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Versions: (draft-muley-pwe3-redundancy) 00 01 02 03 04 05 06 07 08 09 RFC 6718

Network Working Group                                           P. Muley
Internet-Draft                                               M. Aissaoui
Intended status: Informational                                  M. Bocci
Expires: August 19, 2012                                  Alcatel-Lucent
                                                       February 16, 2012


                         Pseudowire Redundancy
                     draft-ietf-pwe3-redundancy-06

Abstract

   This document describes a framework comprised of a number of
   scenarios and associated requirements for pseudowire (PW) redundancy.
   A set of redundant PWs is configured between provider edge (PE) nodes
   in single segment PW applications, or between Terminating PE nodes in
   Multi-Segment PW applications.  In order for the PE/T-PE nodes to
   indicate the preferred PW to use for forwarding PW packets to one
   another, a new PW status is required to indicate the preferential
   forwarding status of active or standby for each PW in the redundancy
   set.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 19, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the



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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Reference Models . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  PE Architecture  . . . . . . . . . . . . . . . . . . . . .  5
     3.2.  PW Redundancy Network Reference Scenarios  . . . . . . . .  5
       3.2.1.  Single Multi-Homed CE  . . . . . . . . . . . . . . . .  5
       3.2.2.  Multiple Multi-Homed CEs . . . . . . . . . . . . . . .  7
       3.2.3.  Single-Homed CE With MS-PW Redundancy  . . . . . . . .  8
       3.2.4.  PW Redundancy Between MTU-s in H-VPLS  . . . . . . . .  9
       3.2.5.  PW Redundancy Between VPLS Network Facing PEs
               (n-PEs)  . . . . . . . . . . . . . . . . . . . . . . . 10
       3.2.6.  Redundancy in a VPLS Bridge Module Model . . . . . . . 11
   4.  Generic PW Redundancy Requirements . . . . . . . . . . . . . . 12
     4.1.  Protection Switching Requirements  . . . . . . . . . . . . 12
     4.2.  Operational Requirements . . . . . . . . . . . . . . . . . 13
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   7.  Major Contributing Authors . . . . . . . . . . . . . . . . . . 13
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15













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1.  Introduction

   The objective of PW redundancy is to provide sparing of attachment
   circuits (ACs), Provider Edge nodes (PEs), and Pseudowires (PWs) to
   eliminate single points of failure, while ensuring that only one
   active path between a pair of Customer Edge nodes (CEs).

   In single-segment PW (SS-PW) applications, protection for the PW is
   provided by the PSN layer.  This may be a Resource Reservation
   Protocol with Traffic Engineering (RSVP-TE) labeled switched path
   (LSP) with a fast-Reroute (FRR) backup or an end-to-end backup LSP.
   PSN protection mechanisms cannot protect against failure of the a PE
   node or the failure of the remote AC.  Typically, this is supported
   by dual-homing a Customer Edge (CE) node to different PE nodes which
   provide a pseudowire emulated service across the PSN.  A set of PW
   mechanisms is therefore required that enables a primary and one or
   more backup PWs to terminate on different PE nodes.

   In multi-segment PW (MS-PW) applications, PSN protection mechanisms
   cannot protect against the failure of a switching PE (S-PE).  A set
   of mechanisms that support the operation of a primary and one or more
   backup PWs via a different set of S-PEs is therefore required.  The
   paths of these PWs are diverse in the sense that they are switched at
   different S-PE nodes.

   In both of these applications, PW redundancy is important to maximise
   the resiliency of the emulated service.

   This document describes framework for these applications and its
   associated operational requirements.  The framework utilizes a new PW
   status, called the Preferential Forwarding Status of the PW.  This is
   separate from the operational states defined in RFC4447 [RFC4447].
   The mechanisms for PW redundancy are modeled on general protection
   switching principles.


