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Versions: (draft-pdutta-l2vpn-vpls-ldp-mac-opt) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 RFC 7361

Network Working Group                                           P. Dutta
Internet-Draft                                                  F. Balus
Intended status: Standards Track                          Alcatel-Lucent
Expires: December 29, 2014                                     O. Stokes
                                                        Extreme Networks
                                                            G. Calvignac
                                                                  Orange
                                                                D. Fedyk
                                                         Hewlett-Packard
                                                           June 27, 2014


     LDP Extensions for Optimized MAC Address Withdrawal in H-VPLS
                  draft-ietf-l2vpn-vpls-ldp-mac-opt-13

Abstract

   RFC4762 describes a mechanism to remove or unlearn MAC addresses that
   have been dynamically learned in a Virtual Private LAN Service (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 from
   RFC4762, which enables a Provider Edge(PE) device to remove only the
   MAC addresses that need to be relearned.  Additional extensions to
   RFC4762 MAC Withdrawal procedures are specified to provide optimized
   MAC flushing for the Provider Backbone Bridging (PBB)VPLS specified
   in RFC7041.

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 [RFC2119].

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference



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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 31, 2014.

   Copyright Notice

   Copyright (c) 2014 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.

































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.1.  MAC Flush on activation of backup spoke PW . . . . . . . .  7
       3.1.1.  PE-rs initiated MAC Flush  . . . . . . . . . . . . . .  8
       3.1.2.  MTU-s initiated MAC flush  . . . . . . . . . . . . . .  8
     3.2.  MAC Flush on failure . . . . . . . . . . . . . . . . . . .  9
     3.3.  MAC Flush in PBB-VPLS  . . . . . . . . . . . . . . . . . .  9
   4.  Problem Description  . . . . . . . . . . . . . . . . . . . . . 10
     4.1.  MAC Flush Optimization in VPLS Resiliency  . . . . . . . . 10
       4.1.1.  MAC Flush Optimization for regular H-VPLS  . . . . . . 10
       4.1.2.  MAC Flush Optimization for native Ethernet access  . . 12
     4.2.  Black holing issue in PBB-VPLS . . . . . . . . . . . . . . 13
   5.  Solution Description . . . . . . . . . . . . . . . . . . . . . 14
     5.1.  MAC Flush Optimization for VPLS Resiliency . . . . . . . . 14
       5.1.1.  MAC Flush Parameters TLV . . . . . . . . . . . . . . . 15
       5.1.2.  Application of the MAC Flush TLV in Optimized MAC
               Flush  . . . . . . . . . . . . . . . . . . . . . . . . 16
       5.1.3.  MAC Flush TLV Processing Rules for Regular VPLS  . . . 16
       5.1.4.  Optimized MAC Flush Procedures . . . . . . . . . . . . 17
     5.2.  LDP MAC Flush Extensions for PBB-VPLS  . . . . . . . . . . 18
       5.2.1.  MAC Flush TLV Processing Rules for PBB-VPLS  . . . . . 20
       5.2.2.  Applicability of the MAC Flush Parameters TLV  . . . . 21
   6.  Operational Considerations . . . . . . . . . . . . . . . . . . 22
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 23
     7.1 New LDP TLV  . . . . . . . . . . . . . . . . . . . . . . . . 23
     7.2 New Registry for MAC Flush Flags . . . . . . . . . . . . . . 23
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   9.  Contributing Author  . . . . . . . . . . . . . . . . . . . . . 24
   10.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 24
   11.  References  . . . . . . . . . . . . . . . . . . . . . . . . . 24
     11.1.  Normative References  . . . . . . . . . . . . . . . . . . 24
     11.2.  Informative References  . . . . . . . . . . . . . . . . . 24
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25




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



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   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.

   [RFC7041] describes how Provider Backbone Bridging (PBB) can be
   integrated with VPLS to allow for useful PBB capabilities while
   continuing to avoid the use of Multiple Spanning Tree Protocol (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-MAC (Customer MAC) Addresses that need to be
   handled in the VPLS PEs depending on the location of the I-component
   in the PBB-VPLS topology.

   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.  Note that the H-VPLS topology
   in [RFC4762] describes two tier hierarchy to VPLS as the basic
   building block of H-VPLS, but it is possible to have multi-tier
   hierarchy in an H-VPLS.





























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   Figure 1, is reproduced below from [RFC4762] illustrating dual-homing
   in H-VPLS.

