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Versions: 00 01 02 03 04 draft-ietf-mpls-mldp-node-protection

Network Working Group                                  IJ. Wijnands, Ed.
Internet-Draft                                                  E. Rosen
Intended status: Standards Track                                 K. Raza
Expires: August 27, 2012                             Cisco Systems, Inc.
                                                             J. Tantsura
                                                                Ericsson
                                                                A. Atlas
                                                        Juniper Networks
                                                       February 24, 2012


                          mLDP Node Protection
              draft-wijnands-mpls-mldp-node-protection-00

Abstract

   This document describes procedures to support node protection for
   Point-to-Multipoint and Multipoint-to-Multipoint Label Switched Paths
   (MP LSPs) built by LDP ("Label Distribution Protocol"), or simply
   mLDP.  In order to protect a node N, the Point of Local Repair (PLR)
   LSR of N must learn the Merge Point (MPT) LSR(s) of node N such that
   traffic can be redirected to them in case node N fails.  Redirecting
   the traffic around the failed node N depends on existing P2P LSPs
   originated from the PLR LSR to the MPT LSRs while bypassing LSR node
   N.

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
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 27, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   This document may contain material from IETF Documents or IETF
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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.






























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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Conventions used in this document  . . . . . . . . . . . .  5
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  PLR Determination  . . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Transit node procedure . . . . . . . . . . . . . . . . . .  5
     2.2.  MP2MP root node procedure  . . . . . . . . . . . . . . . .  6
     2.3.  PLR information encoding . . . . . . . . . . . . . . . . .  7
   3.  Using the T-LDP session  . . . . . . . . . . . . . . . . . . .  9
   4.  Link or node failure . . . . . . . . . . . . . . . . . . . . . 10
   5.  Re-convergence after node/link failure . . . . . . . . . . . . 11
     5.1.  Node failure . . . . . . . . . . . . . . . . . . . . . . . 12
     5.2.  Link failure . . . . . . . . . . . . . . . . . . . . . . . 12
     5.3.  Switching to new primary path  . . . . . . . . . . . . . . 12
   6.  mLDP Capabilities for Node Protection  . . . . . . . . . . . . 13
     6.1.  PLR capability . . . . . . . . . . . . . . . . . . . . . . 13
     6.2.  MPT capability . . . . . . . . . . . . . . . . . . . . . . 13
     6.3.  The Protected LSR  . . . . . . . . . . . . . . . . . . . . 14
     6.4.  The Node Protection Capability . . . . . . . . . . . . . . 14
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   8.  IANA considerations  . . . . . . . . . . . . . . . . . . . . . 15
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 16
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     10.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
























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1.  Introduction

   This document describes procedures to support node protection for
   Point-to-Multipoint and Multipoint-to-Multipoint Label Switched Paths
   (MP-LSPs) built by LDP ("Label Distribution Protocol"), or simply
   mLDP.  In order to protect a node N, the Point of Local Repair (PLR)
   of N must learn the Merge Point (MPT) LSR(s) of node N such that
   traffic can be redirected to them in case node N fails.  Redirecting
   the traffic around the failed node N depends on existing P2P LSPs
   originating from the PLR LSR to the MPT LSR(s) while bypassing node
   N. The procedures to setup these P2P LSPs are outside the scope of
   this document, but one can imagine using RSVP-TE or LDP LFA based
   techniques to accomplish this.

   There are different solutions for a PLR LSR to learn the downstream
   MPT LSR(s).  One solution is documented in
   [I-D.zhao-mpls-mldp-protections].  This solution is based on
   'tunneling' the MPT LSR(s) through node N via the existing LDP
   session towards the PLR, like as ships-in-the-night.  The downside of
   that approach is that as soon as node N fails, no signaling is
   possible between the MPT LSR(s) and PLR LSR.  A direct consequence of
   this is that the MPT LSR(s) have no mechanism to signal a withdraw to
   the PLR to stop forwarding packets after the MPT LSR(s) have re-
   converged.  The PLR has to associate a timer with the forwarding
   state towards the MPT LSR(s) to stop forwarding.  Determining a good
   timer value is challenging since it depends on many variables which
   could change over time.

   After a PLR decides to stop forwarding towards a MPT LSR, another
   problem is releasing the label that PLR was using.  The PLR has no
   mechanism to send a label release to the MPT LSR such that it can
   release the label and return it to the free pool.  This more or less
   breaks the LDP design.