2.  Terminology

   o  Up PW: A PW which has been configured (label mapping exchanged
      between PEs) and is not in any of the PW defect states specified
      in [RFC4447].  Such a PW is is available for forwarding traffic.

   o  Down PW: A PW that has either not been fully configured, or has
      been configured and is in any one of the PW defect states
      specified in [RFC4447].  Such a PW is not available for forwarding
      traffic.





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   o  Active PW.  An UP PW used for forwarding user, OAM and control
      plane traffic.

   o  Standby PW.  An UP PW that is not used for forwarding user traffic
      but may forward OAM and specific control plane traffic.

   o  PW Endpoint: A PE where a PW terminates on a point where Native
      Service Processing is performed, e.g., A Single Segment PW (SS-PW)
      PE, a Multi-Segment Pseudowire (MS-PW) Terminating PE (T-PE), or a
      Hierarchical VPLS MTU-s or PE-rs.

   o  Primary PW: the PW which a PW endpoint activates (i.e. uses for
      forwarding) in preference to any other PW when more than one PW
      qualifies for active state.  When the primary PW comes back up
      after a failure and qualifies for the active state, the PW
      endpoint always reverts to it.  The designation of Primary is
      performed by local configuration for the PW at the PE.

   o  Secondary PW: when it qualifies for the active state, a Secondary
      PW is only selected if no Primary PW is configured or if the
      configured primary PW does not qualify for active state (e.g., is
      DOWN).  By default, a PW in a redundancy PW set is considered
      secondary.  There is no Revertive mechanism among secondary PWs.

   o  Revertive protection switching.  Traffic will be carried by the
      primary PW if it is UP and a wait-to-restore timer expires and the
      primary PW is made the Active PW.

   o  Non-revertive protection switching.  Traffic will be carried by
      the last PW selected as a result of previous active PW entering
      Operationally DOWN state.

   o  Manual selection of PW.  The ability for the operator to manually
      select the primary/secondary PWs.

   o  MTU-s: A hierarchical virtual private LAN service Multi-Tenant
      Unit switch, as defined in RFC4762 [RFC4762].

   o  PE-rs: A hierarchical virtual private LAN service switch, as
      defined in RFC4762.

   o  n-PE: A network facing provider edge node, as defined in RFC4026
      [RFC4026].

   This document uses the term 'PE' to be synonymous with both PEs as
   per RFC3985[RFC3985] and T-PEs as per RFC5659 [RFC5659].

   This document uses the term 'PW' to be synonymous with both PWs as



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   per RFC3985 and SS-PWs, MS-PWs, and PW segments as per RFC5659.


3.  Reference Models

   The following sections describe show the reference architecture of
   the PE for PW redundancy and its usage in different topologies and
   applications.

3.1.  PE Architecture

   Figure 1 shows the PE architecture for PW redundancy, when more than
   one PW in a redundant set is associated with a single AC.  This is
   based on the architecture in Figure 4b of RFC3985 [RFC3985].  The
   forwarder selects which of the redundant PWs to use based on the
   criteria described in this document.

              +----------------------------------------+
              |                PE Device               |
              +----------------------------------------+
     Single   |                 |        Single        | PW Instance
      AC      |                 +      PW Instance     X<===========>
              |                 |                      |
              |                 |----------------------|
      <------>o                 |        Single        | PW Instance
              |    Forwarder    +      PW Instance     X<===========>
              |                 |                      |
              |                 |----------------------|
              |                 |        Single        | PW Instance
              |                 +      PW Instance     X<===========>
              |                 |                      |
              +----------------------------------------+

                Figure 1: PE Architecture for PW redundancy

3.2.  PW Redundancy Network Reference Scenarios

   This section presents a set of reference scenarios for PW redundancy.

3.2.1.  Single Multi-Homed CE

   The following figure illustrates an application of single segment
   pseudowire redundancy.  This scenario is designed to protect the
   emulated service against a failure of one of the PEs or ACs attached
   to the multi-homed CE.  Protection against failures of the PSN
   tunnels is provided using PSN mechanisms such as MPLS Fast Reroute,
   so that these failures do not impact the PW.




