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Versions: (draft-ietf-pwe3-endpoint-fast-protection) 00 01 02 03 04 05 RFC 8104

Internet Engineering Task Force                               Yimin Shen
Internet-Draft                                          Juniper Networks
Intended status: Standards Track                          Rahul Aggarwal
Expires: July 7, 2017                                        Arktan, Inc
                                                          Wim Henderickx
                                                                   Nokia
                                                          Yuanlong Jiang
                                                     Huawei Technologies
                                                         January 3, 2017


                  PW Endpoint Fast Failure Protection
              draft-ietf-pals-endpoint-fast-protection-05

Abstract

   This document specifies a fast mechanism for protecting pseudowires
   (PWs) transported by IP/MPLS tunnels against egress endpoint
   failures, including egress AC (attachment circuit) failure, egress PE
   (provider edge) failure, multi-segment PW terminating PE failure, and
   multi-segment PW switching PE failure.  Operating on the basis of
   multi-homed CE (customer edge), redundant PWs, upstream label
   assignment and context specific label switching, the mechanism
   enables local repair to be performed by the router upstream adjacent
   to a failure.  The router can restore a PW in the order of tens of
   milliseconds, by rerouting traffic around the failure to a protector
   through a pre-established bypass tunnel.  Therefore, the mechanism
   can be used to reduce traffic loss before global repair reacts to the
   failure and the network converges on the topology changes due to the
   failure.

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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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 7, 2017.




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Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   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
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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
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Specification of Requirements . . . . . . . . . . . . . . . .   4
   3.  Reference Models for Egress Endpoint Failures . . . . . . . .   4
     3.1.  Single-Segment PW . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Multi-Segment PW  . . . . . . . . . . . . . . . . . . . .   8
   4.  Theory of Operation . . . . . . . . . . . . . . . . . . . . .   9
     4.1.  Applicability . . . . . . . . . . . . . . . . . . . . . .   9
     4.2.  Local Repair  . . . . . . . . . . . . . . . . . . . . . .  10
     4.3.  Context Identifier  . . . . . . . . . . . . . . . . . . .  13
       4.3.1.  Semantics . . . . . . . . . . . . . . . . . . . . . .  13
       4.3.2.  FEC . . . . . . . . . . . . . . . . . . . . . . . . .  14
       4.3.3.  IGP Advertisement and Path Computation  . . . . . . .  15
     4.4.  Protection Models . . . . . . . . . . . . . . . . . . . .  16
       4.4.1.  Co-located Protector  . . . . . . . . . . . . . . . .  16
       4.4.2.  Centralized Protector . . . . . . . . . . . . . . . .  17
     4.5.  Transport Tunnel  . . . . . . . . . . . . . . . . . . . .  19
     4.6.  Bypass Tunnel . . . . . . . . . . . . . . . . . . . . . .  20
     4.7.  Examples of Forwarding State  . . . . . . . . . . . . . .  21
       4.7.1.  Co-located Protector Model  . . . . . . . . . . . . .  21
       4.7.2.  Centralized Protector Model . . . . . . . . . . . . .  25
   5.  Restorative and Revertive Behaviors . . . . . . . . . . . . .  28
   6.  LDP Extensions  . . . . . . . . . . . . . . . . . . . . . . .  29
     6.1.  Egress Protection Capability TLV  . . . . . . . . . . . .  30
     6.2.  PW Label Distribution from Primary PE to Protector  . . .  31
     6.3.  PW Label Distribution from Backup PE to Protector . . . .  31
     6.4.  Protection FEC Element TLV  . . . . . . . . . . . . . . .  32
       6.4.1.  Encoding Format for PWid with IPv4 PE Addresses . . .  33
       6.4.2.  Encoding Format for Generalized PWid with IPv4 PE
               Addresses . . . . . . . . . . . . . . . . . . . . . .  34
       6.4.3.  Encoding Format for PWid with IPv6 PE Addresses . . .  35
       6.4.4.  Encoding Format for Generalized PWid with IPv6 PE



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               Addresses . . . . . . . . . . . . . . . . . . . . . .  36
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  38
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  38
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  39
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  39
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  39
     10.2.  Informative References . . . . . . . . . . . . . . . . .  40
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  41

1.  Introduction

   Per [RFC3985, RFC4447, RFC5659], a pseudowire (PW) or PW segment can
   be thought of as a connection between a pair of forwarders hosted by
   two PEs, carrying an emulated layer-2 service over a packet switched
   network (PSN).  In the single-segment PW (SS-PW) case, a forwarder
   binds a PW to an attachment circuit (AC).  In the multi-segment PW
   (MS-PW) case, a forwarder on a terminating PE (T-PE) binds a PW
   segment to an AC, while a forwarder on a switching PE (S-PE) binds
   one PW segment to another PW segment.  In each direction between the
   PEs, PW packets are transported by a PSN tunnel, which is also called
   a transport tunnel.

   In order to protect the PW service against network failures, it is
   necessary to protect every link and node along the entire data path.
   For the traffic in a given direction, this include ingress AC,
   ingress (T-)PE, intermediate routers of transport tunnel, S-PEs,
   egress (T-)PE, and egress AC.  To minimize service disruption upon a
   failure, it is also desirable that each of these components is
   protected by a fast protection mechanism based on local repair.  Such
   mechanism generally involves a bypass path that is pre-computed and
   pre-installed in the data plane on the router upstream adjacent to an
   anticipated failure.  This router is referred to as a "point of local
   repair" (PLR).  The bypass path has the property that it can guide
   traffic around the failure, while remaining unaffected by the
   topology changes resulting from the failure.  When the failure
   occurs, the PLR can invoke the bypass path to achieve fast
   restoration for the service.

   Today, fast protection against ingress AC failure and ingress (T-)PE
   failure can be achieved by using a multi-homed CE and redundant ACs,
   such as multi-chassis link aggregation group (MC-LAG).  Fast
   protection against the failure of an intermediate router of transport
   tunnel can be achieved through RSVP fast-reroute [RFC4090] or IP/LDP
   fast-reroute [RFC5714, RFC5286].  However, there is no equivalent
   mechanism that can be used against an egress AC failure, an egress
   (T-)PE failure, or an S-PE failure.  For these failures, service
   restoration has to rely on global repair or control plane
   convergence.  Global repair normally involves the ingress CE or the



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   ingress (T-)PE switching traffic to an alternative path, based on
   remote failure detection via PW status notification, end-to-end OAM,
   and others.  Control plane convergence relies on control protocols to
   react on the topology changes due to a failure.  Compared to local
   repair, these mechanisms are relatively slow in reacting to a failure
   and restoring traffic.

   This document is intended to serve the above need.  It specifies a
   fast protection mechanism based on local repair to protect PWs
   against the following endpoint failures.

   a.  Egress AC failure.

   b.  Egress PE failure: Link or node failure of an egress PE of an SS-
       PW, or a T-PE of an MS-PW.

   c.  Switching PE (S-PE) failure: Link or node failure of an S-PE of
       an MS-PW.

   The mechanism is applicable to LDP signaled PWs.  It is relevant to
   networks with redundant PWs and multi-homed CEs.  It is designed on
   the basis of MPLS upstream label assignment and context-specific
   label switching [RFC5331].  Fast protection refers to its ability to
   restore traffic in the order of tens of milliseconds.  Compared with
   global repair and control plane convergence, this mechanism can
   provide faster service restoration.  However, it is intended to
   complement these mechanisms, rather than replacing them, as networks
   rely on them to eventually move traffic to fully functional
   alternative paths.

2.  Specification of Requirements

   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 RFC2119.

3.  Reference Models for Egress Endpoint Failures

   This document refers to the following topologies to describe egress
   endpoint failures and protection procedures.

3.1.  Single-Segment PW









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                  |<-------------- PW1 --------------->|

              - PE1 -------------- P1 ---------------- PE2 -
             /                                              \
            /                                                \
         CE1                                                  CE2
            \                                                /
             \                                              /
              - PE3 -------------- P2 ---------------- PE4 -

                  |<-------------- PW2 --------------->|

                                 Figure 1

   In Figure 1, the IP/MPLS network consists of PE and P routers.  It
   provides a PW service between CE1 and CE2.  Each CE is multi-homed
   via two ACs to two PEs.  This forms two divergent paths between the
   CEs.  The first path uses PW1 between PE1 and PE2, and the second
   path uses PW2 between PE3 and PE4.  The transport tunnels of the PWs
   and other links between the routers are not shown in this figure for
   clarity.

