Internet Engineering Task Force (IETF) R. Gandhi, Ed.

Internet Engineering Task Force (IETF) R. Gandhi, Ed.
Request for Comments: 8537 Cisco Systems, Inc.
Updates: 4090, 7551 H. Shah
Category: Standards Track Ciena
ISSN: 2070-1721 J. Whittaker
Verizon
February 2019

Updates to the Fast Reroute Procedures for Co-routed Associated
Bidirectional Label Switched Paths (LSPs)

Abstract

Resource Reservation Protocol (RSVP) association signaling can be
used to bind two unidirectional Label Switched Paths (LSPs) into an
associated bidirectional LSP. When an associated bidirectional LSP
is co-routed, the reverse LSP follows the same path as its forward
LSP. This document updates the fast reroute procedures defined in
RFC 4090 to support both single-sided and double-sided provisioned
associated bidirectional LSPs. This document also updates the
procedure for associating two reverse LSPs defined in RFC 7551 to
support co-routed bidirectional LSPs. The fast reroute procedures
can ensure that, for the co-routed LSPs, traffic flows on co-routed
paths in the forward and reverse directions after a failure event.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8537.

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Copyright Notice

Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction ....................................................3
1.1. Assumptions and Considerations .............................4
2. Conventions Used in This Document ...............................4
2.1. Key Word Definitions .......................................4
2.2. Terminology ................................................4
2.2.1. Forward Unidirectional LSPs .........................5
2.2.2. Reverse Co-routed Unidirectional LSPs ...............5
3. Problem Statement ...............................................5
3.1. Fast Reroute Bypass Tunnel Assignment ......................6
3.2. Node Protection Bypass Tunnels .............................6
3.3. Bidirectional LSP Association at Midpoints .................7
4. Signaling Procedure .............................................8
4.1. Associated Bidirectional LSP Fast Reroute ..................8
4.1.1. Restoring Co-routing with Node Protection
Bypass Tunnels ......................................9
4.1.2. Unidirectional Link Failures .......................10
4.1.3. Revertive Behavior after Fast Reroute ..............10
4.1.4. Bypass Tunnel Provisioning .........................10
4.1.5. One-to-One Bypass Tunnel ...........................11
4.2. Bidirectional LSP Association at Midpoints ................11
5. Compatibility ..................................................11
6. Security Considerations ........................................12
7. IANA Considerations ............................................12
8. References .....................................................12
8.1. Normative References ......................................12
8.2. Informative References ....................................13
Appendix A. Extended Association ID ..............................14
Acknowledgments ...................................................16
Authors' Addresses ................................................16

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1. Introduction

The Resource Reservation Protocol (RSVP) (Extended) ASSOCIATION
Object is specified in [RFC6780] and can be used generically to
associate Multiprotocol Label Switching (MPLS) and Generalized MPLS
(GMPLS) Traffic Engineering (TE) Label Switched Paths (LSPs).
[RFC7551] defines mechanisms for binding two point-to-point (P2P)
unidirectional LSPs [RFC3209] into an associated bidirectional LSP.
There are two models described in [RFC7551] for provisioning an
associated bidirectional LSP: single-sided and double-sided. In both
models, the reverse LSP of the bidirectional LSP may or may not be
co-routed and follow the same path as its forward LSP.

In some packet transport networks, there are requirements where the
reverse LSP of a bidirectional LSP needs to follow the same path as
its forward LSP [RFC6373]. The MPLS Transport Profile (MPLS-TP)
[RFC6370] architecture facilitates the co-routed bidirectional LSP by
using GMPLS extensions [RFC3473] to achieve congruent paths.
However, RSVP association signaling allows enabling co-routed
bidirectional LSPs without having to deploy GMPLS extensions in the
existing networks. The association signaling also allows taking
advantage of the existing TE and fast reroute mechanisms in the
network.

[RFC4090] defines fast reroute extensions for RSVP-TE LSPs, which are
also applicable to the associated bidirectional LSPs. [RFC8271]
defines fast reroute procedures for GMPLS signaled bidirectional LSPs
such as coordinating bypass tunnel assignments in the forward and
reverse directions of the LSP. The mechanisms defined in [RFC8271]
are also useful for the fast reroute of associated bidirectional
LSPs.

This document updates the fast reroute procedures defined in
[RFC4090] to support both single-sided and double-sided provisioned
associated bidirectional LSPs. This document also updates the
procedure for associating two reverse LSPs defined in [RFC7551] to
support co-routed bidirectional LSPs. The fast reroute procedures
can ensure that for the co-routed LSPs, traffic flows on co-routed
paths in the forward and reverse directions after fast reroute.

