S-BFD Control, PW-ACH/ L2SS-
encapsulated" (i.e., S-BFD without IP/UDP headers; see
Section 5.3). This is to allow the identification of the
encased S-BFD payload when demultiplexing the VCCV control
channel.
2.4. S-BFD CV Types
3. Capability Selection
When multiple S-BFD CV Types are advertised, and after applying the
rules in [RFC5885], the set that both ends of the pseudowire have in
common is determined. If the two ends have more than one S-BFD CV
Type in common, the following list of S-BFD CV Types is considered in
the order of the lowest list number CV Type to the highest list
number CV Type, and the CV Type with the lowest list number is used:
1. TBD1 - S-BFD IP/UDP-encapsulated, for PW Fault Detection only.
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2. TBD2 - S-BFD PW-ACH/ L2SS-encapsulated (without IP/UDP headers),
for PW Fault Detection only.
The order of capability selection between S-BFD and BFD is defined as
follows:
+----------------------------+---------+----------+-----------------+
| Advertised capabilities of | BFD | SBFD | Both S-BFD and |
| PE1/ PE2 | Only | Only | BFD |
+----------------------------+---------+----------+-----------------+
| BFD Only | BFD | None | BFD Only |
| | | | |
| S-BFD Only | None | S-BFD | S-BFD only |
| | | | |
| Both S-BFD and BFD | BFD | S-BFD | Both SBFD and |
| | only | only | BFD |
+----------------------------+---------+----------+-----------------+
Table 2: Capability Selection Matrix for BFD and S-BFD
4. Security Considerations
Security considerations for VCCV are addressed in Section 10 of
[RFC5085]. The introduction of the S-BFD Connectivity Verification
(CV) Types introduces no new security risks for VCCV.
Implementations of the additional CV Types defined herein are subject
to the same security considerations as defined in [RFC5085] as well
as [I-D.ietf-bfd-seamless-base].
The IP/UDP encasulation of S-BFD makes use of the TTL/Hop Limit
procedures described in the Generalized TTL Security Mechanism (GTSM)
[RFC5082]) as a security mechanism.
This specification does not raise any additional security issues
beyond these.
5. IANA Considerations
5.1. MPLS CV Types for the VCCV Interface Parameters Sub-TLV
The VCCV Interface Parameters Sub-TLV codepoint is defined in
[RFC4446], and the VCCV CV Types registry is defined in [RFC5085].
This section lists the new BFD CV Types.
IANA has augmented the "MPLS VCCV Connectivity Verification (CV)
Types" registry in the Pseudowire Name Spaces reachable from
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[IANA-PWE3]. These are bitfield values. CV Type values are
specified in Section 2 of this document.
MPLS Connectivity Verification (CV) Types:
Bit (Value) Description Reference
=========== =========== ==============
TBD1(0xY) S-BFD IP/UDP-encapsulated, This document
for PW Fault Detection only
TBD2(0xZ) S-BFD PW-ACH-encapsulated, This document
for PW Fault Detection only
5.2. L2TPv3 CV Types for the VCCV Capability AVP
This section lists the new requests for S-BFD "L2TPv3 Connectivity
Verification (CV) Types" to be added to the existing "VCCV Capability
AVP" registry in the L2TP name spaces. The Layer Two Tunneling
Protocol "L2TP" Name Spaces are reachable from [IANA-L2TP]. IANA is
requested to assign the following L2TPv3 Connectivity Verification
(CV) Types in the VCCV Capability AVP Values registry.
