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rfc:rfc7783

Internet Engineering Task Force (IETF) T. Senevirathne Request for Comments: 7783 Consultant Updates: 6325 J. Pathangi Category: Standards Track Dell ISSN: 2070-1721 J. Hudson

                                                               Brocade
                                                         February 2016
                 Coordinated Multicast Trees (CMT)
      for Transparent Interconnection of Lots of Links (TRILL)

Abstract

 TRILL (Transparent Interconnection of Lots of Links) facilitates
 loop-free connectivity to non-TRILL networks via a choice of an
 Appointed Forwarder for a set of VLANs.  Appointed Forwarders provide
 VLAN-based load sharing with an active-standby model.  High-
 performance applications require an active-active load-sharing model.
 The active-active load-sharing model can be accomplished by
 representing any given non-TRILL network with a single virtual
 RBridge (also referred to as a virtual Routing Bridge or virtual
 TRILL switch).  Virtual representation of the non-TRILL 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,
 which only requires a software upgrade, provides flexibility to
 RBridges in selecting a desired path of association to a given TRILL
 multi-destination distribution tree.  This document updates RFC 6325.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7783.

Senevirathne, et al. Standards Track [Page 1] RFC 7783 Coordinated Multicast Trees for TRILL February 2016

Copyright Notice

 Copyright (c) 2016 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.

Table of Contents

 1. Introduction ....................................................3
    1.1. Scope and Applicability ....................................4
 2. Conventions Used in This Document ...............................5
    2.1. Acronyms and Phrases .......................................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 .............................................8
    5.1. Distribution Tree Assignment ...............................8
    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
    5.7. Backward Compatibility ....................................12
 6. Security Considerations ........................................13
 7. IANA Considerations ............................................13
 8. References .....................................................14
    8.1. Normative References ......................................14
    8.2. Informative References ....................................15
 Acknowledgments ...................................................16
 Contributors ......................................................16
 Authors' Addresses ................................................16

Senevirathne, et al. Standards Track [Page 2] RFC 7783 Coordinated Multicast Trees for TRILL February 2016

1. Introduction

 TRILL (Transparent Interconnection of Lots of Links), as 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) [IS-IS] as its control plane and uses a TRILL
 Header that includes a Hop Count.
 [RFC6325], [RFC7177], and [RFC6439] provide methods for
 interoperability between TRILL and Ethernet end stations and bridged
 networks.  [RFC6439] provides an active-standby solution, where only
 one of the RBridges (aka Routing Bridges or TRILL switches) on a link
 with end stations is in the active forwarding state for end-station
 traffic for any given VLAN.  That RBridge is referred to as the
 Appointed Forwarder (AF).  All frames ingressed into a TRILL network
 via the AF are encapsulated with the TRILL Header with a nickname
 held by the ingress AF RBridge.  Due to failures, reconfigurations,
 and other network dynamics, the AF for any set of VLANs may change.
 RBridges maintain forwarding tables that contain bindings for
 destination Media Access Control (MAC) addresses and Data Labels
 (VLAN or Fine-Grained Labels (FGLs)) to egress RBridges.  In the
 event of an AF change, forwarding tables of remote RBridges may
 continue to forward traffic to the previous AF.  That traffic may get
 discarded at the egress, causing traffic disruption.
 High-performance applications 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, may have end stations and/or bridges
 attached to the RBridges.  These devices typically are multi-homed to
 several RBridges and treat all of the uplinks independently using a
 Local Active-Active Link Protocol (LAALP) [RFC7379], such as a single
 Multi-Chassis Link Aggregation (MC-LAG) bundle or Distributed
 Resilient Network Interconnect [802.1AX].  The AF designation
 presented in [RFC6439] requires each of the edge RBridges to exchange
 TRILL Hello packets.  By design, an LAALP 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 designation methods
 presented in [RFC6439] cannot be applied to the 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 require similar representations.

