L2VPN Working Group                                  Pranjal Kumar Dutta
                                                           Marc Lasserre
Internet Draft                                            Alcatel-Lucent
Intended status: Standard
Expires: October 2009                                        Olen Stokes
                                                        Extreme Networks

                                                        April 26, 2009


       LDP Extensions for Optimized MAC Address Withdrawal in H-VPLS
                 draft-ietf-l2vpn-vpls-ldp-mac-opt-00.txt


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 October 26, 2009.

Abstract

   [RFC4762] describes a mechanism to remove or unlearn MAC addresses
   that have been dynamically learned in a VPLS Instance for faster
   convergence on topology change. The procedure also removes the MAC
   addresses in the VPLS that does not require relearning due to such
   topology change. This document defines an extension to MAC Address
   Withdrawal procedure with empty MAC List [RFC4762], which enables a
   Provider Edge(PE) device to remove only the MAC addresses that needs
   to be relearned.




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Conventions used in this document

   In examples, "C:" and "S:" indicate lines sent by the client and
   server respectively.

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

Table of Contents

   1. Introduction...................................................3
   2. Problem Description............................................4
   3. Optimized MAC Flush Mechanism..................................6
   4. PE-ID TLV......................................................7
   5. Application of PE-ID TLV in Optimized MAC Flush...............10
   5.1   PE-ID TLV Processing Rules.................................10
   5.2 Optimized MAC Flush Procedures...............................11
   6. General Applicability of PE-ID TLV............................13
   7. Security Considerations.......................................13
   8. IANA Considerations...........................................14
   9. Acknowledgments...............................................14
   10. References...................................................15
      10.1. Normative References....................................15
      10.2. Informative References..................................15
   Author's Addresses...............................................16

Terminology

   This document uses the terminology defined in [RFC5036], [RFC4447]
   and [RFC4762]. Throughout this document VPLS means the emulated
   bridged LAN service offered to a customer. H-VPLS means the
   hierarchical connectivity or layout of MTU-s and PE devices offering
   the VPLS[RFC4762]. The terms spoke node and MTU-s in H-VPLS are used
   interchangeably.












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1. Introduction

   A method of Virtual Private LAN Service (VPLS), also known as
   Transparent LAN Service (TLS) is described in [RFC4762]. A VPLS is
   created using a collection of one or more point-to-point pseudowires
   (PWs) [RFC4664] configured in a flat, full-mesh topology. The mesh
   topology provides a LAN segment or broadcast domain that is fully
   capable of learning and forwarding on Ethernet MAC addresses at the
   PE devices.

   This VPLS full mesh core configuration can be augmented with
   additional non-meshed spoke nodes to provide a Hierarchical VPLS
   (H-VPLS) service[RFC4762].

    MAC Address Withdrawal mechanism is described in [RFC4762] to
   remove or unlearn MAC addresses for faster convergence on topology
   change in dual-homed H-VPLS[RFC4762]. In dual-homed H-VPLS, an edge
   device termed as MTU-s is connected to two PE devices via primary
   spoke PW and backup spoke PW respectively. Such redundancy is
   designed to protect against the failure of primary spoke PW or
   primary PE device. When MTU-s switches over to backup PW, it is
   required to flush the MAC addresses learned in the VPLS in upstream
   PE devices participating in full mesh, to avoid black holing of
   frames to those addresses. Note that forced switchover to backup PW
   can be also performed at MTU-s administratively due to maintenance
   activities on the primary spoke PW.

   When backup PW is made active by MTU-s, it triggers LDP Address
   Withdraw Message with list of MAC addresses to be flushed. The
   message is forwarded over the LDP session(s) associated with the
   newly activated PW. In order to minimize the impact on LDP
   convergence time when MAC List TLV contains a large number of MAC
   addresses, it may be preferable to send a LDP Address Withdraw
   Message with an empty MAC List. Throughout this document the term
   MAC Flush Message is used to specify LDP Address Withdraw Message
   with empty MAC List described in [RFC4762] unless specified
   otherwise.

   As per the processing rules in [RFC4762] a PE device on receiving
   a MAC flush message removes all MAC addresses associated with
   the specified VPLS instance (as indicated in the FEC TLV) except the
   MAC addresses learned over the newly activated PW. The PE device
   further triggers MAC flush message to each remote PE device


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   connected to it in the VPLS full mesh.