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   CE1 is dual-homed to PE1 and PE3.  A dual homing control protocol,
   the details of which are outside the scope of this document, selects
   which AC CE1 should use to forward towards the PSN, and which PE (PE1
   or PE3) should forward towards CE1.

            |<-------------- Emulated Service ---------------->|
            |                                                  |
            |          |<------- Pseudo Wire ------>|          |
            |          |                            |          |
            |          |    |<-- PSN Tunnels-->|    |          |
            |          V    V                  V    V          |
            V    AC    +----+                  +----+     AC   V
      +-----+    |     | PE1|==================|    |     |    +-----+
      |     |----------|....|...PW1.(active)...|....|----------|     |
      |     |          |    |==================|    |          | CE2 |
      | CE1 |          +----+                  |PE2 |          |     |
      |     |          +----+                  |    |          +-----+
      |     |          |    |==================|    |
      |     |----------|....|...PW2.(standby)..|    |
      +-----+    |     | PE3|==================|    |
                 AC    +----+                  +----+

              Figure 2: PW Redundancy with One Multi-Homed CE

   In this scenario, only one of the PWs should be used for forwarding
   between PE1 / PE3, and PE2.  PW redundancy determines which PW to
   make active based on the forwarding state of the ACs so that only one
   path is available from CE1 to CE2.

   Consider the example where the AC from CE1 to PE1 is initially active
   and the AC from CE1 to PE3 is initially standby.  PW1 is made active
   and PW2 is made standby in order to complete the path to CE2.

   On failure of the AC between CE1 and PE1, the forwarding state of the
   AC on PE3 transitions to Active.  The preferential forwarding state
   of PW2 therefore needs to become active, and PW1 standby, in order to
   reestablish connectivity between CE1 and CE2.  PE3 therefore uses PW2
   to forward towards CE2, and PE2 uses PW2 instead of PW1 to forward
   towards CE1.  PW redundancy in this scenario requires that the
   forwarding status of the ACs at PE1 and PE3 be signaled to PE2 so
   that PE2 can choose which PW to make active.

   Changes occurring on the dual homed side of network due to a failure
   of the AC or PE are not propagated to the ACs on the other side of
   the network.  Furthermore, failures in the PSN are not be propagated
   to the attached CEs.





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3.2.2.  Multiple Multi-Homed CEs

   This scenario, illustrated in Figure 3, is also designed to protect
   the emulated service against failures of the ACs and failures of the
   PEs.  Here, both CEs, CE1 and CE2, are dual-homed to their respective
   PEs, PE1 and PE2, and PE3 and PE4.  The method used by the CEs to
   choose which AC to use to forward traffic towards the PSN is
   determined by a dual-homing control protocol.  The details of this
   protocol are outside the scope of this document.

   Note that the PSN tunnels are not shown in this figure for clarity.
   However, it can be assumed that each of the PWs shown is encapsulated
   in a separate PSN tunnel.  Protection against failures of the PSN
   tunnels is provided using PSN mechanisms such as MPLS Fast Reroute,
   so that these failures do not impact the PW.

         |<-------------- Emulated Service ---------------->|
         |                                                  |
         |          |<------- Pseudowire ------->|          |
         |          |                            |          |
         |          |    |<-- PSN Tunnels-->|    |          |
         |          V    V                  V    V          |
         V    AC    +----+                  +----+     AC   V
   +-----+    |     |....|.......PW1........|....|     |    +-----+
   |     |----------| PE1|......   .........| PE3|----------|     |
   | CE1 |          +----+      \ /  PW3    +----+          | CE2 |
   |     |          +----+       X          +----+          |     |
   |     |          |    |....../ \..PW4....|    |          |     |
   |     |----------| PE2|                  | PE4|--------- |     |
   +-----+    |     |....|.....PW2..........|....|     |    +-----+
              AC    +----+                  +----+     AC

