





Internet Engineering Task Force (IETF)                     D. Fedyk, Ed.
Request for Comments: 6329                                Alcatel-Lucent
Category: Standards Track                          P. Ashwood-Smith, Ed.
ISSN: 2070-1721                                                   Huawei
                                                                D. Allan
                                                                Ericsson
                                                                N. Bragg
                                                           Ciena Limited
                                                            P. Unbehagen
                                                                   Avaya
                                                              April 2012


    IS-IS Extensions Supporting IEEE 802.1aq Shortest Path Bridging

Abstract

   802.1aq Shortest Path Bridging (SPB) has been standardized by the
   IEEE as the next step in the evolution of the various spanning tree
   and registration protocols.  802.1aq allows for true shortest path
   forwarding in a mesh Ethernet network context utilizing multiple
   equal cost paths.  This permits it to support much larger Layer 2
   topologies, with faster convergence, and vastly improved use of the
   mesh topology.  Combined with this is single point provisioning for
   logical connectivity membership, which includes point-to-point,
   point-to-multipoint, and multipoint-to-multipoint variations.  This
   memo documents the IS-IS changes required to support this IEEE
   protocol and provides some context and examples.

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/rfc6329.









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Copyright Notice

   Copyright (c) 2012 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 ....................................................4
   2. Terminology .....................................................4
   3. Conventions Used in This Document ...............................5
   4. 802.1aq Overview ................................................6
      4.1. Multi-Topology Support .....................................8
      4.2. Data Path SPBM - Unicast ...................................8
      4.3. Data Path SPBM - Multicast (Head-End Replication) ..........9
      4.4. Data Path SPBM - Multicast (Tandem Replication) ............9
      4.5. Data Path SPBV Broadcast ..................................11
      4.6. Data Path SPBV Unicast ....................................11
      4.7. Data Path SPBV Multicast ..................................12
   5. SPBM Example ...................................................12
   6. SPBV Example ...................................................14
   7. SPB Supported Adjacency types ..................................16
   8. SPB IS-IS Adjacency Addressing .................................16
   9. IS-IS Area Address and SYSID ...................................17
   10. Level 1/2 Adjacency ...........................................17
   11. Shortest Path Default Tie-Breaking ............................17
   12. Shortest Path ECT .............................................18
   13. Hello (IIH) Protocol Extensions ...............................19
      13.1. SPB-MCID Sub-TLV .........................................20
      13.2. SPB-Digest Sub-TLV .......................................21
      13.3. SPB Base VLAN Identifiers (SPB-B-VID) Sub-TLV ............23
   14. Node Information Extensions ...................................24
      14.1. SPB Instance (SPB-Inst) Sub-TLV ..........................24
           14.1.1. SPB Instance Opaque ECT-ALGORITHM
                   (SPB-I-OALG) Sub-TLV ..............................28
   15. Adjacency Information Extensions ..............................29
      15.1. SPB Link Metric (SPB-Metric) Sub-TLV .....................29
           15.1.1. SPB Adjacency Opaque ECT-ALGORITHM
                   (SPB-A-OALG) Sub-TLV ..............................30
   16. Service Information Extensions ................................30
      16.1. SPBM Service Identifier and Unicast Address
            (SPBM-SI) Sub-TLV ........................................30
      16.2. SPBV MAC Address (SPBV-ADDR) Sub-TLV .....................32
   17. Security Considerations .......................................34
   18. IANA Considerations ...........................................34
   19. References ....................................................35
      19.1. Normative References .....................................35
      19.2. Informative References ...................................36
   20. Acknowledgments ...............................................36








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1.  Introduction

   802.1aq Shortest Path Bridging (SPB) [802.1aq] has been standardized
   by the IEEE as the next step in the evolution of the various spanning
   tree and registration protocols.  802.1aq allows for true shortest
   path forwarding in an Ethernet mesh network context utilizing
   multiple equal cost paths.  This permits SPB to support much larger
   Layer 2 topologies, with faster convergence, and vastly improved use
   of the mesh topology.  Combined with this is single point
   provisioning for logical connectivity membership, which includes
   point-to-point (E-LINE), point-to-multipoint (E-TREE), and
   multipoint-to-multipoint (E-LAN) variations.

   The control protocol for 802.1aq is IS-IS [IS-IS] augmented with a
   small number of TLVs and sub-TLVs.  This supports two Ethernet
   encapsulating data paths, 802.1ad (Provider Bridges) [PB] and 802.1ah
   (Provider Backbone Bridges) [PBB].  This memo documents those TLVs
   while providing some overview.

   Note that 802.1aq requires no state machine or other substantive
   changes to [IS-IS].  802.1aq simply requires a new Network Layer
   Protocol Identifier (NLPID) and set of TLVs.  In the event of
   confusion between this document and [IS-IS], [IS-IS] should be taken
   as authoritative.

2.  Terminology

   In addition to well-understood IS-IS terms, this memo uses
   terminology from IEEE 802.1 and introduces a few terms:

   802.1ad        Provider Bridges (PBs) - Q-in-Q encapsulation
   802.1ah        Provider Backbone Bridges (PBBs), MAC-IN-MAC
                  encapsulation
   802.1aq        Shortest Path Bridging (SPB)
   Base VID       VID used to identify a VLAN in management operations
   B-DA           Backbone Destination Address 802.1ah PBB
   B-MAC          Backbone MAC Address
   B-SA           Backbone Source Address in 802.1ah PBB header
   B-VID          Backbone VLAN ID in 802.1ah PBB header
   B-VLAN         Backbone Virtual LAN
   BPDU           Bridge PDU
   BridgeID       64-bit quantity = (Bridge Priority:16)<<48 | SYSID:48
   BridgePriority 16-bit relative priority of a node for tie-breaking
   C-MAC          Customer MAC.  Inner MAC in 802.1ah PBB header
   C-VID          Customer VLAN ID
   ECT-ALGORITHM  32-bit unique ID of an SPF tie-breaking set of rules
   ECT-MASK       64-bit mask XORed with BridgeID during tie-breaking
   E-LAN          Bidirectional Logical Connectivity between >2 UNIs



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   E-LINE         Bidirectional Logical Connectivity between two UNIs
   E-TREE         Asymmetric Logical Connectivity between UNIs
   FDB            Filtering Database: {DA/VID}->{next hops}
   I-SID          Ethernet Services Instance Identifier used for
                  Logical Grouping for E-LAN/LINE/TREE UNIs
   LAN            Local Area Network
   LSDB           Link State Database
   LSP            Link State PDU
   MAC            Media Access Control
   MAC-IN-MAC     Ethernet in Ethernet framing as per 802.1ah [PBB]
   MDT            Multicast Distribution Tree
   MMRP           Multiple MAC Registration Protocol 802.1ak [MMRP]
   MT             Multi-Topology.  As used in [MT]
   MT ID          Multi-Topology Identifier (12 bits).  As used in [MT]
   NLPID          Network Layer Protocol Identifier: IEEE 802.1aq= 0xC1
   NNI            Network-Network Interface
   Q-in-Q         Additional S-VID after a C-VID (802.1ad) [PB]
   PBB            Provider Backbone Bridge - forwards using PBB
   Ingress Check  Source Forwarding Check - drops misdirected frames
   (S,G)          Source & Group - identity of a source-specific tree
   (*,G)          Any Source & Group - identity of a shared tree
   S-VID          Service VLAN ID
   SA             Source Address
   SPB            Shortest Path Bridging - generally all of 802.1aq
   SPB            Shortest Path Bridge - device implementing 802.1aq
   SPB-instance   Logical SPB instance correlated by MT ID
   SPBM           Device implementing SPB MAC mode
   SPBV           Device implementing SPB VID mode
   SPSourceID     20-bit identifier of the source of multicast frames
   SPT            Shortest Path Tree computed by one ECT-ALGORITHM
   SPT Region     A set of SPBs with identical VID usage on their NNIs
   SPVID          Shortest Path VLAN ID: a C-VID or S-VID that
                  identifies the source
   STP            Spanning Tree Protocol
   UNI            User-Network Interface: customer-to-SPB attach point
   VID            VLAN ID: 12-bit logical identifier after MAC header
   VLAN           Virtual LAN: a logical network in the control plane

3.  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].