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1.1. Assumptions and Considerations

The following assumptions and considerations apply to this document:

o The fast reroute procedure for the unidirectional LSPs is defined
in [RFC4090] and is not modified by this document.

o The fast reroute procedure when using unidirectional bypass
tunnels is defined in [RFC4090] and is not modified by this
document.

o This document assumes that the fast reroute bypass tunnels used
for protected associated bidirectional LSPs are also associated
bidirectional.

o This document assumes that the fast reroute bypass tunnels used
for protected co-routed associated bidirectional LSPs are also co-
routed associated bidirectional.

o The fast reroute procedure to coordinate the bypass tunnel
assignment defined in this document may be used for protected
associated bidirectional LSPs that are not co-routed but requires
that the downstream Point of Local Repair (PLR) and Merge Point
(MP) pair of the forward LSP matches the upstream MP and PLR pair
of the reverse LSP.

o Unless otherwise specified in this document, the fast reroute
procedures defined in [RFC4090] are used for associated
bidirectional LSPs.

2. Conventions Used in This Document

2.1. Key Word Definitions

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
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

2.2. Terminology

The reader is assumed to be familiar with the terminology defined in
[RFC2205], [RFC3209], [RFC4090], [RFC7551], and [RFC8271].

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2.2.1. Forward Unidirectional LSPs

Two reverse unidirectional P2P LSPs are set up in opposite directions
between a pair of source and destination nodes to form an associated
bidirectional LSP. In the case of single-sided provisioned LSP, the
originating LSP with a REVERSE_LSP Object [RFC7551] is identified as
a forward unidirectional LSP. In the case of double-sided
provisioned LSP, the LSP originating from the higher node address (as
source) and terminating on the lower node address (as destination) is
identified as a forward unidirectional LSP.

2.2.2. Reverse Co-routed Unidirectional LSPs

Two reverse unidirectional P2P LSPs are set up in opposite directions
between a pair of source and destination nodes to form an associated
bidirectional LSP. A reverse unidirectional LSP originates on the
same node where the forward unidirectional LSP terminates, and it
terminates on the same node where the forward unidirectional LSP
originates. A reverse co-routed unidirectional LSP traverses along
the same path as the forward-direction unidirectional LSP in the
opposite direction.

3. Problem Statement

As specified in [RFC7551], in the single-sided provisioning case, the
RSVP-TE tunnel is configured only on one endpoint node of the
bidirectional LSP. An LSP for this tunnel is initiated by the
originating endpoint with the (Extended) ASSOCIATION Object
containing Association Type set to "Single-Sided Associated
Bidirectional LSP" and the REVERSE_LSP Object inserted in the RSVP
Path message. The remote endpoint then creates the corresponding
reverse TE tunnel and signals the reverse LSP in response using the
information from the REVERSE_LSP Object and other objects present in
the received RSVP Path message. As specified in [RFC7551], in the
double-sided provisioning case, the RSVP-TE tunnel is configured on
both endpoint nodes of the bidirectional LSP. Both forward and
reverse LSPs are initiated independently by the two endpoints with
the (Extended) ASSOCIATION Object containing Association Type set to
"Double-Sided Associated Bidirectional LSP". With both single-sided
and double-sided provisioned bidirectional LSPs, the reverse LSP may
or may not be congruent (i.e., co-routed) and follow the same path as
its forward LSP.

Both single-sided and double-sided associated bidirectional LSPs
require solutions to the following issues for fast reroute to ensure
co-routing after a failure event.

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3.1. Fast Reroute Bypass Tunnel Assignment

In order to ensure that the traffic flows on a co-routed path after a
link or node failure on the protected co-routed LSP path, the
midpoint PLR nodes need to assign matching bidirectional bypass
tunnels for fast reroute. Such bypass assignment requires
coordination between the PLR nodes in both the forward and reverse
directions when more than one bypass tunnel is present on a PLR node.