           Figure 3: Multiple Multi-Homed CEs with PW Redundancy

   PW1 and PW4 connect PE1 to PE3 and PE4, respectively.  Similarly, PE2
   has PW2 and PW3 connect PE2 to PE4 and PE3.  PW1, PW2, PW3 and PW4
   are all UP.  In order to support N:1 or 1:1 protection, only one PW
   MUST be selected to forward traffic.  This document defines an
   additional PW state that reflects this forwarding state, which is
   separate from the operational status of the PW.  This is the
   'Preferential Forwarding Status'.

   If a PW has a preferential forwarding status of 'active', it can be
   used for forwarding traffic.  The actual UP PW chosen by the combined
   set of PEs that interconnect the CEs is determined by considering the
   preferential forwarding status of each PW at each PE.  The mechanisms
   for achieving this selection are outside the scope of this document.
   Only one PW is used for forwarding.



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   The following failure scenario illustrates the operation of PW
   redundancy in Figure 2.  In the initial steady state, when there are
   no failures of the ACs, one of the PWs is chosen as the active PW,
   and all others are chosen as standby.  The dual-homing protocol
   between CE1 and PE1/PE2 chooses to use the AC to PE2, while the
   protocol between CE2 and PE3/PE4 chooses to use the AC to PE4.
   Therefore the PW between PE2 and PE4 is chosen as the active PW to
   complete the path between CE1 and CE2.

   On failure of the AC between the dual-homed CE1 and PE2, the
   preferential forwarding status of the PWs at PE1, PE2, PE3 and PE4
   needs to change so as to re-establish a path from CE1 to CE2.
   Different mechanisms can be used to achieve this and these are beyond
   the scope of this document.  After the change in status the algorithm
   for selection of PW needs to revaluate and select PW to forward
   traffic.  In this application each dual-homing algorithm, i.e., {CE1,
   PE1, PE2} and {CE2, PE3, PE4}, selects the active AC independently.
   There is therefore a need to signal the active status of each AC such
   that the PEs can select a common active PW for forwarding between CE1
   and CE2.

   Changes occurring on one side of network due to a failure of the AC
   or PE are not propagated to the ACs on the other side of the network.
   Furthermore, failures in the PSN are not be propagated to the
   attached CEs.  Note that End-to-end native service protection
   switching can also be used to protect the emulated service in this
   scenario.  In this case, PW3 and PW4 are not necessary.

   If the CEs do not perform native service protection switching, they
   may instead may use load balancing across the paths between the CEs.

3.2.3.  Single-Homed CE With MS-PW Redundancy

   This application is shown in Figure 4.  The main objective is to
   protect the emulated service against failures of the S-PEs.
















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       Native   |<----------- Pseudowires ----------->|  Native
       Service  |                                     |  Service
        (AC)    |     |<-PSN1-->|     |<-PSN2-->|     |  (AC)
          |     V     V         V     V         V     V   |
          |     +-----+         +-----+         +-----+   |
   +----+ |     |T-PE1|=========|S-PE1|=========|T-PE2|   |   +----+
   |    |-------|......PW1-Seg1.......|.PW1-Seg2......|-------|    |
   | CE1|       |     |=========|     |=========|     |       | CE2|
   |    |       +-----+         +-----+         +-----+       |    |
   +----+        |.||.|                          |.||.|       +----+
                 |.||.|         +-----+          |.||.|
                 |.||.|=========|     |========== .||.|
                 |.||...PW2-Seg1......|.PW2-Seg2...||.|
                 |.| ===========|S-PE2|============ |.|
                 |.|            +-----+             |.|
                 |.|============+-----+============= .|
                 |.....PW3-Seg1.|     | PW3-Seg2......|
                  ==============|S-PE3|===============
                                |     |
                                +-----+

              Figure 4: Single-Homed CE with MS-PW Redundancy

   CE1 is connected to PE1 and CE2 to PE2, respectively.  There are
   three multi-segment PWs.  PW1 is switched at S-PE1, PW2 is switched
   at S-PE2, and PW3 is switched at S-PE3.

