TRILL Working Group                                  Tissa Senevirathne
Internet Draft                                                    CISCO
Intended status: Standard Track                    Janardhanan Pathangi
Updates: 6325                                                      DELL
                                                             Jon Hudson

                                                        October 2, 2013
Expires: April 2014

                Coordinated Multicast Trees (CMT) for TRILL

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Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
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   publication of this document. Please review these documents

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   carefully, as they describe your rights and restrictions with
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   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.


   TRILL facilitates loop free connectivity to non-TRILL legacy
   networks via choice of an Appointed Forwarder for a set of VLANs.
   Appointed Forwarder provides load sharing based on VLAN with an
   active-standby model. Mission critical operations such as High
   Performance Data Centers require active-active load sharing model.
   Active-Active load sharing model can be accomplished by representing
   any given non-TRILL legacy network with a single virtual RBridge.
   Virtual representation of the non-TRILL legacy network with a single
   RBridge poses serious challenges in multi-destination RPF (Reverse
   Path Forwarding) check calculations. This document specifies
   required enhancements to build Coordinated Multicast Trees (CMT)
   within the TRILL campus to solve related RPF issues. CMT provides
   flexibility to RBridges in selecting  desired path of association to
   a given TRILL multi-destination distribution tree.

Table of Contents

   1. Introduction...................................................3
      1.1. Scope and Applicability...................................5
      1.2. Contributors..............................................5
   2. Conventions used in this document..............................5
      2.1. Acronyms..................................................5
   3. The AFFINITY sub-TLV...........................................6
   4. Multicast Tree Construction and Use of Affinity Sub-TLV........6
      4.1. Update to RFC 6325........................................7
      4.2. Announcing virtual RBridge nickname.......................8
      4.3. Affinity Sub-TLV Capability...............................8
   5. Theory of operation............................................9
      5.1. Distribution Tree provisioning............................9
      5.2. Affinity Sub-TLV advertisement............................9
      5.3. Affinity sub-TLV conflict resolution......................9
      5.4. Ingress Multi-Destination Forwarding.....................10
         5.4.1. Forwarding when n < k...............................10
      5.5. Egress Multi-Destination Forwarding......................11
         5.5.1. Traffic Arriving on an assigned Tree to RBk-RBv.....11
         5.5.2. Traffic Arriving on other Trees.....................11
      5.6. Failure scenarios........................................11
         5.6.1. Edge RBridge RBk failure............................11

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      5.7. Backward compatibility...................................12
   6. Security Considerations.......................................12
   7. IANA Considerations...........................................13
   8. References....................................................13
      8.1. Normative References.....................................13
      8.2. Informative References...................................14
   9. Acknowledgments...............................................14
   Appendix A. Change History.......................................15

1. Introduction

   TRILL (Transparent Interconnection of Lots of Links) presented in
   [RFC6325] and other related documents, provides methods of utilizing
   all available paths for active forwarding, with minimum
   configuration. TRILL utilizes IS-IS (Intermediate System to
   Intermediate System) as its control plane and uses a TRILL header
   with hop count.

    [RFC6325], [6327bis] and [RFC6439] provide methods for
   interoperability between TRILL and Legacy networks. [RFC6439],
   provide an active-standby solution, where only one of the RBridges
   on a link with end stations is in the active forwarding state for
   end station traffic for any given VLAN. The RBridge in active
   forwarding state for any given VLAN is referred to as the Appointed
   Forwarder (AF). All frames ingressed into a TRILL network via the
   Appointed Forwarder are encapsulated with the TRILL header with a
   nickname held by the ingress AF RBridge. Due to failures, re-
   configurations and other network dynamics, the Appointed Forwarder
   for any set of VLANs may change. RBridges maintain forwarding tables
   that contain destination MAC address and VLAN to egress RBridge
   binding. In the event of AF change, forwarding tables of remote
   RBridges may continue to forward traffic to the previous AF and that
   traffic may get discarded at the egress, causing traffic disruption.