   In general, a CE may operate the ACs in two modes when sending
   traffic to the remote CE, i.e. active-standby mode and active-active
   mode.

   o  In the active-standby mode, the CE chooses one AC as active AC and
      the corresponding path as active path, and uses the other AC as
      standby AC and the corresponding path as standby path.  The CE
      only sends traffic on the active AC as long as the active path is
      operational.  The CE will only send traffic on the standby AC
      after it detects a failure of the active path.  Note that the CE
      may receive traffic on the active or standby AC, depending on
      whether the remote CE chooses the same active path for the traffic
      of the reverse direction.  In this document, even if both CEs
      choose the same active path, each CE should still anticipate
      receiving traffic on a standby AC, because the traffic may be
      redirected to the standby path by the fast protection mechanism.

   o  In the active-active mode, the CE treats both ACs and their
      corresponding paths as active, and sends traffic on both ACs in a
      load balance fashion.  In the reverse direction, the CE may
      receive traffic on both ACs.

   The above modes assume the traffic to be data traffic which is not
   bound to specific AC.  This does not include control protocol traffic
   between the CEs, when the CE-CE control protocol sessions or
   adjacencies established on the two ACs are considered as distinct,



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   rather than having a primary and backup relationship.  In general, a
   dual-homed CE should not make any explicit or implicit assumptions
   regarding specific AC from which it receives packets from the remote
   CE.

   For either mode, when considering the traffic flowing in a given
   direction over an active path, this document views the ACs, PEs and
   PWs to serve primary or backup roles.  In particular, the ACs, PEs
   and PW along this active path have primary roles, while those along
   the other path have backup roles.  Note that in the active-active
   mode, each AC, PE, and PW on an active path has a primary role, and
   also a backup role protecting the other path which is also active.

   For Figure 1, the following roles are assumed for the traffic going
   from CE1 to CE2 via PW1.

      Primary ingress AC: CE1-PE1

      Primary ingress PE: PE1

      Primary PW: PW1

      Primary egress PE: PE2

      Primary egress AC: PE2-CE2

      Backup ingress AC: CE1-PE3

      Backup ingress PE: PE3

      Backup PW: PW2

      Backup egress PE: PE4

      Backup egress AC: PE4-CE2

   Based on this schema, this document describes egress endpoint
   failures and the fast protection mechanism on the per-active-path and
   per-direction basis.  In this case, an egress AC failure refers to
   the failure of the AC PE2-CE2, and an egress node failure refers to
   the failure of PE2.  The ultimate goal is that when a failure occurs,
   the traffic should be locally repaired, so that it can eventually
   reach CE2 via the backup egress PE (PE4) and the backup egress AC
   (PE4-CE2).

   Subsequent to the local repair, either the current active path should
   heal after control plane converges on the new topology, or the
   ingress CE should switch traffic from the primary path to the backup



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   path, depending on the failure scenario.  In the latter case, the
   ingress CE may perform the path switchover triggered by end-to-end
   OAM (in-band or out-band), PW status notification, CE-PE control
   protocols (e.g.  LACP), and others.  In the active-standby mode, this
   will promote the standby path to new active path.  In the active-
   active mode, it will make the other active path carry all the traffic
   between the two CEs.  In any case, this phase of restoration falls
   into the control plane convergence and global repair category, and
   hence is out of the scope of this document.  The purpose of the fast
   protection mechanism in this document is to reduce traffic loss
   before this phase of restoration takes place.

   Note that in Figure 1, if the traffic in the reverse direction (i.e.
   from CE2 to CE1) traverses the AC CE2-PE2 and PE2 as active path, the
   failure of PE2 and the failure of the AC PE2-CE2 will be considered
   as ingress failures of the traffic.  If CE2 can detect the failures,
   it may protect the traffic by switching it to the backup path via the
   AC CE2-PE4 and PE4.  However, this is categorized as ingress endpoint
   failure protection, and hence is not handled by the mechanism
   described in this document.

   Figure 2 shows another possible scenario, where CE1 is single-homed
   to PE1, while CE2 remains multi-homed to PE2 and PE4.  From the
   perspective of egress endpoint protection for the traffic going from
   CE1 to CE2 over PW1, this scenario is the same as the scenario shown
   in Figure 1.

                   |<-------------- PW1 --------------->|

                      ------------- P1 ---------------- PE2 -
                     /                                       \
                    /                                         \
          CE1 -- PE1                                          CE2
                    \                                         /
                     \                                       /
                      ------------- P2 ---------------- PE4 -

                   |<-------------- PW2 --------------->|

                                 Figure 2

   For clarity, primary egress AC, primary egress PE, backup egress AC,
   and backup egress PE may simply be referred to as primary AC, primary
   PE, backup AC, and backup PE, respectively, when the context of a
   discussion is egress endpoint.






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3.2.  Multi-Segment PW

                  |<--------------- PW1 --------------->|
                  |<----- SEG1 ----->|<----- SEG2 ----->|

             - TPE1 -------------- SPE1 --------------- TPE2 -
            /                                                 \
           /                                                   \
        CE1                                                     CE2
           \                                                   /
            \                                                 /
             - TPE3 -------------- SPE2 --------------- TPE4 -

                  |<----- SEG3 ----->|<----- SEG4 ----->|
                  |<--------------- PW2 --------------->|

                                 Figure 3

   Figure 3 shows a topology that is similar to Figure 1 but in an MS-PW
   environment.  PW1 and PW2 are both MS-PWs.  PW1 is established
   between TPE1 and TPE2, and switched between segments SEG1 and SEG2 at
   SPE1.  PW2 is established between TPE3 and TPE4, and switched between
   segments SEG3 and SEG4 at SPE2.  CE1 is multi-homed to TPE1 and TPE3.
   CE2 is multi-homed to TPE2 and TPE4.  The transport tunnels of the PW
   segments are not shown in this figure for clarity.

   In this document, the following primary and backup roles are assigned
   for the traffic going from CE1 to CE2:

      Primary ingress AC: CE1-TPE1

      Primary ingress T-PE: TPE1

      Primary PW: PW1

      Primary S-PE: SPE1

      Primary egress T-PE: TPE2

      Primary egress AC: TPE2-CE2

      Backup ingress AC: CE1-TPE3

      Backup ingress T-PE: TPE3

      Backup PW: PW2

      Backup S-PE: SPE2



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      Backup egress T-PE: TPE4

      Backup egress AC: TPE4-CE2

   In this case, an egress AC failure refers to the failure of the AC
   TPE2-CE2.  An egress node failure refers to the failure of TPE2.  An
   S-PE failure refers to the failure of SPE1.

   For consistency with the SS-PW scenario, primary T-PEs and a primary
   S-PEs may simply be referred to as primary PEs in this document,
   where specifics are not required.  Similarly, backup T-PEs and backup
   S-PEs may be referred to as backup PEs.

4.  Theory of Operation

   The fast protection mechanism in this document provides three types
   of protection for PWs, corresponding to the three types of failures
   described in Section 1.

   a.  Egress AC protection

   b.  Egress (T-)PE node protection

   c.  S-PE node protection

4.1.  Applicability

   The mechanism is applicable to LDP signaled PWs in an environment
   where an egress CE is multi-homed to a primary PE and a backup PE and
   there exists a backup PW, as described in Section 3.  The procedure
   for S-PE node protection is applicable when there exists a backup
   S-PE on the backup PW.

   The mechanism assumes IP/MPLS transport tunnels, and is applicable to
   tunnels with single path and ECMPs (equal cost multiple paths).  As
   an example of ECMPs, imagine a tunnel carrying one or multiple PWs
   and traversing a router with ECMPs to a primary PE.  The ECMPs
   consist of at least one direct link to the PE, and some multi-hop
   paths to the PE.  Due to the direct link, the router is considered as
   a penultimate hop of the tunnel, and can perform local detection and
   repair for an egress node failure.  The router normally uses a
   hashing algorithm to distribute PW packets over the ECMPs, on a per-
   PW or per-flow basis.  Upon a failure of the direct link, i.e.
   transit link failure, the router removes the link from the hashing
   algorithm, which automatically redistributes the traffic of the link
   to the other paths of the ECMPs, achieving local repair.  This
   scenario is not the focus of this document.  Upon a failure of the
   PE, i.e. egress node failure, the router SHOULD perform local repair



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   by rerouting the entire traffic of the ECMPs, as the failure will
   affect every path.  If the router does not have a fast or reliable
   mechanism to detect the egress node failure, it is RECOMMENDED that
   the router SHOULD treat the failure of the direct link as an egress
   node failure.

