CCAMP Working Group                                         Mike Taillon
Internet-Draft                                                Tarek Saad
Intended Status: Standards Track                           Rakesh Gandhi
Expires: April 15, 2013                                         Zafar Ali
                                                      Cisco Systems, Inc
                                                         October 12, 2012


    Extensions to Resource Reservation Protocol For Fast Reroute of
           Bidirectional Co-routed Traffic Engineering LSPs
            draft-tsaad-ccamp-rsvpte-bidir-lsp-fastreroute-00


Abstract

   This document defines RSVP-TE signaling extensions to support Fast
   Reroute (FRR) of bidirectional co-routed Traffic Engineering (TE)
   LSPs. These extensions enable the re-direction of bi-directional
   traffic and signaling onto bypass tunnels that ensure co-routedness
   of data and signaling paths in the forward and reverse directions
   after FRR. In addition, the RSVP-TE signaling extensions allow the
   coordination of bypass tunnel assignment protecting a common facility
   in both forward and reverse directions prior to or post failure
   occurrence.


Status of this Memo

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Copyright and License Notice

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   document authors. All rights reserved.

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   described in the Simplified BSD License.



Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3. Link Failure With Node-protection Bypass Tunnels  . . . . . . .  5
     3.1. Behavior Before Local Repair  . . . . . . . . . . . . . . .  5
       3.1.1. Downstream Merge Point Label Discovery  . . . . . . . .  6
       3.1.2. Upstream Merge Point Label Discovery  . . . . . . . . .  6
     3.2. Behavior Post Link Failure After FRR  . . . . . . . . . . .  6
     3.3. Behavior Post Link Failure To Re-coroute  . . . . . . . . .  6
   4. Bypass Tunnel Assignment  . . . . . . . . . . . . . . . . . . .  8
     4.1. DOWNSTREAM_BYPASS_ASSIGNMENT Object . . . . . . . . . . . .  8
     4.2. Bypass Tunnel Assignment Signaling Procedure  . . . . . . . 10
   5. Compatibility  . . . . . . . . . . . . . . . . . . . .  . . . . 10
   6. Security Considerations . . . . . . . . . . . . . . . . . . . . 10
   7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 11
   8. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 11
   9. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12














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1. Introduction

   Co-routed bidirectional tunnels are signaled using GMPLS signaling
   procedures specified in [RFC3473] and [RFC3471]. Existing procedures
   defined in [RFC4090] describe the behavior of the Point of Local
   Repair (PLR) to reroute traffic and signaling onto the bypass tunnel
   in the event of a failure for unidirectional LSPs. These procedures
   are applicable to unidirectional protected LSPs, and don't address
   issues that arise employing FRR for bidirectional co-routed Label
   Switched Paths (LSPs).

   When using current FRR procedures with bidirectional co-routed LSPs,
   it is possible in some cases (e.g. when using node-protecting bypass
   tunnels post a link failure event and when RSVP signaling is sent
   in-fiber and in-band with data), the RSVP signaling refreshes may
   stop reaching some nodes along the primary bidirectional LSP path
   after the PLRs complete rerouting traffic and signaling onto the
   bypass tunnels. This is caused by the asymmetry of paths that may be
   taken by the bidirectional LSP's signaling in the forward and reverse
   directions after FRR reroute. In such cases, the RSVP soft-state
   timeout eventually causes the protected bidirectional LSP to be
   destroyed, and consequently impacts protected traffic flow after FRR.
   This problem exists when using either unidirectional or bidirectional
   bypass tunnels to protect the primary co-routed bidirectional LSP.

   When co-routed bidirectional bypass tunnels are used to locally
   protect bidirectional LSPs, the upstream and downstream PLRs may
   independently assign different bidirectional bypass tunnels in the
   forward and reverse direction. Currently, there is no means to
   coordinate the bypass tunnel selection between the downstream and
   upstream PLRs. In case of mismatch and after FRR, data traffic and
   signaling may flow over asymmetric paths in the forward and reverse
   directions which may be undesirable for certain applications.

   This document proposes solutions to the above problems by providing
   corrective actions in the control plane to complement FRR procedures
   of [RFC4090] in order to maintain the RSVP soft-state for
   bidirectional protected LSPs and achieve symmetry in the paths
   followed by data and signaling in the forward and reverse directions
   post FRR. The document also extends RSVP signaling so it is possible
   that the bypass tunnel selected by the upstream PLR matches the one
   selected by the downstream PLR.


2. Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this



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   document are to be interpreted as described in RFC 2119 [RFC2119].

   The reader is assumed to be familiar with the terminology in [RSVP]
   and [RSVP-TE].

   LSR: Label-Switch Router.

   LSP: An MPLS Label-Switched Path.  In this document, an LSP will
   always be explicitly routed.

   Local Repair: Techniques used to repair LSP tunnels quickly when a
   node or link along the LSP's path fails.

   PLR: Point of Local Repair. The head-end LSR of a backup tunnel or a
   detour LSP.

   Facility Backup: A local repair method in which a bypass tunnel is
   used to protect one or more protected LSPs that traverse the PLR, the
   resource being protected, and the Merge Point in that order.

   Protected LSP: An LSP is said to be protected at a given hop if it
   has one or multiple associated backup tunnels originating at that
   hop.

   Bypass Tunnel: An LSP that is used to protect a set of LSPs passing
   over a common facility.

   Backup Tunnel: The LSP that is used to backup up one of the many LSPs
   in many-to-one backup.

   NHOP Bypass Tunnel: Next-Hop Bypass Tunnel. A backup tunnel that
   bypasses a single link of the protected LSP.

   NNHOP Bypass Tunnel: Next-Next-Hop Bypass Tunnel. A backup tunnel
   that bypasses a single node of the protected LSP.

   Backup Path: The LSP that is responsible for backing up one protected
   LSP.  A backup path refers to either a detour LSP or a backup tunnel.

   MP: Merge Point. The LSR where one or more backup tunnels rejoin the
   path of the protected LSP downstream of the potential failure. The
   same LSR may be both an MP and a PLR simultaneously.

   CSPF: Constraint-based Shortest Path First.

   Downstream PLR: A PLR that locally detects a fault and reroutes
   traffic in the same direction of the protected bidirectional LSP RSVP
   Path signaling.



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   Upstream PLR: A PLR that locally detects a fault and reroutes traffic
   in the opposite direction of the protected bidirectional LSP RSVP
   Path signaling.

   Point of Remote Repair (PRR): an upstream PLR that triggers reroute
   of traffic and signaling based on procedures described in this
   document.


3. Link Failure With Node-protection Bypass Tunnels


                            T1
                       +------<<-----+
                      /               \       <-RESV
            [R1]---[R2]----[R3]--x--[R4]---[R5]---[R6]
               ->            \               /
                  PATH        +------>>-----+
                                       T2

            Protected LSP:  [R1-R2-R3-R4-R5-R6]
            R3's Backup T2: [R3-R5]
            R4's Backup T1: [R4-R2]

         Figure 1: Flow of RSVP signaling post FRR after failure


   Consider the Traffic Engineered (TE) network shown in Figure 1.
   Assume every link in the network is protected with a node- protection
   bypass tunnel. For the protected bidirectional co-routed LSP whose
   active/head is on router R1 and passive/tail is on router R6, each
   traversed router (a potential PLR) independently assigns a node-
   protection bypass tunnel. Consider a link R3-R4 on the LSP path
   fails.

   The proposed solution introduces two phases to invoking FRR
   procedures by the PLR post the link failure. The first phase
   comprises of FRR procedures to fast reroute data traffic onto bypass
   tunnels in the forward and reverse direction. The second phase re-
   coroutes the data and signaling in cases where they go over
   asymmetric paths in the forward and reverse directions after the
   first phase.

3.1. Behavior Before Local Repair

   To correctly reroute data traffic over a node-protection tunnel, the
   downstream and upstream PLRs have to know, in advance, the downstream
   and upstream Merge Point (MP) labels so that data in the forward and



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   reverse directions can be tunneled through the bypass tunnel post FRR
   respectively.

3.1.1. Downstream Merge Point Label Discovery

   For unidirectional primary LSPs, [RFC4090] defines procedures for the
   downstream PLR to obtain the downstream MP label from recorded labels
   of the RSVP Resv message received at the downstream PLR.

3.1.2. Upstream Merge Point Label Discovery

   To obtain the upstream MP label, existing methods to record upstream
   MP label in the RRO of the RSVP Path message are used. The upstream
   PLR can obtain the upstream MP label from the recorded label in the
   RRO of the received RSVP Path message.