   The solution described in this document does not 'tunnel' the MPT
   LSR(s) information but explicitly signals it from the MPT LSR(s) to
   the PLR LSR(s) via a Targeted LDP (T-LDP) session [RFC5036].  By
   using a T-LDP session to signal between the MPT LSR(s) and the PLR
   LSR(s), we don't suffer from the above problems faced by
   [I-D.zhao-mpls-mldp-protections].  By having a T-LDP session with the
   PLR, most of the (m)LDP features currently defined should just work,
   like Make-Before-Break (MBB), Graceful Restart (GR), Typed Wildcard
   FEC support, etc.  All this is achieved at the expense of having an
   additional T-LDP session between an MPT and PLR LSR.







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1.1.  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 [RFC2119].

   The terms "node" is used to refer to an LSR and used interchangeably.
   The terms "PLR" and "MPT" are used as shorthand to refer to "PLR LSR"
   and "MPT LSR" respectively.

1.2.  Terminology

   mLDP:  Multipoint extensions to LDP.

   PLR:  Point of Local Repair (the LSR that redirects the traffic to
      one or more Merge Point LSRs).

   MPT:  Merge Point (the LSR that merges the backup LSP with primary
      LSP.  Note, there can be multiple MPT LSRs for a single MP-LSP
      node protection).

   T-LDP:  Targeted LDP session.

   MP LSP:  Multi-Point LSP (either a P2MP or MP2MP LSP).


2.  PLR Determination

   In order for a MPT to establish a T-LDP session with the PLR, it
   first has to learn the PLR for a particular MP LSP.  It is the
   responsibility of the protected node N to advertise the PLR address
   to the MPT.  The PLR address for a MP LSP on node N is the address of
   the upstream LDP peer, but only when node N is NOT the root node of
   the MP2MP LSP.  If node N is the root node, the procedures are
   slightly different as described in Section 2.2.  The procedures that
   follow assume that all the participating nodes (N, PLRs, MPTs) are
   enabled (e.g. by a user configuration) to support and implement this
   feature.

2.1.  Transit node procedure

   Below we are describing the procedures when the protected node is a
   transit node along the path to the root.








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            root
             ^
             |
           (LSR1)
          .  |  .
         .   |   .
        .   (N)   .
        .   /  \  .
         . /    \.
       (LSR2)  (LSR3)
          |      |
                      Figure 1.

   N: The node being protected,
   ...: Backup LSPs from LSR1 to the LSR2 and LSR3.


   Node N uses the root address of the MP LSP to determine the upstream
   LSR for a given MP LSP following the procedures as documented in
   [RFC6388] section 2.4.1.1.  The upstream LSR in figure 1 is LSR1
   because it is the first hop along the shortest path to reach the root
   address.  After determining the upstream LSR, node N (which is
   feature enabled), MUST advertise the address of LSR1 as the PLR
   address to the downstream members of the MP LSP (i.e.  LSR2 and LSR3)
   if the given downstream member has announced support for node
   protection (see Section 6) for Capability negotiation).  For the
   format and encoding of PLR address information, see Section 2.3.

2.2.  MP2MP root node procedure

   In this section we are describing the procedures for when the
   protected node is the root of a MP2MP LSP.  Consider figure 2 below;

             |
           (LSR1)
          .  |  .
         .   |   .
        .   (N)   . root
        .   /  \  .
         . /    \.
      (LSR2)....(LSR3)
         |        |
                      Figure 2.

   N: The MP2MP root node being protected.
   ...: Backup LSPs between LSR1, LSR2 and LSR3.

   Assume that LSR1, LSR2 and LSR3 are all members of a MP2MP LSP for



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   which N is the root node.  Since N is the root of the MP2MP LSP,
   there is no upstream LSR and no 'single' PLR LSR for protecting node
   N's.  In order to protect node N, all the members of the MP2MP must
   participate in protecting node N by acting both as PLR and MPT LSR.
   An LSR will act as MPT for traffic coming from the other LSR(s) and
   it will act as PLR for traffic it is sending to the other LSR(s).
   Since node N knows the members of the MP2MP LSP, it will advertise
   the member list to its directly connected members, excluding the
   member it is sending to.  For example, node N will advertise
   {LSR3,LSR1} list to LSR2 excluding LSR2 from it.  Instead of
   advertising a single PLR when node N is not the root, a list of PLRs
   is advertised using the procedures documented in Section 2.3.