VCCV Capability AVP (Attribute Type 96) Values
----------------------------------------------
L2TPv3 Connectivity Verification (CV) Types:
Bit (Value) Description Reference
=========== =========== ==============
TBD1(0xY) S-BFD IP/UDP-encapsulated, This document
for PW Fault Detection only
TBD2(0xZ) S-BFD L2SS-encapsulated, This document
for PW Fault Detection only
5.3. PW Associated Channel Type
As per the IANA considerations in [RFC5586], IANA is requested to
allocate the following Channel Types in the "MPLS Generalized
Associated Channel (G-ACh) Types" registry:
IANA has reserved a new Pseudowire Associated Channel Type value as
follows:
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Registry:
TLV
Value Description Follows Reference
------ ---------------------------------- ------- ---------------
TBD3 S-BFD Control, PW-ACH/L2SS No [This document]
encapsulation
(without IP/UDP Headers)
6. Acknowledgments
The authors would like to thank Nobo Akiya, Stewart Bryant, Greg
Mirsky, and Pawel Sowinski, Yuanlong, Andrew Malis, and Alexander
Vainshtein for providing input to this document and for performing
thorough reviews and useful comments.
7. Contributors
Mallik Mudigonda
Cisco Systems, Inc.
Email: mmudigon@cisco.com
8. References
8.1. Normative References
[I-D.ietf-bfd-seamless-base]
Akiya, N., Pignataro, C., Ward, D., Bhatia, M., and J.
Networks, "Seamless Bidirectional Forwarding Detection
(S-BFD)", draft-ietf-bfd-seamless-base-09 (work in
progress), April 2016.
[I-D.ietf-bfd-seamless-ip]
Akiya, N., Pignataro, C., and D. Ward, "Seamless
Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6
and MPLS", draft-ietf-bfd-seamless-ip-04 (work in
progress), April 2016.
[I-D.ietf-l2tpext-sbfd-discriminator]
Govindan, V. and C. Pignataro, "Advertising Seamless
Bidirectional Forwarding Detection (S-BFD) Discriminators
in Layer Two Tunneling Protocol, Version 3 (L2TPv3)",
draft-ietf-l2tpext-sbfd-discriminator-05 (work in
progress), April 2016.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to Edge
Emulation (PWE3)", BCP 116, RFC 4446,
DOI 10.17487/RFC4446, April 2006,
<http://www.rfc-editor.org/info/rfc4446>.
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
<http://www.rfc-editor.org/info/rfc5082>.
[RFC5085] Nadeau, T., Ed. and C. Pignataro, Ed., "Pseudowire Virtual
Circuit Connectivity Verification (VCCV): A Control
Channel for Pseudowires", RFC 5085, DOI 10.17487/RFC5085,
December 2007, <http://www.rfc-editor.org/info/rfc5085>.
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009,
<http://www.rfc-editor.org/info/rfc5586>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<http://www.rfc-editor.org/info/rfc5880>.
[RFC5885] Nadeau, T., Ed. and C. Pignataro, Ed., "Bidirectional
Forwarding Detection (BFD) for the Pseudowire Virtual
Circuit Connectivity Verification (VCCV)", RFC 5885,
DOI 10.17487/RFC5885, June 2010,
<http://www.rfc-editor.org/info/rfc5885>.
8.2. Informative References
[I-D.akiya-bfd-seamless-alert-discrim]
Akiya, N., Pignataro, C., and D. Ward, "Seamless
Bidirectional Forwarding Detection (S-BFD) Alert
Discriminator", draft-akiya-bfd-seamless-alert-discrim-03
(work in progress), October 2014.
[IANA-L2TP]
Internet Assigned Numbers Authority, "Layer Two Tunneling
Protocol "L2TP"", May 2015,
<http://www.iana.org/assignments/l2tp-parameters>.
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[IANA-PWE3]
Internet Assigned Numbers Authority, "Pseudowire Name
Spaces (PWE3)", January 2016,
<http://www.iana.org/assignments/pwe3-parameters>.
[RFC6391] Bryant, S., Ed., Filsfils, C., Drafz, U., Kompella, V.,
Regan, J., and S. Amante, "Flow-Aware Transport of
Pseudowires over an MPLS Packet Switched Network",
RFC 6391, DOI 10.17487/RFC6391, November 2011,
<http://www.rfc-editor.org/info/rfc6391>.
Authors' Addresses
Vengada Prasad Govindan
Cisco Systems, Inc.
Email: venggovi@cisco.com
Carlos Pignataro
Cisco Systems, Inc.
Email: cpignata@cisco.com
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