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Network Working Group                                       Quintin Zhao
Internet-Draft                                                  Tao Chou
Intended status: Standards Track                       Huawei Technology
Expires: January 1, 2014                                     Boris Zhang
                                                    Telus Communications
                                                              Emily Chen
                                                           June 30, 2013


        P2MP Based mLDP Node Protection Mechanisms for mLDP LSP
                draft-zhao-mpls-mldp-protections-04.txt

Abstract

   This document outlines the procedures and protocol extensions for the
   protection of mLDP nodes within Multi-Protocol Label Switching (MPLS)
   networks using P2MP-based backup LSPs.

Status of this Memo

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

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   This Internet-Draft will expire on January 1, 2014       .

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as



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   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
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   Without obtaining an adequate license from the person(s) controlling
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   it for publication as an RFC or to translate it into languages other
   than English.


Table of Contents

   1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirement Language . . . . . . . . . . . . . . . . . . . . .  3
   3.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     3.1.  Requirements . . . . . . . . . . . . . . . . . . . . . . .  5
     3.2.  Scope  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  mLDP Node Protection Example . . . . . . . . . . . . . . . . .  5
   5.  Signaling Procedures for P2MP Based Node Protection  . . . . .  7
     5.1.  The Computation of the Backup Path . . . . . . . . . . . .  7
     5.2.  The Procedures for Merge Point, Protected Node, Pn
           Node and PLR Node  . . . . . . . . . . . . . . . . . . . .  8
       5.2.1.  Merge Point's Procedures . . . . . . . . . . . . . . .  8
       5.2.2.  Protected Node's Procedures  . . . . . . . . . . . . .  8
       5.2.3.  Pn Node's Procedures . . . . . . . . . . . . . . . . .  8
       5.2.4.  PLR Node's Procdures . . . . . . . . . . . . . . . . .  9
     5.3.  PLR Switching Over Considerations  . . . . . . . . . . . .  9
     5.4.  The Procedures after the Reconvergence . . . . . . . . . . 10
     5.5.  Considerations for MP2MP LSP Node Protection . . . . . . . 10
       5.5.1.  MP Node Procedure  . . . . . . . . . . . . . . . . . . 11
       5.5.2.  PLR Node Procedure . . . . . . . . . . . . . . . . . . 12
       5.5.3.  Switchover Procedure . . . . . . . . . . . . . . . . . 12
     5.6.  Protocol Extensions for mLDP Based Node Protection . . . . 12
       5.6.1.  mLDP Based MP Protection Capability Parameter TLV  . . 12
       5.6.2.  mLDP Based MP Node Protection Status Elements  . . . . 13
       5.6.3.  mLDP Backup FEC Element Encoding . . . . . . . . . . . 13
     5.7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . 15
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 16
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17



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1.  Terminology

   This document uses terminology discussed in [RFC6388] and [I-D.ietf-
   mpls-ldp-multi-topology].  Additional key terms and terminology are
   listed here:

   o  PLR: The node upon which traffic is logically redirected onto the
      preset backup path is called Point of Local Repair (PLR).

   o  MP: The node upon which the backup path and the primary path merge
      is called the Merge Point (MP).

   o  N: The node which is protected by the backup path.

   o  Pn: The nodes on the backup path that protect node N.

   o  MT-ID: A 16 bit value used to represent the Multi-Topology ID.

   o  Default MT Topology: A topology that is built using the MT-ID
      default value of 0.

   o  MT Topology: A topology that is built using the corresponding
      MT-ID.

   o  MRT: Maximally Redundant Trees.  A pair of trees where the path
      from any node X to the root R along the first tree and the path
      from the same node X to the root along the second tree share the
      minimum number of nodes and the minimum number of links.


2.  Requirement Language

   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].


3.  Introduction

   To meet user demands, operators and service providers continue to
   deploy multicast applications using Multicast LDP (mLDP) across MPLS
   networks.  For real-time applications, such as stock trading, on-line
   games, and multimedia teleconferencing, traditional node protection
   mechanisms (such as IGP-mLDP convergence based mechanisms) fail to
   adhere to the protection switching time which is required to minimize
   the interruption of applications.

   Instead of replying the IGP-mLDP convergenvce for failure protection,



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   pre-computing, establishing a backup path before the failure and
   switching over to the backup path when the protected node fails is a
   better solution.

   But two major challenges exist with this aforementioned solution.
   The first is how to compute an absolutely disjointed backup path for
   each node in a multicast tree; the second is how to signal and setup
   the backup path.