   It should be noted that the MP2MP root node protection mechanism
   don't replace the Root Node Redundancy (RNR) procedures as described
   in [RFC6388] section 7.  The node protection procedures in this draft
   will help restoring traffic for the existing MP2MP LSPs after node
   failure, but a new root node has to be elected eventually in order to
   allow new MP2MP LSPs to be created.

2.3.  PLR information encoding

   The upstream LSR address is conveyed via an LDP Notification message
   with MP Status, where the MP status contains a new "PLR Status Value
   Element" that specifies the address of the PLR.

   The new "PLR Status Value Element" is encoded as follows;

   PLR Status Element:

    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        |           Length              |    Address    ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~   Family      | Num PLR entry |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               |
   |                         PLR entry (0 or more)                 ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where

      Type: PLR (Type=3 to be assigned by IANA)

      Length: The Length field encodes the length of the Status Value
      following the Length field.  The encoded Length varies based on



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      the Address Family and the number of PLR entries.

      Address Family: Two octet quantity containing a value from IANA's
      "Address Family Numbers" registry that encodes the address family
      for the PLR Address encoded in the PLR entry.

      Num PLR entry: Number of "PLR entries" encoded in the Status Value
      Element, followed by "Num PLR entry" field (please see format of a
      PLR entry below).


   The format of a "PLR Entry" is 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |A|        Reserved             |       PLR address             ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   ~                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where

      A bit: 0 = Withdraw, 1 = Add.

      Reserved: 15 bits, must be zero on transmit and ignored on receipt

      PLR address: PLR Address encoded according to Address Family field
      encoded in the PLR Status Value Element.

   The size of a "PLR Entry" is the 2 octets ("A bit + Reserved") + PLR
   address length.  The length of the PLR address is depending on the
   Address Family as encoded in the PLR Status Value Element.  The size
   of a "PLR entry" is 6 octets and 18 octets respectively for an IPv4
   PLR address and an IPv6 PLR address.

   If the PLR address on N changes for a give MP LSP, N needs to trigger
   a new PLR Status to update the MPT(s).  A node N can advertise or
   withdraw a given PLR from its PLR set by setting "A bit" to 1 or 0
   respectively in corresponding PLR entry.  Removing a PLR address is
   likely due to a link failure, see the procedures as documented in
   Section 5.  To remove all PLR addresses belonging to the encoded
   Address Family, an LSR N MUST encode PLR Status Value Element with no
   PLR entry and "Num PLR entry" field MUST be set to zero.

   Along with the PLR MP Status a MP FEC TLV MUST be included in the LDP
   Notification message so that a receiver is able to associate the PLR
   Status with the MP LSP.



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3.  Using the T-LDP session

   The receipt of a PLR MP Status (with PLR addresses) for a MP LSP on a
   receiving LSR makes it an MPT for node protection.  If not already
   established, the MPT LSR MUST establish a T-LDP session with all of
   the learned PLR addresses using the procedures as documented in
   [I-D.napierala-mpls-targeted-mldp].

   Using Figure 1 as the reference topology, let us assume that both
   LSR2 and LSR3 are MPTs and have established a T-LDP session with the
   PLR being LSR1.  Assume that both LSR2 and LSR3 have a FEC <R,X> with
   a upstream LSR N and label Ln assigned to FEC towards N. The MPTs
   will create a secondary upstream LSR (using the received PLR address)
   and assign a Label Lpx to FEC <R,X> towards PLR for it.  The MPTs
   will do that for each PLR address that was learned for the MP LSP.
   In this example, the MPTs will have a FEC <R,X> with two local labels
   associated with it.  Ln that was assigned to N via the normal mLDP
   procedures, and Label Lpx that was assigned for PLR (LSR1) for the
   purpose of node protecting MP LSP via node N. Note, when the
   protected node is a MP2MP root node, there will be an upstream LSR
   for each PLR address that was advertised along with a unique Label
   Lpx.