3.2. Behavior Post Link Failure After FRR

   The downstream PLR R3 and upstream PLR R4 independently trigger fast
   reroute procedures to redirect traffic onto respective bypass tunnels
   T2 and T1 in the forward and reverse direction. The downstream PLR R3
   also reroutes RSVP Path state onto the bypass tunnel T2 using
   procedures described in [RFC4090]. Note, at this point, router R4
   stops receiving RSVP Path refreshes for the protected bidirectional
   LSP while primary protected traffic continues to flow over bypass
   tunnels.

3.3. Behavior Post Link Failure To Re-coroute

   The downstream Merge Point (MP) R5 that receives rerouted protected
   LSP RSVP Path message through the bypass tunnel, in addition to the
   regular MP processing defined in RF4090, gets promoted to a Point of
   Remote Repair (PRR role) and performs the following actions to re-
   coroute signaling and data traffic over the same path in both
   directions:


   For unidirectional bypass tunnels:

      - Checks for presence of a bypass tunnel in the reverse direction
        that terminates on the Downstream PLR R3. Note: the Downstream
        PLR R3's address is extracted from the "IPV4 tunnel sender
        address" in the SENDER_TEMPLATE object.

      - If present, checks whether the primary LSP traffic and signaling
        is already rerouted over the found bypass tunnel. If not, PRR R5
        activates FRR reroute procedures to direct traffic and signaling
        (RSVP Resv) over the found bypass tunnel T3 in reverse



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        direction.

      - If not present, PRR R5 attempts to auto-provision a bypass
        tunnel that terminates on the downstream PLR R3. For
        unidirectional bypass tunnels, if co-routedness in forward and
        reverse direction is desired, the reverse path bypass tunnel can
        be inferred from the forward bypass tunnel path (e.g. by
        reflecting the RRO recorded in the forward direction as ERO for
        the reverse direction).

      - If PRR R5 is unable to successfully provision a bypass tunnel
        that terminates on the downstream PLR, it may send an immediate
        RSVP Notify message back to the head-end. The head-end may tear
        and re-setup the LSP immediately.


   For bidirectional bypass tunnels:

      - The PRR follows similar procedures described in the solution to
        second problem in order to identify the bypass tunnel, and
        reroute traffic and signaling in the reverse path.

   If MP R5 receives multiple RSVP Path messages through multiple bypass
   tunnels (e.g. as a result of multiple failures), the PRR should
   identify/provision a bypass tunnel that terminates on the farthest
   downstream PLR along the protected LSP path (closest to the
   bidirectional tunnel headend) and activate the reroute procedures
   mentioned above.

                                            <- RSVP RESV
            [R1]---[R2]----[R3]--X--[R4]---[R5]---[R6]
                RSVP PATH -> \             /
                              +<<------->>+
                              Bypass Tunnel
                            traffic + signaling

                 Protected LSP:  [R1-R2-R3-R4-R5-R6]
                 R3's Backup T2: [R3-R5]
                 R5's Backup T3: [R4-R2]

         Figure 2: Flow of RSVP signaling post FRR after re-coroute

   Figure 2 describes the path taken by traffic and signaling after
   completing re-coroute of data and signaling in the forward and
   reverse paths described earlier.






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4. Bypass Tunnel Assignment Coordination

   This document defines one additional RSVP object,
   DOWNSTREAM_BYPASS_ASSIGNMENT, to extend RSVP-TE for fast-reroute
   signaling.  This object is backward compatible with LSRs that do not
   recognize it (see section 3.10 in [RSVP]).

4.1. DOWNSTREAM_BYPASS_ASSIGNMENT Object

   The DOWNSTREAM_BYPASS_ASSIGNMENT object is used to coordinate the
   backup used for the protected LSP by the downstream and upstream PLRs
   in the forward and reverse direction respectively prior or post the
   failure occurrence. This object MUST only be inserted into the Path
   message by the downstream PLR and MUST NOT be changed by downstream
   LSRs. The DOWNSTREAM_BYPASS_ASSIGNMENT object has the following
   format:


       The IPv4 DOWNSTREAM_BYPASS_ASSIGNMENT object (Class-Num of the
       form 11bbbbbb with value = TBA, C-Type = TBA) has the following
       format:


          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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |            Length (bytes)      | Class-Num (TBA)|C-Type (TBA) |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |       Bypass Tunnel ID         |       Reserved               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                IPv4 Bypass Source Address                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                IPv4 Bypass Destination Address                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

















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       The IPv6 DOWNSTREAM_BYPASS_ASSIGNMENT object (Class-Num of the
       form 11bbbbbb with value = TBA, C-Type = TBA) has the following
       format:


          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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |            Length (bytes)      | Class-Num (TBA)|C-Type (TBA) |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |       Bypass Tunnel ID         |       Reserved               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                IPv6 Bypass Source Address                     |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                IPv6 Bypass Destination Address                |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      Bypass Source Address

            The bypass tunnel source IPV4 or IPV6 address.