   The lowercase forms with an initial capital "Must", "Must Not",
   "Shall", "Shall Not", "Should", "Should Not", "May", and "Optional"
   in this document are to be interpreted in the sense defined in




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   [RFC2119], but are used where the normative behavior is defined in
   documents published by SDOs other than the IETF.

4.  802.1aq Overview

   This section provides an overview of the behavior of [802.1aq] and is
   not intended to be interpreted as normative text.  For the definitive
   behavior, the reader should consult [802.1aq].  Nonetheless,
   lowercase forms with initial capitalization of the conventions in RFC
   2119 are used in this section to give the reader an indication of the
   intended normative behaviors as above.

   802.1aq utilizes 802.1Q-based Ethernet bridging.  The filtering
   database (FDB) is populated as a consequence of the topology computed
   from the IS-IS database.  For the reader unfamiliar with IEEE
   terminology, the definition of Ethernet behavior is almost entirely
   in terms of "filtering" (of broadcast traffic) rather than
   "forwarding" (the explicit direction of unicast traffic).  This
   document uses the generic term "forwarding", and it has to be
   understood that these two terms simply represent different ways of
   expressing the same behaviors.

   802.1aq supports multiple modes of operation depending on the type of
   data plane and the desired behavior.  For the initial two modes of
   802.1aq (SPBV and SPBM), routes are shortest path, are forward- and
   reverse-path symmetric with respect to any source/destination pair
   within the SPB domain, and are congruent with respect to unicast and
   multicast.  Hence, the shortest path tree (SPT) to a given node is
   congruent with the multicast distribution tree (MDT) from a given
   node.  The MDT for a given VLAN is a pruned subset of the complete
   MDT for a given node that is identical to its SPT.  Symmetry and
   congruency preserve packet ordering and proper fate sharing of
   Operations, Administration, and Maintenance (OAM) flows by the
   forwarding path.  Such modes are fully supported by existing
   [802.1ag] and [Y.1731] OAM mechanisms.

   VLANs provide a natural delineation of service instances.  802.1aq
   supports two modes, SPB VID (SPBV) and SPB MAC (SPBM).  In SPBV,
   multiple VLANS can be used to distribute load on different shortest
   path trees (each computed by a different tie-breaking rule) on a
   service basis.  In SPBM, service instances are delineated by I-SIDs
   but VLANs again can be used to distribute load on different shortest
   path trees.

   There are two encapsulation methods supported.  SPBM can be used in a
   PBB network implementing PBB (802.1ah [PBB]) encapsulation.  SPBV can
   be used in PB networks implementing VLANs, PB (802.1aq [PB]), or PBB




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   encapsulation.  The two modes can co-exist simultaneously in an SPB
   network.

   The practical design goals for SPBV and SPBM in the current 802.1aq
   specification are networks of size 100 nodes and 1000 nodes
   respectively.  However, since SPBV can be sparsely used in an SPB
   region it can simply span a large SPB region with a small number of
   SPVIDs.

   In SPBM and SPBV each bridge has at least one unique "known" MAC
   address which is advertised by IS-IS in the SYSID.

   In the forwarding plane, SPBM uses the combination of one or more
   B-VIDs and "known" Backbone-MAC (B-MAC) addresses that have been
   advertised in IS-IS.  The term Backbone simply implies an
   encapsulation that is often used in the backbone networks, but the
   encapsulation is useful in other types of networks where hiding
   C-MACs is useful.

   The SPBM filtering database (FDB) is computed and installed for
   unicast and multicast MAC addresses, while the SPBV filtering
   database is computed and installed for unidirectional VIDs (referred
   to as SPVIDs), after which MAC reachability is learned (exactly as in
   bridged Ethernet) for unicast MACs.

   Both SPBV and SPBM use source-specific multicast trees.  If they
   share the same ECT-ALGORITHM (32-bit worldwide unique definition of
   the computation), the tree is the same SPT.  For SPBV, (S,G) is
   encoded by a source-specific VID (the SPVID) and a standard Group MAC
   address.  For SPBM, (S,G) is encoded in the destination B-MAC address
   as the concatenation of a 20-bit SPB wide unique nodal nickname
   (referred to as the SPSourceID) and the 24-bit I-SID together with
   the B-VID that corresponds to the ECT-ALGORITHM network wide.

   802.1aq supports membership attributes that are advertised with the
   I-SID (SPBM) or Group Address (SPBV) that defines the group.
   Individual members can be transmitters (T) and/or receivers (R)
   within the group, and the multicast state is appropriately sized to
   these requests.  Multicast group membership is possible even without
   transmit membership by performing head-end replication to the
   receivers thereby eliminating transit multicast state entirely.

   Some highly connected mesh networks provide for path diversity by
   offering multiple equal cost alternatives between nodes.  Since
   congruency and symmetry Must be honored, a single tree may leave some
   links under-utilized.  By using different deterministic tie-breakers,
   up to 16 shortest paths of arbitrary diversity are possible between
   any pair of nodes.  This distributes the traffic on a VLAN basis.



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   SPBV and SPBM May share a single SPT with a single ECT-ALGORITHM or
   use any combination of the 16 ECT-ALGORITHMs.  An extensible
   framework permits additional or alternative algorithms with other
   properties and parameters (e.g., ECMP, (*,G)) to also be supported
   without any changes in this or the IEEE documents.

4.1.  Multi-Topology Support

   SPB incorporates the multi topology features of [MT] thereby allowing
   multiple logical SPB instances within a single IS-IS instance.

   To accomplish this, all SPB-related information is either explicitly
   or implicitly associated with a Multi-Topology Identifier (MT ID).
   SPB information related to a given MT ID thus forms a single logical
   SPB instance.

   Since SPB has its own adjacency metrics and those metrics are also
   associated with an MT ID, it is possible to have different adjacency
   metrics (or infinite metrics) for SPB adjacencies that are not only
   distinct from IP or other NLPIDs riding in this IS-IS instance, but
   also distinct from those used by other SPB instances in the same
   IS-IS instance.

   Data plane traffic for a given MT ID is intrinsically isolated by the
   VLANs assigned to the SPB instance in question.  Therefore, VLANs
   (represented by VIDs in TLVs and in the data plane) Must Not overlap
   between SPB instances (regardless of how the control planes are
   isolated).

   The [MT] mechanism when applied to SPB allows different routing
   metrics and topology subsets for different classes of services.

   The use of [MT] other than the default MT ID #0 is completely
   OPTIONAL.

   The use of [MT] to separate SPB from other NLPIDs is also OPTIONAL.