   It is not preferable that a PLR is always sending traffic to an MPT
   over the backup P2P LSP.  The PLR should only send traffic over the
   backup P2P LSP if node N fails.  The receipt of a FEC Label Mapping
   alone over the T-LDP session from MPT on a PLR conveys the label
   information but does not convey the node being protected.  The
   information about a protected node is known to the MPT LSR and needs
   to be communicated to the PLR as well.  For this reason, the FEC
   Label Mapping (FEC <R,X> : Lpx) sent by the MPT over the T-LDP
   session to the PLR MUST include a Status TLV with MP Status including
   a new LDP MP status Value Element called the "Protected Node Status
   Value Element".  This new value element is used to specify the
   address of the node being protected.  The "Protected Node Status
   Value Element" has the following format;


     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    Type = 4   |           Length              | Address Family
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    |        Node address                           ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~               |
    +-+-+-+-+-+-+-+-+




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      Type : Protected Node (Type = 4 to be assigned by IANA)

      Length: The Length field encodes the length of the Status Value
      following the Length field.  The encoded Length varies based on
      the Address Family and is 4 octets and 16 octets respectively for
      an IPv4 address and an IPv6 address.

      Address Family: Two octet quantity containing a value from IANA's
      "Address Family Numbers" registry that encodes the address family
      for the Node Address.

      Node address: Protected node address encoded according to Address
      Family field.

   When a PLR receives a Label Mapping for FEC <R,X> that includes a
   Protected Node Status, it will only use that label binding once the
   Node advertised in the Status value becomes unreachable.  If the LSP
   is a MP2MP LSP, the PLR would have assign a Label Mapping for the
   upstream MP2MP FEC Element to the MPT ([RFC6388] section 3) for FEC
   <R,X>.  This label binding on the MPT MUST only be used once node N
   becomes unreachable.

   The procedures to determine if a node is unreachable is a local
   decision and not spelled out in this draft.  Typical link failure or
   Bidirectional Forwarding Detection (BFD) can be used to determine and
   detect node unreachability.


4.  Link or node failure

   Consider the following topology;


               root
                ^
                |
            . (LSR1)
          .   / |  .
         .  (M) |   .
         .    \ |    .
          .    (N)   .
           .   /  \  .
            . /    \.
          (LSR2)  (LSR3)
             |      |
                        Figure 3.

   N: The node being protected



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   M: The backup node to protect link LSR1 - N
   ...; Backup LSPs from LSR1 to LSR2 and LSR3.


   Assume that LSR1 is the PLR for protected node N, LSR2 and LSR3 are
   MPTs for node N. When LSR1 discovered that node N is unreachable, it
   can't determine whether it is the 'LSR1 - N' link or node N that
   failed.  In Figure 3, the link between LSR1 and N is also protected
   using Fast ReRoute (FRR) [RFC4090] link protection via node M. LSR1
   MAY potentially invoke 2 protection mechanisms at the same time,
   redirection the traffic due to link protection via node M to N, and
   for node protection directly to LSR1 and LSR2.  If only the link
   failed, LSR2 and LSR3 will receive duplicate packets due to the two
   protection mechanisms.  To prevent duplicate packets to be forwarded
   to LSR2 and LSR3, either the primary upstream LSRs or the secondary
   upstream LSRs should be forwarding MPLS packets, but never both at
   the same time.  The selection between the primary upstream LSR or
   (one or more) secondary upstream LSRs is based on the reachability of
   N. As long as N is reachable, N is the primary upstream LSR by which
   the MPLS packets are forwarded.  Once N becomes unreachable, the
   secondary upstream LSRs that where installed for node protection are
   activated.  Note that detecting if N is unreachable is a local
   decision and not spelled out in this draft.  Typical link failure or
   Bidirectional Forwarding Detection (BFD) can be used to determine and
   detect node unreachability.


5.  Re-convergence after node/link failure

   Consider the following topology;

               root
                ^
             _  |
           /. (LSR1)
         /.   /. |  .\
        /.  (M). |   .\
      (P).    \. |    .\
        \.     ( N )   .(Q)
         \.   /     \   ./
          \. /       \ ./
         (LSR2)     (LSR3)
            |          |
                        Figure 4.

   N: The node being protected.
   M: The backup node to protect link 'LSR1 - N'.
   P and Q: The nodes on the new primary path after N failure.



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   ...: P2P backup LSPs.

