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Versions: (draft-wijnands-mpls-mldp-node-protection) 00 01 02 03 04 05 06 07 08 RFC 7715

Network Working Group                                  IJ. Wijnands, Ed.
Internet-Draft                                                   K. Raza
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: April 1, 2016                                          A. Atlas
                                                  Juniper Networks, Inc.
                                                             J. Tantsura
                                                                Ericsson
                                                                 Q. Zhao
                                                       Huawei Technology
                                                      September 29, 2015


                          mLDP Node Protection
                draft-ietf-mpls-mldp-node-protection-08

Abstract

   This document describes procedures to support node protection for
   Point-to-Multipoint and Multipoint-to-Multipoint Label Switched Paths
   (MP LSPs) that have been built by the "Multipoint Label Distribution
   Protocol"(mLDP) [RFC6388].  In order to protect a node N, the Point
   of Local Repair (PLR) Label Switched Router (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 Point-to-Point (P2P)
   Label Switched Paths (LSPs).  The pre-established LSPs originate from
   the PLR LSR and terminate on the MPT LSRs while bypassing LSR 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
   working documents as Internet-Drafts.  The list of current Internet-
   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 April 1, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the



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   document authors.  All rights reserved.

   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
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Conventions used in this document  . . . . . . . . . . . .  3
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  PLR Determination  . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Transit node procedure . . . . . . . . . . . . . . . . . .  4
     2.2.  MP2MP root node procedure  . . . . . . . . . . . . . . . .  5
     2.3.  PLR information encoding . . . . . . . . . . . . . . . . .  6
   3.  Using the tLDP session . . . . . . . . . . . . . . . . . . . .  8
   4.  Link or node failure . . . . . . . . . . . . . . . . . . . . . 10
     4.1.  Re-convergence after node/link failure . . . . . . . . . . 11
       4.1.1.  Node failure . . . . . . . . . . . . . . . . . . . . . 11
       4.1.2.  Link failure . . . . . . . . . . . . . . . . . . . . . 12
       4.1.3.  Switching to new primary path  . . . . . . . . . . . . 12
   5.  mLDP Capabilities for Node Protection  . . . . . . . . . . . . 13
     5.1.  PLR capability . . . . . . . . . . . . . . . . . . . . . . 13
     5.2.  MPT capability . . . . . . . . . . . . . . . . . . . . . . 13
     5.3.  The Protected LSR  . . . . . . . . . . . . . . . . . . . . 13
     5.4.  The Node Protection Capability . . . . . . . . . . . . . . 14
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   7.  IANA considerations  . . . . . . . . . . . . . . . . . . . . . 15
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 16
   9.  Contributor Addresses  . . . . . . . . . . . . . . . . . . . . 16
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     10.2. Informative References . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17










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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) that have been built by the "Multipoint Label Distribution
   Protocol"(mLDP) [RFC6388].  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.  The pre-established LSPs originate
   from the PLR LSR and terminate on the MPT LSRs while bypassing LSR N.
   The procedures to setup these P2P LSPs are outside the scope of this
   document, but one can imagine using Resource Reservation Protocol for
   Traffic Engineering (RSVP-TE) [RFC5420] or Label Distribution
   Protocol (LDP) Loop Free Alternative (LFA) [RFC5286] based techniques
   to accomplish this.

   The solution described in this document notifies the PLR(s) of the
   MPT LST(s) via signalling using a Targeted LDP (tLDP) session
   [RFC7060].  By having a tLDP session with the PLR, no additional
   procedures need to be defined in order to support Make-Before-Break
   (MBB), Graceful Restart (GR) and Typed Wildcard FEC support.  All
   this is achieved at the expense of having additional tLDP sessions
   between each MPT and PLR LSR.

   In order to allow a node to be protected against failure, the LSRs
   providing the PLR and the MPT functionality as well as the protected
   node MUST support the functionality described in this document.  LDP
   capability negotiation [RFC5561] is used to signal the availability
   of the functionality between the participating nodes; these nodes
   MUST support capability negotiation.

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








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   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).

   tLDP:  Targeted LDP.

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

   root node:  The root of either a P2MP or MP2MP LSP as defined in
      [RFC6388].


2.  PLR Determination

   In order for a MPT to establish a tLDP session with a 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 address of
   the PLR 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 the upstream LDP peer is unable to
   function as PLR, the procedures in this document do not apply and are
   out of the scope.  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 the
   PLR determination feature.

   The procedures as documented in this document requires the protected
   node to be directly connected to the PLR and MPT nodes.  This is
   because mLDP depends on unicast routing to determine the upstream LSR
   and unicast routing (by default) only has information about the next-
   hop and not beyond that.  Support for non-directly connected PLR and
   MPT nodes is outside the scope of this document.

2.1.  Transit node procedure

   Find below the procedures for 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 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 has the
   node protection 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 5 during Capability negotiation).
   For the format and encoding of PLR address information, see
   Section 2.3.

   Note, in order for the protected traffic to reach nodes LSR2 and
   LSR3, LSR1 MUST have two unidirectinal LSPs to LSR2 and LSR3,
   bypassing node N. The procedures for setting up these LSPs are
   outside the scope of this documemnt.