                                                            PE2-rs
                                                          +--------+
                                                          |        |
                                                          |   --   |
                                                          |  /  \  |
      CE-1                                                |  \S /  |
        \                                                 |   --   |
         \                                                +--------+
          \  MTU-s                          PE1-rs        /   |
          +--------+                      +--------+     /    |
          |        |                      |        |    /     |
          |   --   |   Primary PW         |   --   |---/      |
          |  /  \  |- - - - - - - - - - - |  /  \  |          |
          |  \S /  |                      |  \S /  |          |
          |   --   |                      |   --   |---\      |
          +--------+                      +--------+    \     |
            /      \                                     \    |
           /        \                                     +--------+
          /          \                                    |        |
         CE-2         \                                   |  --    |
                       \     Secondary PW                 | /  \   |
                        - - - - - - - - - - - - - - - - - | \S /   |
                                                          |  --    |
                                                          +--------+
                                                            PE3-rs
                 Figure 1: An example of a dual-homed MTU-s

   An example usage of the MAC Flush mechanism is the dual-homed H-VPLS
   where an edge device termed as Multi Tenant Unit switch (MTU-
   s)[RFC4762], 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.  There
   could be multiple methods of dual homing in H-VPLS that are not
   described in [RFC4762].  For example, note the following statement
   from section 10.2.1 in [RFC4762].

   "How a spoke is designated primary or secondary is outside the scope
   of this document.  For example, a spanning tree instance running
   between only the MTU-s and the two PE-rs nodes is one possible
   method.  Another method could be configuration".

   This document intends to clarify several H-VPLS dual-homing models
   that are deployed in practice and various use cases of LDP based MAC
   flush in these models.
2.  Terminology



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   This document uses the terminology defined in [RFC7041], [RFC5036],
   [RFC4447] and [RFC4762].

   Throughout this document Virtual Private LAN Service (VPLS) means the
   emulated bridged LAN service offered to a customer.  H-VPLS means the
   hierarchical connectivity or layout of Multi Tenant Unit switch (MTU-
   s) and Provider Edge Routing and switching capable (PE-rs) devices
   offering the VPLS [RFC4762].

   The terms "Spoke Node" and "MTU-s" in H-VPLS are used
   interchangeably.

   "Spoke PW" means the Pseudowire PW that provides connectivity between
   MTU-s and PE-rs nodes.

   "Mesh PW" means the PW that provides connectivity between PE-rs nodes
   in a VPLS full mesh core.

   "MAC Flush Message" means Label Distribution Protocol (LDP) Address
   Withdraw Message without MAC List TLV.

   A MAC Flush Message in the "context of a Pseudo Wire (PW)" means the
   Message that has been received over the LDP session that is used to
   set up the PW used to provide connectivity in VPLS.  The MAC Flush
   Message carries the context of the PW in terms of Forwarding
   Equivalence Class (FEC) TLV associated with the PW
   [RFC4762][RFC4447].

   In general, "MAC Flush" means the method of initiating and processing
   of MAC Flush Messages across a VPLS instance.

3.  Overview

   When the MTU-s switches over to the backup PW, the requirement is to
   flush the MAC addresses learned in the corresponding Virtual Switch
   Instance (VSI) in peer PE devices participating in the full mesh, to
   avoid black holing of frames to those addresses.  This is
   accomplished by sending an LDP Address Withdraw Message, a new
   message defined in this document, from the PE that is no longer
   connected to the MTU-s with the primary PW. The new message has the
   list of MAC addresses to be removed to all other PEs over the
   corresponding LDP sessions.

   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. When a PE-rs switch in the full-mesh of H-
   VPLS receive this message it also flushes MAC addresses which are not



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   affected due to topology change, thus leading to unnecessary flooding
   and relearning. Throughout this document the term "MAC Flush Message"
   is used to specify LDP Address Withdraw Message with an empty MAC
   List described in [RFC4762]. The solutions described in this document
   are applicable only to LDP Address Withdraw Message with empty MAC
   List.

   In a VPLS topology, the core PWs remain active and learning happens
   on the PE-rs nodes.  However when the VPLS topology changes, the
   PE-rs must relearn using MAC Addresses withdrawal or flush.  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 PW associated with this signaling
   session over which the message was received.  Throughout this
   document we use the terminology "Positive" MAC Flush or "Flush-all-
   but-mine" for this type of MAC Flush Message and its actions.

   This document introduces an optimized "Negative" MAC flush described
   in section 3.2 that can be configured to improve the response to
   topology change in a number of Ethernet topologies where the SLA is
   dependent on minimal disruption and fast restoration of affected
   traffic. This new message is used in the case of Provider Backbone
   Bridging (PBB) topologies to restrict the flushing to a set of
   Service Instances (ISIDs). It is also important to note that the
   Positive MAC Flush described in [RFC4762] MUST always be handled for
   BMACs in cases where the core nodes change or fail. Where there is
   dual or multihomed edge topology, the procedures in this document
   augment [RFC4762] messages providing less disruption for those cases.


3.1.  MAC Flush on activation of backup spoke PW

   This section describes scenarios where MAC Flush withdrawal is
   initiated on activation of backup PW in H-VPLS.
