   Assume that LSR1 has detected that Node N is unreachable and invoked
   both the Link Protection and Node Protection procedures as described
   in this draft.  LSR1 is acting as PLR and sending traffic over both
   the backup P2P LSP to node N (via M) and the P2P LSPs directly to
   LSR2 and LSR3, acting as MPT LSRs.  The procedures following are
   depending on whether the link 'LSR1 - N' has failed or node N itself.

5.1.  Node failure

   If node N failed, both LSR2 and LSR3 will have changed the primary
   upstream LSR to the secondary upstream LSR (LSR1) due to node N being
   unreachable.  With that, the label bindings previously assigned to
   LSR1 will be activated on the MPTs (LSR2 and LSR3) and the label
   binding to N will be disabled.  Traffic is now switched over the
   label bindings that where installed for node protection.

5.2.  Link failure

   If the link 'LSR1 - N' has failed, both LSR2 and LSR3 will not change
   the primary upstream LSR because node N is still reachable.  LSR2 and
   LSR3 will receive traffic over two different bindings, the primary
   label binding assigned to node N (due to link protection via node M)
   as well as over the binding assigned to LSR1 for the node protection.
   Since the secondary upstream LSRs have not been activated, the
   traffic received due to node protection will be dropped.  Node N will
   re-converge and update LSR2 and LSR3 (Section 2.3) with the
   information that the PLR address (LSR1) is no longer applicable and
   must be removed.  In reponse, LSR2 and LSR3 MUST sent a Label
   Withdraw to LSR1 to withdraw the label binding.  This will stop the
   traffic being forwarded over the backup P2P LSPs for node protection.
   LSR1 will respond back with a Label Release as soon as the binding
   has been removed.

5.3.  Switching to new primary path

   The network will eventually re-converge and a new best path to the
   root will be found by LSR2 and LSR3.  LSR1 will find that M is its
   new primary upstream LSR to reach the Root and LSR3 will find Q. Note
   that although the current active upstream LSR can either be node N or
   LSR1 (depending on link or node failure), it does not matter for the
   following procedures.  Both LSR2 and LSR3 SHOULD use the Make-Before-
   Break (MBB) procedures as described in [RFC6388] section 8 to switch
   to the new primary upstream node.  As soon as the new primary
   upstream LSRs M and Q are activated, a Label Withdraw message MUST be
   sent to the old upstream LSR.  Note that an upstream LSR switchover
   from a T-LDP neighbor to a directly connected LDP neighbor is no



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   different compared to switching between two directly connected
   neighbors.  After the Label Withdraw message has been received by
   LSR1 or node N, forwarding will stop and a Label Release will be
   sent.

   When it is determined that after re-convergence there is no more
   interest in the T-LDP session between the MPT and the PLR, the T-LDP
   session MAY be taken down.  It is possible that having no more
   interest in the T-LDP session is temporarily due to link flapping.
   In order to avoid the T-LDP session from flapping, it is RECOMMENDED
   to apply a delay before tearing down the session.  Determining the
   delay is a local implementation matter.


6.  mLDP Capabilities for Node Protection

   In order to describe the capabilities of the participating LSRs , we
   are organizing it per role in the network i.e., Point of Local Repair
   (PLR), Merge Point (MPT), and Protected Node (as depicted in Fig 1).

6.1.  PLR capability

   A PLR node should handle the following conditions;

   1.  Accept an incoming T-LDP session from the MPT LSR.

   2.  Support the receipt of a "Protected Node Status Value Element"
       status in a MP Status TLV over T-LDP session.

   3.  Upon node failure detection, capable of switching traffic towards
       one or more MPT(s) over P2P LSP (bypassing N) using the labels
       previously advertised for MP LSPs over the T-LDP session.

   An LSR capable of performing these actions will advertise it self as
   PLR capable in the Node Protection capability (see Section 6.4).
   This is a unidirectional capability announced from PLR to the
   protected LSR.

6.2.  MPT capability

   An MPT node should handle the following conditions;

   1.  Support the receipt of "PLR Status Value Element" in a MP Status
       TLV from a protected node N.

   2.  Support to transmit "Protected Node Status Value Element" in a MP
       Status TLV to a PLR.




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   A LSR capable of performing these actions will advertise itself as
   the MPT capable in the Node Protection capability (see Section 6.4).
   This is a unidirectional capability from MPT to the protected LSR.

