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Network Working Group                                       Quintin Zhao
Internet-Draft                                                  Tao Chou
Intended status: Standards Track                       Huawei Technology
Expires: January 16, 2014                                    Boris Zhang
                                                    Telus Communications
                                                              Emily Chen
                                                           July 15, 2013


        P2MP Based mLDP Node Protection Mechanisms for mLDP LSP
                draft-zhao-mpls-mldp-protections-05.txt

Abstract

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

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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   This Internet-Draft will expire on January 16, 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
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
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   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Requirement Language . . . . . . . . . . . . . . . . . . .  5
   3.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Scope  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Example of mLDP Node Protection  . . . . . . . . . . . . . . .  6
   6.  Signaling Procedures for P2MP Based Node Protection  . . . . .  7
     6.1.  The Computation of the Backup Path . . . . . . . . . . . .  8
     6.2.  The Procedures for MP, PTN, STN and PLR  . . . . . . . . .  8
       6.2.1.  MP's Procedures  . . . . . . . . . . . . . . . . . . .  8
       6.2.2.  PTN's Procedures . . . . . . . . . . . . . . . . . . .  9
       6.2.3.  STN's Procedures . . . . . . . . . . . . . . . . . . .  9
       6.2.4.  PLR's Procedures . . . . . . . . . . . . . . . . . . . 10
     6.3.  PLR's Switching Over Considerations  . . . . . . . . . . . 10
     6.4.  The Procedures after the Reconvergence . . . . . . . . . . 11
     6.5.  Considerations for MP2MP LSP Node Protection . . . . . . . 11
       6.5.1.  MP's Procedure . . . . . . . . . . . . . . . . . . . . 12
       6.5.2.  PLR's Procedure  . . . . . . . . . . . . . . . . . . . 13
       6.5.3.  Switch over Procedure  . . . . . . . . . . . . . . . . 13
   7.  Protocol Extensions for mLDP Based Node Protection . . . . . . 13
     7.1.  mLDP Based MP Protection Capability Parameter TLV  . . . . 13
     7.2.  mLDP Based MP Node Protection Status Elements  . . . . . . 14
     7.3.  mLDP Backup FEC Element Encoding . . . . . . . . . . . . . 14
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 18
     11.2. Informative References . . . . . . . . . . . . . . . . . . 18
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19




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1.  Introduction

   To meet user demand, operators and service providers continue to
   deploy multicast applications using the Multicast Label Distribution
   Protocol (Multicast LDP - mLDP) across MPLS networks.  For real-time
   applications, such as stock trading, on-line games, and multimedia
   teleconference, traditional node protection mechanisms, such as
   relying on IGP re-convergence to build the new Label Switched Path
   (LSP), fail to achieve a protection switching time less than that
   which is required to minimize the interruption of applications.

   Instead of relying on IGP re-convergence to build the new LSP for
   failure protection, pre-computing and establishing a backup path
   before the failure delivers a better solution, allowing a more rapid
   switch over to the backup path when the protected node fails .

   Providing a pre-computed backup path requires solutions to two
   complex problems:

   o  how to compute a completely disjoint backup path for each node in
      a multicast tree, and

   o  how to signal and setup the computed backup path.

   For a primary Point-to-Multipoint (P2MP) Label Switched Path (LSP)
   created by LDP, there are several methods that could be chosen for
   creating a backup path:

   o  The use of an RSVP-TE (Resource Reservation Protocol - RSVP -
      Traffic Engineering) point-to-point (P2P) tunnel as a logical out-
      going interface, which consequently utilizes the mature high-
      availability technology of RSVP-TE.

   o  The use of an alternative LDP P2P LSP as a packet encapsulation,
      which avoids the complex configuration of P2P RSVP-TE.

   o  Creating a P2MP backup LSP using a loop-free alternative route
      provided by the IGP.

   o  Using multi-topology technology, wherein the backup topology can
      be either statically configured or dynamically computed and
      signaled using IP/LDP Fast-Reroute mechanisms
      [I-D.ietf-rtgwg-mrt-frr-architecture].

   When the backup path is available, there are two methods for packet
   forwarding and protection switch over:





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   Method 1  The traffic sender transmits the stream on both the primary
             and backup path always.  Once the local traffic receiver
             detects a failure, the switch over 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.

   Method 2  The traffic sender transmits only on the primary path
             before the failure.  Traffic is only forwarded to the MP
             through the backup path when failure is detected.  Although
             bandwidth resource usage is minimized, cooperation is
             required to provide adequate switching times and to
             minimize higher-layer and application impact.

