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Versions: 00 01 draft-ietf-mpls-p2mp-te-bypass

Network Working Group                                       J.L. Le Roux
Internet Draft                                            France Telecom
Category: Standard Track
Expires: September 2007                                      R. Aggarwal
                                                        Juniper Networks

                                                            J.P. Vasseur
                                                     Cisco Systems, Inc.

                                                            M. Vigoureux
                                                          Alcatel-Lucent


                                                              March 2007


            P2MP MPLS-TE Fast Reroute with P2MP Bypass Tunnels

                 draft-leroux-mpls-p2mp-te-bypass-01.txt


Status of this Memo

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Abstract

   This document defines procedures for fast reroute protection of
   Point-To-MultiPoint (P2MP) Traffic Engineering Label Switched Paths
   (TE-LSP) in  MultiProtocol Label Switching (MPLS) networks, based
   upon Point-To-MultiPoint bypass tunnels. The motivation for using
   P2MP bypass tunnels is to avoid potentially expensive data
   duplication along the backup path that could occur if point-to-point
   bypass tunnels where used, i.e. to optimize the bandwidth usage,
   during fast reroute protection of a link or a node. During link or
   node failure the traffic carried onto a protected P2MP TE-LSP is
   tunnelled within one or several P2MP bypass tunnels towards a set of
   Merge Points. To avoid data duplication backup labels (i.e. inner
   labels) are assigned by the Point of Local Repair (PLR) following the
   RSVP-TE upstream label assignment procedure.


Conventions used in this document

   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.


Table of Contents

   1.      Terminology.................................................3
   2.      Introduction................................................3
   3.      Solution overview...........................................4
   4.      PLR procedures..............................................6
   4.1.    Before failure..............................................6
   4.1.1.  P2MP Bypass Tunnel(s) Selection.............................6
   4.1.2.  P2MP Backup LSP Signalling..................................7
   4.2.    During failure..............................................8
   5.      MP Procedures...............................................8
   6.      To be included in future revisions..........................9
   7.      Security Considerations.....................................9
   8.      Acknowledgments.............................................9
   9.      References..................................................9
   9.1.    Normative references........................................9
   10.     Authors' Addresses:........................................10
   11.     Intellectual Property Statement............................11











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1. Terminology

   This document uses terminologies defined in [RFC3031], [RFC3209],
   [RFC4090] and [RFC4461]. It defines the following new terms:

   P2MP Bypass tunnel: Point-to-Multipoint Bypass Tunnel. A P2MP TE-
   LSP that is used to protect a set of P2MP TE-LSPs traversing a
   common facility (link or node).

   P2MP Facility Backup: A local repair method in which a P2MP bypass
   tunnel is used to protect one or more P2MP TE-LSPs that
   traverse the Point of Local Repair (P2MP Bypass Ingress) and the
   resource being protected.

   Backup P2MP LSP: The LSP that is used to backup up one of the
   many protected P2MP LSPs in P2MP Facility Backup.

   Backup S2L sub-LSP: A S2L sub-LSP of a backup P2MP LSP.

   PLR: Point of Local Repair: Head-end LSR of the bypass tunnel

   MP: Merge Point: LSR where a primary LSP and its backup LSP merge.

                        .
2. Introduction

   [RFC4090] defines fast reroute extensions to RSVP-TE [RFC3209] for
   local protection of Point-To-Point (P2P) Traffic Engineered Label
   Switched Paths (TE LSP) in MultiProtocol Label Switching (MPLS)
   networks. Two techniques are defined: the one-to-one backup method,
   which creates a detour LSP for each protected LSP at each point of
   local repair (PLR), and the facility backup method, which creates a
   bypass tunnel that can be used to protect a set of TE LSPs by taking
   advantage of MPLS label stacking.