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3.1.1.  PE-rs initiated MAC Flush

   [RFC4762] specifies that on failure of the primary PW, it is the
   PE3-rs (Figure 1) that initiates MAC flush towards the core.  However
   note that PE3-rs can initiate MAC Flush only when PE3-rs is dual
   homing "aware" - that is, there is some redundancy management
   protocol running between MTU-s and its host PE-rs devices.  The scope
   of this document is applicable to several dual-homing or multihoming
   protocols.  The document illustrates that multihoming can be improved
   with the Negative MAC flush.  One example is BGP based multi-homing
   in LDP based VPLS that uses the procedures defined in [I-D.ietf-
   l2vpn-vpls-multihoming].  In this method of dual-homing, PE3-rs would
   neither forward any traffic to MTU-s nor would it receive any traffic
   from MTU-s while PE1-rs is acting as a primary (or designated
   forwarder).

3.1.2.  MTU-s initiated MAC flush

   When dual homing is achieved by manual configuration in MTU-s, the
   hosting PE-rs devices are dual homing "agnostic" and PE3-rs can not
   initiate MAC Flush messages.  PE3-rs can send or receive traffic over
   the backup PW since the dual-homing control is with MTU-s only.  When
   the backup PW is made active by the MTU-s, the MTU-s triggers a MAC
   Flush Message.  The message is sent over the LDP session associated
   with the newly activated PW.  On receiving the MAC Flush Message from
   MTU-s, PE3-rs (PE-rs device with now-active PW) would flush all the
   MAC addresses it has learned except the ones learned over the newly
   activated spoke PW.  PE3-rs further initiates a MAC Flush Message to
   all other PE devices in the core.  Note that forced switchover to
   backup PW can be also performed at MTU-s administratively due to
   maintenance activities on the former primary spoke PW.

   MTU-s initiated method of MAC flushing is modeled after Topology
   Change Notification (TCN) in Rapid Spanning Tree Protocol (RSTP)
   [IEEE.802.1Q-2011].  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.

   The MAC Flush information is propagated in the control plane.  The
   control plane message propagation is associated with the data path
   and hence follows similar rules for propagation as the forwarding in
   the LDP data plane.  For example PE-rs nodes follow the data plane
   "split-horizon" forwarding rules in H-VPLS (Refer to section 4.4 in
   [RFC4762]).  Therefore a MAC Flush is propagated in the context of



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   mesh PW(s) when it is received in the context of a spoke PW.  When a
   PE-rs node receives a MAC Flush in the context of a mesh PW then it
   is not propagated to other mesh PWs.


3.2.  MAC Flush on failure

   MAC Flush on failure or "negative" MAC flush is introduced in this
   document. Negative MAC flush is an improvement on the current
   practice of sending a MAC Flush Message with an empty MAC list
   described in section 3.1.1.  We use the term "negative" MAC flush or
   "Flush-all-from-me" for this kind of flushing action as opposed to
   "positive" MAC Flush action in [RFC4762]. In negative MAC flush, the
   MAC Flush is initiated by PE1-rs (Figure 1) on detection of failure
   of the primary spoke PW. The MAC Flush is sent to all participating
   PE-rs devices in the VPLS full-mesh.  PE1-rs should initiate MAC
   flush only if PE1-rs is dual homing aware.  (If PE1-rs is dual homing
   agnostic, the policy is do not initiate a MAC flush on failure, since
   that could cause unnecessary flushing in the case of single homed
   MTU-s.)  The specific dual-homing protocols for this scenario are
   outside the scope of this document but the operator can choose to use
   the optimized MAC flush described in this document or the [RFC4762]
   procedures.

   The procedure for negative MAC flush is beneficial and results in
   less disruption than the [RFC4762] procedures including when the MTU-
   s is dual homed with a variety of Ethernet technologies not just LDP.
   The Negative MAC flush is a more targeted MAC flush and the other PE-
   rs nodes will flush only the specified MACs.  This targeted MAC flush
   cannot be achieved with the MAC Address Withdraw Message defined in
   [RFC4762].    The negative MAC flush typically results in a smaller
   set of MACs to be flushed and results in less disruption for these
   topologies.

   Note that in the case of negative flush the list SHOULD be only the
   MACs for the affected MTU-s.  If the list is empty then the negative
   flush will result in flushing and relearning all attached MTU-s's for
   the originating PE-rs.

3.3.  MAC Flush in PBB-VPLS

   [RFC7041] 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 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 PE-rs
   devices.  This document describes extensions to LDP MAC Flush
   procedures described in [RFC4762] required to build desirable



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   capabilities to PBB-VPLS solution.

   The solution proposed in this document is generic and is applicable
   when Multi Segment Pseudowires (MS-PW)s [RFC6073] are used in
   interconnecting PE devices in H-VPLS.  There could be other H-VPLS
   models not defined in this document where the solution may be
   applicable.


4.  Problem Description

   This section describes the problems in detail with respective to
   various MAC flush actions described in section 3.

4.1.  MAC Flush Optimization in VPLS Resiliency

   This section describes the optimizations required in MAC flush
   procedures when H-VPLS resiliency is provided by primary and backup
   spoke PWs.

