Internet Engineering Task Force                               Yimin Shen
Internet-Draft                                          Juniper Networks
Intended status: Standards Track                          Rahul Aggarwal
Expires: May 13, 2016                                        Arktan, Inc
                                                          Wim Henderickx
                                                          Alcatel-Lucent
                                                          Yuanlong Jiang
                                                     Huawei Technologies
                                                       November 10, 2015


                  PW Endpoint Fast Failure Protection
              draft-ietf-pals-endpoint-fast-protection-01

Abstract

   This document specifies a fast mechanism for protecting pseudowires
   against egress endpoint failures, including egress attachment circuit
   failure, egress PE failure, multi-segment PW terminating PE failure,
   and multi-segment PW switching PE failure.  Designed on the basis of
   multi-homed CE, 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 PW traffic in the order of tens of milliseconds, by
   transmitting the traffic 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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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 13, 2016.






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Copyright Notice

   Copyright (c) 2015 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
   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
   2.  Specification of Requirements . . . . . . . . . . . . . . . .   4
   3.  Reference Models for Egress Endpoint Failures . . . . . . . .   4
     3.1.  Single-Segment PW . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Multi-Segment PW  . . . . . . . . . . . . . . . . . . . .   7
   4.  Theory of Operation . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Applicability . . . . . . . . . . . . . . . . . . . . . .   9
     4.2.  Local Repair and Protector  . . . . . . . . . . . . . . .   9
     4.3.  Context Identifier  . . . . . . . . . . . . . . . . . . .  12
       4.3.1.  Semantics . . . . . . . . . . . . . . . . . . . . . .  12
       4.3.2.  Advertisement and Path Computation  . . . . . . . . .  13
     4.4.  Protection Models . . . . . . . . . . . . . . . . . . . .  13
       4.4.1.  Co-located Protector  . . . . . . . . . . . . . . . .  14
       4.4.2.  Centralized Protector . . . . . . . . . . . . . . . .  15
     4.5.  Transport Tunnel  . . . . . . . . . . . . . . . . . . . .  17
     4.6.  Bypass Tunnel . . . . . . . . . . . . . . . . . . . . . .  18
     4.7.  Forwarding State on Protector . . . . . . . . . . . . . .  18
       4.7.1.  Examples of Co-located Protector  . . . . . . . . . .  19
       4.7.2.  Examples of Centralized Protector . . . . . . . . . .  19
   5.  Revertive Behavior  . . . . . . . . . . . . . . . . . . . . .  19
   6.  LDP Extensions  . . . . . . . . . . . . . . . . . . . . . . .  21
     6.1.  Egress Protection Capability TLV  . . . . . . . . . . . .  21
     6.2.  PW Label Distribution from Primary PE to Protector  . . .  23
     6.3.  PW Label Distribution from Backup PE to Protector . . . .  23
     6.4.  Protection FEC Element TLV  . . . . . . . . . . . . . . .  24
       6.4.1.  Encoding Format for PWid  . . . . . . . . . . . . . .  24
       6.4.2.  Encoding Format for Generalized PWid  . . . . . . . .  26
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  27
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  27
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  27
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  27



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     10.1.  Normative References . . . . . . . . . . . . . . . . . .  27
     10.2.  Informative References . . . . . . . . . . . . . . . . .  29
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   Per RFC 3985, RFC 4447 and RFC 5659, 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 layer-2 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.  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 router 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 achievable by using a multi-homed CE and redundant
   ACs, such as multi-chassis link aggregation group (MC-LAG).  Fast
   protection against failure of intermediate router of transport tunnel
   can be achievable through RSVP fast-reroute (RFC 4090) or IP/LDP
   fast-reroute (RFC 5714, RFC 5286).  However, there is a lack of
   equivalent mechanism against egress AC failure, egress (T-)PE
   failure, and S-PE failure.  For these failures, service restoration
   has to rely on global repair or control plane repair.  Global repair
   normally involves ingress CE or ingress (T-)PE switching traffic to
   another fully functional path, based on remote failure detection via
   PW status notification, end-to-end OAM, etc.  Control plane repair
   relies on control protocols to converge 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.




