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Versions: (draft-gandhi-shah-teas-assoc-corouted-bidir) 00 01 02 03 04 draft-ietf-teas-assoc-corouted-bidir-frr

TEAS Working Group                                        R. Gandhi, Ed.
Internet-Draft                                             Cisco Systems
Intended Status: Standards Track                                 H. Shah
Expires: September 16, 2016                                        Ciena
                                                        Jeremy Whittaker
                                                                 Verizon
                                                          March 15, 2016


         RSVP-TE Extensions For Associated Co-routed Bidirectional
                        Label Switched Paths (LSPs)
              draft-gandhishah-teas-assoc-corouted-bidir-01


Abstract

   In packet transport networks, there are requirements where reverse
   unidirectional LSP of a bidirectional LSP needs to follow the same
   path as its forward unidirectional LSP.  This document describes how
   the RSVP association signaling is used to bind two co-routed
   point-to-point unidirectional LSPs into an associated co-routed
   bidirectional LSP in single-sided provisioning case.  Fast-reroute
   procedures are defined to ensure that the traffic flows on the
   co-routed path after a failure event.


Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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Copyright Notice

   Copyright (c) 2016 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



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   Provisions Relating to IETF Documents
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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  3
     2.1.  Key Word Definitions . . . . . . . . . . . . . . . . . . .  3
     2.2.  Reverse Co-routed Unidirectional LSPs  . . . . . . . . . .  3
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Message and Object Definitions . . . . . . . . . . . . . . . .  5
     4.1.  Extended ASSOCIATION Object  . . . . . . . . . . . . . . .  5
   5.  Signaling Procedure  . . . . . . . . . . . . . . . . . . . . .  6
     5.1.  Co-routed Bidirectional LSP Association  . . . . . . . . .  6
     5.2.  Fast-Reroute For Associated Co-routed Bidirectional LSP  .  7
   6.  Compatibility  . . . . . . . . . . . . . . . . . . . . . . . .  8
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     9.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     9.2.  Informative References . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10



















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1.  Introduction

   In packet transport networks, there are requirements where a reverse
   Multi-Protocol Label Switching (MPLS) Label Switched Path (LSP) of a
   bidirectional LSP needs to follow the same path as its forward LSP
   [RFC6373].

   The Resource Reservation Protocol (RSVP) Extended ASSOCIATION Object
   is specified in [RFC6780] which can be used generically to associate
   (G)MPLS LSPs.  [RFC7551] defines mechanisms for binding two point-to-
   point unidirectional LSPs [RFC3209] into an associated bidirectional
   LSP.  There are two models described for provisioning the
   bidirectional LSP, single-sided and double-sided.  Only the single-
   sided provisioned bidirectional LSPs are considered in this document.

   The MPLS Transport Profile (TP) [RFC6370] architecture facilitates
   the co-routed bidirectional LSP by using GMPLS extensions [RFC3473]
   to achieve congruent paths.  However, the RSVP association signaling
   allows to enable co-routed bidirectional LSPs without having to
   deploy GMPLS extensions in the existing networks.  The association
   signaling also allows to take advantage of the existing Traffic
   Engineering (TE) mechanisms in the network.

   [GMPLS-FRR] defines fast-reroute procedures for GMPLS signaled LSPs
   to ensure traffic flows on a co-routed path after a failure event on
   the primary LSP path.  [GMPLS-FRR] defined fast-reroute mechanisms
   are equally applicable to the associated co-routed bidirectional
   LSPs.

   This document describes how Extended ASSOCIATION Object is used to
   bind two reverse co-routed unidirectional LSPs into an associated
   co-routed bidirectional LSP in single-sided provisioning case.
   Fast-reroute procedures are defined to ensure the traffic flows on
   the co-routed path after a failure event.


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", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.2.  Reverse Co-routed Unidirectional LSPs

   Two reverse unidirectional point-to-point (P2P) LSPs are setup in the
   opposite directions between a pair of source and destination nodes to



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   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 of the forward direction
   unidirectional LSP in the opposite direction.


3.  Overview

   As specified in [RFC7551], in single-sided provisioning case, the
   RSVP Traffic Engineering (TE) tunnel is configured only on one
   endpoint.  An LSP for this tunnel is initiated by the originating
   endpoint with Extended ASSOCIATION Object containing Association Type
   set to "single-sided associated bidirectional LSP" and REVERSE_LSP
   Object inserted in the Path message.  The remote endpoint then
   creates the corresponding reverse TE tunnel and signals the reverse
   LSP in response using information from the REVERSE_LSP Object and
   other objects present in the received Path message.  The reverse LSP
   thus created may or may not be congruent i.e. follow the same path as
   its forward LSP.