   The mechanism is applicable to both best-effort and traffic
   engineering (TE) transport tunnels.  For TE transport tunnels which
   require bandwidth protection, TE bypass tunnels with reserved
   bandwidth MAY be used to avoid congestion for rerouted traffic.

   It is also RECOMMENDED that the mechanism SHOULD be used in
   conjunction with global repair and control plane convergence, in such
   a manner that the mechanism temporarily repairs a failed path by
   using a bypass tunnel, and global repair and control plane
   convergence eventually move traffic to a fully functional alternative
   path.

4.2.  Local Repair

   The fast protection ability of the mechanism comes from local repair
   performed by routers upstream adjacent to failures.  Each of these
   routers is referred to as a "point of local repair" (PLR).  A PLR
   MUST be able to detect a failure by using a rapid mechanism, such as
   physical layer failure detection, Bidirectional Forwarding Detection
   (BFD) [RFC5880], Seamless BFD (S-BFD) [RFC7880], and others.  In
   anticipation of the failure, the PLR MUST also pre-establish a bypass
   tunnel to a "protector", and pre-install a bypass route for the
   bypass tunnel in the data plane.  The protector is either a backup PE
   or a router which will forward traffic to a backup PE.  The bypass
   tunnel MUST have the property that it will not be affected by the
   topology changes due to the failure.  Specifically, it MUST NOT
   traverse the primary PE or the penultimate link of the protected
   transport tunnel, or share any SRLG (shared risk link groups) with
   the penultimate link.  Upon detecting the failure, the PLR invokes
   the bypass route in the data plane, and reroutes PW traffic to the
   protector through the bypass tunnel.  The protector in turn sends the
   traffic to the target CE.  This procedure is referred to as local
   repair.

   Different routers may serve as PLR and protector in different
   scenarios.

   o  In egress AC protection, the PLR is the primary PE, and the
      protector is the backup PE (Figure 4).






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                  |<-------------- PW1 --------------->|

              - PE1 -------------- P1 ---------------- PE2 -
             /                                         PLR  \
            /                                           |    \
         CE1                                      bypass|     CE2
            \                                           |    /
             \                                          |   /
              - PE3 -------------- P2 ---------------- PE4 -
                                                    protector

                  |<-------------- PW2 --------------->|

                                 Figure 4

   o  In egress PE node protection, the PLR is the penultimate hop
      router of the transport tunnel of the primary PW, and the
      protector is the backup PE (Figure 5).

                  |<-------------- PW1 --------------->|

              - PE1 -------------- P1 ------- P3 ----- PE2 -
             /                               PLR \          \
            /                                     \          \
         CE1                                 bypass\          CE2
            \                                       \        /
             \                                       \      /
              - PE3 -------------- P2 ---------------- PE4 -
                                                    protector

                  |<-------------- PW2 --------------->|

                                 Figure 5

   o  In S-PE node protection, the PLR is the penultimate hop router of
      the transport tunnel of the primary PW segment, and the protector
      is the backup S-PE (Figure 6).














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                  |<--------------- PW1 --------------->|
                  |<----- SEG1 ----->|<----- SEG2 ----->|

             - TPE1 ----- P1  ----- SPE1 -------------- TPE2 -
            /             PLR \                               \
           /                   \                               \
        CE1               bypass\                               CE2
           \                     \                             /
            \                     \                           /
             - TPE3 --------------- SPE2 -------------- TPE4 -
                                 protector

                  |<----- SEG3 ----->|<----- SEG4 ----->|
                  |<--------------- PW2 --------------->|

                                 Figure 6

   In egress AC protection, a PLR realizes its role based on
   configuration of a "context identifier" introduced in this document
   (Section 4.3).  The PLR establishes a bypass tunnel to the protector
   in the same fashion as a normal PSN tunnel.

   In egress PE and S-PE node protection, a PLR is a transit router on
   the transport tunnel, and it normally does not have knowledge of the
   PW(s) carried by the transport tunnel.  In this document, the PLR
   simply computes and establishes a node protection bypass tunnel in
   the same fashion as the normal IP/MPLS node protection, except that
   with the notion of context identifier, the bypass tunnel will be
   established from the PLR to the protector (Section 4.6).  Conversely,
   when the router is no longer a PLR for egress PE or S-PE node
   protection due to a change in network topology or the transport
   tunnel's path, the router should revert to the role of regular
   transit router, including PLR for transit link and node protection.

   In local repair, a PLR simply switches all the traffic received on
   the transport tunnel to the bypass tunnel.  This requires that the
   protector given by the bypass tunnel MUST be intended for all the PWs
   carried by the transport tunnel.  This is achieved by the ingress PE
   using a context identifier to associate a PW with the specific pair
   of {primary PE, protector} and map the PW to a transport tunnel
   destined for the same {primary PE, protector}. The ingress PE MAY map
   multiple PWs to the transport tunnel, if they share the {primary PE,
   protector} in common.

   In local repair, the PLR keeps PW label intact in packets.  This
   obviates the need for the PLR to maintain bypass routes on a per-PW
   basis, and allows bypass tunnel sharing between PWs.  On the other
   hand, this imposes a requirement on the protector that it MUST be



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   able to forward the packets based on a PW label that is assigned by
   the primary PE, and ensure that the traffic MUST reach the target CE
   via a backup path.  From the protector's perspective, this PW label
   is an upstream assigned label [RFC5331].  To achieve this, the
   protector MUST learn the PW label from the primary PE prior to the
   failure, and install proper forwarding state for the PW label in a
   dedicated label space associated with the primary PE.  During local
   repair, the protector MUST perform PW label lookup in this label
   space.

   The previous examples have shown the scenarios where the protectors
   are backup (T/S-)PEs.  It is also possible that a protector is a
   dedicated router to serve such role, separate from the backup (T/
   S-)PE.  During local repair, the PLR still reroutes traffic to the
   protector through a bypass tunnel.  The protector then forwards the
   traffic to the backup (T/S-)PE, which further forwards the traffic to
   the target CE via a backup AC or a backup PW segment.  More detail
   will be described in Section 4.4.

4.3.  Context Identifier

   A protector may protect multiple primary PEs.  The protector MUST
   maintain a separate label space for each primary PE.  Likewise, the
   PWs terminated on a primary PE may be protected by multiple
   protectors, each for a subset of the PWs.  In any case, a given PW
   MUST be associated with one and only one pair of {primary PE,
   protector}.

   This document introduces the notion of "context identifier" to
   facilitate protection establishment.  A context identifier is an
   IPv4/v6 address assigned to each ordered pair of {primary PE,
   protector}. The address MUST be globally unique, or unique in the
   address space of the network where the primary PE and the protector
   reside.

4.3.1.  Semantics

   The semantics of a context identifier is twofold.

   o  A context identifier identifies a primary PE and an associated
      protector.  It represents the primary PE as PW destination on a
      per protector basis.  A given primary PE may be protected by
      multiple protectors, each for a subset of the PWs terminated on
      the primary PE.  A distinct context identifier MUST be assigned to
      each {primary PE, protector} pair.

      The ingress PE of a PW learns the context identifier of the PW's
      {primary PE, protector} from the primary PE via Interface_ID TLV



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      [RFC3471, RFC3472] in the LDP Label Mapping message of the PW.
      The ingress PE then sets up or resolves a transport tunnel with
      the context identifier, rather than a private IP address of the
      primary PE, as destination.  This destination not only makes the
      transport tunnel reach the primary PE, but also conveys the
      identity of the protector to the PLR, which MUST use the context
      identifier as destination for the bypass tunnel to the protector.
      The ingress PE MUST map only the PWs terminated by the exact
      primary PE and protected by the exact protector to the transport
      tunnel.

   o  A context identifier indicates the primary PE's label space on the
      protector.  The protector may protect PWs for multiple primary
      PEs.  For each primary PE, it MUST maintain a separate label space
      to store the PW labels assigned by that primary PE.  It associates
      a PW label with a label space via the context identifier of the
      {primary PE, protector}, as below.

      In addition to the normal LDP PW signaling, the primary PE MUST
      have a targeted LDP session with the protector, and advertise PW
      labels to the protector via LDP Label Mapping messages
      (Section 6).  The primary PE MUST attach the context identifier to
      each message.  Upon receiving the message, the protector MUST
      install the advertised PW label in the label space identified by
      the context identifier.

      When a PLR sets up or resolves a bypass tunnel to the protector,
      it MUST use the context identifier rather than a private IP
      address of the protector as destination.  The protector MUST use
      the bypass tunnel, either the MPLS tunnel label or IP tunnel
      destination address, as the pointer to the corresponding label
      space.  The protector MUST forward PW packets received on the
      bypass tunnel based on label lookup in that label space.