   [RSVP-P2MP] defines extensions to RSVP-TE for setting up Point-To-
   Multipoint (P2MP) TE LSPs. It specifies extensions to one-to-one and
   facility backup Fast Reroute procedures defined in [RFC4090] so as to
   support fast reroute protection of P2MP TE LSPs.
   The facility backup solution defined in [RSVP-P2MP] only relies on
   P2P bypass tunnels for link and node protection. This faces the
   following limitations:

        - The protection of a downstream link of a P2MP TE LSP on a
        branch LSR may require a P2P Bypass LSP that uses another
        downstream link of the P2MP LSP, and this leads to twice the
        traffic on that link during failure, which is inefficient.
        Finding a bypass path that avoids all downstream links on the
        P2MP LSP would be a solution but this is often not achievable in
        lowly meshed topologies.


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        - The protection of a P2MP TE LSP against node failures
        requires, when the protected node is a Branch LSR, a set of P2P
        Next-Next-Hop (NNHOP) Bypass tunnels toward all LSRs downstream
        to the  protected node. During failure the PLR has to replicate
        traffic on each P2P NNHOP bypass tunnel. If there are K next-
        next-hops, this may lead to K times the traffic on some links,
        which is not acceptable (as K is of the order of magnitude of
        the squared node degree).

        - Similarly the protection of a P2MP TE LSP against the failure
        of a LAN interface that connects a branch LSR and a set of K
        downstream LSRs requires one P2P bypass tunnel per downstream
        LSR, which may lead to K times the traffic on some links during
        failure.

   To overcome these limitations it is highly desirable to define
   extensions to the fast reroute facility backup solution, so as to
   support P2MP bypass tunnels. This retains the scalability advantages
   of MPLS label stacking and avoids sending multiple copies of a packet
   on some links during failure.

   This draft specifies extensions to the Fast ReRoute (FRR) procedures
   defined in [RFC4090] and [RSVP-P2MP] to support local repair of P2MP
   TE LSP with P2MP bypass tunnels.

   Procedures defined in [RFC3209], [RFC4090] and [RSVP-P2MP] MUST be
   followed unless specified below.

3. Solution overview

   The P2MP Facility Backup method defined in this document relies on
   the use of P2MP bypass tunnels. Similarly to the P2P case, the same
   P2MP bypass tunnel can be used to protect a set of P2MP TE LSPs, by
   taking advantage of MPLS label stacking.

   A P2MP Bypass tunnel can be used to protect a P2MP TE-LSP against
   downstream link or node failures. There are various options for the
   protection of a downstream link or node:

        - Rely on a single P2MP bypass tunnel whose leaf LSRs exactly
           matches the set of Merge Points (MP). Merge points are
           transit or egress LSRs on the protected P2MP LSP downstream
           to the PLR or downstream to the protected element (link or
           node).
        - Rely on a single P2MP Bypass tunnel whose set of leaf LSRs is
           a superset of the set of MPs. Leaf LSRs which are not MP have
           to drop the traffic.
        - Rely on a combination of P2MP bypass LSPs whose leaf LSRs are
           a subset of the set of MP but there combination encompass all
           MPs.


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   These three options differ in terms of bandwidth optimization and
   control plane state minimization. Option 1 increases the number of
   states compared to option 2 (it implies more P2MP bypass LSPs), but
   is less expensive in terms of bandwidth (traffic only sent to MPs).
   With point-to-multipoint hierarchy there is always a tension between
   minimizing the amount of control plane state and minimizing bandwidth
   consumption. Choosing one of these options is a decision local to the
   PLR. The choice depends on the desired trade-off between control
   plane and data plane optimization, and the operational complexity
   associated with the different options.

   When the P2MP facility backup method is used, during failure the PLR
   MUST send data for each protected P2MP LSP into the set of one or
   more P2MP bypass tunnel. Label stacking is used: the inner label is
   the backup label for the backup P2MP LSP, that will be used on the MP
   to forward traffic to the corresponding protected P2MP LSP, and the
   outer label is the P2MP bypass tunnel label.