               LSP1 -->
      +-----+           +-----+           +-----+           +-----+
      |  A  +-----------+  B  +-----------+  C  |-----------+  D  |
      +-----+           +-----+           +-----+           +-----+
                                                   <-- LSP2

      Figure 1: An Example of Associated Co-routed Bidirectional LSP

   As shown in Figure 1, LSP1 is provisioned on the originating endpoint
   A.  The creation of reverse LSP2 on the remote endpoint D is
   triggered by the LSP1.  LSP2 follows the path in the reverse
   direction using the EXPLICIT_ROUTE Object (ERO) from the received
   REVERSE_LSP Object in the Path message of LSP1 [RFC7551].

   For co-routed bidirectional LSP, the originating endpoint A can
   ensure that the reverse LSP follows the same path as the forward LSP
   (e.g. A-B-C-D) by populating the ERO in the REVERSE_LSP Object using
   the hops traversed by the forward LSP in the reverse order (e.g. D-C-
   B-A).

   The associated co-routed bidirectional LSP when using above
   mechanisms defined in [RFC7551] requires solutions for the following
   issues:

   o  Multiple forward and reverse LSPs of a bidirectional LSP may be



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   present at mid-point nodes with identical Extended ASSOCIATION
   Objects.  In order to ensure co-routed-ness, the mid-point node must
   identify the correct matching co-routed associated forward and
   reverse LSPs.  To ensure this, additional information is required in
   the Extended ASSOCIATION Object that is unique per co-routed
   associated forward and reverse LSPs.

   o  The ERO for the reverse LSP signaled by the originating endpoint
   may contain loose next-hop(s) in case of loosely routed LSPs (e.g.
   inter-domain LSPs).  The mid-point and endpoint nodes need to ensure
   that the loose next-hop expansion for the reverse LSP is on the co-
   routed path for the bidirectional LSP.  As such, an expanding node
   may require the recorded path of the forward LSP.

   o  In order to ensure that the traffic flows on the co-routed path
   after a link or node failure on the LSP path, the mid-point Point of
   Local Repair (PLR) nodes need to know that the associated
   bidirectional LSP is co-routed.  This way mid-point PLR nodes can
   assign co-routed bidirectional bypass tunnels for fast-reroute.  Such
   bypass assignment also requires co-ordination between the forward and
   reverse direction PLR nodes.


4.  Message and Object Definitions

4.1.  Extended ASSOCIATION Object

   The Extended ASSOCIATION Object is populated using the rules defined
   in [RFC7551] for the Association Type "single-sided associated
   bidirectional LSP".

   The Extended Association ID is set by the originating node to the
   value specified as following.



       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      LSP Source Address                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Flags               |            LSP-ID             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 2: IPv4 Extended Association ID Format






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       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                      LSP Source Address                       |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Flags               |            LSP-ID             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 3: IPv6 Extended Association ID Format



   LSP Source Address

      IPv4/IPv6 source address of the originating LSP.

   LSP-ID

      16-bits LSP-ID of the originating LSP.

   Flags

      Bit 0: COROUTED-LSP: When set, this flag indicates the associated
      bidirectional LSP is co-routed.

      Bit 1-15: Not used.  Must be set to 0.


5.  Signaling Procedure

5.1.  Co-routed Bidirectional LSP Association

   In general, the processing rules for the Extended ASSOCIATION Object
   as specified in [RFC6780] and [RFC7551] are followed for co-routed
   bidirectional LSP association.

   The originating head-end node MUST add Extended ASSOCIATION Object
   with Association Type set to "single-sided associated bidirectional
   LSP" and the extended association ID set to the value specified in
   Section 4.1 of this document in the RSVP Path message.  The COROUTED-
   LSP flag MUST be set to indicate the nodes on the LSP path that the
   bidirectional LSP is co-routed.  In addition, the originating head-
   end node MUST add EXPLICIT_ROUTE Object (ERO) in the REVERSE_LSP
   Object by using the hops traversed by the forward LSP in the reverse
   order to ensure that reverse LSP follows the same path as forward
   direction LSP in the opposite direction.  When the ERO contains one



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   or more loose next-hop(s), the originating endpoint MUST add
   RECORD_ROUTE Object (RRO) in the Path message of the forward LSP to
   record the hops traversed by the LSP.

   As defined in [RFC7551], the remote endpoint simply copies the
   contents of the received Extended ASSOCIATION Object including the
   extended association ID in the Path message of the reverse LSP's
   Extended ASSOCIATION Object.  In addition, the remote endpoint builds
   the ERO of the reverse LSP using the ERO from the received
   REVERSE_LSP Object of the forward LSP.  If ERO contains one or more
   loose next-hop(s), the remote endpoint SHOULD use the recorded hops
   from the RRO in the forward LSP to expand the loose next-hop(s), to
   ensure that the reverse LSP follows the same path as the forward LSP.