<-- Bypass N -->
+-----+ +-----+
| H +---------+ I |
+--+--+ +--+--+
| |
| |
LSP1 --> | LSP1 --> | LSP1 --> LSP1 -->
+-----+ +--+--+ +--+--+ +-----+ +-----+
| A +--------+ B +----X----+ C +--------+ D +--------+ E |
+-----+ +--+--+ +--+--+ +-----+ +-----+
<-- LSP2 | <-- LSP2 | <-- LSP2 <-- LSP2
| |
| |
+--+--+ +--+--+
| F +---------+ G |
+-----+ +-----+
<-- Bypass S -->

Figure 1: Multiple Bidirectional Bypass Tunnels

As shown in Figure 1, there are two bypass tunnels available: bypass
tunnel N (on path B-H-I-C) and bypass tunnel S (on path B-F-G-C).
The midpoint PLR nodes B and C need to coordinate bypass tunnel
assignment to ensure that traffic in both directions flows through
either bypass tunnel N or bypass tunnel S after the link B-C failure.

3.2. Node Protection Bypass Tunnels

When using a node protection bypass tunnel with a protected
associated bidirectional LSP, after a link failure, the forward and
reverse LSP traffic can flow on different node protection bypass
tunnels in the upstream and downstream directions.

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<-- Bypass N -->
+-----+ +-----+
| H +------------------------+ I |
+--+--+ +--+--+
| <-- Rerouted-LSP2 |
| |
| |
| LSP1 --> LSP1 --> | LSP1 --> LSP1 -->
+--+--+ +-----+ +--+--+ +-----+ +-----+
| A +--------+ B +----X----+ C +--------+ D +--------+ E |
+-----+ +--+--+ +-----+ +--+--+ +-----+
<-- LSP2 | <-- LSP2 <-- LSP2 | <-- LSP2
| |
| |
| Rerouted-LSP1 --> |
+--+--+ +--+--+
| F +------------------------+ G |
+-----+ +-----+
<-- Bypass S -->

Figure 2: Node Protection Bypass Tunnels

As shown in Figure 2, after the link B-C failure, the downstream PLR
node B reroutes the protected forward LSP1 traffic over bypass tunnel
S (on path B-F-G-D) to reach downstream MP node D, whereas the
upstream PLR node C reroutes the protected reverse LSP2 traffic over
bypass tunnel N (on path C-I-H-A) to reach the upstream MP node A.
As a result, the traffic in the forward and reverse directions flows
on different bypass tunnels, which can cause the co-routed associated
bidirectional LSP to be no longer co-routed. However, unlike GMPLS
LSPs, the asymmetry of paths in the forward and reverse directions
does not result in RSVP soft-state timeout with the associated
bidirectional LSPs.

3.3. Bidirectional LSP Association at Midpoints

In packet transport networks, a restoration LSP is signaled after a
link failure on the protected LSP path, and the protected LSP may or
may not be torn down [RFC8131]. In this case, multiple forward and
reverse LSPs of a co-routed associated bidirectional LSP may be
present at midpoint nodes with identical (Extended) ASSOCIATION
Objects. This creates an ambiguity at midpoint nodes to identify the
correct associated LSP pair for fast reroute bypass assignment (e.g.,
during the recovery phase of the RSVP graceful restart procedure).

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LSP3 --> LSP3 --> LSP3 -->
LSP1 --> LSP1 --> LSP1 --> LSP1 -->
+-----+ +-----+ +-----+ +-----+ +-----+
| A +--------+ B +----X----+ C +--------+ D +--------+ E |
+-----+ +--+--+ +--+--+ +-----+ +-----+
<-- LSP2 | <-- LSP2 | <-- LSP2 <-- LSP2
<-- LSP4 | | <-- LSP4 <-- LSP4
| |
| LSP3 --> |
+--+--+ +--+--+
| F +---------+ G |
+-----+ +-----+
<-- Bypass S -->
<-- LSP4

Figure 3: Restoration LSP Setup after Link Failure

As shown in Figure 3, the protected LSPs (LSP1 and LSP2) are an
associated LSP pair; similarly, the restoration LSPs (LSP3 and LSP4)
are an associated LSP pair. Both pairs belong to the same associated
bidirectional LSP and carry identical (Extended) ASSOCIATION Objects.
In this example, the midpoint node D may mistakenly associate LSP1
with the reverse LSP4 instead of the reverse LSP2 due to the matching
(Extended) ASSOCIATION Objects. This may cause the co-routed
associated bidirectional LSP to be no longer co-routed after fast
reroute. Since the bypass assignment needs to be coordinated between
the forward and reverse LSPs, this can also lead to undesired bypass
tunnel assignments.