   This method of MAC flushing is modeled after Topology Change
   Notification (TCN) in Rapid Spanning Tree Protocol (RSTP)[802.1w].
   When a bridge switches from failed link to the backup link, the
   bridge sends out a TCN message over the newly activated link. The
   upstream bridge upon receiving this message flushes its entire MAC
   addresses except the ones received over this link and sends the TCN
   message out of its other ports in that spanning tree instance. The
   message is further relayed along the spanning tree by the other
   bridges.

   When a PE device in the full-mesh of H-VPLS receives a MAC flush
   message it also flushes the MAC addresses which are not affected
   due to topology change, thus leading to unnecessary flooding and
   relearning. This document describes the problem and a solution to
   optimize the MAC flush procedure in [RFC4762] so that flush only
   the set of MAC addresses that require relearning when topology
   changes in H-VPLS.

   [L2VPN-SIG] describes about inter-AS VPLS deployments models where
   Multi-Segment PWs (MS-PW) may be used. The solution proposed in
   this document is generic and is applicable to MS-PWs in H-VPLS.

2.  Problem Description

   Figure.1 describes a dual-homed H-VPLS scenerio for a VPLS instance
   where the problem with the existing MAC flush method in [RFC4762] is
   explained.















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                                 PE-1                         PE-3
                               +--------+                  +--------+
                               |        |                  |        |
                               |   --   |                  |   --   |
   Customer Site 1             |  /  \  |------------------|  /  \  |->
     CE-1               /------|  \ s/  |                  |  \S /  |
       \     primary spoke PW  |   --   |           /------|   --   |
        \             /        +--------+          /       +--------+
         \    (MTU-s)/              |    \        /             |
          +--------+/               |     \      /              |
          |        |                |      \    /               |
          |   --   |                |       \  /                |
          |  /  \  |                |      H-VPLS Full Mesh Core|
          |  \S /  |                |       / \                 |
          |   --   |                |      /   \                |
         /+--------+\               |     /     \               |
        /     backup spoke PW       |    /       \              |
       /              \        +--------+         \--------+--------+
      CE-2             \       |        |                  |        |
   Customer Site 2      \------|  --    |                  |  --    |
                               | /  \   |------------------| /  \   |->
                               | \s /   |                  | \S /   |
                               |  --    |                  |  --    |
                               +--------+                  +--------+
                                 PE-2                         PE-4

           Figure 1: Dual homed MTU-s in two tier hierarchy H-VPLS


    In Figure.1, the MTU-s is dual-homed to PE-1 and PE-2. Only the
   primary spoke PW is active at MTU-s, thus PE-1 acting as the primary
   device to reach the full mesh in the VPLS instance. The MAC
   addresses of nodes located at access sites (behind CE1 and CE2) are
   learned at PE-1 over the primary spoke PW. PE-2, PE-3 and PE-4 learn
   those MAC addresses on their respective mesh PWs terminating to
   PE-1.

   When MTU-s switches to backup spoke PW and activates it, PE-2


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   becomes the primary device to reach the full mesh core. Traffic
   entering the H-VPLS from CE-1 and CE-2 is diverted by MTU-s to the
   backup spoke PW. For faster convergence MTU-s may desire to unlearn
   or remove the MAC addresses that have been learned in the upstream
   VPLS full-mesh through PE-1. MTU-s may send MAC flush message to
   PE-2 once the backup PW has been made active. As per the processing
   rules defined in [RFC4762], PE-2 flushes the entire MAC addresses
   learned in the VPLS from the PWs terminating at PE-1, PE-3 and PE-4
   except the ones learned over the newly activated spoke PW.

   In the H-VPLS core, PE devices are connected in full mesh unlike the
   spanning tree connectivity in bridges. So the MAC addresses that
   require flushing and relearning at PE-2 are only the MAC addresses
   those have been learned on the PW connected to PE-1.

   PE-2 further relays MAC flush messages to all other PE devices in
   the full mesh. Same processing rule applies at all those PE devices.
   For example, at PE-3 the entire MAC addresses learned from the PWs
   connected to PE-1 and PE-4 are flushed and relearned subsequently.
   As the number of PE devices in the full-mesh increases, the number
   of unaffected MAC addresses flushed in a VPLS instance also
   increases, thus leading to unnecessary flooding and relearning. With
   large number of VPLS instances provisioned in the H-VPLS network
   topology the amount of unnecessary flooding and relearning
   increases.