4.1.1.  MAC Flush Optimization for regular H-VPLS

   Figure 2, shows a dual-homed H-VPLS scenario for a VPLS instance
   where the problem with the existing MAC flush method explained in
   section 3.


























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                                 PE1-rs                       PE3-rs
                               +--------+                  +--------+
                               |        |                  |        |
                               |   --   |                  |   --   |
   Customer Site 1             |  /  \  |------------------|  /  \  |->Z
   X->CE-1               /-----|  \s /  |                  |  \s /  |
       \     primary spoke PW  |   --   |           /------|   --   |
        \             /        +--------+          /       +--------+
         \    (MTU-s)/              |    \        /             |
          +--------+/               |     \      /              |
          |        |                |      \    /               |
          |   --   |                |       \  /                |
          |  /  \  |                |      H-VPLS Full Mesh Core|
          |  \s /  |                |       / \                 |
          |   --   |                |      /   \                |
         /+--------+\               |     /     \               |
        /     backup spoke PW       |    /       \              |
       /              \        +--------+         \--------+--------+
   Y->CE-2             \       |        |                  |        |
   Customer Site 2      \------|  --    |                  |  --    |
                               | /  \   |------------------| /  \   |->
                               | \s /   |                  | \s /   |
                               |  --    |                  |  --    |
                               +--------+                  +--------+
                                 PE2-rs                      PE4-rs

           Figure 2: Dual homed MTU-s in two tier hierarchy H-VPLS

   In Figure 2, the MTU-s is dual-homed to PE1-rs and PE2-rs.  Only the
   primary spoke PW is active at MTU-s, thus PE1-rs is acting as the
   active device (designated forwarder) 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 PE1-rs over the primary spoke PW.
   Let's say X represents a set of such MAC addresses located behind
   CE-1.  MAC Z represents one of a possible set of other destination
   MACs. As packets flow from X to other MACs in the VPLS network,
   PE2-rs, PE3-rs and PE4-rs learn about X on their respective mesh PWs
   terminating at PE1-rs.  When MTU-s switches to the backup spoke PW
   and activates it, PE2-rs becomes the active device (designated
   forwarder) to reach the full mesh core for MTU-s.  Traffic entering
   the H-VPLS from CE-1 and CE-2 is diverted by the MTU-s to the spoke
   PW to PE2-rs.  Traffic destined from PE2-rs, PE3-rs and PE4-rs to X
   will be blackholed till MAC address aging timer expires (default is 5
   minutes) or a packet flows from X to other addresses through PE2-rs.

   For example, if after the backup spoke PW is active, if a packet
   flows from MAC Z to MAC X, packets from MAC Z travel from PE3-rs to
   PE-1rs and are dropped.  However, if a packet with MAC X as source



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   and MAC Z as destination arrives at PE2-rs, PE2-rs will now learn MAC
   X is on the backup spoke PW and will forward to MAC Z. At this point
   traffic from PE3-rs to MAC X will go to PE2-rs, since PE-3rs has also
   learned about MAC X. Therefore a mechanism is required to make this
   learning more timely in cases where traffic is not bidirectional.

   To avoid traffic blackholing the MAC addresses that have been learned
   in the upstream VPLS full-mesh through PE1-rs, must be relearned or
   removed from the MAC FIBs in the VSIs at PE2-rs, PE3-rs and PE4-rs.
   If PE1-rs and PE2-rs are dual-homing agnostic then on activation of
   the standby PW from MTU-s, a MAC flush message will be sent by MTU-s
   to PE2-rs that will flush all the MAC addresses learned in the VPLS
   instance at PE2-rs from all the other PWs but the PW connected to
   MTU-s.

   PE2-rs further relays the MAC flush messages to all other PE-rs
   devices in the full mesh.  The same processing rule applies at all
   those PE-rs devices: all the MAC addresses are flushed but the ones
   learned on the PW connected to PE2-rs.  For example, at PE3-rs all of
   the MAC addresses learned from the PWs connected to PE1-rs and PE4-rs
   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-rs 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, described below, is required
   that will flush only the MAC addresses learned from the respective
   PWs between PE1-rs and other PE devices in the full-mesh minimizing
   the relearning and flooding in the network.  In the example above,
   only the MAC addresses in set X and Y (shown in Figure 2) need to be
   flushed across the core.

   The same case is applicable when PE1-rs and PE2-rs are dual homing
   aware and participate in a designated forwarder election.  When
   PE2-rs becomes the active device for MTU-s then PE2-rs MAY initiate
   MAC flush towards the core.  The receiving action of the MAC Flush in
   other PE-rs devices is the same as in MTU-s initiated MAC Flush. This
   is the [RFC4762] specified behavior.

