L2VPN Working Group                                  Pranjal Kumar Dutta
                                                            Florin Balus
Internet Draft                                            Alcatel-Lucent
Intended status: Standard
Expires: April 29, November 20, 2012                                   Olen Stokes
                                                        Extreme Networks

                                                     Geraldine Calvignac
                                                         France Telecom

                                                       October 31, 2011

                                                        May 20, 2012

       LDP Extensions for Optimized MAC Address Withdrawal in H-VPLS

Status of this Memo

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   [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 MAC
   addresses in the VPLS that do not require relearning due to such
   topology change.

   This document defines an enhancement to the MAC Address Withdrawal
   procedure with empty MAC List [RFC4762], which enables a Provider
   Edge(PE) device to remove only the MAC addresses that need to be

   Additional extensions to [RFC4762] MAC Withdrawal procedures are
   specified to provide optimized MAC flushing for the PBB-VPLS
   specified in [PBB-VPLS Model].

Table of Contents

      1.1. Conventions used in this document.........................3
   2. Introduction...................................................3
   3. Problem Description............................................5
      3.1. MAC Flush optimization in VPLS resiliency.................5
         3.1.1. MAC Flush optimization for regular H-VPLS............5
         3.1.2. MAC Flush optimization for native Ethernet access....7
      3.2. Black holing issue in PBB-VPLS............................8
   4. Solution description...........................................9
      4.1. MAC Flush Optimization for VPLS resiliency................9
         4.1.1. MAC Flush Parameters TLV format.....................10
         4.1.2. Application of MAC Flush TLV in Optimized MAC Flush.11
         4.1.3. MAC Flush TLV Processing Rules for regular H-VPLS...12
         4.1.4. Optimized MAC Flush Procedures......................12
      4.2. LDP MAC Withdraw Extensions for PBB-VPLS.................14
         4.2.1. MAC Flush TLV Processing Rules for PBB-VPLS.........15
   5. Security Considerations.......................................16
   6. IANA Considerations...........................................17
   7. Acknowledgments...............................................17
   8. References....................................................17
      8.1. Normative References.....................................17
      8.2. Informative References...................................17
   Author's Addresses...............................................18

1.1. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119.

   This document uses the terminology defined in [PBB-VPLS Model],
   [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.

2. 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]. Throughout this document this configuration
   is referred to as "regular" H-VPLS.

   [PBB-VPLS Model] describes how Provider Backbone Bridging (PBB) can
   be integrated with VPLS to allow for useful PBB capabilities while
   continuing to avoid the use of MSTP in the backbone. The combined
   solution referred to as PBB-VPLS results in better scalability in
   terms of number of service instances, PWs and C-MACs that need to be
   handled in the VPLS PEs.

   A MAC Address Withdrawal mechanism for VPLS is described in [RFC4762]
   to remove or unlearn MAC addresses for faster convergence on topology
   change in resilient H-VPLS topologies.

   An example of usage of the MAC Flush mechanism is the dual-homed
   H-VPLS where 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 the MTU-s switches over to the backup PW, it is required to
   flush the MAC addresses learned in the corresponding VSI in peer 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 the backup PW is made active
   by the MTU-s, it triggers LDP Address Withdraw Message with a 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 and scalability when a
   MAC List TLV contains a large number of MAC addresses, many
   implementations use 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 MAC Address Withdrawal 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 a MAC flush message to each remote PE
   device 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 a 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 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 it flushes only the
   set of MAC addresses that require relearning when topology changes in
   H-VPLS. The solution proposed in this document is generic and is
   applicable when MS-PWs are used in interconnecting PE devices in

   [PBB-VPLS Model] describes how PBB can be integrated with VPLS to
   allow for useful PBB capabilities while continuing to avoid the use
   of MSTP in the backbone. The combined solution referred as PBB-VPLS
   results in better scalability in terms of number of service
   instances, PWs and C-MACs that need to be handled in the VPLS PEs.

   This document describes also extensions to LDP MAC Flush procedures
   described in [RFC4762] required to build desirable capabilities to
   PBB-VPLS solution.

   Section 3 covers the problem space. Section 4 describes the solution
   and the required TLV extensions.

3. Problem Description

3.1. MAC Flush optimization in VPLS resiliency

3.1.1. MAC Flush optimization for regular H-VPLS

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

                                 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 is acting as the
   active 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 the backup spoke PW and activates it, PE-2
   becomes the active device to reach the full mesh core. Traffic
   entering the H-VPLS from CE-1 and CE-2 is diverted by the MTU-s to
   the spoke PW to PE-2. To avoid traffic blackholing the MAC addresses
   that have been learned in the upstream VPLS full-mesh through PE-1
   must be relearned or removed from the MAC FIBs of PE-2, PE-3 and PE-
   As per the processing rules defined in [RFC4762], on activation of
   the standby PW from MTU-s,a MAC flush message will be sent by MTU-s
   to PE-2 that will flush all the MAC addresses learned in the VPLS
   from all the other PWs but the PWs connected to MTU-s.