   For a primary LDP P2MP LSP, there are several methods to choose for a
   backup path:

   o  The use of an RSVP-TE P2P tunnel as a logical out-going interface,
      which consequently utilizes the mature high availability
      technologies of RSVP-TE.

   o  The use of an LDP P2P LSP as a packet encapsulation, wherein
      complex configuration of P2P RSVP-TE can be skipped.

   o  Creating a P2MP backup LSP according to IGP's loop-free
      alternative route.

   o  Using multi topology technology, wherein the backup topology can
      be either statically configured or dynamically computed/ signaled
      using mechanisms specified in the draft of [I-D.ietf-rtgwg-mrt-
      frr-architecture].

   When the backup path is present, there are two options for packet
   forwarding and protection switchover:

   o  Option 1 The traffic sender transmits the stream on both the
      primary and backup path.  Once the local traffic receiver detects
      a failure, the switchover will be relatively fast.  However, the
      disadvantage of this method is that it consumes bandwidth because
      duplicate traffic will be sent on the primary and backup paths.

   o  Option 2 The traffic sender transmits only on the primary path.
      Although bandwidth resource usage is minimized, cooperation is
      required to provide adequate switching times and to minimize high-
      layer application impact.

   Ideally, if the switching time performance can be equal or better
   than that of Option 1, it is reasonable to choose option 2 to avoid
   bandwidth wastage.  Some recommendations in this document are based
   upon this consideration.

   Note that the computation and configuration of the primary topology
   and backup topology are out of the scope of this draft.  The



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   algorithm can be LFA based, MRT based, or based off of any other
   algorithms/method available including the static and offline tools.
   In addition, detecting failure is also outside the scope of this
   document.

   Compared to a P2P LSP based solution (specified in the draft of
   I-D.wijnands-mpls-mldp-node-protection), this P2MP LSP based solution
   not only uses mLDP mechanisms for both the primary path and backup
   paths, but also avoids unnecessary packet duplication.

   The remainder of this document specifies the signalling procedures
   and protocol extensions for the P2MP LSP based mLDP node protection
   solution which was briefly introduced above.

3.1.  Requirements

   A number of requirements have been identified that allow the optimal
   set of mechanisms to develop.  These currently include:

   o  Computation of a disjointed (link and node) backup path within the
      multicast tree

   o  Minimization of protection convergence time

   o  Minimization of operation and maintenance cost

   o  Optimization of bandwidth usage

   o  More protect scenario coverage

3.2.  Scope

   The method to detect failure is outside the scope of this document.

   The protections of leaf and root nodes are also outside the scope of
   this document.


4.  mLDP Node Protection Example

   By using IGP-FRR or Multi Topology Routing (including the MRT MT
   routing), LDP can build the backup mLDP LSP among PLR, Pn, and MPs
   (the downstream nodes of the protected node).  In the case of a large
   number of downstream nodes, this mechanism can avoid unnecessary
   packet duplication between PLR and the merge points.






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                               +------------+ Point of Local Repair/
                               |     R1     | Switchover Point
                               +------------+ (Upstream LSR)
                                  /       \
                                 /         \
                              10/           \20
                               /             \
                              /               \
                             /                 \
                       +----------+        +-----------+
        Protected Node |    R2    |        |     R3    |
                       +----------+        +-----------+
                         |       \         /        |
                         |        \       /         |
                         |         \     /          |
                       10|        10\   /20       20|
                         |           \ /            |
                         |            \             |
                         |           / \            |
                         |          /   \           |
                         |         /     \          |
                         |        /       \         |
                       +-----------+      +-----------+ Merge Point
                       |    R4     |      |    R5     | (Downstream LSR)
                       +-----------+      +-----------+


          Figure 1: mLDP Local Protection using mLDP LSP Example

   In Figure 1, R2 is on the preferential path from R4/5 to R1, and the
   secondary path is through R3.  In this case, the mLDP LSP will be
   established according to the IGP preferential path as R1--R2--R4/R5.
   As an example, this figure takes R2 as the Protected Node though the
   Protected Node can be any Transit node of the mLDP LSP.  (We assume
   that all the nodes in Figure 1 support this mLDP based node
   protection method, including Pn.)