   Ideally, if the switching time performance can be equal to or better
   than that of Method 1, it is reasonable to choose Method 2 to avoid
   bandwidth wastage.  This consideration has been taken into account in
   making the recommendations in this document.

   Note that for the computation and configuration of the primary
   topology, the algorithm used could be the Loop-free Alternate (LFA)
   based [RFC5286], Maximally Redundant Tree (MRT) based
   [I-D.ietf-rtgwg-mrt-frr-architecture] , or based on any other
   algorithms or methods available including static and offline tools;
   any such method can be used in conjunction with the mechanisms
   described in this document , which is limited to determining the
   nodes that should be spanned by the backup paths for the protection
   of a node in the primary multicast tree.  In addition, the mechanism
   for detecting the node failure that will result in switchover to the
   backup pathis also outside the scope of this document.

   Compared to a P2P LSP based solution, this P2MP LSP based solution
   not only uses mLDP mechanisms for both the primary path and backup
   paths, but also avoids unnecessary packet duplication where multiple
   P2P backup paths for the same node pass through.common nodes.

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


2.  Terminology

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





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

   o  Merge Point(MP):The node(s) where the primary path and the backup
      path rejoin and merge.  Since the backup path is a multicast tree
      there will generally be more than one merge point.

   o  Primary Transit Node (PTN): The node between the PLR and MP on the
      primary path.

   o  Secondary Transit Node (STN): A node on the backup path between
      the PLR and MP.  There might be more than one STN on the backup
      path between the PLR and MP nodes.

2.1.  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.  Requirements

   A number of requirements have been identified that will allow the
   optimal set of mechanisms to be developed.  These are:

   o  Computation of a possible disjoint (link and node) backup path
      within the multicast tree.  In the case that there is no backup
      path available, there will be no backup path setup using the
      solution described in this draft will not be applicable.

   o  Minimize the PLR's switch over time from the primary path to the
      backup path when failure happens;

   o  Minimization of operation and maintenance cost;

   o  The solution should work without other protocol extensions other
      than the protocol extensions specified in this draft.

   o  The solution should work for all network topologies deployed in
      the users' network as long as there is a alternative backup path
      available.


4.  Scope

   This document specifies the signaling procedures and protocol
   extensions for the P2MP LSP based mLDP transit node protection



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   solution.

   The method used for detecting the node failure is out the scope of
   this document.

   Protection of the leaf and root nodes of the multicast tree is also
   out of scope of this document.

   The protection mechanism for the case of multiple failures happening
   at the same time is out of scope of this document.

   In the case that there is no backup path computed from the backup
   path computation algorithms, then there will be no backup path setup
   to protect the transit node failures.


5.  Example of mLDP Node Protection

   By using the procedures introduced in section 5 plus the available
   backup path computation algorithms, MP can initiate the building of
   the backup mLDP LSP starting from the PLR, avoiding the PTN and
   reaching the MPs.  In the case of a large number of MPs, the solution
   introduced in this draft can avoid unnecessary packet duplication
   between PLR and the merge points.  If a backup multicast tree is
   built rather than individual LSPs from the PLR to each MP then common
   transit points on the backup tree that would otherwise have multiple
   unicast LSPs passing through them will be saved some bandwidth on
   their incoming links.























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                                     |
                                     V
                               +------------+ Point of Local Repair/
                               |     R1     | Switch over Point
                               +------------+ (Upstream LSR)
                                   /    \
                                10/      \20 (cost)
                                 /        \
                                V          V
             Primary     +----------+  +-----------+ Secondary
           Transit Node  |    R2    |  |     R3    |Transit Node
             (PTN)       +----------+  +-----------+  (STN)
                              |    \     /    |
                            10|   10\   /20   |20
                              |      \ /      |
                              |       \       |
                              |      / \      |
                              V     V   V     V
                         +-----------+ +-----------+ Merge Point
                         |    R4     | |    R5     | (Downstream LSR)
                         +-----------+ +-----------+
                              |               |
                              V               V

          Figure 1: mLDP Local Protection using mLDP LSP Example

   In Figure 1, R2 is on the preferential signalling/data path from R4/5
   to R1, and the secondary signalling/data path from R4/R5 to R1 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 PTN though the PTN 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.)

   In this scenario, if R2 is protected by two P2P LSPs as R1--R3--R4
   and R1--R3--R5 , the traffic will be duplicated on the link between
   R1 and R3 when the primary traffic is switched into the secondary
   path, and R3 will receive two copies of the multicast packages.  But,
   if R2 is protected by a mLDP LSP instead, R3 will only receive one
   copy of the stream, and thus there will be no packet duplication on
   the link between R1 and R3 when the failure happens.