4.1.2.  MAC Flush Optimization for native Ethernet access

   The analysis in section 4.1.1 applies also to the native Ethernet
   access into a VPLS.  In such a scenario one active and one or more
   standby endpoints terminate into two or more VPLS or H-VPLS PE-rs
   devices.  Examples of these dual homed access are ITU-T [ITU.G8032]
   access rings or any proprietary multi-chassis LAG emulations.  Upon



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   failure of the active native Ethernet endpoint on PE1-rs, an
   optimized MAC flush is required to be initiated by PE1-rs to ensure
   that on PE2-rs, PE3-rs and PE4-rs only the MAC addresses learned from
   the respective PWs connected to PE1-rs are being flushed.

4.2.  Black holing issue in PBB-VPLS

   In a PBB-VPLS deployment a B-component VPLS (B-VPLS) may be used as
   infrastructure to support one or more I-component instances.  The
   B-VPLS control plane (LDP Signaling) and learning of "Backbone" MACs
   (BMACs) replaces I-component control plane and learning of customer
   MACs (CMACs) throughout the MPLS core.  This raises an additional
   challenge related to black hole avoidance in the I-component domain
   as described in this section.  Figure 3 describes the case of a CE
   device (node A) dual-homed to two I-component instances located on
   two PBB-VPLS PEs (PE1-rs and PE2-rs).
   IP/MPLS Core
                          +--------------+
                          |PE2-rs        |
                         +----+          |
                         |PBB |   +-+    |
                         |VPLS|---|P|    |
                       S/+----+  /+-+\   |PE3-rs
                       / +----+ /     \+----+
                 +---+/  |PBB |/  +-+  |PBB |   +---+
         CMAC X--|CE |---|VPLS|---|P|--|VPLS|---|CE |--CMAC Y
                 +---+ A +----+   +-+  +----+   +---+
                   A      |PE1-rs        |        B
                          |              |
                          +--------------+
   Figure 3: PBB Black holing Issue - CE Dual-Homing use case

   The link between PE1-rs and CE-A is active (marked with A) while the
   link between CE-A and PE2-rs 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 B-VPLS
   instances on PE1-rs are associated with BMAC B1 and PE2-rs with BMAC
   B2.

   As the packets flow from CMAC X to CMAC Y through PE1-rs with BMAC
   B1, the remote PE-rs devices participating in the B-VPLS with the
   same ISID (for example, PE3-rs) will learn the CMAC X associated with
   BMAC B1 on PE1-rs.  Under a failure condition of the link between CE-
   A and PE1-rs and on activation of the link to PE2-rs, the remote PE-
   rs devices (for example, PE3-rs) will forward the traffic destined
   for customer MAC X to BMAC B1 resulting in PE1-rs blackholing that
   traffic until the aging timer expires or a packet flows from X to Y
   through the PE2-rs, BMAC B2.  This may take a long time (default



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   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 the BMAC associated with the
   PE-rs in the B-VPLS domain where the failure occurred.  This will
   automatically flush the CMAC to BMAC association in the remote PE-rs
   devices.  This solution 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 which propagates the I-component events through the
   backbone infrastructure (B-VPLS) is required in order to flush only
   the CMAC to BMAC associations in the remote PBB-VPLS capable PE-rs
   devices.  Since there are no I-component 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.

5.  Solution Description

   This section describes the solution for the problem space described
   in section 4.

5.1.  MAC Flush Optimization for VPLS Resiliency

   The basic principle of the optimized MAC flush mechanism is explained
   with reference to Figure 2.  The optimization is achieved by
   initiating MAC Flush on failure as described in section 3.2.

   PE1-rs would initiate MAC Flush towards the core on detection of
   failure of primary spoke PW between MTU-s and PE1-rs (or status
   change from active to standby [RFC6718] ).  This method is referred
   to as "MAC Flush on Failure" throughout this document.  The MAC Flush
   message would indicate to receiving PE-rs devices to flush all MACs
   learned over the PW in the context of the VPLS for which the MAC
   flush message is received.  Each PE-rs device in the full mesh that
   receives the message identifies the VPLS instance and its respective
   PW that terminates in PE1-rs from the FEC TLV received in the message
   and/or LDP session.  Thus the PE-rs device flushes only the MAC
   addresses learned from that PW connected to PE1-rs, 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 the MAC Flush TLV.  A MAC Flush TLV carries information
   on the desired action at the PE-rs device receiving the message and
   is used for optimized MAC flushing in VPLS.  The MAC Flush TLV can



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   also be used for [RFC4762] style of MAC Flush as explained in section
   3.

5.1.1.  MAC Flush Parameters TLV

   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(TBDA)|           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 PE-rs devices unaware of the new TLV can just
   propagate it transparently.  In the case of an B-VPLS network that
   has PBB-VPLS in the core with no I-components attached this message
   can still be useful to edge B-VPLS that do have the I-components with
   the ISIDs and understand the message.  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-component 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



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   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
   5.2.

   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 the MAC
   Flush message in [RFC4762].