4.3.2.  FEC

   In an MPLS network, a context identifier represents a FEC (Forwarding
   Equivalence Class) for transport tunnels and bypass tunnels destined
   for it.  For examples, it may be encoded in an LDP Prefix FEC
   Element, or in the "tunnel end point address" of an RSVP Session
   object.  The FEC is associated with unique forwarding state on PLRs
   and protector, which cannot be shared with other FECs.  Some MPLS
   protocols (e.g.  LDP) support FEC aggregation [RFC3031].  In this
   case, FEC aggregation MUST NOT be applied to a context identifier's
   FEC, and every router MUST assign a unique label to the FEC.






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4.3.3.  IGP Advertisement and Path Computation

   Using a context identifier as destination for both transport tunnel
   and bypass tunnel requires coordination between the primary PE and
   the protector in IGP advertisement of the context identifier in
   routing domain and TE domain.  The context identifier should be
   advertised in such a way that all the routers on the tunnels MUST be
   able to independently reach the following common view of paths.

   o  The transport tunnel MUST have the primary PE as path endpoint.

   o  The bypass tunnel MUST have the protector as path endpoint.  In
      egress PE and S-PE node protection, the path MUST avoid the
      primary PE.

   There are generally two categories of approaches to achieve the
   above.

   o  The first category does not require an ingress PE or a PLR to have
      knowledge of the PW egress endpoint protection schema.  It does
      not require any IGP extension for context identifier
      advertisement.  A context identifier is advertised by the primary
      PE and the protector as an address reachable via both routers.
      The ingress PE and the PLR can compute paths by using a normal
      method, such as Dijkstra, CSPF (constrained shortest path first),
      LFA [RFC5286] and MRT [RFC7812].  One example is to advertise a
      context identifier as a virtual proxy node connected to the
      primary PE and the protector, with the link between the proxy node
      and the primary PE having a more preferable IGP and TE metric than
      the link between the proxy node and the protector.  The transport
      tunnel will follow the shortest path or a TE path to the primary
      PE, and be terminated by the primary PE.  The PLR will no longer
      view itself as a penultimate hop of the transport tunnel, but
      rather two hops away from the proxy node, via the primary PE.
      Hence, a node protection bypass tunnel will be available via the
      protector to the proxy node, but actually be terminated by the
      protector.

   o  The second category requires a PLR to have knowledge of the PW
      egress endpoint protection schema.  The primary PE advertises the
      context identifier as a regular IP address, while the protector
      advertises it by using an explicit "context identifier" object,
      which MUST be understood by the PLR.  The "context identifier"
      object requires an IGP extension.  In both the routing domain and
      the TE domain, the context identifier is only reachable via the
      primary PE.  This ensures that the transport tunnel is terminated
      by the primary PE.  The PLR views itself as the penultimate hop of
      the transport tunnel, and based on the IGP "context identifier"



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      object, it establishes or resolves a bypass tunnel to the
      advertiser (i.e. the protector), while avoiding the primary PE.

   The mechanism in this document intends to be flexible on the approach
   used by a network, as long as it satisfies the above requirements for
   transport tunnel path and bypass tunnel path.  In theory, the network
   can use one approach for context ID X and another approach for
   context ID Y.  For a given context ID, all relevant routers,
   including primary PE, protector, and PLR, must support and agree on
   the chosen approach.  The coordination between the routers can be
   achieved by configuration.

4.4.  Protection Models

   There are two protection models based on the location of a protector.
   A network MAY use either model or both.

4.4.1.  Co-located Protector

   In this model, the protector is a backup PE that is directly
   connected to the target CE via a backup AC, or it is a backup S-PE on
   a backup PW.  That is, the protector is co-located with the backup
   (S-)PE.  Examples of this model have been shown in Figure 4, Figure 5
   and Figure 6 in Section 4.2.

   In egress AC protection and egress PE node protection, when a
   protector receives traffic from the PLR, it forwards the traffic to
   the CE via the backup AC.  This is shown in Figure 7, where PE2 is
   the PLR for egress AC failure, P3 is the PLR for PE2 failure, and PE4
   (backup PE) is the protector.

                 |<-------------- PW1 --------------->|

             - PE1 -------------- P1 ------- P3 ----- PE2 ----
            /                               PLR \     PLR     \
           /                                     \     |       \
        CE1                                 bypass\    |bypass  CE2
           \                                       \   |       /
            \                                       \  |      /
             - PE3 -------------- P2 ---------------- PE4 ----
                                                   protector

                 |<-------------- PW2 --------------->|

                                 Figure 7

   In S-PE node protection, when a protector receives traffic from the
   PLR, it forwards the traffic over the next segment of the backup PW.



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   The T-PE of the backup PW in turn forwards the traffic to the CE via
   a backup AC.  This is shown in Figure 8, where P1 is the PLR for SPE1
   failure, and SPE2 (backup S-PE) is the protector for SPE1.  SPE2
   receives traffic from P1, swaps SEG1's label to SEG4's label, and
   forwards the traffic over a transport tunnel to TPE4.

                  |<--------------- PW1 --------------->|
                  |<----- SEG1 ----->|<----- SEG2 ----->|

             - TPE1 ----- P1  ----- SPE1 -------------- TPE2 -
            /             PLR \                               \
           /                   \                               \
        CE1               bypass\                               CE2
           \                     \                             /
            \                     \                           /
             - TPE3 --------------- SPE2 -------------- TPE4 -
                                 protector

                  |<----- SEG3 ----->|<----- SEG4 ----->|
                  |<--------------- PW2 --------------->|

                                 Figure 8

   In the co-located protector model, the number of context identifiers
   needed by a network is the number of distinct {primary PE, backup PE}
   pairs.  From the perspective of scalability, the model is suitable
   for networks where the number of primary PEs and the average number
   of backup PEs per primary PE are both relatively low.

4.4.2.  Centralized Protector

   In this model, the protector is a dedicated P router or PE router
   that serves the role.  In egress AC protection and egress PE node
   protection, the protector may or may not be a backup PE directly
   connected to the target CE.  In S-PE node protection, the protector
   may or may not be a backup S-PE on the backup PW.

   In egress AC protection and egress PE node protection, if the
   protector is not directly connected to the CE, it forwards the
   traffic to a backup PE, which in turn forwards the traffic to the CE
   via a backup AC.  This is shown in Figure 9, where the protector
   receives traffic from P3 (PLR for egress PE failure) or PE2 (PLR for
   egress AC failure), swaps PW1's label to PW2's label, and forwards
   the traffic via a transport tunnel to PE4 (backup PE).  The protector
   may be protecting other PWs and other primary PEs as well, which is
   not shown in this figure for clarity.





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                  |<------------- PW1 --------------->|

              - PE1 ------------- P1 ------- P3 ----- PE2 --
             /                              PLR \     PLR   \
            /                                    \     /     \
           /                                bypass\   /bypass \
          /                                        \ /         \
       CE1                                      protector       CE2
          \                                         \          /
           \                                transport\        /
            \                                  tunnel \      /
             \                                         \    /
              - PE3 ------------- P2 -----------------PE4 --

                  |<------------- PW2 --------------->|

                                 Figure 9

   In S-PE node protection, if the protector is not a backup S-PE, it
   forwards the traffic to the backup S-PE, which in turn forwards the
   traffic over the next segment of the backup PW.  Finally, the T-PE of
   the backup PW forwards the traffic to the CE via the backup AC.  This
   is shown in Figure 10, where the protector receives traffic from P1
   (PLR), swaps SEG1's label to SEG3's label, and forwards the traffic
   via a transport tunnel to SPE2 (backup S-PE).  SPE2 in turn performs
   MS-PW switching from SEG3's label to SEG4's label, and forwards the
   traffic over a transport tunnel to TPE4 (backup T-PE).  The protector
   may be protecting other PW segments and other primary S-PEs as well,
   which is not shown in this figure for clarity.






















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                  |<--------------- PW1 --------------->|
                  |<----- SEG1 ----->|<----- SEG2 ----->|

             - TPE1 ----- P1  ----- SPE1 -------------- TPE2 -
            /             PLR \                               \
           /                   \                               \
          /               bypass\                               \
         /                       \                               \
      CE1                     protector                           CE2
         \                        \                              /
          \               transport\                            /
           \                 tunnel \                          /
            \                        \                        /
             - TPE3 --------------- SPE2 -------------- TPE4 -

                  |<----- SEG3 ----->|<----- SEG4 ----->|
                  |<--------------- PW2 --------------->|

                                 Figure 10

   The centralized protector model allows multiple primary PEs to share
   one protector.  Each primary PE may need only one protector.
   Therefore, the number of context identifiers needed by a network may
   be bound to the number of primary PEs.