6.3.  The Protected LSR

   A protected node should handle the following conditions;

   1.  Determine the PLR and MPT capability for directly connected
       upstream and downstream LSRs for a given MP FEC.

   2.  Support transmitting of "PLR Status Value Element" in a MP Status
       TLV to one or more downstream MPT LSRs.

   The protected LSR does not advertise any capability for mLDP Node
   Protection because it does not need to receive any of the defined MP
   Status values as described above.  However, the protected node does
   play an important role in the signaling and setup of the node
   protection.  For a given FEC, the protected node can only send PLR
   information to a downstream LSR if the PLR has signaled the PLR
   capability and the downstream LSR has signaled the MPT capability.
   When the downstream LSR (acting as MPT) receives the PLR status, it
   can implicitly infer that the advertised LSR(s) are PLR capable.  The
   MPT LSR can now proceed with setting up a T-LDP session with the
   PLR(s) and MP LSP node protection signaling.

6.4.  The Node Protection Capability

   We define a single capability "MP Node Protection Capability" to
   announce the PLR and MPT capability.

   The format of the capability parameter TLV is 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F| MP Node Prot Cap. (IANA)  |           Length = 2          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |S| Reserved    |P|M| Reserved  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Where

      U/F bits: MUST be set to 1 and 0 respectively (as per [RF5561])

      MP Node Protection Capability: TLV type (value to be assigned by
      IANA)



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      Length: MUST be set to 2.

      S bit: Set to 1 to announce and 0 to withdraw the capability (as
      per [RFC5561])

      P bit: PLR capable for MP LSP node protection

      M bit: MPT capable for MP LSP node protection

      Reserved: Must be zero on transmit and ignored on receipt

   The above capability can be sent in an LDP Initialization message to
   announce capability at the session establishment time, or it can be
   sent in LDP Capability message to dynamically update (announce or
   withdraw) its capability towards its peer using procedures specified
   in [RFC5561].

   An LSR that supports the PLR functionality LSR MAY send this
   capability to its downstream MP peers with "P" bit set; whereas, an
   LSR that supports an the MPT functionality MAY send this capability
   to its upstream peer with "M" bit set.  Moreover, an LSR that
   supports both the PLR and MPT functionality MAY sent this capability
   to its peers with both "P" and "M" bit set.


7.  Security Considerations

   The same security considerations apply as those for the base mLDP
   specification, as described in [RFC6388].


8.  IANA considerations

   IANA is requested to allocate two new code points from the "LDP MP
   Status Value Element type" registry;

      PLR Status Value Element - 3

      Protected Node Status Value Element - 4

   IANA is requested to assign one new code points for a new Capability
   Parameter TLVs from the LDP registry "TLV Type Name Space",
   corresponding to the advertisement of the the new MP Status values.
   The values is:

      MP Node Protection Capability - TBD





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9.  Acknowledgments

   The authors like to thank Nagendra Kumar for his input on this draft.


10.  References

10.1.  Normative References

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

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

   [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.

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

   [I-D.napierala-mpls-targeted-mldp]
              Napierala, M. and E. Rosen, "Using LDP Multipoint
              Extensions on Targeted LDP Sessions",
              draft-napierala-mpls-targeted-mldp-02 (work in progress),
              October 2011.

10.2.  Informative References

   [I-D.zhao-mpls-mldp-protections]
              Zhao, Q. and E. Chen, "Protection Mechanisms for Label
              Distribution Protocol P2MP/MP2MP Label Switched Paths",
              draft-zhao-mpls-mldp-protections-01 (work in progress),
              November 2011.

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











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Authors' Addresses

   IJsbrand Wijnands (editor)
   Cisco Systems, Inc.
   De kleetlaan 6a
   Diegem  1831
   Belgium

   Email: ice@cisco.com


   Eric Rosen
   Cisco Systems, Inc.
   1414 Massachusetts Avenue
   Boxborough  MA 01719
   USA

   Email: erosen@cisco.com


   Kamran Raza
   Cisco Systems, Inc.
   2000 Innovation Drive
   Ottawa  Ontario K2K-3E8
   Canada

   Email: skraza@cisco.com


   Jeff Tantsura
   Ericsson
   300 Holger Way
   San Jose  CA 95134
   USA

   Email: jeff.tantsura@ericsson.com


   Alia Atlas
   Juniper Networks
   10 Technology Park Drive
   Westford  MA  01886
   USA

   Email: akatlas@juniper.net






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