2.2.  MP2MP root node procedure

   Find below the procedures for when the protected node is the root of
   a MP2MP LSP.  Consider figure 2 below;













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             |
           (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
   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. In order to protect node N, all the directly connected 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
   doesn't replace the Root Node Redundancy (RNR) procedures as
   described in [RFC6388] section 7.  The node protection procedures in
   this document will help in 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.

   Note, in order for the protected traffic to be exchanged between
   nodes LSR1, LSR2 and LSR3, bidirectional LSPs have to exist between
   the LSRs, bypassing node N. The procedures for setting up these LSPs
   are outside the scope of this documemnt.

2.3.  PLR information encoding

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

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




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   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 =  TBA-1 |           Length              |  Addr Family  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Addr Fam cont | Num PLR entry |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               |
   |                         PLR entry (1 or more)                 ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where

      Type: PLR Status Value Element (Type TBA-1 to be assigned by IANA)

      Length: The Length field is an unsigned integer that encodes the
      length of the Status Value following the Length field.  The
      encoded Length varies based on the Addr Family and the number of
      PLR entries.

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

      Num PLR entry: Element as an unsigned, integer followed by that
      number of "PLR entry" fields in the format specified 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             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                  PLR address (cont)                           ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where

      A bit: 0 = Withdraw, 1 = Add.

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





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      PLR address: PLR Address encoded according to Address Family field
      encoded in the PLR Status Value Element.  Note, the length of the
      PLR address field is specific to the Address Family that is
      encoded.

   The size of a "PLR Entry" is the 2 octets ("A bit + Reserved") + PLR
   address length.  The length of the PLR address is dependent 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 given MP LSP, N needs to
   trigger a new PLR Status to update the MPT(s).  Node N can advertise
   or withdraw a given PLR from its PLR set by setting the "A bit" to 1
   or 0 respectively in the corresponding PLR entry.  Removing a PLR
   address is likely due to a link failure; see the procedures as
   documented in Section 4.1.  To remove all PLR addresses belonging to
   the encoded Address Family, an LSR N MUST encode a PLR Status Value
   Element with no PLR entry and "Num PLR entry" field MUST be set to
   zero.

   Both the PLR Status and an MP FEC TLV [RFC5036] MUST be included in
   the LDP Notification message so that a receiver is able to associate
   the PLR Status with the MP LSP.


3.  Using the tLDP 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 tLDP session with all of
   the learned PLR addresses using the procedures as documented in
   [RFC7060].

   Using Figure 1 as the reference topology, let us assume that both
   LSR2 and LSR3 are MPTs and have established a tLDP 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 assigned 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.  Label Ln that was assigned to N using the the
   normal mLDP procedures, and Label Lpx that was assigned to PLR (LSR1)
   for the purpose of node protection.  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.




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   The receipt of a FEC Label Mapping alone over the tLDP 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 tLDP session to the PLR MUST include a Status TLV with
   MP Status and 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 = TBA-2  |           Length              | Addr  Family  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Addr Fam cont |        Node address                           ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      Type : Protected Node Status Value Element (Type TBA-2 to be
      assigned by IANA)

      Length: The Length field is an unsigned integer that encodes the
      length of the Status Value following the Length field.  The
      encoded Length varies based on the Address Family and is 6 octets
      (for Address Family + IPv4 address and 18 octets for Address
      Family + IPv6 address.

      Addr Family: Two octet quantity containing a value from IANA's
      [AFI] 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 assigned 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 document.  Typically link
   failure or Bidirectional Forwarding Detection (BFD) can be used to



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   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
   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 discovers that node N is unreachable, it
   cannot immediately determine whether it is the link from LSR1 to N or
   the actual node N that has 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 both protection
   mechanisms at the same time, that is redirection of the traffic using
   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
   the packets twice due to the two protection mechanisms.  To prevent
   duplicate packets being forwarded to the receivers on the tree, LSR2
   and LSR3 need to determine from which upstream node they should
   accept the packets.  This can be either from the primary upstream LSR
   N or from the secondary upstream LSR1, but never both at the same
   time.  The selection between the primary upstream LSR or (one or
   more) secondary upstream LSRs (on LSR2 and LSR3) is based on the
   reachability of the protected node N. As long as N is reachable from
   an MPT, the MPT should accept and forward the MPLS packets from N.
   Once N becomes unreachable, the LSPs from secondary upstream PLR LSRs
   (LSR1 in our example) are activated.  Note that detecting if N is
   unreachable is a local decision and not spelled out in this document.



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   Typically link failure or Bidirectional Forwarding Detection (BFD)
   can be used to determine and detect node unreachability.

4.1.  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 failure of node N.
   ...: 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 example.  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 sequence of events is
   dependent on whether the link from LSR1 to N has failed or node N
   itself.  The nodes downstream from the protected node (and
   participating in node protection) MUST have the capability to
   determine that the protected node has become unreachable.  Otherwise
   the procedures below can not be applied.

4.1.1.  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 to the
   label bindings that were installed for node protection.