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   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 egress 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 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 (RFC 5331).  Fast protection refers to its ability to
   restore traffic in the order of tens of milliseconds.  Compared with
   global repair and control plane repair, this mechanism can provide
   faster service restoration.  However, it is intended to complement
   those mechanisms, rather than replacing them in any fashion.

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 RFC 2119.

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

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

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

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

                                 Figure 1




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   In Figure 1, the IP/MPLS network consists of PE and P routers.  It
   provides an emulation of a layer-2 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 established between
   PE1 and PE2, and the second path uses PW2 established 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 realizes 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 reverse direction.  In this document, even if both CEs choose
      the same active path, each CE should still anticipate to receive
      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.

   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 are primary, while those along the
   other path are backup.  Note that in the active-active mode, the
   backup path is an active path by itself, carrying its own share of
   traffic while protecting the other active path.

   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



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      Primary egress AC: CE2-PE2

      Backup ingress AC: CE1-PE3

      Backup ingress PE: PE3

      Backup PW: PW2

      Backup egress PE: PE4

      Backup egress AC: CE2-PE4

   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 CE2-PE2, 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
   (CE2-PE4).

   Subsequent to the local repair, either the 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 path,
   depending on the failure scenario.  In the later case, the ingress CE
   may perform such switchover based on end-to-end OAM (in-band or out-
   band), PW status notification, CE-PE control protocols (e.g.  LACP),
   etc.  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.  In any case, this phase of
   restoration falls into the control plane repair 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 an egress endpoint failure of the traffic of a given
   direction may be detected by the egress CE as an ingress endpoint
   failure for the traffic of reverse direction, except when the failure
   is on a link of the primary egress PE in the IP/MPLS network, or when
   the traffic of reverse direction takes a different active path.  If
   the CE can detect the failure, it may protect the traffic of reverse
   direction by switching it to the backup path.  However, this is
   categorized as ingress endpoint failure protection, and should be
   handled by other mechanisms.

   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



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   CE1 to CE2 over PW1, this scenario is not much different than
   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.

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.




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   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: CE2-TPE2

      Backup ingress AC: CE1-TPE3

      Backup ingress T-PE: TPE3

      Backup PW: PW2

      Backup S-PE: SPE2

      Backup egress T-PE: TPE4

      Backup egress AC: CE2-TPE4

   In this case, an egress AC failure refers to the failure of the AC
   CE2-TPE2.  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




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4.1.  Applicability

   The mechanism is applicable to LDP signaled PWs.  It is applicable to
   an environment where an egress CE is multi-homed to a primary PE and
   a backup PE and there exists a backup PW in the network.  In S-PE
   node protection, it also assumes a backup S-PE on the backup PW.

   The mechanism assumes IP/MPLS transport tunnels for PWs.  If
   transport tunnels are LDP and there is a possibility of EMCP to a
   primary PE, it is recommended to enable control word for PWs.
   Imagine a scenario where an LDP tunnel traverse a router with ECMP to
   the primary PE, and the ECMP includes a direct link to the primary
   PE.  If a PW does not have control word, its traffic may be forwarded
   in a load balance fashion over multiple branches of the ECMP,
   including this link.  When the link fails, the router will treat it
   as an egress PE failure and reroute the portion of traffic traversing
   the link.  Meanwhile, the rest of traffic will remain on the other
   ECMP branches to the primary PE.  This will create a situation where
   the egress CE will receive traffic from both primary PE and backup
   PE, which may not be desirable for a service sensitive to packet
   misordering.

