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Internet Engineering Task Force (IETF)                    R. Gandhi, Ed.Request for Comments: 8537                           Cisco Systems, Inc.Updates:4090,7551                                              H. ShahCategory: Standards Track                                          CienaISSN: 2070-1721                                             J. Whittaker                                                                 Verizon                                                           February 2019Updates to the Fast Reroute Procedures for Co-routed AssociatedBidirectional 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 inRFC 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 inRFC 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 inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttps://www.rfc-editor.org/info/rfc8537.Gandhi, et al.               Standards Track                    [Page 1]

RFC 8537        Associated Bidirectional LSP Fast Reroute  February 2019Copyright Notice   Copyright (c) 2019 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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 Contents1. Introduction ....................................................31.1. Assumptions and Considerations .............................42. Conventions Used in This Document ...............................42.1. Key Word Definitions .......................................42.2. Terminology ................................................42.2.1. Forward Unidirectional LSPs .........................52.2.2. Reverse Co-routed Unidirectional LSPs ...............53. Problem Statement ...............................................53.1. Fast Reroute Bypass Tunnel Assignment ......................63.2. Node Protection Bypass Tunnels .............................63.3. Bidirectional LSP Association at Midpoints .................74. Signaling Procedure .............................................84.1. Associated Bidirectional LSP Fast Reroute ..................8           4.1.1. Restoring Co-routing with Node Protection                  Bypass Tunnels ......................................94.1.2. Unidirectional Link Failures .......................104.1.3. Revertive Behavior after Fast Reroute ..............104.1.4. Bypass Tunnel Provisioning .........................104.1.5. One-to-One Bypass Tunnel ...........................114.2. Bidirectional LSP Association at Midpoints ................115. Compatibility ..................................................116. Security Considerations ........................................127. IANA Considerations ............................................128. References .....................................................128.1. Normative References ......................................128.2. Informative References ....................................13Appendix A.  Extended Association ID ..............................14   Acknowledgments ...................................................16   Authors' Addresses ................................................16Gandhi, et al.               Standards Track                    [Page 2]

RFC 8537        Associated Bidirectional LSP Fast Reroute  February 20191.  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.Gandhi, et al.               Standards Track                    [Page 3]

RFC 8537        Associated Bidirectional LSP Fast Reroute  February 20191.1.  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 Document2.1.  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 inBCP 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].Gandhi, et al.               Standards Track                    [Page 4]

RFC 8537        Associated Bidirectional LSP Fast Reroute  February 20192.2.1.  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.Gandhi, et al.               Standards Track                    [Page 5]

RFC 8537        Associated Bidirectional LSP Fast Reroute  February 20193.1.  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.Gandhi, et al.               Standards Track                    [Page 6]

RFC 8537        Associated Bidirectional LSP Fast Reroute  February 2019              <-- 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).Gandhi, et al.               Standards Track                    [Page 7]

RFC 8537        Associated Bidirectional LSP Fast Reroute  February 2019          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 Procedure4.1.  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 toGandhi, et al.               Standards Track                    [Page 8]

RFC 8537        Associated Bidirectional LSP Fast Reroute  February 2019      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 inSection 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 trafficGandhi, et al.               Standards Track                    [Page 9]

RFC 8537        Associated Bidirectional LSP Fast Reroute  February 2019   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 inSection 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 inSection 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 protectedGandhi, et al.               Standards Track                   [Page 10]

RFC 8537        Associated Bidirectional LSP Fast Reroute  February 2019   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 inSection 3.2 of [RFC4090]   and one-to-one backup described inSection 3.1 of [RFC4090].  As   described inSection 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 inAppendix 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 theGandhi, et al.               Standards Track                   [Page 11]

RFC 8537        Associated Bidirectional LSP Fast Reroute  February 2019   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.  References8.1.  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>.Gandhi, et al.               Standards Track                   [Page 12]

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 inRFC2119 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>.Gandhi, et al.               Standards Track                   [Page 13]

RFC 8537        Associated Bidirectional LSP Fast Reroute  February 2019Appendix 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].Gandhi, et al.               Standards Track                   [Page 14]

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.Gandhi, et al.               Standards Track                   [Page 15]

RFC 8537        Associated Bidirectional LSP Fast Reroute  February 2019Acknowledgments   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: rgandhi@cisco.com   Himanshu Shah   Ciena   Email: hshah@ciena.com   Jeremy Whittaker   Verizon   Email: jeremy.whittaker@verizon.comGandhi, et al.               Standards Track                   [Page 16]