   Mission critical applications such as High Performance Data Centers
   require resiliency during failover. The active-active forwarding
   model minimizes impact during failures and maximizes the available
   network bandwidth. A typical deployment scenario, depicted in Figure
   1, which may have either End Stations and/or Legacy bridges attached
   to the RBridges.  These Legacy devices typically are multi-homed to
   several RBridges and treat all of the uplinks as a single Multi-
   Chassis Link Aggregation (MC-LAG) bundle. The Appointed Forwarder
   designation presented in [RFC6439] requires each of the edge
   RBridges to exchange TRILL hello packets. By design, an MC-LAG does
   not forward packets received on one of the member ports of the MC-
   LAG to other member ports of the same MC-LAG. As a result the AF

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   designation methods presented in [RFC6439] cannot be applied to
   deployment scenario depicted in Figure 1.

   An active-active load-sharing model can be implemented by
   representing the edge of the network connected to a specific edge
   group of RBridges by a single virtual RBridge. Each virtual RBridge
   MUST have a nickname unique within its TRILL campus. In addition to
   an active-active forwarding model, there may be other applications
   that may requires similar representations.

   Sections 4.5.1 and 4.5.2 of [RFC6325] as updated by [clearcor]
   specify distribution tree calculation and RPF (Reverse Path
   Forwarding) check calculation algorithms for multi-destination
   forwarding. These algorithms strictly depend on link cost and parent
   RBridge priority. As a result, based on the network topology, it may
   be possible that a given edge RBridge, if it is forwarding on behalf
   of the virtual RBridge, may not have a candidate multicast tree that
   the edge RBridge can forward traffic on because there is no tree for
   which the virtual RBridge is a leaf node from the edge RBridge.

   In this document we present a method that allows RBridges to specify
   the path of association for real or virtual child nodes to
   distribution trees. Remote RBridges calculate their  forwarding
   tables and derive the RPF for distribution trees based on the
   distribution tree association advertisements. In the absence of
   distribution tree association advertisements, remote RBridges derive
   the SPF (Shortest Path First) based on the algorithm specified in
   section 4.5.1 of [RFC 6325].

   Other applications, beside the above mentioned active-active
   forwarding model, may utilize the distribution tree association
   framework presented in this document to associate to distribution
   trees through a preferred path.

   This proposal requires presence of multiple multi-destination trees
   within the TRILL campus and updating all the RBridges in the network
   to support the new Affinity sub-TLV (Section 3. ). It is expected
   that both of these requirements will be met as they are control
   plane changes, and will be common deployment scenarios. In case
   either  of the above two conditions are not met RBridges MUST
   support a fallback option for interoperability. Since the fallback
   is expected to be a temporary phenomenon till all RBridges are
   upgraded, this proposal gives guidelines for such fallbacks, and
   does not mandate or specify any specific set of fallback options.

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1.1. Scope and Applicability

   This document specifies an Affinity sub-TLV to solve associated RPF
   issues at the active-active edge. Specific methods in this document
   for making use of the Affinity sub-TLV are applicable where multiple
   RBridges are connected to an edge device through multi-chassis link
   aggregation or to a multiport server or some similar arrangement
   where the RBridges cannot see each other's Hellos.

   This document DOES NOT provide other required operational elements
   to implement active-active edge solution, such as methods of multi-
   chassis link aggregation. Solution specific operational elements are
   outside the scope of this document and will be covered in solution
   specific documents. (See, for example [TRILLPN].)

   Examples provided in this document are for illustration purposes

1.2. Contributors

   The work in this document is a result of much passionate discussions
   and contributions from following individuals. Their names are listed
   in alphabetical order:

   Ayan Banerjee, Dinesh Dutt, Donald Eastlake, Mingui Zhang, Radia
   Perlman, Sam Aldrin, Shivakumar Sundaram and Zhai Hongjun.

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying [RFC2119] significance.