4.5.  Transport Tunnel

   A PW is associated with a pair of {primary PE, protector}, which is
   represented by a unique context identifier.  The ingress PE of the PW
   sets up or resolves a transport tunnel by using the context
   identifier rather than a private IP address of the primary PE as
   destination.  This not only ensures that the PW is transported to the
   primary PE, but also facilitates bypass tunnel establishment at PLR,
   because the context identifier contains the identity of the protector
   as well.  This is also the case for a multi-segment PW, where the
   ingress PE and egress PE are T/S-PEs.

   An ingress PE learns the association between a PW and a context
   identifier from the primary PE, which MUST advertise the context
   identifier as a "third party next hop" via the IPv4/v6 Interface_ID
   TLV [RFC3471, RFC3472] in the LDP Label Mapping message of the PW.

   In an ECMP scenario, a transport tunnel may have multiple penultimate
   hop routers.  Each of them SHOULD act as a PLR independently.  Also
   in an ECMP scenario, a penultimate hop router may have ECMPs to the
   primary PE.  At least one path of the ECMPs must be a direct link to
   the primary PE, qualifying the router as a penultimate hop.  The
   other paths of the ECMPs may be direct links or indirect paths to the



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   primary PE.  In egress PE node protection and S-PE node protection,
   when a node failure is detected, or a link failure is detected on a
   direct link and treated as a node failure, the penultimate hop router
   SHOULD act as a PLR and reroute the entire traffic of the ECMPs to
   the protector.

4.6.  Bypass Tunnel

   A PLR may protect multiple PWs associated with one or multiple pairs
   of {primary PE, protector}. The PLR MUST establish a bypass tunnel to
   each protector for each context identifier associated with that
   protector.  The destination of the bypass tunnel MUST be the context
   identifier (Section 4.3.1).  Since the PLR is a transit router of the
   transport tunnel, it SHOULD derive the context identifier from the
   destination of the transport tunnel.

   For examples, in Figure 7 and Figure 9, a bypass tunnel is
   established from PE2 (PLR for egress AC failure) to the protector,
   and another bypass tunnel is established from P3 (PLR for egress node
   failure) to the protector.  In Figure 8 and Figure 10, a bypass
   tunnel is established from P1 (PLR for S-PE failure) to the
   protector.

   In local repair, a PLR reroutes traffic to the protector through a
   bypass tunnel, with PW label intact in the packets.  This normally
   involves pushing a label to the label stack, if the bypass tunnel is
   an MPLS tunnel, or pushing an IP header to the packets, if the bypass
   tunnel is an IP tunnel.  Upon receipt of the packets, the protector
   forwards them based on the PW label.  Specifically, the protector
   uses the bypass tunnel as a context to determine the primary PE's
   label space.  If the bypass tunnel is an MPLS tunnel, the protector
   should have assigned a non-reserved label to the bypass tunnel, and
   hence this label can serve as the context.  This label is also called
   a "context label", as it is actually bound to the context identifier.
   If the bypass tunnel is an IP tunnel, the context identifier should
   be the destination address of IP header.

   To be useful for local repair, a bypass tunnel MUST have the property
   that it is not affected by any topology changes caused by the
   failure.  It MUST NOT traverse the primary PE or the penultimate link
   of the transport tunnel, or share any SRLG with the penultimate link.
   A bypass tunnel may be a TE tunnel with reserved bandwidth to avoid
   traffic congestion for rerouted traffic.  A bypass tunnel should
   remain effective during local repair, until the traffic is moved to
   an alternative path, i.e. either the same PW over a fully functional
   transport tunnel, or another fully functional PW.





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   There is little or no benefit to protect a bypass tunnel.  Therefore,
   a bypass tunnel SHOULD NOT be protected against a transit link
   failure, transit node failure, or egress node failure.

4.7.  Examples of Forwarding State

   This section provides some detailed examples of forwarding state on
   PLR, protector, and other relevant routers.

   A protector learns PW labels from all the primary PEs that it
   protects (Section 6.2), and maintains the PW labels in separate label
   spaces on a per primary PE basis.  In the control plane, each label
   space is identified by the context identifier of the corresponding
   {primary PE, protector}.  In the forwarding plane, the label space is
   indicated by the bypass tunnel(s) destined for the context
   identifier.

4.7.1.  Co-located Protector Model

   In Figure 11, PE4 is a co-located protector that protects PW1 against
   egress AC failure and egress node failure.  It maintains a label
   space for PE2, which is identified by the context identifier of {PE2,
   PE4}. It learns PW1's label from PE2, and installs an forwarding
   entry for the label in that label space.  The nexthop of the
   forwarding entry indicates a label pop with outgoing interface
   pointing to the backup AC PE4-CE2.

























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             |<-------------- PW1 --------------->|

         - PE1 -------------- P1 ------- P3 ----- PE2 ------
        /                               PLR \     PLR       \
       /                                     \     |         \
      /                                       \    |          \
   CE1                                 bypass P4   P5 bypass   CE2
      \                                        \   |          /
       \                                        \  |         /
        \                                        \ |        /
         - PE3 -------------- P2 ---------------- PE4 ------
                                               protector

             |<-------------- PW2 --------------->|

            PW1's label assigned by PE2: 100
            PW2's label assigned by PE4: 200
            On P3: </t>
                Incoming label of transport tunnel to PE2: 1000
                Outgoing label of transport tunnel to PE2: implicit null
                Outgoing label of bypass tunnel to PE4: 2000
            On PE2:
                Outgoing label of bypass tunnel to PE4: 3000
            On PE4:
                Context label (incoming label of bypass tunnels): 999

            Forwarding state on P3:
            label 1000 -- primary nexthop: pop, to PE2
                          backup nexthop:  swap 2000, to P4

            Forwarding state on PE2:
            label 100 -- primary nexthop: pop, to CE2
                         backup nexthop:  push 3000, to P5

            Forwarding state on P4:
            label 2000 -- nexthop: swap 999, to PE4

            Forwarding state on P5:
            label 3000 -- nexthop: swap 999, to PE4

            Forwarding state on PE4:
            label 200 -- nexthop: pop, to CE2
            label 999 -- nexthop: label table of PE2's label space

            Label table of PE2's label space on PE4:
            label 100 -- nexthop: pop, to CE2

                                 Figure 11



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   In Figure 12, SPE2 is a co-located protector that protects PW1
   against S-PE failure.  It maintains a label space for SPE1, which is
   identified by the context identifier of {SPE1, SPE2}. It learns
   SEG1's label from SPE1, and installs a forwarding entry in the label
   space.  The nexthop of the forwarding entry indicates a label swap to
   SEG4's label and a label push with the label of a transport tunnel to
   TPE4.












































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            |<--------------- PW1 --------------->|
            |<----- SEG1 ----->|<----- SEG2 ----->|

       - TPE1 ----- P1  ----- SPE1 --- P3 ------- TPE2 -
      /             PLR \                               \
     /                   \                               \
  CE1              bypass P2                              CE2
     \                     \                             /
      \                     \                           /
       - TPE3 --------------- SPE2 --- P4 ------- TPE4 -
                           protector

            |<----- SEG3 ----->|<----- SEG4 ----->|
            |<--------------- PW2 --------------->|

           SEG1's label assigned by SPE1: 100
           SEG2's label assigned by TPE2: 200
           SEG3's label assigned by SPE2: 300
           SEG4's label assigned by TPE4: 400
           On P1:
               Incoming label of transport tunnel to SPE1: 1000
               Outgoing label of transport tunnel to SPE1: implicit null
               Outgoing label of bypass tunnel to SPE2: 2000
           On SPE1:
               Outgoing label of transport tunnel to TPE2: 3000
           On SPE2:
               Outgoing label of transport tunnel to TPE4: 4000
               Context label (incoming label of bypass tunnel): 999

           Forwarding state on P1:
           label 1000 -- primary nexthop: pop, to SPE1
                         backup nexthop:  swap 2000, to P2

           Forwarding state on SPE1:
           label 100 -- nexthop: swap 200, push 3000, to P3

           Forwarding state on P2:
           label 2000 -- nexthop: swap 999, to SPE2

           Forwarding state on SPE2:
           label 300 -- nexthop: swap 400, push 4000, to P4
           label 999 -- nexthop: label table of SPE1's label space

           Label table of SPE1's label space on SPE2:
           label 100 -- nexthop: swap 400, push 4000, to P4

                                 Figure 12




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4.7.2.  Centralized Protector Model

   In the centralized protector model, for each primary PW of which the
   protector is not a backup (S-)PE, the protector MUST also learn the
   label of the backup PW from the backup (S-)PE (Section 6.3).  This is
   the backup (S-)PE that the protector will forward traffic to.  The
   protector MUST install a forwarding entry with a label swap from the
   primary PW's label to the backup PW's label and a label push with the
   label of a transport tunnel to the backup (S-)PE.