5.1.2.  Application of the MAC Flush TLV in Optimized MAC Flush

   When optimized MAC flush is supported, the MAC Flush TLV MUST be sent
   as in existing LDP Address Withdraw Message with empty MAC List but
   from the core PE-rs on detection of failure of its local/primary
   spoke PW.  The N bit in TLV MUST be set to 1 to indicate Flush-all-
   from-me.  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-component context the C bit MUST be set (C= 1).
   See section 5.2 for details of its usage in PBB-VPLS context.

   Note that the assumption is the MAC flush TLV is understood by all
   devices before it is turned on in any network.  See Operational
   Considerations section 6.

   When optimized MAC flush is not supported, the MAC withdraw
   procedures defined in [RFC4762], where either the MTU-s or PE2-rs
   send the MAC Withdraw message, SHOULD be used. This includes the case
   where the network is being changed to support optimized MAC flush but
   not all devices are capable of understanding the optimized MAC flush.


   For the case of B-VPLS devices the optimized MAC flush message SHOULD
   be supported.

5.1.3.  MAC Flush TLV Processing Rules for Regular VPLS

   This section describes the processing rules of the MAC Flush TLV that
   MUST be followed in the context of optimized MAC flush procedures in
   VPLS.



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   When optimized MAC flush is supported, a multi-homing PE-rs initiates
   a MAC flush message towards the other related VPLS PE-rs devices 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-rs
   device receiving the MAC Flush TLV SHOULD follow the same processing
   rules as described in this section.

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

   When a PE-rs 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. It is assumed
   when these procedures are used all nodes support the MAC Flush
   Message. See section 6 Operational Considerations for details.

   When Optimized MAC flush is not supported, a MAC Flush TLV is
   received with N = 0 in the MAC flush message then the receiving PE-rs
   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.

   Regardless of whether Optimized MAC flush is supported, if a PE-rs
   device receives a MAC flush with a MAC Flush TLV option (N = 0 or N=
   1) and a valid MAC address list, it SHOULD ignore the option and deal
   with MAC addresses explicitly as per [RFC4762].

5.1.4.  Optimized MAC Flush Procedures

   This section expands on the optimized MAC flush procedure in the
   scenario in Figure 2.

   When Optimized MAC flush is being used a PE-rs that is dual homing
   aware SHOULD send MAC address messages with a MAC Flush TLV and N=1
   provided the other PEs understand the new messages. Upon receipt of
   the MAC flush message, PE2-rs 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.  The same action is followed by PE3-rs and
   PE4-rs.

   Figure 4 shows another redundant H-VPLS topology to protect against
   failure of MTU-s device.  In this case, since there is more than a
   single MTU-S a protocol such as provider RSTP [IEEE.802.1Q-2011] may
   be used as selection algorithm for active and backup PWs in order to



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   maintain the connectivity between MTU-s devices and PE-rs devices at
   the edge.  It is assumed that PE-rs devices can detect failure on PWs
   in either direction through OAM mechanisms such as VCCV procedures
   for instance.

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

                  Figure 4: Redundancy with Provider RSTP

   MTU-1, MTU-2, PE1-rs and PE2-rs participate in provider RSTP.  By
   configuration in RSTP it is ensured that the PW between MTU-1 and
   PE1-rs is active and the PW between MTU-2 and PE2-rs 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 PE2-rs.  When PE1-rs
   detects the failing PW to MTU-1, it MAY trigger MAC flush into the
   full mesh with a MAC Flush TLV that carries N=1.  Other PE-rs devices
   in the full mesh that receive the MAC flush message identify their
   respective PWs terminating on PE1-rs and flush all the MAC addresses
   learned from it.

   [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-rs devices.  To provide
   redundancy against failure of the inter-domain spoke, full mesh of
   inter-domain spokes can be setup between border PE-rs devices and
   provider RSTP may be used for selection of the active inter-domain
   spoke.  In case of inter-domain spoke PW failure, PE-rs initiated MAC
   withdrawal MAY be used for optimized MAC flushing within individual
   domains.

   Further, the procedures are applicable with any native Ethernet
   access topologies multi-homed to two or more VPLS PE-rs devices.  The
   text in this section 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-rs that detects the failure in the primary Ethernet access.

5.2.  LDP MAC Flush 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



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   of a topology change (e.g. failure of a primary link of a VPLS PE-rs
   device 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 affected.

   These goals can be achieved by including the 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
   SHOULD use the information from the new TLV to flush only the related
   FIB entry/entries in the I-component instance(s).

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

   o  PBB BMAC List Sub-TLV:

   Type: IANA TBDB

   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.

   o  PBB ISID List Sub-TLV:

   Type: IANA TBDC

   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



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   FIB(s) where the MAC Flush needs to take place.