   To avoid data replication on the PLR, the same backup label MUST be
   used for all S2L sub-LSPs of a given backup P2MP LSP, tunneled within
   the same P2MP bypass tunnel. This backup label will indicate to the
   Merge Points that packets received with that label should be switched
   along the protected P2MP LSP.

   For that purpose upstream label assignment procedures defined in
   [MPLS-UPSTREAM] and RSVP-TE extensions for upstream label assignment
   defined in [RSVP-UP] MUST be used. To signal a backup P2MP LSP, the
   same backup label, is distributed by the PLR to all MPs belonging to
   a same P2MP Bypass tunnel, in the context of this P2MP bypass tunnel.
   This requires the backup P2MP LSP to be signalled prior to the
   failure.

   On the MP, backup S2L sub-LSPs (i.e. S2L sub-LSPs of the backup P2MP
   LSP) are merged with protected S2L sub-LSPs. A MP (i.e. the bypass
   tunnel leaf LSRs), maintains a context specific ILM for the P2MP
   Bypass tunnel. This can be implemented by maintaining a different
   context specific ILM for each LSR that is the root of a P2MP Bypass
   tunnel, or by maintaining a different context specific ILM for each
   P2MP Bypass tunnel. The context of an inner label (i.e a backup label)
   is determined by the underlying P2MP bypass tunnel on which it is
   received. This requires deactivating PHP on the P2MP bypass tunnel. A
   label, in a given Bypass tunnel specific ILM, is mapped to the
   outgoing interface(s) and label(s) of the corresponding protected
   P2MP LSP.









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4. PLR procedures

4.1. Before failure

4.1.1. P2MP Bypass Tunnel(s) Selection

   To protect a P2MP TE LSP against a downstream link or node failure, a
   PLR MUST select a set of one or more P2MP bypass tunnel(s), denoted
   {B1.Bm}, as follows:

        - The bypass tunnel(s) MUST NOT traverse the protected
        link/node/SRLG.

        - The set of leaf LSRs of bypass tunnels {B1.Bm}, denoted {LSR1.
        LSRn} must include a set of Merge Points (MP), on the protected
        P2MP LSP. These Merge Points are transit or egress LSRs on the
        protected P2MP LSP downstream to the PLR or downstream to the
        protected element (link or node). We will denote this set of
        Merge Points as {MP1.MPq}. Note that the case where some MPs are
        LSRs downstream to the PLR but not downstream to the failed
        element allows avoiding sending twice the traffic on downstream
        links during failure.

        - In the event of failure of the protected link or node, traffic
        received on the protected P2MP LSP by the PLR, can be delivered
        to all the leaves of the protected P2MP LSP downstream to the
        PLR, if it is tunnelled to {MP1.MPq} over the set of one or more
        P2MP bypass tunnel(s) {B1.Bm}.

   The PLR will assign upstream labels to Merge Points {MP1.MPq} for the
   backup P2MP LSP. The same backup label will be assigned to all Merge
   Points belonging to the same P2MP Bypass tunnel.

   A MP may actually be leaf LSR of multiple bypass tunnels, but will be
   associated to only one bypass tunnel. That is a PLR will signal the
   P2MP backup LSP to that MP, for a single P2MP bypass tunnel context.

   {LSR1.LSRn} may be a superset of {MP1.MPq}, that is some leaf LSRs of
   a given P2MP bypass tunnel, noted {LSRx.LSRy}, may not belong to
   {MP1.MPq}. The PLR will not assign upstream labels for the backup
   P2MP LSP to these LSRs {LSRx.LSRy}. During failure packets with a
   backup label will also be delivered onto the P2MP bypass tunnel to
   {LSRx.LSRy} which will discard these packets based on no entry for
   this label in the context specific ILM for that bypass tunnel. This
   requires that {LSRx.LSRy} create a context specific ILM for that
   bypass tunnel.




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   PHP MUST be deactivated on the P2MP Bypass tunnel, in order to allow
   MPs to determine the context for the backup labels assigned by the
   PLR.