   In Figure 13, the protector is a centralized protector that protects
   PW1 against egress AC failure and egress node failure.  It maintains
   a label space for PE2, which is identified by the context identifier
   of {PE2, protector}. It learns PW1's label from PE2, and PW2's label
   from PE4.  It installs a forwarding entry for PW1's label in the
   label space.  The nexthop of the forwarding entry indicates a label
   swap to PW2's label and a label push with the label of a transport
   tunnel to PE4.

               |<-------------- PW1 --------------->|

           - PE1 ------------- P1 ------- P3 ------ PE2 ----
          /                              PLR \      PLR     \
         /                                    \      /       \
        /                              bypass P5    P6 bypass \
       /                                        \  /           \
      /                                          \/             \
   CE1                                      protector            CE2
      \                                           \             /
       \                                transport  \           /
        \                                  tunnel  P7         /
         \                                          \        /
          \                                          \      /
           - PE3 ------------- P2 ----------------- PE4 ----

               |<-------------- PW2 --------------->|

            PW1's label assigned by PE2: 100
            PW2's label assigned by PE4: 200
            On P3:
                Incoming label of transport tunnel to PE2: 1000
                Outgoing label of transport tunnel to PE2: implicit null
                Outgoing label of bypass tunnel to protector: 2000
            On PE2:
                Outgoing label of bypass tunnel to protector: 3000
            On protector:
                Context label (incoming label of bypass tunnels): 999
                Outgoing label of transport tunnel to PE4: 4000



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            Forwarding state on P3:
            label 1000 -- primary nexthop: pop, to PE2
                          backup nexthop:  swap 2000, to P5

            Forwarding state on PE2:
            label 100 -- primary nexthop: pop, to CE2
                         backup nexthop:  push 3000, to P6

            Forwarding state on P5:
            label 2000 -- nexthop: swap 999, to protector

            Forwarding state on P6:
            label 3000 -- nexthop: swap 999, to protector

            Forwarding state on P7:
            label 4000 -- nexthop: pop, to PE4

            Forwarding state on PE4:
            label 200 -- nexthop: pop, to CE2

            Forwarding state on protector:
            label 999 -- nexthop: label table of PE2's label space

            Label table of PE2's label space on protector:
            label 100 -- nexthop: swap 200, push 4000, to P7

                                 Figure 13

   In Figure 14, the protector is a centralized protector that protects
   the PW segment SEG1 of PW1 against the node failure of SPE1.  It
   maintains a label space for SPE1, which is identified by the context
   identifier of {SPE1, protector}. It learns SEG1's label from SPE1,
   and learns SEG3's label from SPE2.  It installs a forwarding entry
   for SEG1's label in the label space.  The nexthop of the forwarding
   entry indicates a label swap to SEG3's label and a label push with
   the label of a transport tunnel to TPE4.

               |<--------------- PW1 --------------->|
               |<----- SEG1 ----->|<----- SEG2 ----->|

          - TPE1 ----- P1 ----- SPE1 --- P2 -------- TPE2 -
         /            PLR \                                \
        /                  \                                \
       /            bypass P4                                \
      /                     \                                 \
     /                       \                                 \
  CE1                     protector                             CE2
     \                        \                                /



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      \                        \                              /
       \             transport P5                            /
        \                tunnel  \                          /
         \                        \                        /
          - TPE3 -------------- SPE2 --- P3 -------- TPE4 -

               |<----- SEG3 ----->|<----- SEG4 ----->|
               |<--------------- PW2 --------------->|

           SEG1's label assigned by SPE1: 100
           SEG2's label assigned by TPE2: 200
           SEG3's label assigned by SPE2: 300
           SEG4's label assigned by TPE4: 400
           On P1:
               Incoming label of transport tunnel to SPE1: 1000
               Outgoing label of transport tunnel to SPE1: implicit null
               Outgoing label of bypass tunnel to protector: 2000
           On SPE1:
               Outgoing label of transport tunnel to TPE2: 3000
           On SPE2:
               Outgoing label of transport tunnel to TPE4: 4000
           On protector:
               Context label (incoming label of bypass tunnel): 999
               Outgoing label of transport tunnel to SPE2: 5000

           Forwarding state on P1:
           label 1000 -- primary nexthop: pop, to SPE1
                         backup nexthop:  swap 2000, to P4

           Forwarding state on SPE1:
           label 100 -- nexthop: swap 200, push 3000, to P2

           Forwarding state on P4:
           label 2000 -- nexthop: swap 999, to protector

           Forwarding state on P5:
           label 5000 -- nexthop: pop, to SPE2

           Forwarding state on SPE2:
           label 300 -- nexthop: swap 400, push 4000, to P3

           Forwarding state on protector:
           label 999 -- nexthop: label table of SPE1's label space

           Label table of SPE1's label space on protector:
           label 100 -- nexthop: swap 300, push 5000, to P5

                                 Figure 14



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5.  Restorative and Revertive Behaviors

   Subsequent to local repair, there are three strategies for a network
   to restore traffic to a fully functional alternative path.

   o  Global repair

      If the ingress CE is multi-homed (Figure 1), it MAY switch the
      traffic to the backup AC which is bound to the backup PW.
      Alternatively, if the ingress PE hosts a backup PW (Figure 2), the
      ingress PE MAY switch the traffic to the backup PW.  These
      procedures are referred to as global repair.  Possible triggers of
      global repair include PW status notification, Virtual Circuit
      Connectivity Verification (VCCV) [RFC5085, RFC5885], BFD, end-to-
      end OAM between CEs, and others.

   o  Control plane convergence

      In egress PE node protection and S-PE node protection, it is
      possible that the failure is limited to the link between the PLR
      and the primary PE, whereas the primary PE is still operational.
      In this case, the PLR or an upstream router on the transport
      tunnel MAY reroute the tunnel around the link via an alternative
      path to the primary PE.  Thus, the transport tunnel can heal and
      continue to carry the PW to the primary PE.  This procedure is
      driven by control plane convergence on the new topology.

   o  Local reversion

      The PLR MAY move traffic back to the primary PW, after the failure
      is resolved.  In egress AC protection, upon detecting that the
      primary AC is restored, the PLR MAY start forwarding traffic over
      the AC again.  Likewise, in egress PE node protection and S-PE
      node protection, upon detecting that the primary PE is restored,
      the PLR MAY re-establish the transport tunnel to the primary PE,
      and move the traffic from the bypass tunnel back to the transport
      tunnel.  These procedures are referred to as local reversion.

   It is RECOMMENDED that the fast protection mechanism SHOULD be used
   in conjunction with global repair.  Particularly in the case of
   egress PE and S-PE node failures, if the ingress PE or the protector
   loses communication with the egress PE or S-PE for an extensive
   period of time, LDP session may go down.  Consequently, the ingress
   PE may bring down the primary PW completely, or the protector may
   remove the forwarding entry of the primary PW label.  In either case,
   the service will be disrupted.  In other words, although the
   mechanism can temporarily repair traffic, control plane state may
   eventually expire if the failure persists.  Therefore, global repair



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   SHOULD take place in a timely manner to move traffic to a fully
   functional alternative path.

   Control plane convergence may automatically happen as control plane
   protocols react to the new topology.  However, it is only applicable
   to the specific link failure scenario described above.

   Local reversion is optional.  In the circumstances where the failure
   is caused by resource flapping, local reversion MAY be dampened to
   limit potential disruption.  Local reversion MAY be disabled
   completely by configuration.

6.  LDP Extensions

   As described in previous sections, a targeted LDP session MUST be
   established between each pair of primary PE and protector.  The
   primary PE sends Label Mapping message over this session to advertise
   primary PW labels to the protector.  In the centralized protector
   model, a targeted LDP session MUST also be established between a
   backup (S-)PE and the protector.  The backup PE sends Label Mapping
   message over this session to advertise backup PW labels to the
   protector.

   To support the procedures, this document defines a new "Protection
   FEC Element" TLV.  The Label Mapping messages of both the LDP
   sessions above MUST carry this TLV to identify a primary PW.
   Specifically, in the centralized protector model, the Protection FEC
   Element TLV advertised by a backup (S-)PE MUST match the one
   advertised by the primary PE, so that the protector can associate the
   primary PW's label with the backup PW's label, and perform a label
   swap.  The backup (S-)PE builds such a Protection FEC Element TLV
   based on local configuration.