Senevirathne, et al. Standards Track [Page 3] RFC 7783 Coordinated Multicast Trees for TRILL February 2016

 Sections 4.5.1 and 4.5.2 of [RFC6325], as updated by [RFC7780],
 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 on
 which it (the edge RBridge) can forward traffic, 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 [RFC6325], as updated by [RFC7780].  This document
 updates [RFC6325] by changing, when Coordinated Multicast Trees (CMT)
 sub-TLVs are present, [RFC6325] mandatory provisions as to how
 distribution trees are constructed.
 In addition to the above-mentioned active-active forwarding model,
 other applications may utilize the distribution tree association
 framework presented in this document to associate to distribution
 trees through a preferred path.
 This proposal requires (1) the presence of multiple multi-destination
 trees within the TRILL campus and (2) that all the RBridges in the
 network be updated 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 is not met, RBridges MUST
 support a fallback option for interoperability.  Since the fallback
 is expected to be a temporary phenomenon until all RBridges are
 upgraded, this proposal gives guidelines for such fallbacks and does
 not mandate or specify any specific set of fallback options.

1.1. Scope and Applicability

 This document specifies an Affinity sub-TLV to solve RPF issues at
 the active-active edge.  Specific methods in this document for making
 use of the Affinity sub-TLV are applicable where a virtual RBridge is
 used to represent multiple RBridges connected to an edge Customer
 Equipment (CE) device through an LAALP, such as MC-LAG or some
 similar arrangement where the RBridges cannot see each other's
 Hellos.

Senevirathne, et al. Standards Track [Page 4] RFC 7783 Coordinated Multicast Trees for TRILL February 2016

 This document does not provide other required operational elements to
 implement an active-active edge solution, such as MC-LAG methods.
 Solution-specific operational elements are outside the scope of this
 document and will be covered in other documents.  (See, for example,
 [RFC7781].)
 Examples provided in this document are for illustration purposes
 only.

2. Conventions Used in This Document

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

2.1. Acronyms and Phrases

 The following acronyms and phrases are used in this document:
 AF: Appointed Forwarder [RFC6439].
 CE: Customer Equipment device, that is, a device that performs
    forwarding based on 802.1Q bridging.  This also can be an
    end station or a server.
 Data Label: VLAN or FGL.
 FGL: Fine-Grained Label [RFC7172].
 LAALP: Local Active-Active Link Protocol [RFC7379].
 MC-LAG: Multi-Chassis Link Aggregation.  A proprietary extension to
    [802.1AX] that facilitates connecting a group of links from an
    originating device (A) to a group of discrete devices (B).
    Device (A) treats all of the links in a given MC-LAG 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 received on the multi-chassis link bundle
    out of the same multi-chassis link bundle.  Figure 1 depicts a
    specific use case example.

Senevirathne, et al. Standards Track [Page 5] RFC 7783 Coordinated Multicast Trees for TRILL February 2016

 RPF: Reverse Path Forwarding.  See Section 4.5.2 of [RFC6325].
 Virtual RBridge: A purely conceptual RBridge that represents an
    active-active edge group and is in turn represented by a nickname.
    For example, see [RFC7781].

3. The Affinity Sub-TLV

 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 or
 MT Capability TLVs that are within Link State PDUs (LSPs), as
 described in [RFC7176].  [RFC7176] specifies the code point and data
 structure for the Affinity sub-TLV.