6.  Signaling Procedures for P2MP Based Node Protection

   This section introduces the signaling procedures of P2MP LSP's node
   protection using P2MP-based backup LSP for a Protected Node N.




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6.1.  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 [[anchor9: EBD: Needs references.]], etc.
      The disjoint path can be provided by MT, MRT, etc.  Choosing the
      candidates is a local decision and can be determined by
      configuration.

   o  The STN node MUST be chosen from the IGP next-hops on the shortest
      path toward the PLR within the topology specified in the FRR mLDP
      FEC element by the MT-ID (Multi-Topology Identifier) [[anchor10:
      EBD: Multi-Topology IDs need some explanation - it appears here
      without any introduction and I (for one) have no idea why there
      might be several and what they might cover.]] field.  The
      candidate upstream LSRs MUST NOT include the PTN.

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

6.2.   The Procedures for MP, PTN, STN and PLR

   The procedures for P2MP Based Node Protection described in this
   document assumes the PLR is capable of node failure detection.  In
   procedures described here covers the scenario where there is only one
   PTN between the PLR and MP.  The cases where there are more than one
   PTNs between PLR and MP is out scope of this document.

   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.

6.2.1.  MP'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



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   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
   from the PTN after the MP has sent the label mapping message to the
   PTN, based on the PLR and PTN info, the MP 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
   Label mapping message with the new FRR FEC (see section 7.3 for
   details), 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 7.3

6.2.2.  PTN'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
   identify, 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).

6.2.3.  STN's Procedures

   When one node receives such aforementioned label mapping messages
   which inlcudes the mLDP FRR type of FECs, if it is not the PLR, it
   can consider itself a STN and will choose its backup upstream node
   toward PLR on the corresponding topology's shortest IGP path.  To
   avoid the backup LSP going through the PTN, additional path selection
   rule(s) should be applied.  A simple method is for the transit nodes
   to not choose the specified PTN 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.

   When a STN on the backup mLSP fails before the backup LSP is put into
   use, this will trigger a recalculation of the backup LSP(s).





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6.2.4.  PLR's Procedures

   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 7.3) 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 receive
   and merge this traffic back to the primary LSP.  The switch over
   manner on PLR is specified in detail in the later section of this
   document.

6.3.  PLR's Switching Over Considerations

   This section provides two modes for Switch over when failure occurs
   using the Protection Method 2 described in section 1 where there is
   only one copy of the traffic sent out from the PLR both before the
   PTN fails and after the PTN fails.

   Depending on the capability of the MP node, MP node can set Node
   Failure (detection required) Flag in two modes.

   Mode 1:   The MP sets the Node Failure Required Flag (in the P2MP
             Based MP Node Protection Status Element) as 'Y'.  This
             means that the MP requires the PLR to have the capability
             of detecting the PTN's failure.  In this case, if the PLR
             doesn't have the node failure detection capability, then
             the backup path will not be setup and no protection is
             setup for the PTN.  If the PLR has the capability of
             detecting the PTN's failure, the backup path can be setup
             correctly and only after PLR detects that PTN's failure,
             there will be backup traffic forwarded through the backup
             path to the MP(s).

   Mode 2:   The MP sets the Node Failure Required Flag, in the P2MP
             Based MP Node Protection Status Element, set as 'N'.  This
             means that the MP has the capability of dropping duplicated
             multicast packages and doesn't require the PLR to have the
             capability of detecting the PTN's failure.  In this case,
             PLR switches the traffic to the backup path once it detects
             the link failure between PLR and PTN no matter it is caused



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             by the PTN's failure or not.  In the case that it is a link
             failure case, and the link protection is also deployed,
             then the MP will receive two copies of the traffic, one
             copy from the normal link protection path, and one copy
             from the node protection path through STN.  MP must take
             the responsibility to drop one of the two duplicate
             traffics when link fails between PLR and PTN.

6.4.  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.  STN 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.

6.5.  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.

                                   |
                                   V
                            +------------+ Point of Local Repair/
                            |     R1     | Switch over Point
                            +------------+ (Upstream LSR for Downstream flow)
                                /    \
                             10/      \20 (cost)
                              /        \
                             V          V
          Primary     +----------+  +-----------+ Secondary
        Transit Node  |    R2    |  |     R3    |Transit Node
          (PTN)       +----------+  +-----------+  (STN)
                           |    \     /    |
                         10|   10\   /20   |20
                           |      \ /      |
                           |       \       |
                           |      / \      |
                           V     V   V     V
                      +-----------+ +-----------+ Merge Point
                      |    R4     | |    R5     | (Downstream LSR
                      +-----------+ +-----------+  for Downstream flow)
                           |               |
                           V               V