5.2.1.  MAC Flush TLV Processing Rules for PBB-VPLS

   The following steps describe the details of the processing rules for
   the MAC Flush TLV in the context of PBB-VPLS. In general these
   procedures are similar to the VPLS case but are tailored to PBB which
   may have a large number of MAC addresses. In PBB there are two sets
   of MAC addresses Backbone (outer) MACs (BMACs) and Customer (inner)
   MACs (CMACs).  C-MACs are associated to remote B-MACs by learning.
   There are also ISIDs which are similar to VLANs for this description.
   In order to get the behavior similar to the Regular VPLS case there
   are some differences in the interpretation of the Optimized MAC flush
   message.

   1. Positive Flush of CMACs. This is equivalent to the [RFC4762] MAC
   flush in a PBB context. In this case the N bit is set to 0; the C bit
   is Set to 1 and CMACs are to be flushed. However since CMACs are
   related to BMACs in an ISID context there is further refinement of
   flushing scope possible.

      - If an ISID needs to be flushed (All CMACs within that ISID) then
      ISIDs are listed in the appropriate TLV. If all ISIDs are to have
      the CMACs flushed then the ISID TLV can be empty.  It is typical
      to flush a single ISID only since each ISID is associated with one
      or more interfaces (typically one in the case of dual homing). In
      the PBB case flushing the ISID is equivalent to the empty MAC list
      in [RFC4762].

      - If only a set of BMAC to CMAC associations need to be flushed,
      then a BMAC list can be included to further refine the list. This
      can be the case if an ISID component has more than one interface
      and a BMAC is used to refine the granularity. Since this is a
      positive MAC flush the intended behavior is flush all CMACs but
      those that are associated with a BMACs in the list.

      Positive Flush of BMACs is also useful for propagating Flush from
      other protocols such as RSTP.

   2. Negative Flush of CMACs. This is the equivalent to the optimized
   MAC flush. In this case the N bit is set to 1; the C bit is Set to 1
   and a list of BMACs is provided so that the respective CMACs can be
   flushed.

      - The ISID list SHOULD be specified. If it is absent then all
      ISIDs require the CMACs to be flushed.

      - A set of BMACs SHOULD be listed since BMAC to CMAC associations



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      need to be flushed and listing BMACs scopes the flush to just
      those BMACs. Again this is typical usage because a PBB VPLS I-
      component interface will have one associated ISID and typically
      one but possibly more than one BMAC each with multiple remotely
      learned CMACs. The BMAC list is included to further refine the
      list for the remote receiver. Since this is a negative MAC flush
      the intended behavior is flush all remote CMACs that are
      associated with any BMACs in the list (in other words from the
      affected interface.)

   The Processing rules on reception of the MAC flush Message are:

   - On a  Backbone Core Bridges (BCB) in if the C-bit is set to 1 then
   the PBB-VPLS SHOULD NOT flush their BMAC FIBs.  The B-VPLS control
   plane SHOULD propagate the MAC Flush following the data-plane split-
   horizon rules to the established B-VPLS topology.

   - On Backbone Edge Bridges (BEB) is as follows:

      - The PBB ISID List is used to determine the particular ISID FIBs
      (I-component) that need to be considered for flushing action.  If
      the PBB ISID List sub-tlv is not included in a received message
      then all the ISID FIBs associated with the receiving B-VPLS SHOULD
      be considered for flushing action.

      - The PBB BMAC List is used to identify from the ISID FIBs in the
      previous step to selectively flush BMAC to CMAC associations
      depending on the N flag specified below.  If PBB BMAC List Sub-TLV
      is not included in a received message then all BMAC to CMAC
      association in all ISID FIBs (I-component) as specified by the
      ISID List are considered for required flushing action, again
      depending on the N flag specified below.

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

      - 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").

      - N=1, all the resulted CMACs 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").

5.2.2.  Applicability of the MAC Flush Parameters TLV

   If MAC Flush Parameters TLV is received by a Backbone Edge Bridges



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   (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-rs devices participating in PBB-VPLS support the MAC Flush
   Parameters TLV.  If this is not possible the MAC Flush Parameters TLV
   SHOULD be disabled as mentioned in section 6 Operational
   Considerations.

   The MAC Flush Parameters TLV is also applicable to regular VPLS
   context as well as explained in section 3.1.1.  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 [ITU.G8032]specification.


6.  Operational Considerations

   As mentioned earlier, if the MAC Flush Parameters TLV is not
   understood by a receiver then it would result in undesired flushing
   action.  To avoid this, one possible solution is to develop an LDP
   based capability negotiation mechanism to negotiate support of
   various MAC Flushing capability between PE-rs devices in a VPLS
   instance.  A negotiation mechanism was discussed and was considered
   outside the scope of this document. Negotiation is not required to
   deploy this optimized MAC flush as described in this document.

   VPLS may be used with or without the optimization.  If an operator
   wants the optimizations for VPLS it is the operator's responsibility
   to make sure the VPLS that are capable of supporting the optimization
   are properly configured.  From operational standpoint, it is
   RECOMMENDED that implementations of the solution provide
   administrative control to select the desired MAC Flushing action
   towards a PE-rs device in the VPLS.  Thus in the topology described
   in figure 2, an implementation could support PE1-rs sending optimized
   MAC Flush towards the PE-rs devices that support the solution and
   PE2-rs device initiating [RFC4762] style of MAC Flush towards the PE-
   rs devices that do not support the optimized solution during
   upgrades. The PE-rs that supports the MAC Flush Parameters TLV MUST
   support the RFC4762 MAC flush procedures since this document only
   augments them.