4.2.  Data Path SPBM - Unicast

   Unicast frames in SPBM are encapsulated as per 802.1ah [PBB].  A
   Backbone Source Address (B-SA), Backbone Destination Address (B-DA),
   Backbone VLAN ID (B-VID), and an I-Component Service Instance ID
   (I-TAG) are used to encapsulate the Ethernet frame.  The B-SA is a
   B-MAC associated with the ingress 802.1aq bridge, usually the "known"
   B-MAC of that entire bridge.  The B-DA is one of the "known" B-MACs
   associated with the egress 802.1aq bridge.  The B-VID and I-TAG are
   mapped based on the physical or logical UNI port (untagged, or tagged
   either by S-TAG or C-TAG) being bridged.  Normal learning and



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   broadcast to unknown C-MACs is applied as per [PBB] at the
   ingress/egress SPBs only.

   Unlike [PBB] on a (*,G) tree, the B-DA forwarding on tandem nodes
   (NNI to NNI) is performed without learning.  Instead, the output of
   802.1aq computations, based on the TLVs specified in this document,
   is used to populate the filtering databases (FDBs).  The FDB entries
   map {B-DA, B-VID} to an outgoing interface and are only populated
   from the IS-IS database and computations.

   The B-SA/B-VID is checked on tandem nodes against the ingress port.
   If the B-SA/B-VID (as a destination) entry in the FDB does not point
   to the port on which the packet arrived, the packet is discarded.
   This is referred to as an ingress check and serves as a very powerful
   loop mitigation mechanism.

4.3.  Data Path SPBM - Multicast (Head-End Replication)

   Head-end replication is supported for instances where there is a
   sparse community of interest or a low likelihood of multicast
   traffic.  Head-end replication requires no multicast state in the
   core.  A UNI port wishing to use head-end replication Must Not
   advertise its I-SID membership with the Transmit (T) bit set but
   instead Must locally and dynamically construct the appropriate
   unicast serial replication to all the other receivers (Receive (R)
   bit set) of the same I-SID.

   When an unknown customer unicast or a multicast frame arrives at an
   SPBM User-Network Interface (UNI) port that has been configured to
   replicate only at the head end, the packet is replicated once for
   each receiver, encapsulated, and sent as a unicast frame.  The set of
   receivers is determined by inspecting the IS-IS database for other
   SPBs that have registered interest in the same I-SID with the R bit
   set.  This R bit / I-SID pair is found in the SPBM Service Identifier
   and Unicast Address (SPBM-SI) sub-TLV.  The packets are encapsulated
   as per the SPBM unicast forwarding above.

4.4.  Data Path SPBM - Multicast (Tandem Replication)

   Tandem replication uses the shortest path tree to replicate frames
   only where the tree forks and there is at least one receiver on each
   branch.  Tandem replication is bandwidth efficient but uses multicast
   FDB entries (state) in core bridges, which might be unnecessary if
   there is little multicast traffic demand.  The head-end replication
   mode is best suited for the case where there is little or no true
   multicast traffic for an I-SID.  Tandem replication is triggered on
   transit nodes when the I-SID is advertised with the T bit set.




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   Broadcast, unknown unicast, or multicast frames arriving at an SPBM
   UNI port are encapsulated with a B-DA multicast address that uniquely
   identifies the encapsulating node (the root of the Multicast
   Distribution Tree) and the I-SID scoping this multicast.

   This B-DA address is a well-formed multicast group address (as per
   802.1Q and 802.1ah) that concatenates the SPSourceID A' with the
   I-SID M (written as DA=<A',M> and uniquely identifying the (S,G)
   tree).  This exact format is given in Figure 1 below:

    M L TYP
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |1|1|0|0|SPSrcMS|  SPSrc [8:15] |  SPSrc [0:7]  | I-SID [16:23] |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | I-SID [8:15]  |  I-SID [0:7]  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 1: SPBM Multicast Address Format
                    (SPSrcMS represents SPSrc [16:19])

   Note: In Figure 1, the index numbering from less significant bit to
      more significant bit within a byte or field within a byte gives
      the wire order of the bits in the address consistent with the IETF
      format in the rest of this document.  (The IEEE convention for
      number representation reverses the bits within an octet compared
      with IETF practice.)

   o  M is the multicast bit, always set to 1 for a multicast DA.  (It
      is the lowest bit in the most significant byte.)

   o  L is the local bit, always set to 1 for an SPBM-constructed
      multicast DA.

   o  TYP is the SPSourceID type.  00 is the only type supported at this
      time.

   o  SPSrc (SPSourceID) is a 20-bit quantity that uniquely identifies a
      SPBM node for all B-VIDs allocated to SPBM operation.  This is
      just the SPSourceID advertised in the SPB Instance (SPB-Inst) sub-
      TLV.  The value SPSourceID = 0 has special significance; it is
      advertised by an SPBM node that has been configured to assign its
      SPSourceID dynamically, which requires LSDB synchronization, but
      where the SPSourceID assignment has not yet completed.

   o  I-SID is the 24-bit I-Component Service ID advertised in the SPBM
      Service Identifier TLV.  It occupies the lower 24 bits of the SPBM
      multicast DA.  The I-SID value 0xfff is reserved for SPBM control
      traffic (refer to the default I-SID in [802.1aq]).



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   This multicast address format is used as the DA on frames when they
   are first encapsulated at ingress to the SPBM network.  The DA is
   also installed into the FDBs on all SPBM nodes that are on the
   corresponding SPT between the source and other nodes that have
   registered receiver interest in the same I-SID.

   Just as with unicast forwarding, the B-SA/B-VID May be used to
   perform an ingress check, but the SPSourceID encoded in the DA and
   the "drop-on-unknown" functionality of the FDB in [PBB] achieve the
   same effect.

   The I-Component at the egress SPBM device has completely standard
   [PBB] behavior and therefore will:

   1) learn the remote C-SA to B-SA relationship and

   2) bridge the original customer frame to the set of local UNI ports
      that are associated with the I-SID.

4.5.  Data Path SPBV Broadcast

   When a packet for an unknown DA arrives at an SPBV UNI port, VID
   translation (or VID encapsulation for untagged Frames) with the
   corresponding SPVID for this VLAN and ingress SPB is performed.

   SPVID forwarding is simply an SPT that follows normal VLAN forwarding
   behavior, with the exception that the SPVID is unidirectional.  As a
   result, shared VLAN learning (SVL) is used between the forward- and
   reverse-path SPVIDs associated with the same Base VID to allow SPBV
   unicast forwarding to operate in the normal reverse learning fashion.

   Ingress check is done by simply verifying that the bridge to which
   the SPVID has been assigned is indeed "shortest path" reachable over
   the link over which the packet tagged with that SPVID arrived.  This
   is computed from the IS-IS database and is implied when the SPVID is
   associated with a specific incoming port.

4.6.  Data Path SPBV Unicast

   When a packet for a known DA arrives at an SPBV UNI port, VID
   translation (or VID encapsulation for untagged Frames) with the
   corresponding SPVID for this VLAN and ingress bridge is performed.

   Since the SPVID will have been configured to follow a source-specific
   SPT and the DA is known, the packet will follow the source-specific
   path towards the destination C-MAC.

   Ingress check is as per the previous SPBV section.