   The procedure of P2MP Based mLDP Node Protection is as follows:

   o  As the Protected Node, R2 should announce its selected upstream
      node R1 to all its downstream nodes, which are R4 and R5 in this
      example.  The node to protect can then be decided by local
      configuration or by its role(transit) in the mLDP LSP.

   o  R4 and R5 can consider R1 as the root node of the backup mLDP LSP
      and can trigger the backup LSP signaling.  In parallel, R4/R5 will
      bind the primary NHLFE(s) to both the backup and primary ILM
      entries, so that the traffic from the backup mLDP LSP can be



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      merged locally to the primary LSP.

   o  PLR can distinguish primary LSP and backup LSP by the signaling
      procedure and can feed traffic on the primary path before failure.
      When R2 node fails, R1 quickly switches the traffic to the preset
      backup path.

   In this scenario, if R2 is protected by two P2P LSPs as R1--R3--R4
   and R1--R3--R5 (similar to the method in the draft of I-D.wijnands-
   mpls-mldp-node-protection), the traffic will be duplicated on R1, and
   R3 will receive two streams.  But, if R2 is protected by a mLDP LSP
   instead, R3 will only receive one stream, and thus there will be no
   packet duplication on R3.


5.  Signaling Procedures for P2MP Based Node Protection

   This section introduces the signaling procedures of P2MP LSP's node
   protection using P2MP-based backup LSP.

5.1.  The Computation of the Backup Path

   Obviously, the backup path can not go through the protected node N.
   This section discusses how to choose the backup upstream LSR to avoid
   N.

   Firstly, find the candidate upstream LSRs as below:

   o  MPs should preferentially choose the upstream LSRs on the shortest
      path as candidates, except node N. If no other upstream LSRs are
      on the shortest path, MPs should choose the next-hop on N's detour
      path as a candidate.  The detour path can be an IGP-FRR path or
      other topology-based disjoint paths.  The IGP-FRR path can be
      provided by LFA, U-Turn, etc.  The disjoint path can be provided
      by MT, MRT (see details in the next section), etc.  Choosing the
      candidates is a local decision and can be determined by
      configuration.

   o  The Pn node MUST be chosen from the IGP next-hops on the shortest
      path toward PLR within the topology specified in the FRR mLDP FEC
      element by MT-ID field.  The candidate upstream LSRs MUST not be
      the node N.

   Thus, each node can choose one upstream node from the candidate
   upstream LSRs as its backup upstream LSR via the algorithm described
   in [RFC6388] section 2.4.1.1.





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5.2.   The Procedures for Merge Point, Protected Node, Pn Node and PLR
      Node

   [Editors Note - The procedures for P2MP Based Node Protection
   described in this document assumes the PLR is capable of node failure
   detection.]

   We assume all the involved nodes have advertised their corresponding
   protection capabilities.  And the following section specifies the
   signaling procedures of P2MP Based Node Protection.

5.2.1.  Merge Point's Procedures

   Each non-Ingress LSR determines its own upstream LSR and sends out a
   label mapping message, in accordance with the procedures documented
   in [RFC6388] without any additional extension.  And its upstream LSR
   will propagate a new label mapping message to its upstream LSR.  In
   such cases, the non-Ingress LSR is the MP node (as R4, R5 in Figure
   1), MP's upstream LSR is the protected node (as R2 in Figure 1), and
   the protected node's upstream node is PLR (as R1 in Figure 1).

   When one MP (as R4/R5 nodes in figure 1) receives the Notification,
   it individually determines its secondary path toward the PLR
   according to the IGP routes.  The algorithms for choosing/computing
   the backup path can be LFA, MRT or others.  After the backup upstream
   LSR is chosen, MP will send out a FRR Label mapping message, which
   includes the mLDP backup tree's key <PLR, protected-node, original-
   mLDP-FEC> and the MT-ID if the backup path is not in the default
   topology.  Note that the label assigned for the primary path and the
   secondary path MUST be different to avoid having the MP feed primary
   traffic to its secondary path's downstream LSRs.  In addition, the
   original-mLDP-FEC of the backup tree key is encoded in a special
   opaque value as introduced in section 4.2.3.

5.2.2.  Protected Node's Procedures

   After the Protected Node (as R2 in Figure 1 ) determines its upstream
   LSR (as R1 in figure 1), it will send the information (PLR's
   indentify, mLDP FEC) via Notification messages to all its downstream
   nodes(MPs) immediately.  If other LSRs become its downstream nodes
   later, it will send such announcements to its new MP(s).