2.1. Acronyms

  MC-LAG: . Multi-Chassis Link Aggregation is a solution specific
  extension to [8021AX], that facilitates connecting group of links
  from an originating device (A) to group discrete devices (B). Device
  (A) treats, all of the links in a given Multi-Chassis Link
  Aggregation bundle as a single logical interface and treats all
  devices in Group (B) as a single logical device for all forwarding
  purposes. Device (A) does not forward packets receive on Multi-

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  Chassis Link bundle out of the same Multi-Chassis link bundle. Figure
  1 depicts a specific use case example.

   CE : Classical Ethernet device, that is a device that performs
   forwarding based on 802.1Q bridging. This also can be end-station or
   a server.

   RPF: Reverse Path Forwarding. See section 4.5.2 of [RFC6325].


   Association of an RBridge to a multi-destination distribution tree
   through a specific path is accomplished by using a new IS-IS sub-
   TLV, the Affinity sub-TLV.

   The AFFINITY sub-TLV appears in Router capability TLVs that are
   within LSP PDUs, as described in [6326bis] which specifies the code
   point and data structure for the Affinity sub-TLV.

4.    Multicast Tree Construction and Use of Affinity Sub-TLV

   Figure 1 and Figure 2 below show the reference topology and a
   logical topology using CMT to provide active-active service.

             /                    \
            |                      |
            |   TRILL Campus       |
            |                      |
             \                    /
                 |       |    |
            -----        |     --------
           |             |             |
       +------+      +------+      +------+
       |      |      |      |      |      |
       |(RB1) |      |(RB2) |      | (RBk)|
       +------+      +------+      +------+
         |..|          |..|          |..|
         |  +----+     |  |          |  |
         |   +---|-----|--|----------+  |
         | +-|---|-----+  +-----------+ |
 MC-     | | |   +------------------+ | |
 LAG--->(| | |)                    (| | |) <- MC-LAG

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       +-------+    .  .  .       +-------+
       | CE1   |                  | CEn   |
       |       |                  |       |
       +-------+                  +-------+

                        Figure 1 Reference Topology

            ------------------              Sample Multicast Tree (T1)
           /                    \
          |                      |                  |
          | TRILL Campus         |                  o RBn
          |                      |                / | \
           \                     /               /  |  ---\
            ---------------------             RB1o  o      o
               |       |    |                    |   RB2    RBk
   |           |       |     ----------          |
               |       |              |          oRBv
           +------+ +------+      +------+
           |      | |      |      |   |
           |(RB1) | |(RB2) |      | (RBk)|
           +------+ +------+      +------+
               |..|       |..|             |..|
               |  +----+  |  |             |  |
               |   +---|--|--|-------------+  |
               | +-|---|--+  +--------------+ |
       MC-     | | |   +------------------+ | |
       LAG--->(| | |)                    (| | |) <- MC-LAG
              +-------+    .  .  .       +-------+
              | CE1   |                  | CEn   |
              |       |                  |       |
              +-------+                  +-------+

                     Figure 2 Example Logical Topology

4.1. Update to RFC 6325

   Section 4.5.1 of [RFC6325], is updated as below:

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   Each RBridge that desires to be the parent RBridge for child Rbridge
   RBy  in a  multi-destination distribution tree x  announces the
   desired association using an Affinity sub-TLV. The child RBridge RBy
   is specified by its nickname (or one of its nicknames if it hold
   more than one).

   When such an Affinity sub-TLV is present, the association specified
   by the affinity sub-TLV MUST be used when constructing the  multi
   destination distribution tree except in case of conflicting Affinity
   sub-TLV which are resolved as specified in Section 5.3.   In the
   absence of such an Affinity sub-TLV, or if there are any RBRidges in
   the campus that are do not support Affinity sub-TLV, distribution
   trees  tree are  calculated as specified in the section 4.5.1 of
   [RFC6325] as updated by [clearcor]. Section 4.3. below specifies how
   to identify RBridges that support Affinity sub-TLV capability.

4.2. Announcing virtual RBridge nickname

   Each edge RBridge RB1 to RBk advertises in its LSP virtual RBridge
   nickname RBv using the Nickname sub-TLV (6), [6326bis], along with
   their regular nickname or nicknames.