   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: all
   the MAC addresses are flushed but the ones learned on the PW to PE2.
   For example, at PE-3 all of the MAC addresses learned from the PWs
   connected to PE-1 and PE-4 are flushed and relearned subsequently.
   Before the relearning happens flooding of unknown destination MAC
   addresses takes place throughout the network. 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. An optimization is
   required that will flush only the MAC addresses learned from the PW
   connected to PE1 to minimize the relearning and flooding in the

   Further the forwarding on MAC Flush by PE-2 delays the over-all MAC
   flush propagation time into the core PEs in full mesh. So it is
   desirable to avoid MAC flush forwarding across multiple PEs as far as
   possible and yet achieve the same desired MAC flushing action.

3.1.2. MAC Flush optimization for native Ethernet access

   The analysis in section 3.1.1 applies also to the native Ethernet
   access into a VPLS where one active and one or more standby endpoints
   into two or more VPLS or H-VPLS PEs are being used. Example of these
   kind of access are ITU-T G.8032 access rings or any proprietary
   multi-chassis LAG emulations.

   Same as in the active/standby PWs case from the previous section,
   upon failure of the active native Ethernet endpoint on PE-1 a MAC
   Flush optimization is required to ensure that on PE-2, PE-3 and PE-4
   only the MAC addresses learned from the PW connected to PE-1 are
   being flushed.

3.2. Black holing issue in PBB-VPLS

   In PBB-VPLS solution a B-component VPLS (B-VPLS) may be used as
   infrastructure for one or more I-component instances. B-VPLS control
   plane (LDP Signaling) replaces I-component control plane throughout
   the MPLS core. This is raising an additional challenge related to
   black hole avoidance in the I-component domain as described in this
   section. Figure 2 describes the case of a CE device (node A) dual-
   homed to two I-component instances located on two PBB-VPLS PEs (PE1
   and PE2).

                            IP/MPLS Core
                          |PE2           |
                         +----+          |
                         |PBB |   +-+    |
                     _   |VPLS|---|P|    |
                       S/+----+  /+-+\   |PE3
                       / +----+ /     \+----+
                 +---+/  |PBB |/  +-+  |PBB |   +---+
         CMAC X--|CE |---|VPLS|---|P|--|VPLS|---|CE |--CMAC Y
                 +---+ A +----+   +-+  +----+   +---+
                   A      |PE1           |        B
                          |              |
        Figure 2: PBB Black holing Issue - CE Dual-Homing use case

   The link between PE1 and CE A is active (marked with A) while the
   link between CE A and PE2 is in Standby/Blocked status. In the
   network diagram CMAC X is one of the MAC addresses located behind CE
   A in the customer domain, CMAC Y is behind CE B and the BVPLS
   instances on PE1 are associated with backbone MAC (BMAC) B1 and PE2
   with BMAC B2.

   As the packets flow from CMAC X to CMAC Y through PE1 of BMAC B1, the
   remote PEs participating in the IVPLS (for example, PE3) will learn
   the CMAC X associated with BMAC B1 on PE1. Under failure of the link
   between CE A and PE1 and activation of link to PE2, the remote PEs
   (for example, PE3) will black-hole the traffic destined for customer
   MAC X to BMAC B1 until the aging timer expires or a packet flows from
   X to Y through the PE B2. This may take a long time (default aging
   timer is 5 minutes) and may affect a large number of flows across
   multiple I-components.

   A possible solution to this issue is to use the existing LDP MAC
   Flush as specified in [RFC4762] to flush in the BVPLS domain the BMAC
   associated with the PE where the failure occurred. This will
   automatically flush the CMAC to BMAC association in the remote PEs.
   This solution though has the disadvantage of producing a lot of
   unnecessary MAC flush in the B-VPLS domain as there was no failure or
   topology change affecting the Backbone domain.

   A better solution is required to propagate the I-component events
   through the backbone infrastructure (B-VPLS) in order to flush only
   the customer MAC to BMAC entries in the remote PBB-VPLS PEs. As there
   are no IVPLS control plane exchanges across the PBB backbone,
   extensions to B-VPLS control plane are required to propagate the I-
   component MAC Flush events across the B-VPLS.