5.2.3.  Pn Node's Procedures

   When one node receives such aforementioned FRR label mapping
   messages, if it is not the PLR, it can consider itself a Pn node and
   will choose its backup upstream node toward PLR on the corresponding
   topology's shortest IGP path.  To avoid the backup LSP going through



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   the Protected Node, additional path selection rule(s) should be
   applied.  A simple method is for the transit nodes to not choose the
   specified Protected Node as its upstream LSR for the backup LSP.
   Other methods, such as the not-via policy, are under study and will
   be added in the future.  To make the primary and backup topologies
   rooted from PLR satisfy the 'maximum disjointed' requirement, they
   can either be configured through static configurations or be signaled
   dynamically through other mechanisms such as MRT.

5.2.4.  PLR Node's Procdures

   When PLR(R1) receives the FRR label mapping message, it can identify
   that it is the PLR by the mLDP backup FEC elements.  Thus, it will
   decode the special opaque value (which contains the primary mLDP FEC
   element, introduced in section 4.2.3) and generate the backup
   forwarding entry for the specific LSP, which is identified by the
   root address and opaque value in the special opaque value.  It will
   also bind the backup forwarding state to the specific primary entry,
   which is indicated by the Protected Node address in the message.
   Note that there might be more than one backup forwarding entry for a
   specific protected node.

   When failure is detected by PLR, it will switch the traffic to the
   backup paths.  MP will also locally choose which traffic to recieve
   and merge this traffic back to the primary LSP.  The switchover
   manner on PLR is specified in detail in the later section of this
   document.

5.3.  PLR Switching Over Considerations

   This section provides two methods for Switchover when failure occurs:

   o  Option 1: If PLR cannot differentiate link and node failure, MP
      must take the responsibility to drop one of the two duplicate
      traffics when failure is detected.  In this case, the Node Failure
      Required Flag (in the P2MP Based MP Node Protection Status
      Element) must be set as 'N'.  PLR will switch the traffic to the
      backup path when failure is detected, and MP will drop traffic on
      the backup path until it sees N fail.

   o  Option 2: If PLR can differentiate link and node failure, PLR MUST
      NOT switch the traffic to the backup path until it detects the
      node N's failure.  In this case, the Node Failure Required Flag,
      in the P2MP Based MP Node Protection Status Element, must be set
      as 'Y'.






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5.4.  The Procedures after the Reconvergence

   When Merge Point(s) see the next hop to Root changed, it/they will
   advertise the new mapping message(s), and the traffic will re-
   converge to the new primary path.  MP will then withdraw the backup
   label after the re-convergence.  Pn will delete the specified backup
   LSP just as in the procedure of deleting normal P2MP LSP.  And the
   entire backup P2MP LSP will be deleted when the node MP leaves the
   backup P2MP LSP.

5.5.  Considerations for MP2MP LSP Node Protection

   When a MP2MP LSP node needs to be protected, it can be treated with
   the same p2mp LSP node protection procedures for each forwarding
   direction.


                               +------------+ Point of Local Repair/
                               |     R1     | Switchover Point
                               +------------+ (Upstream LSR)
                                  /       \
                                 /         \
                              10/           \20
                               /             \
                              /               \
                             V                 V
                       +----------+        +-----------+
        Protected Node |    R2    |        |     R3    |
                       +----------+        +-----------+
                         |       \         /        |
                         |        \       /         |
                         |         \     /          |
                       10|        10\   /20       20|
                         |           \ /            |
                         |            \             |
                         |           / \            |
                         |          /   \           |
                         |         /     \          |
                         V        V       V         V
                       +-----------+      +-----------+ Merge Point
                       |    R4     |      |    R5     | (Downstream LSR)
                       +-----------+      +-----------+


                  Figure 2: MP2MP Example (R1 is the PLR)






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                                  +------------+
                                  |     R1     | Merge Point
                                  +------------+ (downstream LSR)
                                     ^       ^
                                    /         \
                                 10/           \20
                                  /             \
                                 /               \
                                /                 \
                          +----------+        +-----------+
           Protected Node |    R2    |        |     R3    |
                          +----------+        +-----------+
                            ^       ^         ^        ^
                            |        \       /         |
                            |         \     /          |
                          10|        10\   /20       20|
                            |           \ /            |
                            |            \             |
                            |           / \            |
                            |          /   \           |
                            |         /     \          |
                            |        /       \         |
    Point of Local Repair/+-----------+      +-----------+
       (upstream LSR)     |    R4     |      |    R5     |
                          +-----------+      +-----------+


                  Figure 3: MP2MP Example (R4 is the PLR)

   For each direction flow, the MP, PLR and MP nodes use the P2MP node
   protection procedures with the following additional considerations:

5.5.1.  MP Node Procedure

   MP sends a backup label mapping message containing MP2MP downstream
   FRR FEC elements.  When PLR receives a backup label mapping message
   with a MP2MP downstream flag, it sends the backup label mapping
   message with mp2mp upstream FRR FEC elements to Pn and then finally
   to MPs.  This procedure just follows the normal MP2MP LSP procedure.