   It will be possible for any RBridge to determine that RBv is a
   virtual RBridge because each RBridge (RB1 to RBk) this appears to be
   advertising that it is holding RBv is also advertising an Affinity
   sub-TLV asking that RBv be its child in one or more trees.

      Virtual RBridges are ignored when determining the distribution
   tree roots for the campus.

      All RBridges outside the edge group assume that multi-destination
   packets with ingress nickname RBv might use any of the distribution
   trees that any member of the edge group is advertising that it might

4.3. Affinity Sub-TLV Capability.

   RBridges that announce the TRILL version sub-TLV [6326bis] and set
   the Affinity capability bit (Section 7. ) support the Affinity sub-
   TLV and calculation of multi-destination distribution trees and RPF
   checks as specified herein.

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5. Theory of operation

5.1. Distribution Tree provisioning

   Let's assume there are n distribution trees and k edge RBridges in
   the edge group of interest.

   If n >= k

     Let's assume edge RBridges are sorted in numerically ascending
     order by SystemID such that RB1 < RB2 < RBk. Each Rbridge in the
     numerically sorted list is assigned a monotonically increasing
     number j such that; RB1=0, RB2=1, RBi=j and RBi+1=j+1.

     Assign each tree to RBi such that tree number { (tree_number) %
     k}+1 is assigned to RBridge i for tree_number from 1 to n. where n
     is the number of trees and k is the number of RBridges considered
     for tree allocation.

   If n < k

     Distribution trees are assigned to RBridges RB1 to RBn, using the
     same algorithm as n >= k case. RBridges RBn+1 to RBk do not
     participate in active-active forwarding process on behalf of RBv.

5.2. Affinity Sub-TLV advertisement

   Each RBridge in the RB1..RBk domain advertises an Affinity TLV for
   RBv to be its child.

   As an example, let's assume that RB1 has chosen Trees t1 and tk+1 on
   behalf of RBv.

   RB1 advertises affinity TLV; {RBv, Num of Trees=2, t1, tk+1.

   Other RBridges in the RB1..RBk edge group follow the same procedure.

5.3. Affinity sub-TLV conflict resolution

   In TRILL, multi-destination distribution trees are built outward
   from the root. If an RBridges RB1 advertises an Affinity sub-TLV
   with an AFFINITY RECORD that asks for RBridge RBroot to be its child
   in a tree rooted at RBroot, that AFFINITY RECORD is in conflict with
   TRILL distribution tree root determination and MUST be ignored.

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      If an RBridge RB1 advertises an Affinity sub-TLV with an AFFINITY
   RECORD that's ask for nickname RBn to be its child in any tree and
   RB1 is not adjacent to a real or virtual RBridge RBn, that AFFINITY
   RECORD is in conflict with the campus topology and MUST be ignored.

   If different RBridges advertise Affinity sub-TLVs that try to
   associate the same virtual RBridge as their child in the same tree
   or trees, those Affinity sub-TLVs are in conflict for those trees.
   The nicknames of the conflicting RBridges are compared to identify
   which RBridge holds the nickname that is the highest priority to be
   a tree root, with the System ID as the tie breaker

   The RBridge with the highest priority to be a tree root will retain
   the Affinity association. Other RBridges with lower priority to be a
   tree root MUST stop advertising their conflicting Affinity sub-TLV,
   re-calculate the multicast tree affinity allocation, and, if
   appropriate, advertise a new non-conflict Affinity sub-TLV.

   Similarly, remote RBridges MUST honor the Affinity sub-TLV from the
   RBridge with the highest priority to be a tree root (use system-ID
   as the tie-breaker in the event of conflicting priorities) and
   ignore the conflicting Affinity sub-TLV entries advertised by the
   RBridges with lower priorities to be tree roots.