4. Signaling Procedure

4.1. Associated Bidirectional LSP Fast Reroute

For both single-sided and double-sided associated bidirectional LSPs,
the fast reroute procedure specified in [RFC4090] is used. In
addition, the mechanisms defined in [RFC8271] are used as follows:

o The BYPASS_ASSIGNMENT IPv4 subobject (value 38) and IPv6 subobject
(value 39) defined in [RFC8271] are used to coordinate bypass
tunnel assignment between the PLR nodes in both the forward and
reverse directions (see Figure 1). The BYPASS_ASSIGNMENT and
Node-ID address [RFC4561] subobjects MUST be added by the
downstream PLR node in the RECORD_ROUTE Object (RRO) of the RSVP
Path message of the forward LSP to indicate the local bypass
tunnel assignment using the procedure defined in [RFC8271]. The
upstream node uses the bypass assignment information (namely,
bypass tunnel source address, destination address, and Tunnel ID)
in the received RSVP Path message of the protected forward LSP to

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find the associated bypass tunnel in the reverse direction. The
upstream PLR node MUST NOT add the BYPASS_ASSIGNMENT subobject in
the RRO of the RSVP Path message of the reverse LSP.

o The downstream PLR node initiates the bypass tunnel assignment for
the forward LSP. The upstream PLR (forward-direction LSP MP) node
reflects the associated bypass tunnel assignment for the reverse-
direction LSP. The upstream PLR node MUST NOT initiate the bypass
tunnel assignment.

o If the indicated forward bypass tunnel or the associated reverse
bypass tunnel is not found, the upstream PLR SHOULD send a Notify
message [RFC3473] with Error Code "FRR Bypass Assignment Error"
(value 44) and Sub-code "Bypass Tunnel Not Found" (value 1)
[RFC8271] to the downstream PLR.

o If the bypass tunnel cannot be used as described in Section 4.5.3
of [RFC8271], the upstream PLR SHOULD send a Notify message
[RFC3473] with Error Code "FRR Bypass Assignment Error" (value 44)
and Sub-code "Bypass Assignment Cannot Be Used" (value 0)
[RFC8271] to the downstream PLR.

o After a link or node failure, the PLR nodes in both forward and
reverse directions trigger fast reroute independently using the
procedures defined in [RFC4090] and send the forward and protected
reverse LSP modified RSVP Path messages and traffic over the
bypass tunnel. The RSVP Resv signaling of the protected forward
and reverse LSPs follows the same procedure as defined in
[RFC4090] and is not modified by this document.

4.1.1. Restoring Co-routing with Node Protection Bypass Tunnels

After fast reroute, the downstream MP node assumes the role of
upstream PLR and reroutes the reverse LSP RSVP Path messages and
traffic over the bypass tunnel on which the forward LSP RSVP Path
messages and traffic are received. This procedure is defined as
"restoring co-routing" in [RFC8271]. This procedure is used to
ensure that both forward and reverse LSP signaling and traffic flow
on the same bidirectional bypass tunnel after fast reroute.

As shown in Figure 2, when using a node protection bypass tunnel with
protected co-routed LSPs, asymmetry of paths can occur in the forward
and reverse directions after a link failure [RFC8271]. In order to
restore co-routing, the downstream MP node D (acting as an upstream
PLR) MUST trigger the procedure to restore co-routing and reroute the
protected reverse LSP2 RSVP Path messages and traffic over the bypass
tunnel S (on path D-G-F-B) to the upstream MP node B upon receiving
the protected forward LSP modified RSVP Path messages and traffic

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over the bypass tunnel S (on path D-G-F-B) from node B. The upstream
PLR node C stops receiving the RSVP Path messages and traffic for the
reverse LSP2 from node D (resulting in RSVP soft-state timeout), and
it stops sending the RSVP Path messages for the reverse LSP2 over the
bypass tunnel N (on path C-I-H-A) to node A.

4.1.2. Unidirectional Link Failures

The unidirectional link failures can cause co-routed associated
bidirectional LSPs to be no longer co-routed after fast reroute with
both link protection and node protection bypass tunnels. However,
the unidirectional link failures in the upstream and/or downstream
directions do not result in RSVP soft-state timeout with the
associated bidirectional LSPs as upstream and downstream PLRs trigger
fast reroute independently. The asymmetry of forward and reverse LSP
paths due to the unidirectional link failure in the downstream
direction can be corrected by using the procedure to restore co-
routing specified in Section 4.1.1.