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4.7.  Data Path SPBV Multicast

   C-DA multicast addresses May be advertised from SPBV UNI ports.
   These may be configured or learned through the Multiple MAC
   Registration Protocol (MMRP).  MMRP is terminated at the edge of the
   SPBV network and IS-IS carries the multicast addresses.  Tandem SPBV
   devices will check to see if they are on the SPF tree between SPBV
   UNI ports advertising the same C-DA multicast address, and if so will
   install multicast state to follow the SPBV SPF trees.

   Ingress check is as per the previous two SPBV sections.

5.  SPBM Example

   Consider the small example network shown in Figure 2.  Nodes are
   drawn in boxes with the last nibble of their B-MAC address :1..:7.
   The rest of the B-MAC address nibbles are 4455-6677-00xx.  Links are
   drawn as "--" and "/", while the interface indexes are drawn as
   numbers next to the links.  UNI ports are shown as "<==>" with the
   desired I-SID shown at the end of the UNI ports as "i1".

                        +----+           +----+
                        | :4 | 2 ------1 | :5 | <==> i1
                        +----+           +----+
                       1      3         3      2
                      /        \       /        \
                     1          4     3          2
                  +----+        +----+          +----+
          i1 <==> | :1 | 2----1 | :2 | 2------1 | :3 | <==> i1
                  +----+        +----+          +----+
                     3          6     5          3
                      \        /       \        /
                       3      2         1      2
                        +----+           +----+
                        | :6 | 1-------3 | :7 | <==> i1
                        +----+           +----+

                  Figure 2: SPBM Example 7-Node Network

   Using the default ECT-ALGORITHM (00-80-C2-01), which picks the equal
   cost path with the lowest BridgeID, this ECT-ALGORITHM is assigned to
   B-VID 100.  When all links have the same cost, then the 1-hop
   shortest paths are all direct and the 2-hop shortest paths (which are
   of course symmetric) are as follows:

   { 1-2-3,  1-2-5, 1-2-7, 6-2-5,
     4-2-7,  4-1-6, 5-2-7, 6-2-3, 4-2-3 }




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   Node :1's unicast forwarding table therefore routes toward B-MACs :7,
   :3, and :5 via interface/2, while its single-hop paths are all direct
   as can be seen from its FDB given in Figure 3.

   Node :1 originates multicast since it is at the head of the MDT to
   nodes :3, :5, and :7 and is a transmitter of I-SID 1, which nodes :3,
   :5, and :7 all wish to receive.  Node :1 therefore produces a
   multicast forwarding entry whose DA contains its SPSourceID (which is
   the last 20 bits of the B-MAC in the example) and the I-SID 1.  Node
   :1 thereafter sends packets matching this entry to interface if/2
   with B-VID=100.  Node :1's full unicast (U) and multicast (M) table
   is shown in Figure 3.  Note that the IN/IF (incoming interface) field
   is not specified for unicast traffic, and for multicast traffic has
   to point back to the root of the tree, unless it is the head of the
   tree -- in which case, we use the convention if/00.  Since node :1 is
   not transit for any multicast, it only has a single entry for the
   root of its tree for I-SID=1.

          +-------+-------------------+------+-----------------+
          | IN/IF | DESTINATION ADDR  | BVID | OUT/IF(s)       |
          +-------+-------------------+------+-----------------+
         U| if/** |   4455-6677-0002  | 0100 | {if/2           }
         U| if/** |   4455-6677-0003  | 0100 | {if/2           }
         U| if/** |   4455-6677-0004  | 0100 | {if/1           }
         U| if/** |   4455-6677-0005  | 0100 | {if/2           }
         U| if/** |   4455-6677-0006  | 0100 | {if/3           }
         U| if/** |   4455-6677-0007  | 0100 | {if/2           }
         M| if/00 |   7300-0100-0001  | 0100 | {if/2           }

        Figure 3: SPBM Node :1 FDB - Unicast (U) and Multicast (M)

   Node :2, being at the center of the network, has direct 1-hop paths
   to all other nodes; therefore, its unicast FDB simply sends packets
   with the given B-MAC/B-VID=100 to the interface directly to the
   addressed node.  This can be seen by looking at the unicast entries
   (the first 6) shown in Figure 4.















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          +-------+-------------------+------+-----------------+
          | IN/IF | DESTINATION ADDR  | BVID | OUT/IF(s)       |
          +-------+-------------------+------+-----------------+
         U| if/** |   4455-6677-0001  | 0100 | {if/1           }
         U| if/** |   4455-6677-0003  | 0100 | {if/2           }
         U| if/** |   4455-6677-0004  | 0100 | {if/4           }
         U| if/** |   4455-6677-0005  | 0100 | {if/3           }
         U| if/** |   4455-6677-0006  | 0100 | {if/6           }
         U| if/** |   4455-6677-0007  | 0100 | {if/5           }
         M| if/01 |   7300-0100-0001  | 0100 | {if/2,if/3,if/5 }
         M| if/02 |   7300-0300-0001  | 0100 | {if/1           }
         M| if/03 |   7300-0500-0001  | 0100 | {if/1,if/5      }
         M| if/05 |   7300-0700-0001  | 0100 | {if/1,if/3      }

         Figure 4: SPBM Node :2 FDB Unicast (U) and Multicast (M)

   Node :2's multicast is more complicated since it is a transit node
   for the 4 members of I-SID=1; therefore, it requires 4 multicast FDB
   entries depending on which member it is forwarding/replicating on
   behalf of.  For example, node :2 is on the shortest path between each
   of nodes {:3, :5, :7} and :1.  So it must replicate from node :1
   I-SID 1 out on interfaces { if/2, if/3 and if/5 } (to reach nodes :3,
   :5, and :7).  It therefore creates a multicast DA with the SPSourceID
   of node :1 together with I-SID=1, which it expects to receive over
   interface/1 and will replicate out interfaces { if/2, if/3 and if/5
   }.  This can be seen in the first multicast entry in Figure 4.


   Note that node :2 is not on the shortest path between nodes :3 and :5
   nor between nodes :3 and :7; however, it still has to forward packets
   to node :1 from node :3 for this I-SID, which results in the second
   multicast forwarding entry in Figure 4.  Likewise, for packets
   originating at nodes :5 or :7, node :2 only has to replicate twice,
   which results in the last two multicast forwarding entries in Figure
   4.

6.  SPBV Example

   Using the same example network as Figure 2, we will look at the FDBs
   produced for SPBV mode forwarding.  Nodes :1, :5, :3, and :7 wish to
   transmit and receive the same multicast MAC traffic using multicast
   address 0300-0000-000f and at the same time require congruent and
   symmetric unicast forwarding.  In SPBV mode, the only encapsulation
   is the C-TAG or S-TAG, and the MAC addresses SA and DA are reverse-
   path learned, as in traditional bridging.






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                        +----+           +----+
                        | :4 | 2 ------1 | :5 | <==> MMAC ..:f
                        +----+           +----+
                       1      3         3      2
                      /        \       /        \
                     1          4     3          2
                  +----+        +----+          +----+
         MMAC<==> | :1 | 2----1 | :2 | 2------1 | :3 | <==> MMAC ..:f
          ..:f    +----+        +----+          +----+
                     3          6     5          3
                      \        /       \        /
                       3      2         1      2
                        +----+           +----+
                        | :6 | 1-------3 | :7 | <==> MMAC ..:f
                        +----+           +----+

         Figure 5: SPBV Example 7-Node Network

   Assuming the same ECT-ALGORITHM (00-80-C2-01), which picks the equal
   cost path with the lowest BridgeID, this ECT-ALGORITHM is assigned to
   Base VID 100, and for each node the SPVID = Base VID + Node ID (i.e.,
   101, 102..107).  When all links have the same cost, then the 1-hop
   shortest paths are all direct, and the 2-hop shortest paths (which
   are of course symmetric) are as previously given for Figure 2.