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

4.2.  Local Repair and Protector

   The mechanism relies on local repair to be 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 Failure Detection (BFD) (RFC 5880), etc.  In
   anticipation of the failure, the PLR MUST also pre-establish a bypass
   PSN tunnel to a "protector", and pre-install a bypass route in the
   data plane.  The bypass tunnel MUST have the property that it will
   not be affected by the topology changes in the event of the failure.
   Upon detecting the failure, the PLR MUST invoke the bypass route in
   the data plane, and reroute PW traffic to the protector through the
   bypass tunnel.  The protector MUST in turn send 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.





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

                  |<-------------- 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 ----- P4  ----- SPE1 -------------- TPE2 -
            /             PLR \                               \
           /                   \                               \
        CE1               bypass\                               CE2
           \                     \                             /
            \                     \                           /
             - TPE3 --------------- SPE2 -------------- TPE4 -
                                 protector

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

                                 Figure 6

   A PLR can realize its role based on configuration or the signaling of
   transport tunnel.  For example, in the case where the transport
   tunnel is signaled by RSVP, the penultimate hop router can realize
   that it is the PLR for egress (T-)PE or S-PE failure based on the RRO
   in Resv message, which should indicate that the router is one hop
   away from the PE.  The detail of how this could be achieved on a per-
   protocol basis is out of the scope of this document.

   In all scenarios, when a PLR reroutes traffic through a bypass tunnel
   to a protector during local repair, it MUST keep the label of the
   primary PW intact in the packets.  This obviates the need for the PLR
   to maintain bypass routes on a per-PW basis, and allows a bypass
   tunnel to be shared by multiple PWs.

   The procedure also requires that the protector SHOULD be able to
   forward the traffic based on a PW label that is assigned by the
   primary PE, and ensure the traffic to eventually reach the target CE.
   From the protector's perspective, this PW label is an upstream
   assigned label (RFC 5331).  To accomplish this, the protector SHOULD
   learning 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 SHOULD perform PW label lookup in this label space.

   The previous examples have shown the scenarios where the protectors
   are backup (T/S-)PEs.  In other scenarios, a protector may be a
   dedicated router that assumes such role, separate from the backup (T/
   S-)PE.  During local repair, the PLR MUST still reroute traffic to
   the protector through a bypass tunnel.  The protector MUST in turn
   send the traffic to the backup (T/S-)PE, which MUST then send the




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   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
   primary PW SHOULD be associated with one and only one pair of
   {primary PE, protector}.

   An IPv4/v6 address is assigned to each ordered pair of {primary PE,
   protector} to facilitate protection establishment.  This address is
   referred to as a "context identifier".  It 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  It identifies a primary PE and an associated protector.  In other
      words, it identifies a primary PE on a per protector basis.  A
      given primary PE may be protected by multiple protectors, each for
      a subset of the primary PWs terminated on the primary PE.  A
      distinct context identifier MUST be assigned to the primary PE and
      each protector.

      For each primary PW, its ingress PE MUST set up or resolve a
      transport tunnel with destination as the context identifier of the
      {primary PE, protector}, rather than a private IP address of the
      primary PE.  This not only allows the transport tunnel to reach
      the primary PE, but also conveys the identity of the protector to
      the PLR(s) along the transport tunnel.  Each PLR can in turn use
      this information to set up a bypass tunnel to the protector
      without relying on local configuration.

   o  It indentifies 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 MUST associate a PW
      label with a label space via the context identifier of the
      {primary PE, protector}, as described 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 (See



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      Section 6 for detail).  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 resolve a bypass tunnel to the protector, it
      MUST set the destination to the context identifier, rather than a
      private IP address of the protector.  Once established, the bypass
      tunnel, with either its MPLS label or IP tunnel destination
      address, will serve as the identifier of label space.  On the
      protector, all PW packets received on the bypass tunnel MUST be
      forwarded based on a label lookup in that label space.