   Note that P2MP bypass LSPs may be signalled in advance either
   automatically or via configuration, or may be dynamically setup upon
   protected P2MP LSP signalling. Such procedures rely on local
   implementation issues and are beyond the scope of this document.


4.1.2. P2MP Backup LSP Signalling

   The same backup label (i.e. the inner label) MUST be used for all
   backup S2L sub-LSPs which are tunneled within the same P2MP Bypass
   tunnel, so as to avoid traffic replication on the PLR. This label
   MUST be assigned by the PLR using upstream label assignment
   procedures.

   Backup P2MP LSPs MUST be signaled prior to the failure. To signal the
   backup P2MP LSP, the PLR will send one or more Path messages,
   referred to as a backup LSP's Path message, to each MP, as specified
   in [RSVP-P2MP]. A backup LSP's Path message to a given MP comprises
   one or more backup S2L sub-LSPs that transit through this MP.
   A backup Path message MUST be sent to the MP using directed
   signaling; i.e., it is addressed to the MP, without Router Alert
   option.

   As specified in [RSVP-P2MP] it is RECOMMENDED that the PLR use the
   sender template specific method to identify a backup LSP's Path
   message, that is, the PLR will set the source address in the sender
   template to a local PLR address.

   The backup label MUST be assigned by the PLR, in the context of the
   underlying P2MP Bypass tunnel, following upstream label assignment
   and P2MP RSVP-TE context identification procedures defined in [RSVP-
   UP]. Hence, a backup LSP's Path message sent to a given MP MUST
   include an Upstream Assigned Label object carrying the value of the
   backup label. It MUST also include an RSVP-TE P2MP LSP TLV within an
   IF_ID RSVP object, that carries the session object of the underlying
   P2MP Bypass tunnel. This allows the MP to identify the label space of
   the backup label assigned by the PLR. The same backup label MUST be
   sent to all MPs belonging to a given P2MP Bypass tunnel.

   Note that the PLR MUST continue to refresh Path messages for the
   protected P2MP TE LSP along the nominal route.

   The processing of backup S2L sub-LSP SEROs/SRROs MUST follow
   backup LSP ERO/RRO processing described in [RFC4090].





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4.2. During failure

   When the PLR detects a link or/and node failure condition, it has to
   reroute a protected P2MP LSP onto a set of one or more P2MP bypass
   tunnels using as inner label(s) the backup label(s) assigned for this
   P2MP LSP.

   Note that when some MPs are LSRs downstream to the PLR but not
   downstream to the failed element, the PLR MUST stop sending traffic
   directly within the protected P2MP TE LSP towards these MPs. This
   allows avoiding sending twice the traffic on downstream links during
   failure.

   The PLR MUST continue to send Path messages for the backup P2MP LSP.
   The RRO/ERO flags MUST be updated as per defined in [RFC4090]

5. MP Procedures

   A MP receives one or more Path messages for the protected P2MP TE LSP
   and one or more Path messages for the backup P2MP LSP.

   Note that, as specified in [RFC4090], the reception of a backup LSP's
   Path message does not indicate that a failure has occurred or that
   the incoming protected LSP will no longer be used.

   A S2L sub-LSP is received within a Path message for the protected
   P2MP LSP and within a Path message for the backup P2MP LSP. These two
   Path messages are distinguished thanks to the sender-template
   specific method. As specified in [RFC4090], each of these Path
   messages will have a different sender address. The protected LSP can
   be recognized because it will include the FAST_REROUTE object or have
   the "local protection desired" flag set in the SESSION_ATTRIBUTE
   object, or both.

   A MP MUST maintain one context specific ILM table per PLR or per P2MP
   bypass tunnel for which it is a leaf.

   A MP MUST install the upstream assigned label received in a backup
   LSP's Path message, within an ILM specific to the underlying bypass
   tunnel, which is identified by its session object, carried within the
   IF_ID RSVP_HOP object of the backup LSP's Path message. An upstream
   assigned label for a backup P2MP LSP MUST be mapped to the outgoing
   interface(s) and label(s) of the corresponding protected P2MP LSP.