   Since there is no multi-homing running on the ACs, the T-PE nodes
   would advertise 'Active' for the forwarding status based on a
   priority for the PW.  Priorities associate meaning of 'primary PW'
   and 'secondary PW'.  These priorities MUST be used in revertive mode
   as well and paths must be switched accordingly.  The priority can be
   configuration or derivation from the PWid.  Lower the PWid higher the
   priority.  However, this does not guarantee selection of same PW by
   the T-PEs because, for example, mismatch of the configuration of the
   PW priority in each T-PE.  The intent of this application is to have
   T-PE1 and T-PE2 synchronize the transmit and receive paths of the PW
   over the network.  In other words, both T-PE nodes are required to
   transmit over the PW segment which is switched by the same S-PE.
   This is desirable for ease of operation and troubleshooting.

3.2.4.  PW Redundancy Between MTU-s in H-VPLS

   The following figure illustrates the application of use of PW
   redundancy to Hierarchical VPLS (H-VPLS).  Here, a Multi-Tenant Unit
   switch (MTU-s) is dual-homed to two PE router switches (PE-rs).





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                     |<-PSN1-->|     |<-PSN2-->|
                     V         V     V         V
               +-----+         +-----+
               |MTU-s|=========|PE1  |========
               |..Active PW group....| H-VPLS-core
               |     |=========|     |=========
               +-----+         +-----+
                  |.|
                  |.|           +-----+
                  |.|===========|     |==========
                  |...Standby PW group|.H-VPLS-core
                   =============|  PE2|==========
                                +-----+

                Figure 5: MTU-s Dual Homing in H-VPLS Core

   In Figure 5, the MTU-s is dual homed to PE1 and PE2 and has spoke PWs
   to each of them.  The MTU-s needs to choose only one of the spoke PWs
   ( the active PW) to one of the PE to forward the traffic and the
   other to standby status.  The MTU-s can derive the status of the PWs
   based on local policy configuration.  PE1 and PE2 are connected to
   the H-VPLS core on the other side of network.  The MTU-s communicates
   the status of its member PWs for a set of VSIs having common status
   of Active or Standby.  Here the MTU-s controls the selection of PWs
   to forward the traffic.  Signaling using PW grouping with a common
   group-id in PWid FEC Element or Grouping TLV in Generalized PWid FEC
   Element as defined in [RFC4447] to PE1 and PE2 respectively, is
   recommended to scale better.

   Whenever MTU-s performs a switchover, it needs to communicate to PE2
   for the Standby PW group the changed status of active.

   In this scenario, PE devices are aware of switchovers at MTU-s and
   could generate MAC Withdraw Messages to trigger MAC flushing within
   the H-VPLS full mesh.  By default, MTU-s devices should still trigger
   MAC Withdraw messages as currently defined in [RFC4762] to prevent
   two copies of MAC withdraws to be sent (one by MTU-s and another one
   by PEs).  Mechanisms to disable MAC Withdraw trigger in certain
   devices is out of the scope of this document.

3.2.5.  PW Redundancy Between VPLS Network Facing PEs (n-PEs)

   Following figure illustrates the application of use of PW redundancy
   for dual homed connectivity between PE devices in a ring topology.