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4.1.2.  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 response, LSR2 and LSR3 MUST send 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.

4.1.3.  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.  LSR2 will find that P 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 P and Q are activated, a Label Withdraw message MUST be
   sent to the old upstream LSR.  Note that an upstream LSR switchover
   from a tLDP neighbor to a directly connected LDP neighbor is no
   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 tLDP session between the MPT and the PLR, the tLDP
   session MAY be taken down.  It is possible that having no more
   interest in the tLDP session is temporarily due to link flapping.  In
   order to avoid the tLDP session from flapping, it is RECOMMENDED to
   apply a delay before tearing down the session.  Determining the delay
   is a local implementation matter.  If the operator is not concerned
   with the tLDP session flapping and/or other procedures are in place
   to avoid this altogether, there is no need to apply the delay.







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5.  mLDP Capabilities for Node Protection

   In order to describe the capabilities of the participating LSRs, this
   document is 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).

5.1.  PLR capability

   A PLR node should handle the following conditions;

   1.  Accept an incoming tLDP session from the MPT LSR.

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

   An LSR capable of performing these actions will advertise it self as
   PLR capable in the Node Protection capability (see Section 5.4).
   This is a unidirectional capability announced from PLR to the
   protected LSR.

5.2.  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.

   A LSR capable of performing these actions will advertise itself as
   MPT capable in the Node Protection capability (see Section 5.4).
   This is a unidirectional capability from MPT to the protected LSR.

5.3.  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.



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   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 tLDP session with the
   PLR(s) and MP LSP node protection signaling.

5.4.  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| Type = TBA-3              |           Length = 2          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |S| Reserved    |P|M| Reserved  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Where

      U/F bits: MUST be set to 1 and 0 respectively (as per [RFC5561])

      Type: MP Node Protection Capability (Type = TBA-3 to be assigned
      by IANA)

      Length: Unsigned integer, MUST be set to 2.

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

      P bit: Set to 1 to indicate the PLR is capable of MP LSP node
      protection

      M bit: Set to 1 to indicate the MPT is capable of MP LSP node
      protection

      Reserved: MUST be zero on transmit and ignored on receipt




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   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.


6.  Security Considerations

   The procedures in this document add two new TLVs to existing LDP
   messages.  Those TLVs can be protected by the mechanisms that are
   used to protect LDP messages as described in [RFC6388] and [RFC5920].
   If it were possible to attack the mechanisms described in this
   document an LSR (a PLR or a MPT) could be induced to support a large
   number of tLDP sessions and set up an even larger number of LSPs.
   The security mechanisms in [RFC6388] and [RFC5920] are believed to be
   adequate, but an implementation could provide additional protection
   by counting such protection sessions and LSPs and producing a log
   message to the operator if a threshold is crossed.


7.  IANA considerations

   IANA is requested to allocate two new code points from the "LDP MP
   Status Value Element type" registry within the Label Distribution
   Protocol (LDP) Parameters;

      Value | Name                                   | Reference
      ------+----------------------------------------+-----------
      TBA-1 | PLR Status Value Element               | this doc
      ------+----------------------------------------+-----------
      TBA-2 | Protected Node Status Value Element    | this doc

   IANA is requested to assign a new code points for a new Capability
   Parameter TLV.  The code point should be assigned from the IETF
   Consensus range of the "TLV Type Name Space" registry within the LDP
   Parameters.  The lowest available new code point after 0x0970 should
   be used.

      Value | Description                   | Reference | Notes/Reg Date
      ------+-------------------------------+-----------+---------------



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      TBA-3 | MP Node Protection Capability | This doc  |


8.  Acknowledgments

   The authors like to thank Nagendra Kumar, Duan Hong, Martin
   Vigoureux, Kenji Fujihira, Loa Andersson and Ben Campbell for their
   comments on this document.  Also, many thanks to Elwyn Davies and
   Adrian Farrel for the detailed review and contribution to this
   document.


9.  Contributor Addresses

   Below is a list of other contributing authors in alphabetical order:

   Eric Rosen
   Juniper Networks, Inc.
   10 Technology Park Drive
   Westford
   MA 01886
   USA
   erosen@juniper.net


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.

   [RFC7060]  Napierala, M., Rosen, E., and IJ. Wijnands, "Using LDP
              Multipoint Extensions on Targeted LDP Sessions", RFC 7060,
              November 2013.

   [AFI]      "IANA, Address Family Identifier (AFIs), http://



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              www.iana.org/assignments/address-family-numbers/address-
              family-numbers.xhtml", July 2013.

10.2.  Informative References

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

   [RFC5920]  Fang, L., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, July 2010.


Authors' Addresses

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

   Email: ice@cisco.com


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

   Email: skraza@cisco.com


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

   Email: akatlas@juniper.net











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   Jeff Tantsura
   Ericsson
   300 Holger Way
   San Jose  CA 95134
   USA

   Email: jeff.tantsura@ericsson.com


   Quintin Zhao
   Huawei Technology
   125 Nagog Technology Park
   Acton  MA  01719
   USA

   Email: quintin.zhao@huawei.com



































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