   Node :1's SPT for this ECT-ALGORITHM is therefore (described as a
   sequence of unidirectional paths):

          { 1->4, 1->6, 1->2->3, 1->2->5, 1->2->7 }

   The FDBs therefore must have entries for the SPVID reserved for
   packets originating from node :1, which in this case is VID=101.

   Node :2 therefore has an FDB that looks like Figure 6.  In
   particular, it takes packets from VID 101 on interface/01 and sends
   to nodes :3, :5, and :7 via if/2, if/3, and if/5.  It does not
   replicate anywhere else because the other nodes (:4 and :6) are
   reached by the SPT directly from node :1.  The rest of the FDB
   unicast entries follow a similar pattern; recall that the shortest
   path between :4 and :6 is via node :1, which explains replication
   onto only two interfaces from if/4 and if/6.  Note that the
   destination addresses are wild cards, and SVL exists between these
   SPVIDs because they are all associated with Base VID = 100, which
   defines the VLAN being bridged.







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          +-------+-------------------+------+-----------------+
          | IN/IF | DESTINATION ADDR  |  VID | OUT/IF(s)       |
          +-------+-------------------+------+-----------------+
         U| if/01 |   **************  | 0101 | {if/2,if/3,if/5 }
         U| if/02 |   **************  | 0103 | {if/1,if/4,if/6 }
         U| if/04 |   **************  | 0104 | {if/2,if/5      }
         U| if/03 |   **************  | 0105 | {if/1,if/5,if/6 }
         U| if/06 |   **************  | 0106 | {if/2,if/3      }
         U| if/05 |   **************  | 0107 | {if/1,if/3,if/4 }

         Figure 6: SPBV Node :2 FDB Unicast

   Now, since nodes :5, :3, :7 and :1 are advertising membership in the
   same multicast group address :f, Node 2 requires additional entries
   to replicate just to these specific nodes for the given multicast
   group address.  These additional multicast entries are given below in
   Figure 7.

          +-------+-------------------+------+-----------------+
          | IN/IF | DESTINATION ADDR  |  VID | OUT/IF(s)       |
          +-------+-------------------+------+-----------------+
         M| if/01 |   0300-0000-000f  | 0101 | {if/2,if/3,if/5 }
         M| if/02 |   0300-0000-000f  | 0103 | {if/1           }
         M| if/03 |   0300-0000-000f  | 0105 | {if/1,if/5      }
         M| if/05 |   0300-0000-000f  | 0107 | {if/1,if/3      }

         Figure 7: SPBV Node :2 FDB Multicast (M)

7.  SPB Supported Adjacency types

   IS-IS for SPB currently only supports peer-to-peer adjacencies.
   Other link types are for future study.  As a result, pseudonodes and
   links to/from pseudonodes are not considered as part of the IS-IS SPF
   computations and will be avoided if present in the physical topology.
   Other NLPIDs MAY of course use them as per normal.

   IS-IS for SPB Must use the IS-IS three-way handshake for IS-IS point-
   to-point adjacencies described in RFC 5303.

8.  SPB IS-IS Adjacency Addressing

   The default behavior of 802.1aq is to use the normal IS-IS Ethernet
   multicast addresses for IS-IS.

   There are however additional Ethernet multicast addresses that have
   been assigned for 802.1aq for special use cases.  These do not in any
   way change the state machinery or packet formats of IS-IS but simply




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   recommend and reserve different multicast addresses.  Refer to
   [802.1aq] for additional details.

9.  IS-IS Area Address and SYSID

   A stand-alone implementation (supporting ONLY the single NLPID=0xC1)
   of SPB Must use an IS-IS area address value of 0, and the SYSID Must
   be the well-known MAC address of the SPB device.

   Non-stand-alone implementations (supporting other NLPIDs) MUST use
   the normal IS-IS rules for the establishment of a level 1 domain
   (i.e., multiple area addresses are allowed only where immediate
   adjacencies share a common area address).  Level 2 operations of
   course place no such restriction on adjacent area addresses.

10.  Level 1/2 Adjacency

   SPBV and SPBM will operate within either an IS-IS level 1 or level 2.
   As a result, the TLVs specified here MAY propagate in either level 1
   or level 2 LSPs.  IS-IS SPB implementations Must support level 1 and
   May support level 2 operations.  Hierarchical SPB is for further
   study; therefore, these TLVs Should Not be leaked between level 1 and
   level 2.

11.  Shortest Path Default Tie-Breaking

   The default algorithm is ECT-Algorithm = 00-80-c2-01.

   Two mechanisms are used to ensure symmetry and determinism in the
   shortest path calculations.

   The first mechanism addresses the problem when different ends (nodes)
   of an adjacency advertise different values for the SPB-LINK-METRIC.
   To solve this, SPB shortest path calculations Must use the maximum
   value of the two nodes' advertised SPB-LINK-METRICs when accumulating
   and minimizing the (sub)path costs.

   The second mechanism addresses the problem when two equal sums of
   link metrics (sub)paths are found.  To solve this, the (sub)path with
   the fewest hops between the fork/join points Must win the tie.
   However, if both (sub)paths have the same number of hops between the
   fork and join points, then the default tie-breaking Must pick the
   path traversing the intermediate node with the lower BridgeID.  The
   BridgeID is an 8-byte quantity whose upper 2 bytes are the node's
   BridgePriority and lower 6 bytes are the node's SYSID.






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   For example, consider the network in Figure 2 when a shortest path
   computation is being done from node :1.  Upon reaching node :7, two
   competing sub-paths fork at node :1 and join at node :7, the first
   via :2 and the second via :6.  Assuming that all the nodes advertise
   a Bridge Priority of 0, the default tie-breaking rule causes the path
   traversing node :2 to be selected since it has a lower BridgeID
   {0...:2} than node :6 {0...:6}.  Note that the operator may cause the
   tie-breaking logic to pick the alternate path by raising the Bridge
   Priority of node :2 above that of node :6.

   The above algorithm guarantees symmetric and deterministic results in
   addition to having the critical property of transitivity (shortest
   path is made up of sub-shortest paths).

12.  Shortest Path ECT

   Standard ECT Algorithms initially have been proposed ranging from
   00-80-c2-01 to 00-80-c2-10.

   To create diversity in routing, SPB defines 16 variations on the
   above default tie-breaking algorithm; these have worldwide unique
   designations 00-80-C2-01 through 00-80-C2-10.  These designations
   consist of the IEEE 802.1 OUI (Organizationally Unique Identifier)
   value 00-80-C2 concatenated with indexes 0X01..0X10.  These
   individual algorithms are implemented by selecting the (sub)path with
   the lowest value of:

        XOR BYTE BY BYTE(ECT-MASK{ECT-ALGORITHM.index},BridgeID)

   Where:

        ECT-MASK{17} = { 0x00, 0x00, 0xFF, 0x88,
                         0x77, 0x44, 0x33, 0xCC,
                         0xBB, 0x22, 0x11, 0x66,
                         0x55, 0xAA, 0x99, 0xDD,
                         0xEE };

        XOR BYTE BY BYTE  - XORs BridgeID bytes with ECT-MASK

   ECT-MASK{1}, since it XORs with all zeros, yields the default
   algorithm described above (00-80-C2-01); while ECT-MASK{2}, since it
   XORs with a mask of all ones, will invert the BridgeID, essentially
   picking the path traversing the largest Bridge ID.  The other ECT-
   MASKs produce diverse alternatives.  In all cases, the
   BridgePriority, since it is the most significant part of the
   BridgeID, permits overriding the SYSID as the selection criteria and
   gives the operator a degree of control on the chosen ECT paths.




