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

Network Working Group                               Praveen Muley, Ed.
Internet Draft                                  Mustapha Aissaoui, Ed.
Intended Status: Informational                           Matthew Bocci
Expires: January 2011                                   Alcatel-Lucent

                                                           July 8, 2011

                        Pseudowire Redundancy
                   draft-ietf-pwe3-redundancy-04.txt


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.



Status of this Memo

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

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   This Internet-Draft will expire on January 8, 2011






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Copyright Notice

   Copyright (c) 2011 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.


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 [1].



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..................6
   3.2.1. Single Multi-Homed CE....................................6
   3.2.2. Multiple Multi-homed CEs.................................7
   3.3. Single Homed CE with MS-PW redundancy......................9
   3.4. PW redundancy between MTU-s in H-VPLS.....................11
   3.5. PW redundancy between VPLS n-PEs..........................12
   3.6. PW redundancy in VPLS Bridge Module Model.................12
   4. Generic PW redundancy requirements..........................14
   4.1. Protection switching requirements.........................14
   4.2. Operational requirements..................................14
   5. Security Considerations.....................................15
   6. IANA considerations........................................15
   7. Major Contributing Authors..................................15
   8. Acknowledgments............................................16
   9. References.................................................16
   9.1. Normative References......................................16
   9.2. Informative References....................................17


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   Author's Addresses............................................17

1. Introduction

   The objective of PW redundancy is to provide sparign 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 cuported by
   dual-homing a Cutomer Edge (CE) node to different PE nodes which
   provide a pseudowire emulated service across the PSN. A set of PW
   mechanisms is theerfore required that enables a primary and one or
   more backup 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 diferent 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 [2]. The
   mechanisms for PW redundancy are modelled on general protection
   switching principles.



2. Terminology

   o UP PW:  A PW which has been configured (label mapping exchanged
      between PEs) and s not in any of the PW defect states specified
      in [2]. Such a PW is available for forwarding traffic.





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   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 [2]. Such a PW is not available for forwarding
      traffic.

   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 Pswudowire (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
      primary PW if it is UP and a wait-to-restore timer expires and
      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.

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

   This document uses the term 'PW' to be synonymous with both PWs as
           per RFC3985 and SS-PWs, MS-PWs, S-PEs, PW-segment and  PW
           switching point as per RFC5659.



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3. Reference Models

   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 [3]. 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




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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.

   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.





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   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.



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.













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         |<-------------- 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 SS-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 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.

   The following failure scenario illsutrates 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 choen 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


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   needs to change so as to resestablish 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
   running on the two node sets, 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.

3.3. 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 multi-segment pseudowire 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 path 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.









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3.4. PW redundancy between MTU-s in H-VPLS

   Following figure illustrates the application of use of PW redundancy
   to Hierarchical VPLS (H-VPLS). Here, and MTU-s is dual-homed to two
   PE-rs.


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

               Figure 5  Multi-homed MTU-s 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 [2] 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 [5] 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.



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3.5. PW redundancy between VPLS n-PEs

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



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

                 Figure 6   Redundancy in 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.

   [5] 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.

3.6. PW redundancy in VPLS Bridge Module Model













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   ----------------------------+  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
   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 respectively wasted.

   In this scenario, n-PEs can disseminate the status of PWs
   active/standby among themselves 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.








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4. Generic PW redundancy requirements

4.1. Protection switching requirements

   o Protection architecture such as N:1,1:1 or 1+1 can be used. N:1
      protection case is somewhat inefficient in terms of capacity
      consumption hence implementations SHOULD support this method
      while  1:1 being subset and efficient MUST be supported. 1+1
      protection architecture can be supported but is left for further
      study.

   o Non-revertive mode MUST be supported, while revertive mode is an
      optional one.

   o Protection switchover can be operator driven like Manual
      lockout/force switchover or due to signal failure. Both methods
      MUST be supported and signal failure MUST be given higher
      priority than any local or far end request.

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 involved with protection switching MUST support the
      configuration of revertive or non-revertive protection switching
      mode.

   o (T-)PEs involved with protection switching SHOULD support the
      local invocation of protection switching.

   o (T-)PEs involved with protection switching SHOULD support the
      local invocation of a lockout of protection switching.






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   o In standby status PW can still receive packets in order to avoid
      black holing of in-flight packets during switchover. However in
      case of use of VPLS application packets are dropped in standby
      status except for the OAM packets.



5. Security Considerations

   This document expects extensions to LDP that are needed for
   protecting pseudo-wires. It will have the same security properties
   as in LDP [4] and the PW control protocol [2].

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 Kumar Dutta
   Alcatel-Lucent
   Email: pdutta@alcatel-lucent.com

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

   Jonathan Newton
   Cable & Wireless
   Email: Jonathan.Newton@cwmsg.cwplc.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. Acknowledgments

   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

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


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   [2]  Martini, L., et al., "Pseudowire Setup and Maintenance using
         LDP", RFC 4447, April 2006.

   [3]  Bryant, S., et al., " Pseudo Wire Emulation Edge-to-Edge
         (PWE3) Architecture", RFC 3985 March 2005

   [4]  Andersson, L., Minei, I., and B. Thomas, "LDP Specification",
         RFC 5036, January 2001

   [5]  Kompella,V., Lasserrre, M. , et al., "Virtual Private LAN
         Service (VPLS) Using LDP Signalling", RFC 4762, January 2007

9.2. Informative References

   [6]  Martini, L., et al., "Segmented Pseudo Wire", RFC6073, January
         2011.

Author's Addresses

   Praveen Muley
   Alcatel-Lucent
   701 E. Middlefiled Road
   Mountain View, CA, USA
   Email: Praveen.muley@alcatel-lucent.com

  Mustapha Aissaoui
   Alcatel-Lucent
   600 March Rd
   Kanata, ON, Canada K2K 2E6
   Email: mustapha.aissaoui@alcatel-lucent.com

  Matthew Bocci
   Alcatel-Lucent
   Voyager Place
   Shoppenhangers Rd,
   Maidenhead, Berks, UK
   Email: matthew.bocci@alcatel-lucent.com












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