   For the forwarding entries, MP node binds its primary MP2MP
   downstream NHLFE entry to backup MP2MP downstream ILM entry and binds
   its backup MP2MP upstream NHLFE entry to primary MP2MP upstream ILM
   entry.

   For the forwarding entries, MP node binds its primary MP2MP
   downstream NHLFE entry to backup MP2MP downstream ILM entry and binds
   its backup MP2MP upstream NHLFE entry to primary MP2MP upstream ILM



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   entry.

5.5.2.  PLR Node Procedure

   PLR node binds its backup MP2MP downstream NHLFE entry to primary
   MP2MP downstream ILM entry and binds its primary MP2MP upstream NHLFE
   entry to backup MP2MP upstream ILM entry.

5.5.3.  Switchover Procedure

   When the protected node fails, both the affected downstream and
   upstream nodes function as PLR and switch the downstream flow and
   upstream flow to their respective backup paths.

5.6.  Protocol Extensions for mLDP Based Node Protection

5.6.1.  mLDP Based MP Protection Capability Parameter TLV

   A new Capability Parameter TLV is defined as mLDP Based MP Protection
   Capability for node protection.  The following is the format of this
   new Capability Parameter TLV:

       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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |1|0| mLDP Based MP Prot.(IANA) |          Length (= 2)         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |S| Reserved    |
       +-+-+-+-+-+-+-+-+

       S: As specified in [RFC5561]


               Figure 4: mLDP Based MP Protection Capability

   This is an unidirectional capability announcement.

   An LSR, which supports the mLDP based protection procedures, should
   advertise this mLDP Based MP Protection Capability TLV to its LDP
   speakers.  Without receiving this capability announcement, an LSR
   MUST NOT send any message including the mLDP Based MP Node Protection
   Status Element and mLDP Backup FEC Element to its peer.

   Capability Data might be needed to distinguish the capabilities of
   different nodes, such as PLR, MP, N, Pn and so on.






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5.6.2.  mLDP Based MP Node Protection Status Elements

   A new type of LDP MP Status Value Element is introduced for notifying
   upstream LSR information.  It is encoded as follows:



        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |mLDP FRR Type=3|      Length                   |   Reserved    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                    PLR Node Address                           ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                Figure 5:  FRR LDP MP Status Value Element


      mLDP FRR Type:  Type 3 (to be assigned by IANA)

      Length:  If the Address Family is IPv4, the Length MUST be 5;
      if the Address Family is IPv6, the Length MUST be 17.

      PLR Node Address:  The host address of the PLR Node.


5.6.3.  mLDP Backup FEC Element Encoding

   A new type of mLDP backup FEC Element is introduced for notifying
   upstream LSR information.  It is encoded as follows:




















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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |mLDP FEC T=FRR |         Address Family        | Address Length|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                        PLR Node Address                       ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |N| Status code | FEC-Type      |        MT-ID                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Protected Node Address                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Opaque Length              |    Opaque Value ...           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   ~                                                               ~
   |                                                               |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                     Figure 6: mLDP Backup FEC Element


   mLDP FEC Type-FRR:  Type 5 (to be assigned by IANA)

   Length:  If the Address Family is IPv4, the Address Length MUST be 9;
            if the Address Family is IPv6, the Address Length MUST be 33.

   Status code:  1 = Primary path for traffic forwarding
                 2 = Secondary path for traffic forwarding

   FEC-Type: 6 = P2MP FEC type
             7 = MP2MP-up FEC type
             8 = MP2MP-down FEC type

   PLR Node Address:  The host address of the PLR Node.

   Protected Node Address:  The host address of the Protected Node.

   N Bit: Node Failure Required Flag, the occasion of switching traffic's on PLR
           1 = 'Y', switch traffic to backup path only when PLR detects the node failure
           0 = 'N', switch traffic to backup path when PLR detects failure

   Opaque Length:  The length of the opaque value, in octets.







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   Opaque Value: One or more MP opaque value elements, which is the same definition in [RFC6388].
                 For the FRR mLDP FEC element, the Opaque Value MUST be encoded
                 as the Recursive Opaque Value, which is defined in [RFC6512]. The value
                 fields of the Recursive Opaque Value contain the original primary
                 path's mLDP FEC element.