4. Solution description

4.1. MAC Flush Optimization for VPLS resiliency

   The basic principle of the optimized MAC flush mechanism is explained
   with reference to Figure 1.

   PE-1 would initiate MAC Flush towards the core on detection of
   failure of primary spoke PW between MTU-S and PE-1 (or status change
   from active to standby). This method is referred as PE initiated MAC
   Flush throughout this document. The MAC Flush message would indicate
   to receiving PEs to flush all MACs learned over the PW in the context
   of the VPLS over which the MAC flush message is received. Each PE
   device in the full mesh that receives the message identifies the VPLS
   instance and its respective PW that terminates in PE-1 from the FEC
   TLV received in the message. Thus the PE device flushes only the MAC
   addresses learned from that PW connected to PE-1 minimizing the
   required relearning and the flooding throughout the VPLS domain.

   This section defines a generic MAC Flush Parameters TLV for LDP
   [RFC5036]. Through out this document the MAC Flush Parameters TLV is
   referred as MAC Flush TLV. A MAC Flush TLV carries information on the
   desired action at the PE device receiving the message and is used for
   optimized MAC flushing in H-VPLS.  The MAC Flush TLV can also be used
   for [RFC4762] style of MAC Flush as explained in section 3.1.

4.1.1. MAC Flush Parameters TLV format

   The MAC Flush Parameters TLV is described as below:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |1|1| MAC Flush Params TLV(TBD) |           Length              |
   |     Flags     | Sub-TLV Type  |         Sub-TLV Length        |
   |                Sub-TLV Variable Length Value                  |
   |                             "                                 |

   The U and F bits are set to forward if unknown so that potential
   intermediate VPLS PEs unaware of the new TLV can just propagate it
   transparently. The MAC Flush Parameters TLV type is to be assigned by
   IANA. The encoding of the TLV follows the standard LDP TLV encoding
   in [RFC5036].

   The TLV value field contains a one byte Flag field used as described
   below. Further the TLV value may carry one or more sub-TLVs. Any sub-
   TLV definition to the above TLV MUST address the actions in
   combination with other existing sub-TLVs.

   The detailed format for the Flags bit vector is described below:

    0 1 2 3 4 5 6 7


   |C|N|    MBZ    | (MBZ = MUST Be Zero)


   1 Byte Flag field is mandatory. The following flags are defined:

     C flag, used to indicate the context of the PBB-VPLS component in
     which MAC flush is required. For PBB-VPLS there are two contexts of
     MAC flushing - The Backbone VPLS (B-component VPLS) and Customer
     VPLS (I-component VPLS). C flag MUST be ZERO (C=0) when a MAC Flush
     for the B-VPLS is required. C flag MUST be set (C=1) when the MAC
     Flush for I-VPLS is required. In the regular H-VPLS case the C flag
     must be ZERO (C=0) to indicate the flush applies to the current
     VPLS context.

     N flag, used to indicate whether a positive (N=0, Flush-all-but-
     mine) or negative (N=1 Flush-all-from-me) MAC Flush is required.
     The source (mine/me) is defined either as the PW associated with
     the LDP session on which the LDP MAC Withdraw was received or with
     the BMAC(s) listed in the BMAC Sub-TLV. For the optimized MAC Flush
     procedure described in this section the flag must be set (N=1).

     Detailed usage in the context of PBB-VPLS is explained in section

     MBZ flags, the rest of the flags should be set to zero on
     transmission and ignored on reception.

     The MAC Flush TLV SHOULD be placed after the existing TLVs in MAC
     Flush message in [RFC4762].

4.1.2. Application of MAC Flush TLV in Optimized MAC Flush

   For optimized MAC flush, the MAC Flush TLV MAY be sent as in existing
   LDP Address Withdraw Message with empty MAC List but from the core PE
   on detection of failure of its local spoke PW. The N bit in TLV MUST
   be set to 1. If the optimized MAC Flush procedure is used in a
   Backbone VPLS or regular VPLS/H-VPLS context the C bit must be ZERO
   (C=0). If it is used in an I-VPLS context the C bit must be set (C=
   1). See section 4.2 for PBB-VPLS details.

   Note that if MAC Flush TLV is not understood by a receiver (i.e. a
   legacy PE) then it may result in undesired action. For example if a
   MAC Flush Parameters TLV is received with N=1 and receiver does not
   understand that TLV then it would result in flushing of all MACs
   learned in the VSI except the ones learned over the PW.

   To emulate the MAC flush initiation procedures defined in [RFC4762],
   the PE-1 MAY send MAC Flush TLV as an OPTIONAL TLV in the MAC Flush
   Message with N = 0. This would result in same flushing action at
   receiving PE devices.