      Bypass Destination Address

            The bypass tunnel destination IPV4 or IPV6 address.

      Bypass Tunnel ID

            The bypass tunnel identifier.















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4.2. Bypass Tunnel Assignment Signaling Procedure

   In cases where bidirectional bypass tunnels or a mix of
   unidirectional and bidirectional bypass tunnels are used for FRR
   Local Repair for a bidirectional co-routed LSP, it is desirable to
   coordinate the bypass tunnel selected at the downstream and upstream
   PLRs so that rerouted traffic and signaling flows on symmetrical
   paths post FRR. To achieve this, a new RSVP object is defined that
   identifies a bidirectional bypass tunnel that is assigned at a
   downstream PLR to protect a bidirectional LSP.

   The DOWNSTREAM_BYPASS_ASSIGNMENT object is added by each downstream
   PLR in the RSVP Path message of the primary LSP to record the
   downstream bidirectional bypass tunnel assignment. This object is
   sent in the RSVP Path message every time the downstream PLR assigns
   or updates the bypass tunnel assignment so the upstream PLR may
   reflect the assignment too.

   The upstream PLR (downstream MP) that detects a
   DOWNSTREAM_BYPASS_ASSIGNMENT object whose bypass tunnel destination
   matching its own address assigns the matching bidirectional bypass
   tunnel in the reverse direction, and removes the corresponding bypass
   tunnel assignment object before forwarding the RSVP Path message
   downstream. Otherwise, the bypass tunnel assignment object is
   forwarded downstream along in the RSVP Path message.

   In absence of DOWNSTREAM_BYPASS_ASSIGNMENT object, the downstream MP
   can independently assign a bypass tunnel in the reverse direction. In
   the case of downstream MP receiving multiple
   DOWNSTREAM_BYPASS_ASSIGNMENT objects from multiple downstream PLRs,
   the decision of selecting a bypass tunnel in the reverse direction
   can be based on local policy, for example, prefer link protection vs.
   node protection bypass, or prefer the most upstream vs. least
   upstream node protection bypass tunnel. Note, the bypass tunnel
   selection will be corrected after FRR based on the PRR behavior after
   failure.

5. Compatibility

   The DOWNSTREAM_BYPASS_ASSIGNMENT object to be defined with class
   numbers in the form 11bbbbbb, which ensures compatibility with non-
   supporting nodes. Per [RFC2205], nodes not supporting this extension
   will ignore the object but forward it, unexamined and unmodified, in
   all messages resulting from this message.

6. Security Considerations

   This document introduces one new RSVP object. Thus in the event of



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   the interception of a signaling message, slightly more could be
   deduced about the state of the network than was previously the case,
   but this is judged to be a very minor security risk as this
   information is available by other means.

   Otherwise, this document introduces no additional security
   considerations. For general discussion on MPLS and GMPLS related
   security issues, see the MPLS/GMPLS security framework [RFC5920].


7. IANA Considerations

   A new Class-Num for the new DOWNSTREAM_BYPASS_ASSIGNMENT object is
   required.

8. Acknowledgements

   Authors would like to thank George Swallow for his detailed and
   useful comments and suggestions.

9. References

9.1.  Normative References

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

   [RSVP-TE]  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.

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

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

   [RFC3471]  Berger, L., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Signaling Functional Description", RFC
              3471, January 2003.







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Authors' Addresses

   Mike Taillon
   Cisco Systems, Inc.
   EMail: mtaillon@cisco.com


   Tarek Saad
   Cisco Systems, Inc.
   EMail: tsaad@cisco.com


   Rakesh Gandhi
   Cisco Systems, Inc.
   EMail: rgandhi@cisco.com


   Zafar Ali
   Cisco Systems, Inc.
   EMail: zali@cisco.com































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