4.3.2.  Advertisement and Path Computation

   Using a context identifier as destination for both transport tunnel
   and bypass tunnel requires both the primary PE and the protector to
   advertise the context identifier via IGP as an IP address reachable
   through both routers in routing domain and/or TE domain.  This
   imposes the following requirements on path computation for these
   tunnels.

   o  For the transport tunnel, the ingress PE MUST choose the primary
      PE as the endpoint.

   o  For the bypass tunnel, the PLR MUST choose the protector as the
      endpoint.  In egress (T-)PE node protection and S-PE node
      protection, the bypass tunnel MUST avoid the primary (S-)PE.

   The detail of how the primary PE and the protector may advertise a
   context identifier is independent of this mechanism and out of the
   scope of this document.  One approach would be to advertise it as a
   virtual proxy node connected to both routers, with the link between
   the proxy node and the primary PE having a more preferable IGP or TE
   metric than the link between the proxy node and the protector.  The
   ultimate goal is for a path computation algorithm, such as CSPF
   (constrained shortest path first), LFA (RFC 5286) and MRT ([IP-LDP-
   FRR-MRT]), to be able to compute the paths that meet the above
   requirements.

4.4.  Protection Models

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







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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
   (the 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 MUST forward the traffic over the next segment of the backup
   PW.  The T-PE of the backup PW MUST in turn forward the traffic to
   the CE via a backup AC.  This is shown in Figure 8, where P4 is the
   PLR for SPE1 failure, and SPE2 (the backup S-PE) is the protector for
   SPE1.
















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

             - TPE1 ----- P4  ----- 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 backup PEs for any given primary PE
   is relatively small.

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 with a direct
   connection 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, when the
   protector receives traffic from the PLR, if the protector has a
   direct connection (i.e. backup AC) to the CE, it MUST forward the
   traffic to the CE via the backup AC, which is similar to Figure 7.
   Otherwise, it MUST forward the traffic to a backup PE, which MUST
   then forward the traffic to the CE via a backup AC.  This is shown in
   Figure 9, where the protector receives traffic from P3 (the PLR for
   egress PE failure) or PE2 (the PLR for egress AC failure) and
   forwards the traffic to PE4 (the 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
          \                                         \          /
           \                                         \        /
            \                                         \      /
             \                                         \    /
              - PE3 ------------- P2 -----------------PE4 --

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

                                 Figure 9

   In S-PE node protection, when the protector receives traffic from the
   PLR, if the protector is a backup S-PE of the backup PW, it MUST
   forward the traffic over the next segment of the backup PW, and the
   T-PE of the backup PW MUST forward the traffic to the CE via a backup
   AC, which is similar to Figure 8.  Otherwise, the protector MUST
   first forward the traffic to the backup S-PE, which MUST then forward
   the traffic over the next segment of the backup PW.  Finally, the
   T-PE of the backup PW MUST forward the traffic to the CE via a backup
   AC.  This is shown in Figure 10, where the protector forwards traffic
   to SPE2 (the backup S-PE), SPE2 forwards the traffic to TPE4 via
   SEG4, and TPE4 finally forwards traffic to CE2.  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 ----- P4  ----- SPE1 -------------- TPE2 -
            /             PLR \                               \
           /                   \                               \
          /               bypass\                               \
         /                       \                               \
      CE1                     protector                           CE2
         \                        \                              /
          \                        \                            /
           \                        \                          /
            \                        \                        /
             - TPE3 --------------- SPE2 -------------- TPE4 -

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

                                 Figure 10

   The centralized protector model allows multiple primary PEs to share
   one protector.  Each primary PE MAY only need the one protector to
   protect all of its PWs.  The number of context identifiers needed by
   a network is bound to the number of primary PEs.

4.5.  Transport Tunnel

   The ingress PE of a primary PW associates the PW with the primary
   egress PE through LDP signaling.  In addition, as mentioned in
   Section 4.3.1, the ingress PE MUST associate the transport tunnel of
   the PW with the context identifier of the {primary PE, protector},
   and set up or resolve the transport tunnel by using the context
   identifier as destination.  This not only ensures that PW traffic be
   transported to the primary PE, but also facilitates bypass tunnel
   establishment at PLR(s), as the context identifier implies 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.