   For the case of PBB-VPLS this operation is the only method supported
   for specifying ISIDs and the optimization is assumed to be supported
   or should be turned off reverting to flushing using [RFC4762] at the
   Backbone MAC level.





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7.  IANA Considerations

7.1 New LDP TLV

   IANA maintains a registry called "Label Distribution Protocol (LDP)
   Parameters" with a sub-registry called "TLV Type Name Space".

   IANA is requested to allocate three new code points from the
   unassigned range 0x0405-0x04FF as follows. IANA is requested to
   allocate consecutive numbers.

      Value | Description              | Reference  | Notes
      ------+--------------------------+------------+-----------
      TBDA  | MAC Flush Parameters TLV | [This.I-D] |
      TBDB  | PBB BMAC List Sub-TLV    | [This.I-D] |
      TBDC  | PBB ISID List Sub-TLV    | [This.I-D] |

7.2 New Registry for MAC Flush Flags

   IANA is requested to create a new sub-registry under "Label
   Distribution Protocol (LDP) Parameters" called "MAC Flush Flags".

   IANA is requested to populate the registry as follows:

      Bit number | Hex  | Abbreviation | Description      | Reference
      -----------+------+--------------+------------------+-----------
        0        | 0x80 | C            | Context          | [This.I-D]
        1        | 0x40 | N            | Negative flush   | [This.I-D]
        2-7      |      |              | Unassigned       |

   Other new bits are to be assigned by Standards Action.

8.  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]. The extensions defined
   here optimize the flushing and so the risk of security attacks is
   reduced. However, in the event that the configuration of support for
   the new TLV can be spoofed, sub-optimal behavior will be seen.

   Data plane aspects:

   This specification does not have any impact on the VPLS forwarding
   plane but can improve MAC flushing behavior.




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9.  Contributing Author

   The authors would like to thank Marc Lasserre who made a major
   contribution to the development of this document.

   Marc Lasserre

   Alcatel-Lucent

   Email: marc.lasserre@alcatel-lucent.com


10.  Acknowledgements

   The authors would like to thank the following people who have
   provided valuable comments, feedback and review on the topics
   discussed in this document: Dimitri Papadimitriou, Jorge Rabadan,
   Prashanth Ishwar, Vipin Jain, John Rigby, Ali Sajassi, Wim
   Henderickx, Paul Kwok, Maarten Vissers, Daniel Cohn, Nabil Bitar,
   Giles Heron, Adrian Farrel, Ben Niven-Jenkins, Robert Sparks, Susan
   Hares and Stephen Farrell.


11.  References

11.1.  Normative References

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

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

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

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

11.2.  Informative References

   [RFC7041]  Balus, F., Sajassi, A., and N. Bitar, "Extensions to the
              Virtual Private LAN Service (VPLS) Provider Edge (PE)
              Model for Provider Backbone Bridging",RFC 7041,
              November 2013.




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   [I-D.ietf-l2vpn-vpls-multihoming]
              Kothari, B., Kompella, K., Henderickx, W., Balus, F.,
              Palislamovic, S., Uttaro, J., and W. Lin, "BGP based
              Multi-homing in Virtual Private LAN Service",
              draft-ietf-l2vpn-vpls-multihoming-06 (work in progress),
              October 2012.

   [IEEE.802.1Q-2011]
              IEEE, "IEEE Standard for Local and metropolitan area
              networks -- Media Access Control (MAC) Bridges and Virtual
              Bridged Local Area Networks", IEEE Std 802.1Q, 2011.

   [ITU.G8032]
              International Telecommunications Union, "Ethernet ring
              protection switching", ITU-T Recommendation G.8032,
              March 2010.

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

   [RFC6718]  Muley, P., Aissaoui, M., and Bocci, M., "Pseudowire
              Redundancy", RFC 6718, August 2012.

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

Authors' Addresses

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

   Email: pranjal.dutta@alcatel-lucent.com


   Florin Balus
   Alcatel-Lucent
   701 E Middlefield Road
   Mountain View, California  94043
   USA

   Email: florin.balus@alcatel-lucent.com


   Olen Stokes



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   Extreme Networks
   PO Box 14129, RTP
   Raleigh, North Carolina  27709
   USA

   Email: ostokes@extremenetworks.com


   Geraldine Calvginac
   Orange
   2, avenue Pierre-Marzin
   Lannion Cedex,   22307
   France

   Email: geraldine.calvignac@orange.com


   Don Fedyk

   Hewlett-Packard Company
   USA
   Email: don.fedyk@hp.com





























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