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

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

/ \

                    |                      |
                    |     TRILL Campus     |
                    |                      |
                     \                    /
                      --------------------
                         |       |    |
                    -----        |     --------
                   |             |             |
               +------+      +------+      +------+
               |      |      |      |      |      |
               |(RB1) |      |(RB2) |      | (RBk)|
               +------+      +------+      +------+
                 |..|          |..|          |..|
                 |  +----+     |  |          |  |
                 |   +---|-----|--|----------+  |
                 | +-|---|-----+  +-----------+ |
                 | | |   +------------------+ | |
                (| | |)  <-- MC-LAG          (| | |) <-- MC-LAG
               +-------+    .  .  .       +-------+
               | CE1   |                  | CEn   |
               |       |                  |       |
               +-------+                  +-------+
                     Figure 1: Reference Topology

Senevirathne, et al. Standards Track [Page 6] RFC 7783 Coordinated Multicast Trees for TRILL February 2016

  1. ——————- Sample Multicast Tree (T1)

/ \

         |                      |                  |
         |     TRILL Campus     |                  o RBn
         |                      |                / | \
          \                    /                /  |  ---\
           --------------------             RB1 o  o      o
              |       |    |                    |   RB2    RBk
              |       |    --------------       |
              |       |                  |      o RBv
            +------+ +------+          +------+
            |      | |      |          |      |
            |(RB1) | |(RB2) |          | (RBk)|
            +------+ +------+          +------+
              |..|       |..|             |..|
              |  +----+  |  |             |  |
              |   +---|--|--|-------------+  |
              | +-|---|--+  +--------------+ |
              | | |   +------------------+ | |
   MC-LAG -->(| | |)                    (| | |)<-- MC-LAG
             +-------+    .  .  .       +-------+
             | CE1   |                  | CEn   |
             |       |                  |       |
             +-------+                  +-------+
      RBv: virtual RBridge
                  Figure 2: Example Logical Topology

4.1. Update to RFC 6325

 This document updates Section 4.5.1 of [RFC6325] and changes the
 calculation of distribution trees, as specified below:
 Each RBridge that desires to be the parent RBridge for a child
 RBridge (RBy) in a multi-destination distribution tree (Tree x)
 announces the desired association using an Affinity sub-TLV.  The
 child is specified by its nickname.  If an RBridge (RB1) advertises
 an Affinity sub-TLV designating one of its own nicknames (N1) as its
 "child" in some distribution tree, the effect is that nickname N1 is
 ignored when constructing other distribution trees.  Thus, the
 RPF check will enforce the rule that only RB1 can use nickname N1 to
 do ingress/egress on Tree x.  (This has no effect on least-cost path
 calculations for unicast traffic.)
 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 the case of a

Senevirathne, et al. Standards Track [Page 7] RFC 7783 Coordinated Multicast Trees for TRILL February 2016

 conflicting Affinity sub-TLV; such cases 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 do not support the Affinity
 sub-TLV, distribution trees are calculated as specified in
 Section 4.5.1 of [RFC6325], as updated by [RFC7780].  Section 4.3
 below specifies how to identify RBridges that support the Affinity
 sub-TLV.

4.2. Announcing Virtual RBridge Nickname

 Each edge RBridge (RB1 to RBk) advertises its LSP virtual RBridge
 nickname (RBv) by using the Nickname sub-TLV (6) [RFC7176], 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) that 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 their TRILL Header Ingress Nickname field set to RBv
 might use any of the distribution trees that any member of the edge
 group advertises that it might use.

4.3. Affinity Sub-TLV Capability

 RBridges that announce the TRILL Version sub-TLV [RFC7176] and set
 the Affinity capability bit (Section 7) support the Affinity sub-TLV,
 calculation of multi-destination distribution trees, and RPF checks,
 as specified herein.

5. Theory of Operation

5.1. Distribution Tree Assignment

 Let's assume that there are n distribution trees and k edge RBridges
 in the edge group of interest.
 If n >= k
    Let's assume that edge RBridges are sorted in numerically
    ascending order by IS-IS System ID 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,

Senevirathne, et al. Standards Track [Page 8] RFC 7783 Coordinated Multicast Trees for TRILL February 2016

    RBi = j, and RBi + 1 = j + 1.  (See Section 4.5 of [RFC6325], as
    updated by Section 3.4 of [RFC7780], for how tree numbers are
    determined.)
    Assign each tree to RBi such that tree number
    (((tree_number) % k) + 1) is assigned to edge group RBridge i for
    tree_number from 1 to n, where n is the number of trees, k is the
    number of edge group RBridges considered for tree allocation, and
    "%" is the integer division remainder operation.
 If n < k
    Distribution trees are assigned to edge group RBridges RB1 to RBn,
    using the same algorithm as the n >= k case.  RBridges RBn + 1 to
    RBk do not participate in the active-active forwarding process on
    behalf of RBv.