   The association between the transport tunnel and the context
   identifier on the ingress PE MAY be achieved by configuration or an
   auto-discovery mechanism.  In the later case, the ingress PE MAY
   learn the context identifier from the primary (egress) PE, if the
   primary PE advertises the context identifier as "third party next
   hop" in IPv4/v6 Interface_ID TLV (RFC 3471, RFC 3472) in the LDP
   Label Mapping message of the primary PW.






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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 distinct context identifier associated with
   that protector.  The destination of the bypass tunnel MUST be the
   context identifier (Section 4.3.1).  The PLR may derive the context
   identifier from the destination of the transport tunnel that
   traverses it.

   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 P4 (PLR for S-PE failure) to the
   protector.

   During local repair, the 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 traffic, the
   protector MUST in turn forward the traffic based on the PW label.  In
   particular, the protector MUST rely on the bypass tunnel as a context
   to determine the primary PE's label space.  If the bypass tunnel is
   an MPLS tunnel, the protector MUST have assigned a non-reserved label
   to the bypass tunnel during the establishment of the bypass tunnel,
   and hence this label can serve as the context.  If the bypass tunnel
   is an IP tunnel, the protector can simply rely on the context
   identifier carried as the destination address in IP header.

   A bypass tunnel MUST have the property that it is not affected by the
   topology changes caused by the failure.  Therefore, it can be used to
   transmit traffic for local repair.  It SHOULD remain effective, until
   the traffic is moved to another fully functional path.

4.7.  Forwarding State on Protector

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







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4.7.1.  Examples of Co-located Protector

   In Figure 7, 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 CE2-PE4.

   e In Figure 8, 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.

4.7.2.  Examples of Centralized Protector

   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 label swap from the
   primary PW's label to the backup PW's label.

   In Figure 9, 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.

   In Figure 10, 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.

5.  Revertive Behavior

   Subsequent to the local repair performed by the mechanism, there are
   three strategies for a network to restore traffic to a fully
   functional path.




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   o  Global revertive mode

      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
      a global repair include PW status notification, end-to-end OAM,
      and BFD.

   o  Control plane revertive mode

      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 (S-)PE, whereas the primary (S-)PE is still
      operational.  In this case, the PLR or an upstream router along
      the transport tunnel MAY reroute the tunnel around the link via an
      alternative path.  Thus, the transport tunnel can heal and
      continue to carry the traffic of the primary PW to the primary
      (S-)PE.  This procedure is driven by control plane convergence on
      the new topology, and is referred to as control plane repair.

   o  Local revertive mode

      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 primary 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.

   The fast protection mechanism in this document SHOULD be used in
   conjunction with the global revertive mode.  Particularly in the case
   of egress (S-)PE failure, if the ingress PE or the protector loses
   communication with the (S-)PE for an extensive period of time, their
   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 fast protection can
   temporarily repair traffic, control plane state may eventually expire
   if the failure persists.  Therefore, it is recommended that the
   global revertive mode SHOULD be set up in advance, so that traffic
   can be moved to a fully functional backup path afterwards.





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   The control plane revertive mode may automatically happen as part of
   the convergence of control plane protocols.  However, it is only
   applicable to the specific scenarios described above.

   The local revertive mode is optional.  In the circumstances where the
   failure is caused by resource flapping, local reversion MAY be
   dampened to limit potential disruption.  Local revertive mode 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 a protector.  The backup PE sends Label Mapping
   message over this session to advertise backup PW labels to the
   protector.

   To facilitate 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 indicate the identity of 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.

   This document also defines the encoding of Capability Parameter TLV
   (RFC 5561) for a new "Egress Protection Capability", 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, 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.