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             +-------+                     +-------+
             |  PE1  |=====================|  PE2  |====...
             +-------+    PW Group 1       +-------+
                 ||                            ||
   VPLS Domain A ||                            || VPLS Domain B
                 ||                            ||
             +-------+                     +-------+
             |  PE3  |=====================|  PE4  |==...
             +-------+    PW Group 2       +-------+

                  Figure 6: Redundancy in a Ring Topology

   In Figure 6, PE1 and PE3 from VPLS domain A are connected to PE2 and
   PE4 in VPLS domain B via PW group 1 and group 2.  Each of the PEs in
   the respective domains is connected to each other as well as forming
   the ring topology.  Such scenarios may arise in inter-domain H-VPLS
   deployments where rapid spanning tree (RSTP) or other mechanisms may
   be used to maintain loop free connectivity of PW groups.

   [RFC4762] outlines multi-domain VPLS services without specifying how
   multiple redundant border PEs per domain per VPLS instance can be
   supported.  In the example above, PW group 1 may be blocked at PE1 by
   RSTP and it is desirable to block the group at PE2 by virtue of
   exchanging the PW preferential forwarding status of Standby.  How the
   PW grouping should be done here is again deployment specific and is
   out of scope of the solution.

3.2.6.  Redundancy in a VPLS Bridge Module Model

   ----------------------------+  Provider  +------------------------
                               .   Core     .
                   +------+    .            .    +------+
                   | n-PE |======================| n-PE |
        Provider   | (P)  |---------\    /-------| (P)  |  Provider
        Access     +------+    ._    \  /   .    +------+  Access
        Network                .      \/    .              Network
          (1)      +------+    .      /\    .    +------+     (2)
                   | n-PE |----------/  \--------| n-PE |
                   |  (B) |----------------------| (B)  |_
                   +------+    .            .    +------+
                               .            .
   ----------------------------+            +------------------------

                       Figure 7: Bridge Module Model

   In Figure 7, two provider access networks, each having two n-PEs,
   where the n-PEs are connected via a full mesh of PWs for a given VPLS
   instance.  As shown in the figure, only one n-PE in each access



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   network is serving as a Primary PE (P) for that VPLS instance and the
   other n-PE is serving as the backup PE (B).  In this figure, each
   primary PE has two active PWs originating from it.  Therefore, when a
   multicast, broadcast, and unknown unicast frame arrives at the
   primary n-PE from the access network side, the n-PE replicates the
   frame over both PWs in the core even though it only needs to send the
   frames over a single PW (shown with == in the figure) to the primary
   n-PE on the other side.  This is an unnecessary replication of the
   customer frames that consumes core-network bandwidth (half of the
   frames get discarded at the receiving n-PE).  This issue gets
   aggravated when there is three or more n-PEs per provider, access
   network.  For example if there are three n-PEs or four n-PEs per
   access network, then 67% or 75% of core-BW for multicast, broadcast
   and unknown unicast are wasted, respectively.

   In this scenario, n-PEs can disseminate the status of PWs active/
   standby among them and furthermore to have it tied up with the
   redundancy mechanism such that per VPLS instance the status of
   active/backup n-PE gets reflected on the corresponding PWs emanating
   from that n-PE.


4.  Generic PW Redundancy Requirements

4.1.  Protection Switching Requirements

   o  Protection architectures such as N:1,1:1 or 1+1 are possible. 1:1
      protection MUST besupported.  The N:1 protection case is less
      efficient in terms of the resources that must be allocated and
      hence this SHOULD be supported. 1+1 protection architecture MAY be
      suported, but its definition is for further study.

   o  Non-revertive behavior MUST be supported, while revertive behavior
      is OPTIONAL.

   o  Protection switchover can be triggered by the operator e.g. using
      a Manual lockout/force switchover, or it may be triggered by a
      signal failure i.e. a defect in the PW or PSN.  Both methods MUST
      be supported and signal failure triggers MUST be treated with a
      higher priority than any local or far-end operator-initiated
      trigger.

   o  Note that a PE MAY be able to forward packets received from a
      standby status PW in order to avoid black holing of in-flight
      packets during switchover.  However, in the case of use of VPLS,
      all VPLS application packets received from standby PWs MUST be
      dropped, except for OAM packets.