4.1.3.  MAC Flush TLV Processing Rules for regular H-VPLS

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

   For optimized MAC Flush a multi-homing PE initiates MAC flush message
   towards the other related VPLS PEs when it detects a transition
   (failure or to standby) in its active spoke PW. In such case the MAC
   Flush TLV MUST be sent with N= 1. A PE device receiving the MAC Flush
   TLV SHOULD follow the same processing rules as described in this

   Note that if MS-PW is used in VPLS then a MAC flush message is
   processed only at the T-PE nodes since S-PE(s) traversed by the MS-PW
   propagate MAC flush messages without any action. In this section, a
   PE device signifies only T-PE in MS-PW case unless specified

   When a PE device receives a MAC Flush TLV with N = 1, it SHOULD flush
   all the MAC addresses learned from the PW in the VPLS in the context
   on which the MAC Flush message is received.

   If a MAC Flush TLV is received with N = 0 in the MAC flush message
   then the receiving PE SHOULD flush the MAC addresses learned from all
   PWs in the VPLS instance except the ones learned over the PW on which
   the message is received.

   If a PE device receives a MAC flush with the MAC Flush 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 MAC Flush TLV receives a MAC
   flush message with this option, it MUST ignore the option and follow
   the processing rules as per [RFC4762]. However if MAC Flush
   Parameters TLV was sent with N = 1 then it may result in wrong
   flushing action (Positive MAC Flush).

4.1.4. Optimized MAC Flush Procedures

   This section explains the optimized MAC flush procedure in the
   scenario in Figure 1. When the primary spoke PW transition (failure
   or standby transition) is detected by PE-1, it may send MAC flush
   messages to PE-2, PE-3 and PE-4 with MAC Flush TLV  and N = 1. 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. On
   receiving N=1, PE-2 removes all MAC addresses learned from that PW
   over which the message is received. Same action is followed by PE-3
   and PE-4.

   Figure 3 shows another 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.

                 ||                  || \             /||
                 ||  Redundancy      ||  \           / ||
                 ||  Provider RSTP   ||   Full-Mesh .  ||
                 ||                  ||  /           \ ||
                 ||                  || /             \||
                      Backup PW

               Figure 3: 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 MAC Flush TLV that carries N=1. 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 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 scenarios
   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

   Further, the procedures are applicable with any native Ethernet
   access topologies multi-homed to two or more VPLS PEs. The text in
   section 4.1 applies for the native Ethernet case where active/standby
   PWs are replaced with the active/standby Ethernet endpoints. An
   optimized MAC Flush message can be generated by the VPLS-PE that
   detects the failure in the primary Ethernet access.

4.2. LDP MAC Withdraw Extensions for PBB-VPLS

   The use of Address Withdraw message with MAC List TLV is proposed in
   [RFC4762] as a way to expedite removal of MAC addresses as the result
   of a topology change (e.g. failure of a primary link of a VPLS PE and
   implicitly the activation of an alternate link in a dual-homing use
   case). These existing procedures apply individually to B-VPLS and I-
   component domains.

   When it comes to reflecting topology changes in access networks
   connected to I-component across the B-VPLS domain certain additions
   should be considered as described below.

   MAC Switching in PBB is based on the mapping of Customer MACs (CMACs)
   to Backbone MAC(s) (BMACs). A topology change in the access (I-
   domain) should just invoke the flushing of CMAC entries in PBB PEs'
   FIB(s) associated with the I-component(s) impacted by the failure.
   There is a need to indicate the PBB PE (BMAC source) that originated
   the MAC Flush message to selectively flush only the MACs that are

   These goals can be achieved by adding a new MAC Flush Parameters TLV
   in the LDP Address Withdraw message to indicate the particular
   domain(s) requiring MAC flush. On the other end, the receiving PEs
   may use the information from the new TLV to flush only the related
   FIB entry/entries in the I-component instance(s).

   The following sub-TLVs MUST be included in the MAC Flush Parameters
   TLV if the C-flag is set to 1:

   - PBB BMAC List sub-TLV:

   Type: 0x01

   Length: value length in octets. At least one BMAC address must be
   present in the list.

   Value: one or a list of 48 bits BMAC addresses. These are the source
   BMAC addresses associated with the B-VPLS instance that originated
   the MAC Withdraw message. It will be used to identify the CMAC(s)
   mapped to the BMAC(s) listed in the sub-TLV.

   - PBB ISID List sub-TLV:

   Type: 0x02,

   Length: value length in octets. Zero indicates an empty ISID list. An
   empty ISID list means that the flush applies to all the ISIDs mapped
   to the B-VPLS indicated by the FEC TLV.