   This document also defines a new "Egress Protection Capability" TLV
   as a new type of Capability Parameter TLV [RFC5561], to allow a
   protector to announce its capability of processing the above
   Protection FEC Element TLV and performing context specific label
   switching for PW labels.

   The procedures in this section are only applicable, if the protector
   advertises the Egress Protection Capability TLV, the primary PE
   supports the advertisement of the Protection FEC Element TLV, and in
   the centralized protector model, the backup PE also supports the
   advertisement of the Protection FEC Element TLV.







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6.1.  Egress Protection Capability TLV

   A protector MUST advertise the Egress Protection Capability TLV in
   its Initialization message and Capability message, over the LDP
   session with a primary PE.  In the centralized protector model, the
   protector MUST also advertise the TLV over the LDP session with a
   backup PE.  The TLV carries one or multiple context identifiers.  To
   the primary PE, the TLV MUST carry the context identifier of the
   {primary PE, protector}. In the centralized protector model, the TLV
   MUST carry to the backup PE multiple context identifiers, one for
   each {primary PE, protector} where the backup PE serves as a backup
   for the primary PE.  This TLV MUST NOT be advertised by the primary
   PE or the backup PE to the protector.

   The processing of the Egress Protection Capability TLV by a receiving
   router MUST follow the procedures defined in [RFC5561].  In
   particular, the router MUST advertise PW information to the protector
   by using the Protection FEC Element TLV, only after it has received
   the Egress Protection Capability TLV from the protector.  It MUST
   validate each context identifier included in the TLV, and advertise
   the information of only the PWs that are associated with the context
   identifier.  It MUST withdraw previously advertised Protection FEC
   TLVs, when the protector has withdrawn a previously advertised
   context identifier or the entire Egress Protection Capability TLV via
   Capability message.

   The encoding of the Egress Protection Capability TLV is defined as
   below.  It conforms to the format of Capability Parameter TLV
   specified in [RFC5561].

      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|  Egress Protection (TBD)  |              Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |S| Reserved    |                                               |
     +-+-+-+-+-+-+-+-+                                               |
     |                                                               |
     ~                Capability Data = context identifier(s)        ~
     |                                                               |
     |                                               +-+-+-+-+-+-+-+-+
     |                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 15






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   The U-bit MUST be set to 1 so that a receiver MUST silently ignore
   this TLV if unknown to it, and continue processing the rest of the
   message.

   The F-bit MUST be set to 0 since this TLV is sent only in
   Initialization and Capability messages, which are not forwarded.

   The TLV Code Point is TBD.  It needs to be assigned by IANA.

   The S-bit indicates whether the sender is advertising (S=1) or
   withdrawing (S=0) the capability.

   The "Capability Data" is encoded with the context identifiers of the
   {primary PE, protector} pairs for which the advertiser is the
   protector.

6.2.  PW Label Distribution from Primary PE to Protector

   A primary PE MUST advertise a primary PW's label to a protector by
   sending a Label Mapping message.  The message includes a Protection
   FEC Element TLV (see Section 6.4 for encoding), and an Upstream-
   Assigned Label TLV [RFC6389] encoded with the PW's label.  The
   combination of the Protection FEC Element TLV and the PW label
   represents the primary PE's forwarding state for the PW.  The Label
   Mapping message MUST also carry an IPv4/v6 Interface_ID TLV [RFC6389,
   RFC3471] encoded with the context identifier of the {primary PE,
   protector}.

   The protector that receives this Label Mapping message MUST install a
   forwarding entry for the PW label in the label space identified by
   the context identifier.  The nexthop of the forwarding entry MUST
   ensure packets to be sent towards the target CE via a backup AC or a
   backup (S-)PE, depending on the protection scenario.  The protector
   MUST silently discard a Label Mapping message if the included context
   identifier is unknown to it.

6.3.  PW Label Distribution from Backup PE to Protector

   In the centralized protector model, a backup PE MUST advertise a
   backup PW's label to the protector by sending a Label Mapping
   message.  The message includes a Protection FEC Element TLV and a
   Generic Label TLV encoded with the backup PW's label.  This
   Protection FEC Element MUST be identical to the Protection FEC
   Element TLV that the primary PE advertises to the protector
   (Section 6.2).  This is achieved through configuration on the backup
   PE.  The context identifier MUST NOT be encoded in Interface_ID TLV
   in this message.




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   The protector that receives this Label Mapping message MUST associate
   the backup PW with the primary PW, based on the common Protection FEC
   Element TLV.  It MUST distinguish between the Label Mapping message
   from the primary PE and the Label Mapping message from the backup PE
   based on the respective presence and absence of context identifier in
   Interface_ID TLV.  It MUST install a forwarding entry for the primary
   PW's label in the label space identified by the context identifier.
   The nexthop of the forwarding entry MUST indicate a label swap to the
   backup PW's label, followed by a label push or IP header push for a
   transport tunnel to the backup PE.

6.4.  Protection FEC Element TLV

   The Protection FEC Element TLV has type 0x83.  Its format is defined
   as below:

      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(0x83)  |    Reserved   | Encoding Type |    Length     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                                                               |
     ~                         PW Information                        ~
     |                                                               |
     |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 16

   - Encoding Type

      Type of encoding format of PW Information field.  The following
      types are defined, corresponding to the PWid FEC Element and
      Generalized PWid FEC Element defined in [RFC4447].



         1 - PWid FEC Element with IPv4 PE addresses (section 6.4.1)

         2 - Generalized PWid FEC Element with IPv4 PE addresses
         (section 6.4.2)

         3 - PWid FEC Element with IPv6 PE addresses (section 6.4.3)

         4 - Generalized PWid FEC Element with IPv6 PE addresses
         (section 6.4.4)



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   - Length

      Length of PW Information field in octets.

   - PW Information

      Field of variable length that specifies a PW.

6.4.1.  Encoding Format for PWid with IPv4 PE Addresses

      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(0x83)  |    Reserved   |  Enc Type(1)  |   Length(20)  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Ingress PE IPv4 Address                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Egress PE IPv4 Address                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Group ID                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             PW ID                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |C|           PW Type           |           Reserved            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 17

   - Ingress PE IPv4 Address

      IPv4 address of the ingress PE of PW.

   - Egress PE IPv4 Address

      IPv4 address of the egress PE of PW.

   - Group ID

      An arbitrary 32-bit value that represents a group of PWs and that
      is used to create groups in the PW space.

   - PW ID

      A non-zero 32-bit connection ID that, together with the PW Type
      field, identifies a particular PW.

   - Control word bit (C)




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      A bit that flags the presence of a control word on this PW.  If C
      = 1, control word is present; If C = 0, control word is not
      present.

   - PW Type

      A 15-bit quantity that represents the type of PW.

6.4.2.  Encoding Format for Generalized PWid with IPv4 PE Addresses

      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(0x83)  |    Reserved   |  Enc Type(2)  |   Length      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Ingress PE IPv4 Address                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Egress PE IPv4 Address                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |C|           PW Type           |           Reserved            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   AGI Type    |    Length     |             Value             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                    AGI  Value (contd.)                        ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   AII Type    |    Length     |             Value             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                   SAII  Value (contd.)                        ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   AII Type    |    Length     |             Value             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                   TAII Value (contd.)                         ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 18

   - Ingress PE IPv4 Address

      IPv4 address of the ingress PE of PW.

   - Egress PE IPv4 Address

      IPv4 address of the egress PE of PW.

   - Control word bit (C)



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      A bit that flags the presence of a control word on this PW.  If C
      = 1, control word is present; If C = 0, control word is not
      present.

   - PW Type

      A 15-bit quantity that represents the type of PW.

   - AGI Type, Length, Value, AGI Value

      Attachment Group Identifier of PW.

   - SAII Type, Length, Value, SAII Value

      Source Attachment Individual Identifier of PW.

   - TAII Type, Length, Value, TAII Value

      Target Attachment Individual Identifier of PW.

6.4.3.  Encoding Format for PWid with IPv6 PE Addresses

      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(0x83)  |    Reserved   |  Enc Type(3)  |   Length(44)  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                     Ingress PE IPv6 Address                   ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                      Egress PE IPv6 Address                   ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Group ID                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             PW ID                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |C|           PW Type           |           Reserved            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 19

   - Ingress PE IPv6 Address

      IPv6 address of the ingress PE of PW. 16 octets.

   - Egress PE IPv6 Address

      IPv6 address of the egress PE of PW. 16 octets.