    The encoding for this Recursive Opaque Value, as defined in [RFC6512], is shown in Figure 5.


    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Type = 7     |         Length                |               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |
    ~                                                               ~
    |                 P2MP or MP2MP FEC Element                     |
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


          Figure 7: Recursive Opaque Value, defined in [RFC6512]

   The Opaque Value is encoded by MP node and decoded by PLR.  Other
   nodes MUST NOT interpret the opaque value at all.

5.7.  IANA Considerations

   This memo includes the following requests to IANA:

   o  mLDP Based MP Protection Capability

   o  mLDP FRR types for LDP MP Status Value Element

   o  mLDP FEC FRR Element type


6.  Security Considerations

   The same security considerations apply as for the base LDP
   specification, as described in [RFC5036].  The protocol extensions
   specified in this document do not provide any authorization mechanism
   for controlling the set of LSRs that may attempt to join a mLDP
   protection session.  If such authorization is desirable, additional
   mechanisms outside the scope of this document are needed.

   Note that authorization policies should be implemented and/or



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   configure at all the nodes involved.


7.  Acknowledgements

   We would like to thank Nicolai Leymann and Daniel King for their
   valuable suggestions to this draft.  We also would like to thank
   Robin Li, Lujun Wan, Kenji fujihira, Martin Vigoureux, Yaacov
   Weingarten and Eric Osborne for their comments and suggestions to
   the draft.


8.  References

8.1.  Normative References

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

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031, January 2001.

   [RFC5036]  Andersson, L., Minei, I., and B. Thomas, "LDP
              Specification", RFC 5036, October 2007.

   [RFC5561]  Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.
              Le Roux, "LDP Capabilities", RFC 5561, July 2009.

   [RFC6348]  Le Roux, JL. and T. Morin, "Requirements for Point-to-
              Multipoint Extensions to the Label Distribution Protocol",
              RFC 6348, September 2011.

   [RFC6388]  Wijnands, IJ., Minei, I., Kompella, K., and B. Thomas,
              "Label Distribution Protocol Extensions for Point-to-
              Multipoint and Multipoint-to-Multipoint Label Switched
              Paths", RFC 6388, November 2011.

   [RFC6512]  Wijnands, IJ., Rosen, E., Napierala, M., and N. Leymann,
              "Using Multipoint LDP When the Backbone Has No Route to
              the Root", RFC 6512, February 2012.

8.2.  Informative References

   [I-D.ietf-mpls-ldp-multi-topology]
              Zhao, Q., Fang, L., Zhou, C., Li, L., and K. Raza, "LDP
              Extensions for Multi Topology Routing",
              draft-ietf-mpls-ldp-multi-topology-08 (work in progress),
              May 2013.



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   [I-D.wijnands-mpls-mldp-node-protection]
              Wijnands, I., Rosen, E., Raza, K., Tantsura, J., Atlas,
              A., and Q. Zhao, "mLDP Node Protection",
              draft-wijnands-mpls-mldp-node-protection-04 (work in
              progress), June 2013.

   [I-D.ietf-rtgwg-mrt-frr-architecture]
              Atlas, A., Kebler, R., Envedi, G., Csaszar, A., Tantsura,
              J., Konstantynowicz, M., White, R., and M. Shand, "An
              Architecture for IP/LDP Fast-Reroute Using Maximally
              Redundant Trees", draft-ietf-rtgwg-mrt-frr-architecture-02
              (work in progress), February 2013.

   [I-D.enyedi-rtgwg-mrt-frr-algorithm]
              Atlas, A., Envedi, G., Csaszar, A., and A. Gopalan,
              "Algorithms for computing Maximally Redundant Trees for
              IP/LDP Fast- Reroute",
              draft-enyedi-rtgwg-mrt-frr-algorithm-02 (work in
              progress), October 2012.


Authors' Addresses

   Quintin Zhao
   Huawei Technology
   125 Nagog Technology Park
   Acton, MA  01719
   US

   Email: quintin.zhao@huawei.com


   Tao Chou
   Huawei Technology
   156 Beiqing Rd
   Haidian District, Beijing  100095
   China

   Email: tao.chou@huawei.com












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   Boris Zhang
   Telus Communications
   200 Consilium Pl Floor 15
   Toronto, ON  M1H 3J3
   Canada

   Phone:
   Email: Boris.Zhang@telus.com


   Emily Chen
   2717 Seville Blvd, Apt 1205
   Clearwater, FL  33764
   US

   Email: emily.chen220@gmail.com



































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