   Value: one or a list of 24 bits ISIDs that represent the I-component
   FIB(s) where the MAC Flush needs to take place.

4.2.1. MAC Flush TLV Processing Rules for PBB-VPLS

   The following steps describe the details of the processing for the
   related LDP Address Withdraw message:

   . The LDP MAC Withdraw Message, including the MAC Flush Parameters
     TLV is initiated by the PBB PE(s) experiencing a Topology Change
     event in one or multiple customer I-component(s).

          o The flags are set accordingly to indicate the type of MAC
             Flush required for this event: N=0 (Flush-all-but-mine),
             C=1 (Flush only CMAC FIBs).

          o The PBB Sub-TLVs (BMAC and ISID Lists) are included
             according to the context of topology change.

   . On reception of the LDP Address Withdrawal message, the B-VPLS
     instances corresponding to the FEC TLV in the message must
     interpret the content of MAC Flush Parameters TLV. If the C-bit is
     set to 1 then Backbone Core Bridges (BCB) in the PBB-VPLS SHOULD
     NOT flush their BMAC FIBs. The B-VPLS control plane SHOULD
     propagate the MAC Flush following the split-horizon grouping and
     the established B-VPLS topology.

   . The usage and processing rules of MAC Flush Parameters TLV in the
     context of Backbone Edge Bridges (BEB) is as follows:

          o  The PBB ISID List is used to determine the particular ISID
             FIBs (I-VPLS) that need to be flushed. If the ISID List is
             empty then all the ISID FIBs associated with the receiving
             B-VPLS SHOULD be flushed.

          o  The PBB BMAC List is used to identify from the ISID FIBs to
             in the previous step to selectively flush BMAC to CMAC
             associations depending on the N flag specified below.

   .  Next, depending on the N flag value the following actions apply:

          o  N=0, all the CMACs in the selected ISID FIBs SHOULD be
             flushed with the exception of the resulted CMAC list from
             the BMAC List mentioned in the message. ("Flush all but the
             CMACs associated with the BMAC(s) in the BMAC List Sub-TLV
             from the FIBs associated with the ISID list").

          o  N=1, the resulted CMAC list SHOULD be flushed ("Flush all
             the CMACs associated with the BMAC(s) in the BMAC List Sub-
             TLV from the FIBs associated with the ISID list").

   4.2.3 Applicability of MAC Flush Parameters TLV

         If MAC Flush Parameters TLV is received by a BEB in a PBB-VPLS
   that does not understand the TLV then it may result in undesirable
   MAC flushing action. It is RECOMMENDED that all PE devices
   participating in PBB-VPLS support MAC Flush Parameters TLV.

        The MAC Flush Parameters TLV is also applicable to regular VPLS
   context as well. To achieve negative MAC Flush (flush-all-from-me) in
   regular VPLS context, the MAC Flush Parameters TLV SHOULD be encoded
   with C=0 and N = 1 without inclusion of any Sub-TLVs. Negative MAC
   flush is highly desirable in scenarios when VPLS access redundancy is
   provided by Ethernet Ring Protection as specified in ITU-T G.8032
   specification etc.

5. 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:

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

6. IANA Considerations

   The Type field in MAC Flush Parameters TLV is defined as 0x406 and is
   subject to IANA approval.

7. Acknowledgments

   The authors would like to thank the following people who have
   provided valuable comments and feedback on the topics discussed in
   this document: Marc Lasserre, Don Fedyk, Dimitri Papadimitriou, Jorge
   Rabadan, Prashanth Ishwar, Vipin Jain, John Rigby, Ali Sajassi, Wim
   Henderickx, Jorge Rabadan, Maarten Vissers and Daniel Cohn.

8. References

8.1. Normative References

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

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

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

8.2. Informative References

   [PBB-VPLS Model] F. Balus, et Al. "Extensions to VPLS PE model for
             Provider Backbone Bridging", draft-ietf-l2vpn-pbb-vpls-pe-
             model-00.txt, May 2009 (work in progress)

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

Author's Addresses

   Pranjal Kumar Dutta
   701 E Middlefield Road,
   Mountain View, CA 94043
   Email: pranjal.dutta@alcatel-lucent.com

   Florin Balus
   701 E. Middlefield Road
   Mountain View, CA, USA 94043
   Email: florin.balus@alcatel-lucent.com

   Geraldine Calvignac
   France Telecom
   2, avenue Pierre-Marzin
   22307 Lannion Cedex
   Email: geraldine.calvignac@orange-ftgroup.com

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