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                  Figure 2: MP2MP Example (R1 is the PLR)



                                   ^
                                   |
                            +------------+ Merge Point
                            |     R1     | (the downstream LSR for the upstream flow)
                            +------------+
                                ^    ^
                             10/      \20 (cost)
                              /        \
          Primary     +----------+  +-----------+ Secondary
        Transit Node  |    R2    |  |     R3    |Transit Node
          (PTN)       +----------+  +-----------+  (STN)
                           ^   ^       ^   ^
                           |    \     /    |
                         10|   10\   /20   |20
                           |      \ /      |
                           |       \       |
                           |      / \      |
                      +-----------+ +-----------+
           PLR for    |    R4     | |    R5     |
    the upstream flow +-----------+ +-----------+
                           ^               ^
                           |               |



                  Figure 3: MP2MP Example (R4 is the PLR)

   For each direction of MP2MP traffic flows (downstream in Figure 2 or
   upstream in Figure 3, the MP, PLR and MP nodes use the P2MP node
   protection procedures with the following additional considerations:

6.5.1.  MP's 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.




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   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.

6.5.2.  PLR's Procedure

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

6.5.3.  Switch over 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.


7.  Protocol Extensions for mLDP Based Node Protection

   Numerical fields in the formats defined in this section are encoded
   as unsigned integers in network octet and bit order.

7.1.  mLDP Based MP Protection Capability Parameter TLV

   A new Capability Parameter TLV is defined as mLDP Based MP Protection
   Capability for node protection.  The format is illustrated as the
   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |1|0| mLDP Based MP Prot.(IANA) |          Length (= 2)         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |S| Reserved    |
   +-+-+-+-+-+-+-+-+


               Figure 4: mLDP Based MP Protection Capability

   mLDP Based MP Prot.:  TBA1 (to be assigned by IANA)

   S: As specified in [RFC5561]

   This is an unidirectional capability announcement.

   An LSR, which supports the mLDP based protection procedures, should
   advertise mLDP Based MP Protection Capability TLV to its LDP



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   speakers.  Without receiving this capability announcement, an LSR
   MUST NOT send any messages including the mLDP Based MP Node
   Protection Status Element and mLDP Backup FEC Element to its peer.

7.2.  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  |      Length                   |   Reserved    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                    PLR Node Address                           ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                Figure 5:  FRR LDP MP Status Value Element

   mLDP FRR Type:    Type TBA2 (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.

7.3.  mLDP Backup FEC Element Encoding

   A new type of mLDP backup FEC Element is introduced, it is used 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 TBA3 (to be assigned by IANA)

   Address 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.

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

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

   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

   MT-ID:                  Multi-Topology ID.  Unsigned 16 bit integer.

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

   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,



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                           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 the Recursive Opaque Value, as defined in [RFC6512],
   is shown in Figure 7.

   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

   The Opaque Value is encoded by the MP node and decoded by PLR.  Any
   other nodes on the path MUST NOT interpret the opaque value.


8.  IANA Considerations

   The document introduces following new protocol elements that require
   IANA consideration and assignments:

   o  Code Points for "MP Protection Capability" TLV from the "LDP TLV
      Type Name Space" registry within the LDP Parameters



         Registry:
         Range/Value       Description
         --------------    ------------------------------
         TBA1              MP Protection Capability (defined in section 7.1)


     Figure 8: New Code Points for MP Protection Capability Extensions

   o  Code Points for mLDP Based MP Node Protection Status Elements from
      the "LDP TLV Type Name Space" registry within the LDP Parameters






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         Registry:
         Range/Value       Description
         --------------    ------------------------------
         TBA2              Based MP Node Protection Status (defined in section 7.2)


               Figure 9: Based MP Node Protectiin on Status

   o  Code Points for mLDP FRR Type FEC from the the LDP registry
      "Forwarding Equivalence Class (FEC) Type Name Space". within the
      LDP Parameters


           Registry:
           Range/Value        Description
           --------------     ------------------------------
           TBA3               mLDP FRR Type FEC (defined in section 7.3)


                       Figure 10: mLDP FRR Type FEC


9.  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
   configured at all the nodes involved.


10.  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, Eric Osborne and Elwyn Davis for their detailed comments
   and suggestions to the draft.


11.  References






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11.1.  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.

11.2.  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.

   [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., and R. White, "An Architecture
              for IP/LDP Fast-Reroute Using Maximally Redundant Trees",
              draft-ietf-rtgwg-mrt-frr-architecture-03 (work in
              progress), July 2013.




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   [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


   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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