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



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   the primary PE, the TLV SHOULD carry the context identifier of the
   {primary PE, protector}. In the centralized protector model, the TLV
   SHOULD 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 SHOULD 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 SHOULD follow the procedures defined in RFC 5561.  In
   particular, the router SHOULD 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
   SHOULD validate each context identifier included in the TLV, and
   advertise the information of only those PWs that are associated with
   the context identifier.  It SHOULD 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 RFC 5561.

      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 11

   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.




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   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 identifier of the
   {primary PE, protector}.

6.2.  PW Label Distribution from Primary PE to Protector

   A primary PE SHOULD 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 (RFC 6389) 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 SHOULD also carry an IPv4/v6 Interface_ID TLV (RFC
   6389, RFC 3471) encoded with the context identifier of the {primary
   PE, protector}.

   The protector that receives this Label Mapping message SHOULD install
   a forwarding entry for the PW label in the label space identified by
   the context identifier.  The nexthop of the forwarding entry SHOULD
   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
   SHOULD 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 SHOULD advertise a
   backup PW's label to a 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).  The context identifier
   SHOULD NOT be encoded in Interface_ID TLV in this message.

   The protector that receives this Label Mapping message SHOULD
   associate the backup PW with the primary PW, based on the common
   Protection FEC Element TLV.  It SHOULD 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 SHOULD 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 SHOULD 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.




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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 12

   - Encoding Type

      Type of format that PW Information field is encoded.

   - Length

      Length of PW Information field in octets.

   - PW Information

      Field of variable length that specifies a PW

   For Encoding Type, 1 is defined for the PWid FEC Element format, and
   2 is defined for the Generalized PWid FEC Element format (RFC 4447).

6.4.1.  Encoding Format for PWid















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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(1)  |   Length(16)  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Ingress PE Address                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Egress PE Address                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Group ID                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             PW ID                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |C|           PW Type           |           Reserved            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 13

   - Ingress PE Address

      IP address of the ingress PE of PW.

   - Egress PE Address

      IP 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)

      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.






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6.4.2.  Encoding Format for Generalized PWid

      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 Address                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Egress PE 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 14

   - Ingress PE Address

      IP address of the ingress PE of PW.

   - Egress PE Address

      IP address of the egress PE of 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.



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   - 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.

7.  IANA Considerations

   This document defines the encoding of the Capability Parameter TLV
   for the new "Egress Protection Capability" in Section 6.  This would
   require IANA to assign a TLV Code Point to it.

   This document defines a new LDP Protection FEC Element TLV in
   Section 6.  IANA has assigned the type value 0x83 to it.

8.  Security Considerations

   The security considerations discussed in RFC 5036, RFC 5331, RFC
   3209, and RFC 4090 apply to this document.

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, and
   Steward Bryant for valuable comments that helped shape this document
   and improve its clarity.

10.  References

10.1.  Normative References

   [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>.

   [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>.



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   [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>.

   [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>.

   [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>.

   [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
              September 1997, <http://www.rfc-editor.org/info/rfc2205>.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.



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   [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>.

   [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>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <http://www.rfc-editor.org/info/rfc2328>.

   [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>.

   [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>.

   [IP-LDP-FRR-MRT]
              Atlas, A. and R. Kebler, "An Architecture for IP/LDP Fast-
              Reroute Using Maximally Redundant Trees", draft-ietf-
              rtgwg-mrt-frr-architecture (work in progress), 2011.

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>.

Authors' Addresses

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

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







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Internet-Draft     PW Endpoint Fast Failure Protection     November 2015


   Rahul Aggarwal
   Arktan, Inc

   Email: raggarwa_1@yahoo.com


   Wim Henderickx
   Alcatel-Lucent
   Copernicuslaan 50
   2018 Antwerp
   Belgium

   Email: wim.henderickx@alcatel-lucent.be


   Yuanlong Jiang
   Huawei Technologies

   Email: jiangyuanlong@huawei.com
































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