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   To support many other tie-breaking mechanisms in the future, two
   opaque ECT TLVs are defined, which may be used to provide parameters
   to ECT-ALGORITHMs outside of the currently defined space.

   ECT-ALGORITHMs are mapped to VIDs, and then services can be assigned
   to those VIDs.  This permits a degree of traffic engineering since
   service assignment to VID is consistent end to end through the
   network.

13.  Hello (IIH) Protocol Extensions

   IEEE 802.1aq can run in parallel with other network layer protocols
   such as IPv4 and IPv6; therefore, failure of two SPB nodes to
   establish an adjacency MUST NOT cause rejection of an adjacency for
   the purposes of other network layer protocols.

   IEEE 802.1aq has been assigned the NLPID value 0xC1 [RFC6328], which
   MUST be used by Shortest Path Bridges (SPBs) to indicate their
   ability to run 802.1aq.  This is done by including this NLPID value
   in the IS-IS IIH PDU Protocols Supported TLV (type 129).  802.1aq
   frames MUST only flow on adjacencies that advertise this NLPID in
   both directions of the IIH PDUs.  802.1aq computations MUST consider
   an adjacency that has not advertised 0xC1 NLPID in both directions as
   non-existent (infinite link metric) and MUST ignore any IIH SPB TLVs
   they receive over such adjacencies.


   IEEE 802.1aq augments the normal IIH PDU with three new TLVs, which
   like all other SPB TLVs, travel within Multi-Topology [MT] TLVs,
   therefore allowing multiple logical instances of SPB within a single
   IS-IS protocol instance.

   Since SPB can use many VIDs and Must agree on which VIDs are used for
   which purposes, the IIH PDUs carry a digest of all the used VIDs (on
   the NNIs) referred to as the SPB-MCID TLV, which uses a common and
   compact encoding reused from 802.1Q.

   SPB neighbors May support a mechanism to verify that the contents of
   their topology databases are synchronized (for the purposes of loop
   prevention).  This is done by exchanging a digest of SPB topology
   information (computed over all MT IDs) and taking specific actions on
   forwarding entries when the digests indicate a mismatch in topology.
   This digest is carried in the Optional SPB-Digest sub-TLV.

   Finally, SPB needs to know which SPT Sets (defined by ECT-ALGORITHMs)
   are being used by which VIDs, and this is carried in the Base VLAN
   Identifiers (SPB-B-VID) sub-TLV.




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13.1.  SPB-MCID Sub-TLV

   This sub-TLV is added to an IIH PDU to indicate the digest for the
   multiple spanning tree configuration a.k.a. MCID.  This TLV is a
   digest of local configuration of which VIDs are running which
   protocols.  (The information is not to the level of a specific
   algorithm in the case of SPB.)  This information Must be the same on
   all bridges in the SPT Region controlled by an IS-IS instance.  The
   data used to generate the MCID is populated by configuration and is a
   digest of the VIDs allocated to various protocols.  Two MCIDs are
   carried to allow non-disruptive transitions between configurations
   when the changes are non-critical.

    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
   +-+-+-+-+-+-+-+-+
   |Type=SPB-MCID  | = 4
   +-+-+-+-+-+-+-+-+
   |   Length      |    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           MCID (51 Bytes)                     |
   |                           ...............                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Aux   MCID (51 Bytes)                     |
   |                           ...............                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: sub-TLV type 4.

   o  Length: The size of the value defined below (102).

   o  MCID (51 bytes): The complete MCID defined in IEEE 802.1Q, which
      identifies an SPT Region on the basis of matching assignments of
      VIDs to control regimes (xSTP, SPBV, SPBM, etc.).  Briefly, the
      MCID consists of a 1-byte format selector, a 32-byte configuration
      name, a 2-byte revision level, and finally a 16-byte signature of
      type HMAC-MD5 over an array of 4096 elements that contain
      identifiers of the use of the corresponding VID.  Refer to Section
      13.8 of [802.1aq] for the exact format and procedure.  Note that
      the use of the VID does not include specification of a specific
      SPB ECT-ALGORITHM; rather, it is coarser grain.

   o  Aux MCID (51 bytes): The complete MCID defined in IEEE 802.1Q,
      which identifies an SPT Region.  The aux MCID allows SPT Regions
      to be migrated by the allocation of new VLAN to FDB Mappings
      without interruption to existing traffic.





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   The SPB-MCID sub-TLV is carried within the MT-Port-Cap TLV [RFC6165]
   with the MT ID value of 0, which in turn is carried in an IIH PDU.

13.2.  SPB-Digest Sub-TLV

   This sub-TLV is Optionally added to an IIH PDU to indicate the
   current SPB topology digest value.  It is always carried in an
   MT-Port-Cap TLV [RFC6165] with an MT ID value of 0.  This information
   should settle to be the same on all bridges in an unchanging
   topology.  Matching digests indicate (with extremely high
   probability) that the topology view between two SPBs is synchronized;
   this match (or lack of match) is used to control the updating of
   forwarding information.  The SPB Agreement Digest is computed based
   on contributions derived from the current topologies of all SPB MT
   instances and is designed to change when significant topology changes
   occur within any SPB instance.

   During the propagation of LSPs, the Agreement Digest may vary between
   neighbors until the key topology information in the LSPs is common.
   The digest is therefore a summarized means of determining agreement
   between nodes on database commonality, and hence of inferring
   agreement on the distance to all multicast roots.  When present, it
   is used for loop prevention as follows: for each shortest path tree
   where it has been determined the distance to the root has changed,
   "unsafe" multicast forwarding is blocked until the exchanged
   Agreement Digests match, while "safe" multicast forwarding is allowed
   to continue despite the disagreement in digests and hence topology
   views.  Section 28.2 of [802.1aq] defines in detail what constitutes
   "safe" vs. "unsafe".

    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
   +-+-+-+-+-+-+-+-+
   |Type=SPB-Digest| = 5
   +-+-+-+-+-+-+-+-+
   |   Length      | (1 byte)
   +-----+-+---+---+
   | Res |V| A | D | (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Agreement Digest (Length - 1)                   |
   |                            ...............                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: sub-TLV type 5.

   o  Length: The size of the value.

   o  V bit: Agreed digest valid bit.  See Section 28.2 of [802.1aq].



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   o  A (2 bits): The Agreement Number 0-3, which aligns with the BPDU's
      Agreement Number concept [802.1aq].  When the Agreement Digest for
      this node changes, this number is incremented.  The node then
      checks for Agreement Digest match (as below).  The new local
      Agreement Number and the updated local Discarded Agreement Number
      are then transmitted with the new Agreement Digest to the node's
      neighbors in the Hello PDU.  Once an Agreement Number has been
      sent, it is considered outstanding until a matching or more recent
      Discarded Agreement Number is received from the neighbor.

   o  D (2 bits): The Discarded Agreement Number 0-3, which aligns with
      BPDU's Agreement Number concept.  When an Agreement Digest is
      received from a neighbor, this number is set to the received
      Agreement Number to signify that this node has received this new
      agreement and discarded any previous ones.  The node then checks
      whether the local and received Agreement Digests match.  If they
      do, this node then sets:

      the local Discarded Agreement Number = received Agreement Number +
      1

      If the Agreement Digests match, AND received Discarded Agreement
      Number ==
                   local Agreement Number + N (N = 0 || 1)

      then the node has a topology matched to its neighbor.