5.2. Affinity Sub-TLV Advertisement

 Each RBridge in the RB1 through RBk domain advertises an Affinity
 sub-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 the Affinity sub-TLV;
 {RBv, Num of Trees = 2, t1, tk + 1}.
 Other RBridges in the RB1 through 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 by each RBridge so that they all derive the same set of
 distribution trees [RFC6325].
 If RBridge 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.
 If RBridge RB1 advertises an Affinity sub-TLV with an AFFINITY RECORD
 that asks for nickname RBn to be its child in any tree and RB1 is not
 adjacent to RBn nor does nickname RBn identify RB1 itself, that
 AFFINITY RECORD is in conflict with the campus topology and MUST be
 ignored.

Senevirathne, et al. Standards Track [Page 9] RFC 7783 Coordinated Multicast Trees for TRILL February 2016

 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 with each other 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 tiebreaker.
 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-TLVs,
 recalculate the multicast tree affinity allocation, and, if
 appropriate, advertise new non-conflicting Affinity sub-TLVs.
 Similarly, remote RBridges MUST honor the Affinity sub-TLV from the
 RBridge with the highest priority to be a tree root (using System ID
 as the tiebreaker 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
    pruning.
 2. Ingress (by encapsulating with a TRILL Header) and set the Ingress
    Nickname field of the TRILL Header to RBv (the 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 the number of
 RBridges (k) announcing the Affinity sub-TLV), then RBk MUST fall
 back to one of the following:
 1. This RBridge (RBk) should stop forwarding frames from the CE nodes
    and should mark its port towards those CE nodes as disabled.  This
    will prevent the CE nodes from forwarding data to this RBridge.
    Thus, the CE nodes will only use those RBridges that have been
    assigned a tree.

Senevirathne, et al. Standards Track [Page 10] RFC 7783 Coordinated Multicast Trees for TRILL February 2016

  1. 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 handshaking between the tunnel source and
    destination are out of scope for this specification and may be
    addressed in other documents, such as [ChannelTunnel].)
 The above fallback options may be specific to the active-active
 forwarding scenario.  However, as stated above, the Affinity sub-TLV
 may be used in other applications.  In such an 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
 virtual RBridge nickname (RBv) MUST follow the forwarding rules
 specified in [RFC6325].

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 virtual RBridge nickname
 (RBv) MUST follow the forwarding rules specified in [RFC6325].

5.6. Failure Scenarios

 The failure recovery algorithm below is presented only as a
 guideline.  An active-active edge group MAY use other failure
 recovery algorithms; it is recommended that only one algorithm be
 used in an edge group at a time.  Details of such algorithms are
 outside the scope of this document.

5.6.1. Edge RBridge RBk Failure

 Each of the member RBridges of a given virtual RBridge edge group is
 aware of its member RBridges through configuration, LSP
 advertisements, or some other method.

Senevirathne, et al. Standards Track [Page 11] RFC 7783 Coordinated Multicast Trees for TRILL February 2016