5.4. Ingress Multi-Destination Forwarding

   If there is at least one tree on which RBv has affinity via RBk,
   then RBk performs the following operations, for multi-destination
   frames received from a CE node:

   1. Flood to locally attached CE nodes subjected to VLAN and multicast
   2. Ingress  in the TRILL header and assign ingress RBridge nickname
     as RBv. (nickname of the virtual RBridge).
   3. Forward to one of the distribution trees, tree x in which RBv is
     associated with RBk

5.4.1. Forwarding when n < k

     If there is no tree on which RBv can claim affinity via RBk
     (Probably because the number of trees n built is less than number
     of RBridges k announcing the affinity sub-TLV), then RBk MUST fall
     back to one of the following

     1. This RBridge should stop forwarding frames from the CE nodes,
        and should mark that port as disabled. This will prevent CE

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        nodes from forwarding data on to this RBridge, and only use
        those RBridges which have been assigned a tree -                                                            -OR-
     2. This RBridge tunnels multi-destination frames received from
        attached native devices to an RBridge RBy that has an assigned
        tree. The tunnel destination should forward it to the TRILL
        network, and also to its local access links .  (The mechanism
        of tunneling and handshake between the tunnel source and
        destination are out of scope of this specification and may be
        addressed in future documents).

   Above fallback options may be specific to active-active forwarding
   scenario. However, as stated above, Affinity sub-TLV may be used in
   other applications. In such event the application SHOULD specify
   applicable fallback options.

5.5. Egress Multi-Destination Forwarding

5.5.1. Traffic Arriving on an assigned Tree to RBk-RBv

   Multi-destination frames arriving at RBk on a Tree x, where RBk has
   announced the affinity of RBv via x, MUST be forwarded to CE members
   of RBv that are in the frame's VLAN. Forwarding to other end-nodes
   and RBridges that are not part of the network represented by the RBv
   virtual RBridge MUST follow the forwarding rules specified in

5.5.2. Traffic Arriving on other Trees

   Multi-destination frames arriving at RBk on a Tree y, where RBk has
   not announced the affinity of RBv via y, MUST NOT be forwarded to CE
   members of RBv. Forwarding to other end-nodes and RBridges that are
   not part of the network represented by the RBv virtual RBridge MUST
   follow the forwarding rules specified in RFC6325.

5.6. Failure scenarios

   The below failure recovery algorithm is presented only as a
   guideline. Implementations MAY include other failure recover
   algorithms. Details of such algorithms are outside the scope of this

5.6.1. Edge RBridge RBk failure

   Each of the member RBridges of given virtual RBridge edge group is
   aware of its member RBridges through configuration or some other

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   Member RBridges detect nodal failure of a member RBridge through IS-
   IS LSP advertisements or lack thereof.

   Upon detecting a member failure, each of the member RBridges of the
   RBv edge group start recovery timer T_rec for failed RBrdige RBi. If
   the previously failed RBridge RBi has not recovered after the expiry
   of timer T_rec, members RBridges perform distribution tree
   assignment algorithm specified in section 5.1. Each of the member
   RBridges re-advertises the Affinity sub-TLV with new tree
   assignment. This action causes the campus to update the tree
   calculation with the new assignment.

   RBi upon start-up, starts advertising its presence through IS-IS
   LSPs and starts a timer T_i. Member RBridges detecting the presence
   of RBi start a timer T_j. Timer T_j SHOULD be at least < T_i/2.
   (Please see note below)

   Upon expiry of timer T_j, member RBridges recalculate the multi-
   destination tree assignment and advertised the related trees using
   Affinity sub-TLV.

   Upon expiry of timer T_i, RBi recalculate the multi-destination tree
   assignment and advertises the related trees using Affinity TLV.

   Note: Timers T_i and T_j are designed so as to minimize traffic down
   time and avoid multi-destination packet duplication.

5.7. Backward compatibility

   Implementations MUST support backward compatibility mode to
   interoperate with pre Affinity sub-TLV RBRidges in the network. Such
   backward compatibility operation MAY include, however is not limited
   to, tunneling and/or active-standby modes of operations.