3. Optimized MAC Flush Mechanism

   The basic principle of the optimized MAC flush mechanism is
   explained with reference to Figure 1. On switching over to the
   backup spoke PW when MTU-s triggers MAC flush message to PE-2, it
   also communicates the unique PW endpoint identifier (PE-ID) in PE-1,
   the formerly active PE device. In VPLS a PW terminates on a Virtual
   Switching Instance (VSI) in a PE device. The PE-ID is relayed in all
   the subsequent MAC flush messages triggered by PE-2 to its peer PE
   devices in the full mesh. Each PE device that receives the message
   identifies the VPLS (From FEC TLV) and its respective PW that
   terminates in PE-1 (from PE-ID). Thus the PE device flushes only the
   MAC addresses learned from that PW connected to PE-1.





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4. PE-ID TLV

   This document defines a PW Endpoint Identifier (PE-ID) TLV for
   LDP [RFC5036]. The PE-ID TLV carries the unique identifier of a
   generic PW endpoint.

   The encoding of PE-ID TLV follows standard LDP TLV encoding in
   [RFC5036]. A PE-ID TLV contains a list of one or more PE-ID
   Elements. Its encoding is:

      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

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |1|0|  PE-ID  TLV (0x0405)      |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        PE-ID Element 1                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     ~                                                               ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        PE-ID Element n                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 2. PE-ID TLV

   U (Unknown) bit of thus LDP TLV MUST be set to 1. If the PE-ID TLV
   is not understood then it is ignored the receiving device.

   F (Forward) MUST be set to 0. Since the LDP mechanism used here is
   targeted, the TLV is not forwarded if it is not understood by the
   receiving device.

   The Type field MUST be set to 0x405 (subject to IANA approval). This
   identifies the TLV type as PE-ID TLV.

   Length field specifies the total length in octets of the Value
   in PE-ID TLV.

   PE-ID Element 1 to PE-ID Element n:
       There are several types of PE-ID Elements. The PE-ID Element



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       Encoding depends on the type of the PE-ID Element. A PE-ID
       Element uniquely identifies a PW Endpoint.

   A PE-ID Element value is encoded as 1 octet field that specifies the
   element type, 1 octet field that identifies the length in octets of
   the element value, and a variable length field that is type
   dependent element value.

   The PE-ID Element value encoding is:

   PE-ID Element      Type              Length             Value
   Type name

   FEC-128 specific   0x01            2 octets           See below.
   FEC-129 specific   0x02            Variable           See below.

   The type of PE-ID Element depends on the type of FEC Element used to
   provision the respective PW.

   [RFC4447] defines two types of FEC elements that may be used for
   provisioning PWs - Pwid FEC (type 128) and the Generalized ID (GID)
   FEC (type 129).

   The Pwid FEC element includes a fixed-length 32 bit value called the
   PWid. The same PWid value must be configured on the local and remote
   PE prior to PW setup.

   The GID FEC element includes TLV fields for attachment individual
   identifiers (AII) that, in conjunction with an attachment group
   identifier (AGI), serve as PW endpoint identifiers. The endpoint
   identifier on the local PE (denoted as <AGI, source AII or SAII>) is
   called the source attachment identifier (SAI) and the endpoint
   identifier on the remote PE (denoted as <AGI, target AII or TAII>) is
   called the target attachment identifier (TAI). The SAI and TAI can be
   distinct values. This is useful for provisioning models where the
   local PE (with a particular SAI) does not know and must somehow learn
   (e.g. via MP-BGP auto-discovery) of remote TAI values prior to
   launching PW setup messages towards the remote PE.

   FEC-128 specific PE-ID Element
       This sub-type is to be used to identify a PW endpoint only if
       Pwid FEC Element is used for signaling the PW. The encoding of
       this PE-ID element is as follows:



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     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     0x01      |    Length     |           PW type             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           PW ID                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Endpoint Address                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 3. FEC-128 specific PE-ID Element

       PW type
           The PW Type value from PWid FEC element.

       PW ID
           The PW ID value from the Pwid FEC element.

       Endpoint Address
           32-bit LSR-ID from the LDP-ID used in LDP signaling session
           by a PW endpoint.


   FEC-129 specific PE-ID element
       This sub-type is to be used to indentify a PW endpoint only if
       GID FEC Element is used for signaling the PW. The encoding of
       this PE-ID element is as follows:

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     0x02      |    Length     |           PW type             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           AGI TLV                             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           AII TLV                             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 4. FEC-129 specific PE-ID Element


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       PW type
           The PW Type value from GID FEC element.

       PW ID
           The PW ID value from the GID FEC element

       AGI TLV
           The AGI from the corresponding GID Element

       AII TLV
           The AII associated with the PW endpoint.