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4.2.  Operational Requirements

   o  (T-)PEs involved in protecting a PW SHOULD automatically discover
      and attempt to resolve inconsistencies in the configuration of
      primary/secondary PW.

   o  (T-)PEs involved in protecting a PW SHOULD automatically discover
      and attempt to resolve inconsistencies in the configuration of
      revertive/non-revertive protection switching mode.

   o  (T-)PEs that do not automatically discover or resolve
      inconsistencies in the configuration of primary/secondary,
      revertive/non-revertive, or other parameters MUST generate an
      alarm upon detection of an inconsistent configuration.

   o  (T-)PEs participating in PW redundancy MUST support the
      configuration of revertive or non-revertive protection switching
      modes.

   o  (T-)PEs participating in PW redundancy SHOULD support the local
      invocation of protection switching.

   o  (T-)PEs participating in PW redundancy SHOULD support the local
      invocation of a lockout of protection switching.

   o


5.  Security Considerations

   This document requires extensions to LDP that are needed for
   protecting pseudowires.  These will inherit at least the same
   security properties as LDP [RFC5036] and the PW control protocol
   [RFC4447].


6.  IANA Considerations

   This document has no actions for IANA.


7.  Major Contributing Authors

   The editors would like to thank Pranjal Kumar Dutta, Marc Lasserre,
   Jonathan Newton, Hamid Ould-Brahim, Olen Stokes, Dave Mcdysan, Giles
   Heron and Thomas Nadeau who made a major contribution to the
   development of this document.




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   Pranjal Dutta
   Alcatel-Lucent
   Email: pranjal.dutta@alcatel-lucent.com

   Marc Lasserre
   Alcatel-Lucent
   Email: marc.lasserre@alcatel-lucent.com

   Jonathan Newton
   Cable & Wireless
   Email: Jonathan.Newton@cw.com

   Olen Stokes
   Extreme Networks
   Email: ostokes@extremenetworks.com

   Hamid Ould-Brahim
   Nortel
   Email: hbrahim@nortel.com

   Dave McDysan
   Verizon
   Email: dave.mcdysan@verizon.com

   Giles Heron
   Cisco Systems
   Email: giles.heron@gmail.com

   Thomas Nadeau
   Computer Associates
   Email: tnadeau@lucidvision.com


8.  Acknowledgements

   The authors would like to thank Vach Kompella, Kendall Harvey,
   Tiberiu Grigoriu, Neil Hart, Kajal Saha, Florin Balus and Philippe
   Niger for their valuable comments and suggestions.


9.  References

9.1.   Normative References

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

   [RFC3985]  Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-



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              Edge (PWE3) Architecture", RFC 3985, March 2005.

   [RFC4026]  Andersson, L. and T. Madsen, "Provider Provisioned Virtual
              Private Network (VPN) Terminology", RFC 4026, March 2005.

   [RFC4447]  Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
              Heron, "Pseudowire Setup and Maintenance Using the Label
              Distribution Protocol (LDP)", RFC 4447, April 2006.

   [RFC4762]  Lasserre, M. and V. Kompella, "Virtual Private LAN Service
              (VPLS) Using Label Distribution Protocol (LDP) Signaling",
              RFC 4762, January 2007.

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

   [RFC5659]  Bocci, M. and S. Bryant, "An Architecture for Multi-
              Segment Pseudowire Emulation Edge-to-Edge", RFC 5659,
              October 2009.

9.2.  Informative References

   [RFC6073]  Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
              Aissaoui, "Segmented Pseudowire", RFC 6073, January 2011.


Authors' Addresses

   Praveen Muley
   Alcatel-Lucent


   Email: praveen.muley@alcatel-lucent.com


   Mustapha Aissaoui
   Alcatel-Lucent


   Email: mustapha.aissaoui@alcatel-lucent.com


   Matthew Bocci
   Alcatel-Lucent


   Email: matthew.bocci@alcatel-lucent.com




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