 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 RBridge RBi.  If
 the previously failed RBridge RBi has not recovered after the expiry
 of timer T_rec, member RBridges perform the distribution tree
 assignment algorithm specified in Section 5.1.  Each of the member
 RBridges re-advertises the Affinity sub-TLV with the new tree
 assignment.  This action causes the campus to update the tree
 calculation with the new assignment.
 RBi, upon startup, advertises its presence through IS-IS LSPs and
 starts a timer T_i.  Other member RBridges of the edge group,
 detecting the presence of RBi, start a timer T_j.
 Upon expiry of timer T_j, other member RBridges recalculate the
 multi-destination tree assignment and advertise the related trees
 using the Affinity sub-TLV.  Upon expiry of timer T_i, RBi
 recalculates the multi-destination tree assignment and advertises the
 related trees using the Affinity sub-TLV.
 If the new RBridge in the edge group calculates trees and starts to
 use one or more of them before the existing RBridges in the edge
 group recalculate, there could be duplication of packets (for
 example, more than one edge group RBridge could decapsulate and
 forward a multi-destination frame on links into the active-active
 group) or loss of packets (for example, due to the Reverse Path
 Forwarding check, in the rest of the campus, if two edge group
 RBridges are trying to forward on the same tree, those from one will
 be discarded).  Alternatively, if the new RBridge in the edge group
 calculates trees and starts to use one or more of them after the
 existing RBridges recalculate, there could be loss of data due to
 frames arriving at the new RBridge being black-holed.  Timers T_i and
 T_j should be initialized to values designed to minimize these
 problems, keeping in mind that, in general, duplication of packets is
 a more serious problem than dropped packets.  It is RECOMMENDED that
 T_j be less than T_i, and a reasonable default is 1/2 of T_i.

5.7. Backward Compatibility

 Implementations MUST support a backward compatibility modes to
 interoperate with "pre-Affinity sub-TLV" RBridges in the network.
 Such backward compatibility operations MAY include, but are not
 limited to, tunneling and/or active-standby modes of operation.  It
 should be noted that tunneling would require silicon changes.
 However, CMT in itself is a software upgrade.

Senevirathne, et al. Standards Track [Page 12] RFC 7783 Coordinated Multicast Trees for TRILL February 2016

 Example:
 Step 1. Stop using the virtual RBridge nickname for traffic
    ingressing from CE nodes.
 Step 2. Stop performing active-active forwarding.  Fall back to
    active standby forwarding, based on locally defined policies.  The
    definition of such policies is outside the scope of this document
    and may be addressed in other 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
 PDUs (e.g., Hellos) can be enforced using regular IS-IS security
 mechanisms [IS-IS] [RFC5310].  This includes authenticating the
 contents of the PDUs used to transport Affinity sub-TLVs.
 The particular security considerations involved 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

 This document serves as the reference for the registration of
 "Affinity sub-TLV support" (bit 0) in the "TRILL-VER Sub-TLV
 Capability Flags" registry.
 This document mentions the registration of "AFFINITY" (value 17) in
 the "Sub-TLVs for TLV 144" registry, but it is intentionally not
 listed as a reference for that registration; the reference remains
 [RFC7176].

Senevirathne, et al. Standards Track [Page 13] RFC 7783 Coordinated Multicast Trees for TRILL February 2016

8. References

8.1. Normative References

 [IS-IS]    International Organization for Standardization,
            "Information technology -- Telecommunications and
            information exchange between systems -- Intermediate
            System to Intermediate System intra-domain routeing
            information exchange protocol for use in conjunction with
            the protocol for providing the connectionless-mode network
            service (ISO 8473)", ISO/IEC 10589:2002, Second Edition,
            November 2002.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
            and M. Fanto, "IS-IS Generic Cryptographic
            Authentication", RFC 5310, DOI 10.17487/RFC5310,
            February 2009, <http://www.rfc-editor.org/info/rfc5310>.
 [RFC6325]  Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
            Ghanwani, "Routing Bridges (RBridges): Base Protocol
            Specification", RFC 6325, DOI 10.17487/RFC6325, July 2011,
            <http://www.rfc-editor.org/info/rfc6325>.
 [RFC6439]  Perlman, R., Eastlake, D., Li, Y., Banerjee, A., and F.
            Hu, "Routing Bridges (RBridges): Appointed Forwarders",
            RFC 6439, DOI 10.17487/RFC6439, November 2011,
            <http://www.rfc-editor.org/info/rfc6439>.
 [RFC7172]  Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R., and
            D. Dutt, "Transparent Interconnection of Lots of Links
            (TRILL): Fine-Grained Labeling", RFC 7172,
            DOI 10.17487/RFC7172, May 2014,
            <http://www.rfc-editor.org/info/rfc7172>.
 [RFC7176]  Eastlake 3rd, D., Senevirathne, T., Ghanwani, A., Dutt,
            D., and A. Banerjee, "Transparent Interconnection of Lots
            of Links (TRILL) Use of IS-IS", RFC 7176,
            DOI 10.17487/RFC7176, May 2014,
            <http://www.rfc-editor.org/info/rfc7176>.