   Step 1.  Stop using virtual RBridge nickname for traffic ingressing
     from CE nodes
   Step 2.  Stop performing active-active forwarding. And fall back to
     active standby forwarding, based on locally defined policies.
     Definition of such policies is outside the scope of this document
     and may be addressed in future documents.

6. Security Considerations

    In general, the RBridges in a campus are trusted routers and the
   authenticity of their link state information (LSPs) and link local

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   PDUs (Hellos, etc.) can be enforced using regular IS-IS security
   mechanisms [IS-IS] [RFC5410]. This including authenticating the
   contents of the PDUs used to transport Affinity sub-TLVs.

   The particular Security Considerations involve with different
   applications of the Affinity sub-TLV will be covered in the
   document(s) specifying those applications.

   For general TRILL Security Considerations, see [RFC6325].

7. IANA Considerations

   IANA is requested to allocate a capability bit for ''Affinity
   Supported'' in the TRILL-VER sub-TLV. ''Affinity Supported'' capability
   bit and Affinity sub-TLV are specified and allocated in [6326bis].

8. References

8.1. Normative References

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

   [RFC5310] Bhatia, M., ''IS-IS Generic Cryptographic
             Authentication'', RFC 5310, February 2009.

   [RFC6325] Perlman, R., ''RBridge: Base Protocol
             Specification'', RFC 6325, July 2011.

   [6327bis] Eastlake, D., ''RBridge: Adjacency'', draft-eastlake-
             trill-rfc6327bis, Work in Progress, July 2011.

   [RFC6439] Eastlake, D., ''RBridge: Appointed Forwarder'', RFC
             6439, November 2011.

   [6326bis] Eastlake, D., ''Transparent Interconnection of Lots
             of Links (TRILL) Use of IS-IS'', draft-eastlake-isis-
             rfc6326bis, Work in Progress, December 2011.

   [clearcor] Eastlake, D., ''TRILL: Clarifications, Corrections,
             and Updates'', draft-ietf-trill-clear-correct, Work in
             Progress, July 2011.

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   [IS-IS] ISO/IEC, ''Intermediate System to Intermediate System Routing
             Information Exchange Protocol for use in Conjunction with
             the Protocol for Providing the Connectionless-mode Network
             Service (ISO 8473)'' ISO/IEC 10589:2002.

8.2.  Informative References

   [RFC6165] Banerjee, A. and Ward, D. ''Extensions to IS-IS for Layer-2
             Systems'', RFC 6165, April 2011.

   [RFC4971] Vasseur, JP. ''Intermediate System to Intermediate
             System (IS-IS) Extensions for Advertising Router
             Information'', RFC 4971, July 2007.

   [TRILLPN] Zhai,H., ''RBridge: Pseudonode Nickname'', draft-hu-
             trill-pseudonode-nickname, Work in progress, November

   [8021AX] IEEE, ''Link Aggregration'', IEEE Std 802.1AX-2008, November

   [8021Q] IEEE, ''Media Access Control (MAC) Bridges and Virtual
             Bridged Local Area Networks'', IEEE Std 802.1Q-2011,
             August, 2011

9. Acknowledgments

   Authors wish to extend their appreciations towards individuals who
   volunteered to review and comment on the work presented in this
   document and provided constructive and critical feedback. Specific
   acknowledgements are due for Anoop Ghanwani, Ronak Desai, and Varun
   Shah. Very special Thanks to Donald Eastlake for his careful review
   and constructive comments.

   This document was prepared using

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Appendix A. Change History.

   From -01 to -02:

   Replaced all references to ''LAG'' with references to Multi-Chassis
   (MC-LAG) or the like.

   Expanded, Security Considerations section.

   Assorted editorial changes.

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   Authors' Addresses

   Tissa Senevirathne
   Cisco Systems
   375 East Tasman Drive,
   San Jose, CA 95134

   Phone: +1-408-853-2291

   Janardhanan Pathangi
   Dell/Force10 Networks
   Olympia Technology Park,
   Guindy Chennai 600 032

   Phone: +91 44 4220 8400

   Jon Hudson
   130 Holger Way
   San Jose, CA 95134 USA


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