      Whenever the local Discarded Agreement Number relating to a
      neighbor changes, the local Agreement Digest, Agreement Number,
      and Discarded Agreement Number are transmitted.

   o Agreement Digest.  This digest is used to determine when SPB is
      synchronized between neighbors for all SPB instances.  The
      Agreement Digest is a hash computed over the set of all SPB
      adjacencies in all SPB instances.  In other words, the digest
      includes all VIDs and all adjacencies for all MT instances of SPB
      (but not other network layer protocols).  This reflects the fact
      that all SPB nodes in a region Must have identical VID allocations
      (see Section 13.1), and so all SPB instances will contain the same
      set of nodes.  The exact procedure for computing the Agreement
      Digest and its size are defined in Section 28.2 of [802.1aq].

   The SPB-Digest sub-TLV is carried within the MT-Port-Cap TLV
   [RFC6165] (with the MT ID value 0), which in turn is carried in an
   IIH PDU.

   When supported, this sub-TLV MUST be carried on every IIH between SPB
   neighbors, not just when a Digest changes.



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   When one peer supports this TLV and the other does not, loop
   prevention by Agreement Digest Must Not be done by either side.

13.3.  SPB Base VLAN Identifiers (SPB-B-VID) Sub-TLV

   This sub-TLV is added to an IIH PDU to indicate the mappings between
   ECT algorithms and Base VIDs (and by implication the VID(s) used on
   the forwarding path for each SPT Set for a VLAN identified by a Base
   VID) that are in use.  Under stable operational conditions, this
   information should be the same on all bridges in the topology
   identified by the MT-Port-Cap TLV [RFC6165] it is being carried
   within.

    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
   +-+-+-+-+-+-+-+-+
   |Type= SPB-B-VID| = 68
   +-+-+-+-+-+-+-+-+
   |   Length      |    (1 byte)
   +-+-+-+-+-+-+-+-+-----------------------------------------------+
   |        ECT-VID Tuple (1)  (6 bytes)                           |
   +---------------------------------+-----------------------------+
   |      ...                        | ECT-VID Tuple(2) (6 bytes)  |
   +---------------------------------+-----------------------------+
   |                          .....                                |
   +---------------------------------------------------------------+
   |                          .....                                |
   |                          .....                                |
   +---------------------------------------------------------------+

   o  Type: sub-TLV type 6.

   o Length: The size of the value is ECT-VID Tuples*6 bytes.  Each
      6-byte part of the ECT-VID tuple is formatted as follows:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       ECT-ALGORITHM (32 bits)                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Base VID (12 bits)    |U|M|RES|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  ECT-ALGORITHM (4 bytes): The ECT-ALGORITHM is advertised when the
      bridge supports a given ECT-ALGORITHM (by OUI/Index) on a given
      Base VID.  There are 17 predefined IEEE algorithms for SPB with
      index values 0X00..0X10 occupying the low 8 bits and the IEEE
      OUI=00-80-C2 occupying the top 24 bits of the ECT-ALGORITHM.



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   o  Base VID (12 bits): The Base VID that is associated with the SPT
      Set.

   o  Use-Flag (1 bit): The Use-Flag is set if this bridge, or any
      bridge in the LSDB, is currently using this ECT-ALGORITHM and Base
      VID.  Remote usage is discovered by inspection of the U bit in the
      SPB-Inst sub-TLV of other SPB bridges (see Section 14.1)

   o  M bit (1 bit): The M bit indicates if this Base VID operates in
      SPBM (M = 1) or SPBV (M = 0) mode.

   The SPB-B-VID sub-TLV is carried within the MT-Port-Cap TLV
   [RFC6165], which in turn is carried in an IIH PDU.

14.  Node Information Extensions

   All SPB nodal information extensions travel within a new multi-
   topology capability TLV MT-Capability (type 144).

    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
   +-+-+-+-+-+-+-+-+
   |Type = MT-CAP  | = 144
   +-+-+-+-+-+-+-+-+
   |   Length      |     (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |O R R R|       MT ID           | (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     (sub-TLVs ... )

   The format of this TLV is identical in its first 2 bytes to all
   current MT TLVs and carries the MT ID as defined in [MT].

   The O (overload) bit carried in bit 16 has the same semantics as
   specified in [MT], but in the context of SPB adjacencies only.

   There can be multiple MT-Capability TLVs present, depending on the
   amount of information that needs to be carried.

14.1.  SPB Instance (SPB-Inst) Sub-TLV

   The SPB-Inst sub-TLV gives the SPSourceID for this node/topology
   instance.  This is the 20-bit value that is used in the formation of
   multicast DAs for frames originating from this node/instance.  The
   SPSourceID occupies the upper 20 bits of the multicast DA together
   with 4 other bits (see the SPBM 802.1ah multicast DA address format
   section).  This sub-TLV MUST be carried within the MT-Capability TLV
   in the fragment ZERO LSP.  If there is an additional SPB instance, it



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   MUST be declared under a separate MT-Capability TLV and also carried
   in the fragment ZERO LSP.

    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
   +-+-+-+-+-+-+-+-+
   |Type = SPB-Inst| = 1
   +-+-+-+-+-+-+-+-+
   |   Length      |     (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               CIST Root Identifier  (4 bytes)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               CIST Root Identifier (cont)  (4 bytes)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           CIST External Root Path Cost     (4 bytes)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Bridge Priority        |         (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |R R R R R R R R R R R|V|              SPSourceID               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Num of Trees  |       (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  VLAN-ID (1) Tuples    (8 bytes)              |
   |                  ...........................                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      ...........................
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  VLAN-ID (N) Tuples    (8 bytes)              |
   |                  ...........................                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      where VLAN-ID tuples have the format as:

    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
   +-+-+-+-+-+-+-+-+
   |U|M|A|  Res    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       ECT-ALGORITHM (32 bits)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Base VID (12 bits)    |   SPVID (12 bits)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: sub-TLV type 1.

   o  Length: Total number of bytes contained in the value field.





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   o  CIST Root Identifier (64 bits): The CIST Root Identifier is for
      SPB interworking with Rapid STP (RSTP) and Multiple STP (MSTP) at
      SPT Region boundaries.  This is an imported value from a spanning
      tree.

   o  CIST External Root Path Cost (32 bits): The CIST External Root
      Path Cost is the cost to root, derived from the spanning tree
      algorithm.

   o  Bridge Priority (16 bits): Bridge priority is the 16 bits that
      together with the 6 bytes of the System ID form the Bridge
      Identifier.  This allows SPB to build a compatible spanning tree
      using link state by combining the Bridge Priority and the System
      ID to form the 8-byte Bridge Identifier.  The 8-byte Bridge
      Identifier is also the input to the 16 predefined ECT tie-breaker
      algorithms.

   o  V bit (1 bit): The V bit (SPBM) indicates this SPSourceID is auto-
      allocated (Section 27.11 of [802.1aq]).  If the V bit is clear,
      the SPSourceID has been configured and Must be unique.  Allocation
      of SPSourceID is defined in IEEE [802.1aq].  Bridges running SPBM
      will allocate an SPSourceID if they are not configured with an
      explicit SPSourceID.  The V bit allows neighbor bridges to
      determine if the auto-allocation was enabled.  In the rare chance
      of a collision of SPsourceID allocation, the bridge with the
      highest priority Bridge Identifier will win conflicts.  The lower
      priority bridge will be re-allocated; or, if the lower priority
      bridge is configured, it will not be allowed to join the SPT
      Region.

   o  SPSourceID: a 20-bit value used to construct multicast DAs as
      described below for multicast frames originating from the origin
      (SPB node) of the Link State Packet (LSP) that contains this TLV.
      More details are in IEEE [802.1aq].

   o  Number of Trees (8 bits): The Number of Trees is set to the number
      of {ECT-ALGORITHM, Base VID plus flags} tuples that follow.  Each
      ECT-ALGORITHM has a Base VID, an SPVID, and flags described below.
      This Must contain at least the one ECT-ALGORITHM (00-80-C2-01).