4.1.3. Revertive Behavior after Fast Reroute

When the revertive behavior is desired for a protected LSP after the
link is restored, the procedure defined in Section 6.5.2 of [RFC4090]
is followed.

o The downstream PLR node starts sending the RSVP Path messages and
traffic flow of the protected forward LSP over the restored link
and stops sending them over the bypass tunnel [RFC4090].

o The upstream PLR node (when the protected LSP is present) also
starts sending the RSVP Path messages and traffic flow of the
protected reverse LSPs over the restored link and stops sending
them over the bypass tunnel [RFC4090].

o For node protection bypass tunnels (see Figure 2), after restoring
co-routing, the upstream PLR node D SHOULD start sending RSVP Path
messages and traffic for the reverse LSP over the original link
(C-D) when it receives the unmodified RSVP Path messages and
traffic for the protected forward LSP over it and stops sending
them over the bypass tunnel S (on path D-G-F-B).

4.1.4. Bypass Tunnel Provisioning

Fast reroute bidirectional bypass tunnels can be single-sided or
double-sided associated tunnels. For both single-sided and double-
sided associated bypass tunnels, the fast reroute assignment policies
need to be configured on the downstream PLR nodes of the protected

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LSPs that initiate the bypass tunnel assignments. For single-sided
associated bypass tunnels, these nodes are the originating endpoints
of their signaling.

4.1.5. One-to-One Bypass Tunnel

The fast reroute signaling procedure defined in this document can be
used for both facility backup described in Section 3.2 of [RFC4090]
and one-to-one backup described in Section 3.1 of [RFC4090]. As
described in Section 4.5.2 of [RFC8271], in the one-to-one backup
method, if the associated bidirectional bypass tunnel is already in
use at the upstream PLR, it SHOULD send a Notify message [RFC3473]
with Error Code "FRR Bypass Assignment Error" (value 44) and Sub-code
"One-to-One Bypass Already in Use" (value 2) to the downstream PLR.

4.2. Bidirectional LSP Association at Midpoints

In order to associate the LSPs unambiguously at a midpoint node (see
Figure 3), the endpoint node MUST signal the Extended ASSOCIATION
Object and add a unique Extended Association ID for each associated
forward and reverse LSP pair forming the bidirectional LSP. An
endpoint node MAY set the Extended Association ID to the value
formatted according to the structure shown in Appendix A.

o For single-sided provisioned bidirectional LSPs [RFC7551], the
originating endpoint signals the Extended ASSOCIATION Object with
a unique Extended Association ID. The remote endpoint copies the
contents of the received Extended ASSOCIATION Object including the
Extended Association ID in the RSVP Path message of the reverse
LSP's Extended ASSOCIATION Object.

o For double-sided provisioned bidirectional LSPs [RFC7551], both
endpoints need to ensure that the bidirectional LSP has a unique
Extended ASSOCIATION Object for each forward and reverse LSP pair
by selecting appropriate unique Extended Association IDs signaled
by them. A controller can be used to provision a unique Extended
Association ID on both endpoints. The procedure for selecting
unique Extended Association IDs is outside the scope of this
document.

5. Compatibility

This document updates the procedures for fast reroute for associated
bidirectional LSPs defined in [RFC4090] and the procedures for
associating bidirectional LSPs defined in [RFC7551]. The procedures
use the signaling messages defined in [RFC8271]; no new signaling
messages are defined in this document. The procedures ensure that
for the co-routed LSPs, traffic flows on co-routed paths in the

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forward and reverse directions after fast reroute. Operators wishing
to use this function SHOULD ensure that it is supported on all the
nodes on the LSP path. The nodes not supporting this function can
cause the traffic to flow on asymmetric paths in the forward and
reverse directions of the associated bidirectional LSPs after fast
reroute.

6. Security Considerations

This document updates the signaling mechanisms defined in [RFC4090]
and [RFC7551]. It does not introduce any additional security
considerations other than those already covered in [RFC4090],
[RFC7551], [RFC8271], and the MPLS/GMPLS security framework
[RFC5920].

7. IANA Considerations

This document has no IANA actions.

8. References

8.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC2205] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
September 1997, <https://www.rfc-editor.org/info/rfc2205>.

[RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
DOI 10.17487/RFC4090, May 2005,
<https://www.rfc-editor.org/info/rfc4090>.

[RFC4561] Vasseur, J., Ed., Ali, Z., and S. Sivabalan, "Definition
of a Record Route Object (RRO) Node-Id Sub-Object",
RFC 4561, DOI 10.17487/RFC4561, June 2006,
<https://www.rfc-editor.org/info/rfc4561>.