5. Application of PE-ID TLV in Optimized MAC Flush

   For optimized MAC flush, the PE-ID TLV MAY be sent as an OPTIONAL
   parameter in existing LDP Address Withdraw Message with empty MAC
   List. The PE-ID TLV carries the unique PW endpoint identifier in a
   VPLS as described in section 4.

   It is to note that for optimized MAC flush the PE-ID TLV carries
   sufficient information for identifying the VPLS instance and the
   unique VSI Identifier. For backward compatibility with MAC flush
   procedures in [RFC4762] both FEC TLV and PE-ID TLV should be sent in
   the MAC flush message. However the inclusion of the FEC-TLV should be
   based on what would be the desired effect should the PE-ID not be
   understood by the receiver.  In cases where the desired action when
   the PE-ID is not understood would be to behave as described in
   [RFC4762], then the FEC TLV SHOULD be included.  In cases where the
   desired action when the PE-ID is not understood is to take no
   action, then the FEC TLV SHOULD NOT be included. The PE-ID TLV
   SHOULD carry the unique VSI identifier in the VPLS instance
   (specified in the FEC TLV). The PE-ID TLV SHOULD be placed after the
   existing TLVs in MAC Flush message in [RFC4762].

5.1 PE-ID TLV Processing Rules

   This section describes the processing rules of PE-ID TLV that SHOULD
   be followed in the context of MAC flush procedures in an H-VPLS.




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   When an MTU-s triggers MAC flush after activation of backup spoke
   PW, it MAY send the PE-ID TLV that identifies VSI in the formerly
   active PE device. There may be cases where a PE device in full mesh
   initiates MAC flush torwards the core when it detects a spoke PW
   failure. In such a case the PE-ID TLV in MAC flush message
   MAY identify its own VSI in the VPLS instance. Irrespective of
   whether it is the MTU-s or PE device that initiates the MAC flush, a
   PE device receiving the PE-ID TLV SHOULD follow the same processing
   rules as described in this section.

   If MS-PW signaled with GID Element is used in VPLS then a MAC flush
   message is processed only at the T-PE nodes. In this section, a PE
   device signifies only T-PE in MS-PW case unless specified otherwise.

   When a PE device receives a MAC flush with PE-ID TLV, it SHOULD
   flush all the MAC addresses learned in the VPLS from the PW that
   terminates in the remote VSI identified by the PE-ID element.

   If a PE-ID element received in the MAC flush message identifies the
   local VSI, it SHOULD flush the MAC addresses learned from its
   local spoke PW(s) in the VPLS instance.

   If a PE device receives a MAC flush with the PE-ID TLV option
   And a valid MAC address list, it SHOULD ignore the option and deal
   with MAC addresses explicitly as per [RFC4762].

   If a PE device that doesn't support PE-ID TLV receives a MAC flush
   message with this option, it MUST ignore the option and follow the
   processing rules as per [RFC4762].

5.2 Optimized MAC Flush Procedures

   This section explains the optimized MAC flush procedure in the
   scenario in Figure.1.

   When the backup PW is activated by MTU-s, it may send MAC flush
   message to PE-2 with the optional PE-ID TLV. The PE-ID element
   carries the VSI identifier in PE-1 for the VPLS. Upon receipt of the
   MAC flush message, PE-2 identifies the VPLS instance that requires
   MAC flush from the FEC element in the FEC TLV. From the PE-ID TLV,
   PE-2 identifies the PW in the VPLS that terminates in PE-1. PE-2



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   removes all MAC addresses learned from that PW.

   PE-2 relays MAC flush messages with the received PE-ID to all its
   peer PE devices. When the message is received at PE-3, it identifies
   the PW that terminates in the remote VSI in PE-1. PE-3 removes all
   MAC addresses learned on the PW that terminated in PE1.

   There may be redundancy scenerios where a PE device in the full mesh
   may be required to initiate optimized MAC Address Withdrawal.
   Figure 5. shows a redundant H-VPLS topology to protect against
   failure of MTU-s device. Provider RSTP may be used as selection
   algorithm for active and backup PWs in order to maintain the
   connectivity between MTU devices and PE devices at the edge. It is
   assumed that PE devices can detect failure on PWs in either
   direction through OAM mechanisms such as VCCV procedures for
   instance.