   As contents of the Extended ASSOCIATION Objects are unique for each
   associated co-routed bidirectional LSP, a transit node can
   unambiguously identify the associated LSP pair by matching their
   Extended ASSOCIATION Objects.  At a transit LSR, reverse LSP can
   identify the matching forward LSP by checking the originating LSP
   source address and LSP-ID in the extended association ID.  When a
   transit node needs to expand the loose next-hop in the ERO, it SHOULD
   use the recorded hops from the RRO in the forward LSP to ensure that
   the reverse LSP is co-routed.


5.2.  Fast-Reroute For Associated Co-routed Bidirectional LSP

   The procedures defined in [GMPLS-FRR] are used for associated
   co-routed bidirectional LSP to ensure that the traffic flows on a
   co-routed path after a link or node failure.  The COROUTED-LSP flag
   is used by the Point of Local Repair (PLR) nodes to provide fast-
   reroute protection using associated co-routed bypass tunnels.

   As described in [GMPLS-FRR], BYPASS_ASSIGNMENT subobject in the RRO
   is used to co-ordinate bypass tunnel assignment between a forward and
   reverse direction PLR nodes.  This subobject MUST be added by the
   forward direction PLR node in the Path message of the originating
   LSP.  The forward direction PLR node always initiates the bypass
   tunnel assignment for the originating LSP.  The reverse direction PLR
   (forward direction LSP Merge Point (MP)) node simply reflects the
   bypass tunnel assignment for the reverse direction LSP on the
   co-routed path.

   After a link or node failure, PLR nodes in both directions trigger
   fast-reroute independently using the procedures defined in [RFC4090].

   As specified in [GMPLS-FRR], re-corouting procedure can be used to
   reroute the traffic in the reverse direction on the co-routed bypass



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   tunnel path.  Reverse direction PLR node will assume the role of
   Point of Remote Repair (PRR) and trigger the fast-reroute in the
   reverse direction on the matching associated co-routed bypass tunnel
   to ensure that both traffic and RSVP signaling flow on the co-routed
   path after the failure.


6.  Compatibility

   The Extended ASSOCIATION Object has been defined in [RFC6780], with
   class number in the form 11bbbbbb, which ensures compatibility with
   non-supporting nodes.  Per [RFC2205], such nodes will ignore the
   object but forward it without modification.

   This document defines the content of the Extended Association ID for
   the Extended ASSOCIATION Object for co-routed bidirectional LSPs.
   Operators wishing to use this function SHOULD ensure that it is
   supported on the node that is expected to act on the association.


7.  Security Considerations

   This document uses signaling mechanisms defined in [RFC7551] and
   [GMPLS-FRR] and does not introduce any additional security
   considerations other than already covered in [RFC7551], [GMPLS-FRR]
   and the MPLS/GMPLS security framework [RFC5920].

   Using the extended association ID in the intercepted signalling
   message, a node may be able to get additional information of the LSP
   such as co-routed type and the originating node.  This is judged to
   be a very minor security risk as this information is already
   available by other means.


8.  IANA Considerations

   This document does not make any request for IANA action.














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9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2205]  Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

   [RFC4090]  Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
              Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
              May 2005.

   [RFC6780]  Berger, L., Le Faucheur, F., and A. Narayanan, "RSVP
              Association Object Extensions", RFC 6780, October 2012.

   [RFC7551]  Zhang, F., Ed., Jing, R., and Gandhi, R., Ed., "RSVP-TE
              Extensions for Associated Bidirectional LSPs", RFC 7551,
              May 2015.

   [GMPLS-FRR] Taillon, M., Saad, T., Ed., Gandhi, R., Ed., Ali, Z.,
              Bhatia, M., Jin, L., "Extensions to Resource Reservation
              Protocol For Fast Reroute of Traffic Engineering GMPLS
              LSPs", draft-ietf-teas-gmpls-lsp-fastreroute.


9.2.  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, December 2001.

   [RFC3473]  Berger, L., "Generalized Multi-Protocol Label Switching
              (GMPLS) Signaling Resource ReserVation Protocol-Traffic
              Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.

   [RFC5920]  Fang, L., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, July 2010.

   [RFC6370]  Bocci, M., Swallow, G., and E. Gray, "MPLS Transport
              Profile (MPLS-TP) Identifiers", RFC 6370, September 2011.

   [RFC6373]  Andersson, L., Berger, L., Fang, L., Bitar, N., and E.
              Gray, "MPLS Transport Profile (MPLS-TP) Control Plane
              Framework", RFC 6373, September 2011.




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Authors' Addresses


   Rakesh Gandhi (editor)
   Cisco Systems, Inc.

   EMail: rgandhi@cisco.com


   Himanshu Shah
   Ciena

   EMail: hshah@ciena.com


   Jeremy Whittaker
   Verizon

   EMail: jeremy.whittaker@verizon.com
































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