[RFC6780] Berger, L., Le Faucheur, F., and A. Narayanan, "RSVP
ASSOCIATION Object Extensions", RFC 6780,
DOI 10.17487/RFC6780, October 2012,
<https://www.rfc-editor.org/info/rfc6780>.

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RFC 8537 Associated Bidirectional LSP Fast Reroute February 2019

[RFC7551] Zhang, F., Ed., Jing, R., and R. Gandhi, Ed., "RSVP-TE
Extensions for Associated Bidirectional Label Switched
Paths (LSPs)", RFC 7551, DOI 10.17487/RFC7551, May 2015,
<https://www.rfc-editor.org/info/rfc7551>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8271] Taillon, M., Saad, T., Ed., Gandhi, R., Ed., Ali, Z., and
M. Bhatia, "Updates to the Resource Reservation Protocol
for Fast Reroute of Traffic Engineering GMPLS Label
Switched Paths (LSPs)", RFC 8271, DOI 10.17487/RFC8271,
October 2017, <https://www.rfc-editor.org/info/rfc8271>.

8.2. Informative References

[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.

[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
DOI 10.17487/RFC3473, January 2003,
<https://www.rfc-editor.org/info/rfc3473>.

[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
<https://www.rfc-editor.org/info/rfc5920>.

[RFC6370] Bocci, M., Swallow, G., and E. Gray, "MPLS Transport
Profile (MPLS-TP) Identifiers", RFC 6370,
DOI 10.17487/RFC6370, September 2011,
<https://www.rfc-editor.org/info/rfc6370>.

[RFC6373] Andersson, L., Ed., Berger, L., Ed., Fang, L., Ed., Bitar,
N., Ed., and E. Gray, Ed., "MPLS Transport Profile (MPLS-
TP) Control Plane Framework", RFC 6373,
DOI 10.17487/RFC6373, September 2011,
<https://www.rfc-editor.org/info/rfc6373>.

[RFC8131] Zhang, X., Zheng, H., Ed., Gandhi, R., Ed., Ali, Z., and
P. Brzozowski, "RSVP-TE Signaling Procedure for End-to-End
GMPLS Restoration and Resource Sharing", RFC 8131,
DOI 10.17487/RFC8131, March 2017,
<https://www.rfc-editor.org/info/rfc8131>.

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RFC 8537 Associated Bidirectional LSP Fast Reroute February 2019

Appendix A. Extended Association ID

The Extended Association ID in the Extended ASSOCIATION Object
[RFC6780] can be set to the value formatted according to the
structure shown in the following example to uniquely identify
associated forward and reverse LSP pairs of an associated
bidirectional LSP.

An example of the IPv4 Extended Association ID format is shown below:

0 1 2 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 LSP Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | LSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Variable Length ID :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: IPv4 Extended Association ID Format Example

IPv4 LSP Source Address

IPv4 source address of the forward LSP [RFC3209].

LSP ID

16-bit LSP ID of the forward LSP [RFC3209].

Variable Length ID

Variable length Extended Association ID [RFC6780] inserted by the
endpoint node of the associated bidirectional LSP [RFC7551].

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RFC 8537 Associated Bidirectional LSP Fast Reroute February 2019

An example of the IPv6 Extended Association ID format is shown below:

0 1 2 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| IPv6 LSP Source Address |
+ +
| (16 bytes) |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | LSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Variable Length ID :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 5: IPv6 Extended Association ID Format Example

LSP Source Address

IPv6 source address of the forward LSP [RFC3209].

LSP ID

16-bit LSP ID of the forward LSP [RFC3209].

Variable Length ID

Variable length Extended Association ID [RFC6780] inserted by the
endpoint node of the associated bidirectional LSP [RFC7551].

In both IPv4 and IPv6 examples, the Reserved flags MUST be set to 0
on transmission.

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RFC 8537 Associated Bidirectional LSP Fast Reroute February 2019

Acknowledgments

A special thanks to the authors of [RFC8271]; this document uses the
signaling mechanisms defined in that document. The authors would
also like to thank Vishnu Pavan Beeram, Daniele Ceccarelli, Deborah
Brungard, Adam Roach, and Benjamin Kaduk for reviewing this document
and providing valuable comments.

Authors' Addresses

Rakesh Gandhi (editor)
Cisco Systems, Inc.
Canada

Email: [email protected]

Himanshu Shah
Ciena

Email: [email protected]

Jeremy Whittaker
Verizon

Email: [email protected]

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