   As specified in [RSVP-UP], the Resv message sent by a MP to the PLR,
   does not carry any Label Object.

   The processing of backup S2L sub-LSP SEROs/SRROs MUST follow
   backup tunnel ERO/RRO processing described in [RFC4090].




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6. To be included in future revisions

   The following items will be included in further revisions of this
   document:

        - Combination of P2P and P2MP bypass tunnels to protect a given
          link/node. This will allow backward compatibility with LSRs
          that do not support upstream label assignment.

        - Cases where the PLR is not directly upstream to the protected
          element.

        - Partial protection: that is the case where only a subset of
          Merge Points can be covered.

        - New RSPV-TE Attribute flags:

             o A flag in the ATTRIBUTE FLAGS TLV to indicate that
               protection with P2MP bypass tunnels is desired, and to
               record such protection.
             o A flag in the ATTRIBUTE FLAGS TLV to indicate whether
                partial protection is allowed or not and to record
                partial protection.
             o A flag in the ATTRIBUTE FLAGS TLV to indicate that PHP
                must be deactivated, and to record PHP status (this has
                a broader scope so this may belong to a dedicated
                draft).

7. Security Considerations

   No new security issues are raised in this document.

8. Acknowledgments

   We would like to thank Kireeti Kompella and Venu Hemige, for the
   useful comments and discussions.

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.

   [RFC3031] E. Rosen, A. Viswanathan, R. Callon, "MPLS Architecture",
   RFC 3031.

   [RFC3209] D. Awduche et al., "RSVP-TE: Extensions to RSVP for LSP
   Tunnels", RFC3209.

   [RFC4461] S. Yasukawa et al., "Signaling Requirements for Point-to-

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   Multipoint Traffic-Engineered MPLS Label Switched Paths (LSPs)",
   RFC4461.

   [RFC4090] Pan, Swallow, Atlas, et al., "Fast Reroute Extensions to
   RSVP-TE for LSP Tunnels", RFC4090.

   [RSVP-P2MP] Aggarwal, Papadimitriou, Yasukawa et al. "Extensions to
   RSVP-TE for Point to Multipoint TE LSPs", draft-ietf-mpls-rsvp-te-
   p2mp, work in progress.

   [MPLS-UPSTREAM] Aggarwal, Rekhter, Rosen, "MPLS Upstream Label
   Assignment and Context Specific Label Space", draft-ietf-mpls-
   upstream-label, work in progress.

   [RSVP-UP] Aggarwal, Le Roux, " MPLS Upstream Label Assignment for
   RSVP-TE", draft-ietf-mpls-rsvp-upstream, work in progress.


10. Authors' Addresses:

   Jean-Louis Le Roux
   France Telecom
   2, avenue Pierre-Marzin
   22307 Lannion Cedex
   FRANCE
   Email: jeanlouis.leroux@orange-ftgroup.com

   Rahul Aggarwal
   Juniper Networks
   1194 North Mathilda Ave.
   Sunnyvale, CA 94089
   USA
   Email: rahul@juniper.net

   Jean-Philippe Vasseur
   Cisco Systems, Inc.
   1414 Massachusetts avenue
   Boxborough , MA - 01719
   USA
   Email: jpv@cisco.com

   M. Vigoureux
   Alcatel-Lucent France
   Route de Villejust
   91620 Nozay
   FRANCE
   Email: martin.vigoureux@alcatel-lucent.fr






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 11. Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.

   Disclaimer of Validity

   This document and the information contained herein are provided
   on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
   REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
   IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL
   WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY
   WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE
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   Copyright Statement

   Copyright (C) The IETF Trust (2007). This document is subject to the
   rights, licenses and restrictions contained in BCP 78, and except as
   set forth therein, the authors retain all their rights.













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