Senevirathne, et al. Standards Track [Page 14] RFC 7783 Coordinated Multicast Trees for TRILL February 2016

 [RFC7177]  Eastlake 3rd, D., Perlman, R., Ghanwani, A., Yang, H., and
            V. Manral, "Transparent Interconnection of Lots of Links
            (TRILL): Adjacency", RFC 7177, DOI 10.17487/RFC7177,
            May 2014, <http://www.rfc-editor.org/info/rfc7177>.
 [RFC7780]  Eastlake 3rd, D., Zhang, M., Perlman, R., Banerjee, A.,
            Ghanwani, A., and S. Gupta, "Transparent Interconnection
            of Lots of Links (TRILL): Clarifications, Corrections, and
            Updates", RFC 7780, DOI 10.17487/RFC7780, February 2016,
            <http://www.rfc-editor.org/info/rfc7780>.
 [RFC7781]  Zhai, H., Senevirathne, T., Perlman, R., Zhang, M., and Y.
            Li, "Transparent Interconnection of Lots of Links (TRILL):
            Pseudo-Nickname for Active-Active Access", RFC 7781,
            DOI 10.17487/RFC7781, February 2016,
            <http://www.rfc-editor.org/info/rfc7781>.

8.2. Informative References

 [802.1AX]  IEEE, "IEEE Standard for Local and metropolitan area
            networks - Link Aggregation", IEEE Std 802.1AX-2014,
            DOI 10.1109/IEEESTD.2014.7055197, December 2014.
 [ChannelTunnel]
            Eastlake 3rd, D., Umair, M., and Y. Li, "TRILL: RBridge
            Channel Tunnel Protocol", Work in Progress,
            draft-ietf-trill-channel-tunnel-07, August 2015.
 [RFC7379]  Li, Y., Hao, W., Perlman, R., Hudson, J., and H. Zhai,
            "Problem Statement and Goals for Active-Active Connection
            at the Transparent Interconnection of Lots of Links
            (TRILL) Edge", RFC 7379, DOI 10.17487/RFC7379,
            October 2014, <http://www.rfc-editor.org/info/rfc7379>.

Senevirathne, et al. Standards Track [Page 15] RFC 7783 Coordinated Multicast Trees for TRILL February 2016

Acknowledgments

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

Contributors

 The work in this document is a result of many passionate discussions
 and contributions from the following individuals, listed in
 alphabetical order by their first names:
 Ayan Banerjee, Dinesh Dutt, Donald Eastlake, Hongjun Zhai, Mingui
 Zhang, Radia Perlman, Sam Aldrin, and Shivakumar Sundaram.

Authors' Addresses

 Tissa Senevirathne
 Consultant
 Email: tsenevir@gmail.com
 Janardhanan Pathangi
 Dell/Force10 Networks
 Olympia Technology Park
 Guindy Chennai  600 032
 India
 Phone: +91-44-42208400
 Email: Pathangi_Janardhanan@Dell.com
 Jon Hudson
 Brocade
 130 Holger Way
 San Jose, CA  95134
 United States
 Phone: +1-408-333-4062
 Email: jon.hudson@gmail.com

Senevirathne, et al. Standards Track [Page 16]

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