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   - Group ID

      An arbitrary 32-bit value that represents a group of PWs and that
      is used to create groups in the PW space.

   - PW ID

      A non-zero 32-bit connection ID that, together with the PW Type
      field, identifies a particular PW.

   - Control word bit (C)

      A bit that flags the presence of a control word on this PW.  If C
      = 1, control word is present; If C = 0, control word is not
      present.

   - PW Type

      A 15-bit quantity that represents the type of PW.

6.4.4.  Encoding Format for Generalized PWid with IPv6 PE Addresses






























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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Type(0x83)  |    Reserved   |  Enc Type(4)  |   Length      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                     Ingress PE IPv6 Address                   ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                      Egress PE IPv6 Address                   ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |C|           PW Type           |           Reserved            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   AGI Type    |    Length     |             Value             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                    AGI  Value (contd.)                        ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   AII Type    |    Length     |             Value             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                   SAII  Value (contd.)                        ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   AII Type    |    Length     |             Value             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                   TAII Value (contd.)                         ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 20

   - Ingress PE IPv6 Address

      IPv6 address of the ingress PE of PW. 16 octets.

   - Egress PE IPv6 Address

      IPv6 address of the egress PE of PW. 16 octets.

   - Control word bit (C)

      A bit that flags the presence of a control word on this PW.  If C
      = 1, control word is present; If C = 0, control word is not
      present.

   - PW Type

      A 15-bit quantity that represents the type of PW.

   - AGI Type, Length, Value, AGI Value



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      Attachment Group Identifier of PW.

   - SAII Type, Length, Value, SAII Value

      Source Attachment Individual Identifier of PW.

   - TAII Type, Length, Value, TAII Value

      Target Attachment Individual Identifier of PW.

7.  IANA Considerations

   This document defines a new "Egress Protection Capability" TLV in
   Section 6.  The document requests IANA to assign an LDP TLV code
   point for the TLV.

   This document defines a new Protection FEC Element TLV, and uses the
   LDP Protection FEC Type Name Space value 0x83 for it.  The LDP
   Protection FEC Type Name Space for this value needs to reference this
   document, and it is requested to update this reference to the RFC
   number for this document.

   Value  Hex   Name                    Label Advertisement Discipline
   -------------------------------------------------------------------
   131    0x83  Protection FEC Element  DU

8.  Security Considerations

   In this document, PW traffic can be temporarily rerouted by a PLR to
   a protector.  In the centralized protector scenario, the traffic can
   be further rerouted to a backup PE.  In the control plane, there is a
   targeted LDP session between a primary PE and a protector.  In the
   centralized protector scenario, there is also a targeted LDP session
   between a backup PE and a protector.  In all scenarios, traffic
   rerouting via PLRs, protectors and backup PEs is planned and
   anticipated, and backup PEs can be used anyway to host PWs and LDP
   sessions.  Hence, the rerouted traffic and the LDP sessions
   introduced in this document should not be viewed as a new security
   threat.

   In general, [RFC5920] describes the security framework for MPLS
   networks.  [RFC3209] describes the security considerations for RSVP
   LSPs.  [RFC5036] describes the security considerations for the base
   LDP specification.  [RFC5561] describes the security considerations
   which apply when using the LDP capability mechanism.  All these
   security framework and considerations apply to this document as well.





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9.  Acknowledgements

   This document leverages work done by Hannes Gredler, Yakov Rekhter,
   Minto Jeyananth, Kevin Wang and several on MPLS edge protection.
   Thanks to Nischal Sheth and Bhupesh Kothari for their contribution.
   Thanks to John E Drake, Andrew G Malis, Alexander Vainshtein, Stewart
   Bryant, and Mach Chen for valuable comments that helped shape this
   document and improve its clarity.

10.  References

10.1.  Normative References

   [RFC4447]  Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and
              G. Heron, "Pseudowire Setup and Maintenance Using the
              Label Distribution Protocol (LDP)", RFC 4447,
              DOI 10.17487/RFC4447, April 2006,
              <http://www.rfc-editor.org/info/rfc4447>.

   [RFC5331]  Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
              Label Assignment and Context-Specific Label Space",
              RFC 5331, DOI 10.17487/RFC5331, August 2008,
              <http://www.rfc-editor.org/info/rfc5331>.

   [RFC5561]  Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.
              Le Roux, "LDP Capabilities", RFC 5561,
              DOI 10.17487/RFC5561, July 2009,
              <http://www.rfc-editor.org/info/rfc5561>.

   [RFC3471]  Berger, L., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Signaling Functional Description",
              RFC 3471, DOI 10.17487/RFC3471, January 2003,
              <http://www.rfc-editor.org/info/rfc3471>.

   [RFC3472]  Ashwood-Smith, P., Ed. and L. Berger, Ed., "Generalized
              Multi-Protocol Label Switching (GMPLS) Signaling
              Constraint-based Routed Label Distribution Protocol (CR-
              LDP) Extensions", RFC 3472, DOI 10.17487/RFC3472, January
              2003, <http://www.rfc-editor.org/info/rfc3472>.

   [RFC6389]  Aggarwal, R. and JL. Le Roux, "MPLS Upstream Label
              Assignment for LDP", RFC 6389, DOI 10.17487/RFC6389,
              November 2011, <http://www.rfc-editor.org/info/rfc6389>.

   [RFC4090]  Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
              Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
              DOI 10.17487/RFC4090, May 2005,
              <http://www.rfc-editor.org/info/rfc4090>.



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   [RFC5286]  Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
              IP Fast Reroute: Loop-Free Alternates", RFC 5286,
              DOI 10.17487/RFC5286, September 2008,
              <http://www.rfc-editor.org/info/rfc5286>.

   [RFC7812]  Atlas, A., Bowers, C., and G. Enyedi, "An Architecture for
              IP/LDP Fast Reroute Using Maximally Redundant Trees (MRT-
              FRR)", RFC 7812, DOI 10.17487/RFC7812, June 2016,
              <http://www.rfc-editor.org/info/rfc7812>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <http://www.rfc-editor.org/info/rfc3031>.

10.2.  Informative References

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
              <http://www.rfc-editor.org/info/rfc5920>.

   [RFC3985]  Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
              Edge-to-Edge (PWE3) Architecture", RFC 3985,
              DOI 10.17487/RFC3985, March 2005,
              <http://www.rfc-editor.org/info/rfc3985>.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <http://www.rfc-editor.org/info/rfc3209>.

   [RFC5036]  Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
              "LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
              October 2007, <http://www.rfc-editor.org/info/rfc5036>.

   [RFC5659]  Bocci, M. and S. Bryant, "An Architecture for Multi-
              Segment Pseudowire Emulation Edge-to-Edge", RFC 5659,
              DOI 10.17487/RFC5659, October 2009,
              <http://www.rfc-editor.org/info/rfc5659>.

   [RFC5714]  Shand, M. and S. Bryant, "IP Fast Reroute Framework",
              RFC 5714, DOI 10.17487/RFC5714, January 2010,
              <http://www.rfc-editor.org/info/rfc5714>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <http://www.rfc-editor.org/info/rfc5880>.




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Internet-Draft     PW Endpoint Fast Failure Protection      January 2017


   [RFC5085]  Nadeau, T., Ed. and C. Pignataro, Ed., "Pseudowire Virtual
              Circuit Connectivity Verification (VCCV): A Control
              Channel for Pseudowires", RFC 5085, DOI 10.17487/RFC5085,
              December 2007, <http://www.rfc-editor.org/info/rfc5085>.

   [RFC5885]  Nadeau, T., Ed. and C. Pignataro, Ed., "Bidirectional
              Forwarding Detection (BFD) for the Pseudowire Virtual
              Circuit Connectivity Verification (VCCV)", RFC 5885,
              DOI 10.17487/RFC5885, June 2010,
              <http://www.rfc-editor.org/info/rfc5885>.

   [RFC7880]  Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
              Pallagatti, "Seamless Bidirectional Forwarding Detection
              (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
              <http://www.rfc-editor.org/info/rfc7880>.

Authors' Addresses

   Yimin Shen
   Juniper Networks
   10 Technology Park Drive
   Westford, MA  01886
   USA

   Phone: +1 9785890722
   Email: yshen@juniper.net


   Rahul Aggarwal
   Arktan, Inc

   Email: raggarwa_1@yahoo.com


   Wim Henderickx
   Nokia
   Copernicuslaan 50
   2018 Antwerp
   Belgium

   Email: wim.henderickx@nokia.com


   Yuanlong Jiang
   Huawei Technologies

   Email: jiangyuanlong@huawei.com




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