               MTU-1================PE-1===============PE-3
                 ||                  || \             /||
                 ||  Redundancy      ||  \           / ||
                 ||  Provider RSTP   ||   Full-Mesh .  ||
                 ||                  ||  /           \ ||
                 ||                  || /             \||
               MTU-2----------------PE-2===============PE-4
                      Backup PW

               Figure 5. Redundancy with Provider RSTP

   MTU-1, MTU-2, PE-1 and PE-2 participate in provider RSTP. By
   configuration in RSTP it is ensured that the PW between MTU-1 and
   PE-1 is active and the PW between MTU-2 and PE-2 is blocked (made
   backup) at MTU-2 end. When the active PW failure is detected by
   RSTP, it activates the PW between MTU-2 and PE-2. When PE-1 detects
   the failing PW to MTU-1, it may trigger MAC flush into the full mesh
   with PE-ID TLV that carries its own VSI identifier in the VPLS.
   Other PE devices in the full mesh that receive the MAC flush
   message identify their respective PWs terminating on PE-1 and
   flush all the MAC addresses learned from it.

   By default, MTU-2 should still trigger MAC flush as currently


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   defined in [RFC4762] after the backup PW is made active by RSTP.
   Mechanisms to prevent two copies of MAC withdraws to be sent in such
   scenerios is out of scope of this document.

   [RFC4762] describes multi-domain VPLS service where fully meshed
   VPLS networks (domains) are connected together by a single spoke
   PW per VPLS service between the VPLS "border" PE devices. To provide
   redundancy against failure of the inter-domain spoke, full mesh of
   inter-domain spokes can be setup between border PE devices and
   provider RSTP may be used for selection of the active inter-domain
   spoke. In case of inter-domain spoke PW failure, PE initiated MAC
   withdrawal may be used for optimized MAC flushing within individual
   domains.


6. General Applicability of PE-ID TLV

   This document defines the PE-ID TLV and its application in optimized
   flushing of MAC addresses in H-VPLS on topology change. The use of
   PE-ID TLV in MAC flush mechanism is OPTIONAL.

   Different H-VPLS redundancy scenarios are possible. The use of the
   PE-ID TLV applies to H-VPLS dual-homing scenarios described in this
   document. The use of the PE-ID TLV in different scenarios is out of
   scope. The protocols used in redundancy scenarios are outside the
   scope. The document doesn't specify the device that should trigger
   optimized MAC flush. The method to select the appropriate PE-ID in
   various redundancy scenarios is out of scope.

   There may be other L2VPN applications where PE-ID TLV may be
   applicable and such applications are outside the scope of this
   document.


7. Security Considerations

   - Control plane aspects
      - LDP security (authentication) methods as described in [RFC5036]
        is applicable here. Further this document implements security
        considerations as in [RFC4447] and [RFC4762].

   - Data plane aspects


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      - This specification does not have any impact on the VPLS
        forwarding plane.


8. IANA Considerations

    The Type field in PE-ID TLV is defined as 0x405 and is subject to
   IANA approval.

9. Acknowledgments

   The authors would like to thank the following people who have
   provided valuable comments and feedback on the topics discussed in
   this document:

   Florin Balus
   Prashanth Ishwar
   Vipin Jain
   John Rigby
   Ali Sajassi


   This document was prepared using 2-Word-v2.0.template.dot.
























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10. References

10.1. Normative References

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

   [RFC4762]   Lasserre, M. and Kompella, V., "Virtual Private LAN
               Services using LDP", RFC 4762, January 2007.

   [RFC5036]   Andersson, L., et al. "LDP Specification",RFC5036,
               October 2007.


10.2. Informative References

   [L2VPN-SIG]      Rosen, E., et al. .Provisioning, Autodiscovery, and
                    Signaling in L2VPNs., work in progress.

   [RFC4664]        Andersson, L., et al. "Framework for Layer 2
                    Virtual Private Networks (L2VPNs)", RFC 4664,
                    September 2006.

   [RFC4447]        Martini. and et al., "Pseudowire Setup and
                    Maintenance Using Label Distribution Protocol
                    (LDP)", RFC 4447, April 2006.

   [802.1w]         "IEEE Standard for Local and metropolitan area
                    networks. Common specifications Part 3: Media
                    Access Control (MAC) Bridges. Amendment 2: Rapid
                    Reconfiguration", IEEE Std 802.1w-2001.















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Author's Addresses

   Pranjal Kumar Dutta
   Alcatel-Lucent
   701 E Middlefield Road,
   Mountain View, CA 94043
   USA

   Email: pdutta@alcatel-lucent.com


   Marc Lasserre
   Alcatel-Lucent

   Email: marc.lasserre@alcatel-lucent.com


   Olen Stokes
   Extreme Networks
   PO Box 14129
   RTP, NC  27709
   USA
   Email: ostokes@extremenetworks.com


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