   Each VID Tuple consists of:

   o  U bit (1 bit): The U bit is set if this bridge is currently using
      this ECT-ALGORITHM for I-SIDs it sources or sinks.  This is a
      strictly local indication; the semantics differ from the Use-Flag
      found in the Hello, which will set the Use-Flag if it sees other
      nodal U bits are set OR it sources or sinks itself.




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   o  M bit (1 bit): The M bit indicates if this is SPBM or SPBV mode.
      When cleared, the mode is SPBV; when set, the mode is SPBM.

   o  A bit (1 bit): The A bit (SPB), when set, declares this is an
      SPVID with auto-allocation.  The VID allocation logic details are
      in IEEE [802.1aq].  Since SPVIDs are allocated from a small pool
      of 12-bit resources, the chances of collision are high.  To
      minimize collisions during auto-allocation, LSPs are initially
      advertised with the originating bridge setting the SPVID to 0.
      Only after learning the other bridges' SPVID allocations does this
      bridge re-advertise this sub-TLV with a non-zero SPVID.  This will
      minimize but not eliminate the chance of a clash.  In the event of
      a clash, the highest Bridge Identifier is used to select the
      winner, while the loser(s) with lower Bridge Identifier(s) Must
      withdraw their SPVID allocation(s) and select an alternative
      candidate for another trial.  SPVID May also be configured.  When
      the A bit is set to not specify auto-allocation and the SPVID is
      set to 0, this SPBV bridge is used for transit only within the SPB
      region.  If a port is configured with the Base VID as a neighbor
      using RSTP or MSTP, the bridge will act as an ingress filter for
      that VID.

   o  ECT-ALGORITHM (4 bytes): ECT-ALGORITHM is advertised when the
      bridge supports a given ECT-ALGORITHM (by OUI/Index) on a given
      VID.  This declaration Must match the declaration in the Hello PDU
      originating from the same bridge.  The ECT-ALGORITHM and Base VID
      Must match what is generated in the IIHs of the same node.  The
      ECT-ALGORITHM, Base VID tuples can come in any order, however.
      There are currently 17 worldwide unique 802.1aq defined ECT-
      ALGORITHMs given by values 00-80-C2-00 through 00-80-C2-10.

   o  Base VID (12 bits): The Base VID that associated the SPT Set via
      the ECT-ALGORITHM.

   o  SPVID (12 bits): The SPVID is the Shortest Path VID assigned for
      the Base VID to this node when using SPBV mode.  It is not defined
      for SPBM mode and Must be 0 for SPBM mode B-VIDs.














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14.1.1.  SPB Instance Opaque ECT-ALGORITHM (SPB-I-OALG) Sub-TLV

   There are multiple ECT algorithms defined for SPB; however, for the
   future, additional algorithms may be defined including but not
   limited to ECMP- or hash-based behaviors and (*,G) multicast trees.
   These algorithms will use this Optional TLV to define new algorithm
   parametric data.  For tie-breaking parameters, there are two broad
   classes of algorithm, one that uses nodal data to break ties and one
   that uses link data to break ties.  This sub-TLV is used to associate
   opaque tie-breaking data with a node.  This sub-TLV, when present,
   MUST be carried within the MT-Capability TLV (along with a valid SPB-
   Inst sub-TLV).  Multiple copies of this sub-TLV MAY be carried for
   different ECT-ALGORITHMs relating to this node.

   There are of course many other uses of this opaque data that have yet
   to be defined.

    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
   +-+-+-+-+-+-+-+-+
   |Type=SPB-I-OALG| = 2
   +-+-+-+-+-+-+-+-+
   |   Length      |     (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Opaque ECT-ALGORITHM    (4 bytes)            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Opaque ECT Information (variable)            |
   |                   .......................                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: sub-TLV type 2.

   o  Length: Total number of bytes contained in the value field.

   o  ECT-ALGORITHM: ECT-ALGORITHM is advertised when the bridge
      supports a given ECT-ALGORITHM (by OUI/Index) on a given VID.

   o  ECT Information: ECT-ALGORITHM Information of variable length
      which SHOULD be in sub-TLV format with an IANA numbering space
      where appropriate.











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15.  Adjacency Information Extensions

15.1.  SPB Link Metric (SPB-Metric) Sub-TLV

   The SPB-Metric sub-TLV (type 29) occurs within the Multi-Topology
   Intermediate System Neighbor (MT-ISN) TLV (type 222) or within the
   Extended IS Reachability TLV (type 22).  If this sub-TLV is not
   present for an IS-IS adjacency, then that adjacency Must not carry
   SPB traffic for the given topology instance.

    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
   +-+-+-+-+-+-+-+-+
   |Type=SPB-Metric| = 29
   +-+-+-+-+-+-+-+-+
   |   Length      |     (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       SPB-LINK-METRIC                         |   (3 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Num of Ports    |     (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Port Identifier          |   ( 2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: sub-TLV type 29.

   o  Length: Total number of bytes contained in the value field.

   o  SPB-LINK-METRIC: the administrative cost or weight of using this
      link as a 24-bit unsigned number.  This metric applies to the use
      of this link for SPB traffic only.  Smaller numbers indicate lower
      weights and are more likely to carry SPB traffic.  Only one metric
      is allowed per SPB instance per link.  If multiple metrics are
      required, multiple SPB instances Must be used, either within IS-IS
      or within several independent IS-IS instances.  If this metric is
      different at each end of a link, the maximum of the two values
      Must be used in all SPB calculations for the weight of this link.
      The maximum SPB-LINK-METRIC value 2^24 - 1 has a special
      significance; this value indicates that although the IS-IS
      adjacency has formed, incompatible values have been detected in
      parameters configured within SPB itself (for example, different
      regions), and the link Must Not be used for carrying SPB traffic.
      Full details are found in [802.1aq].

   o  Num of Ports: the number of ports associated with this link.

   o  Port Identifier: the standard IEEE port identifier used to build a
      spanning tree associated with this link.



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15.1.1.  SPB Adjacency Opaque ECT-ALGORITHM (SPB-A-OALG) Sub-TLV

   There are multiple ECT algorithms defined for SPB; however, for the
   future, additional algorithms may be defined.  The SPB-A-OALG sub-TLV
   occurs within the Multi-Topology Intermediate System TLV (type 222)
   or the Extended IS Reachability TLV (type 22).  Multiple copies of
   this sub-TLV MAY be carried for different ECT-ALGORITHMs related to
   this adjacency.

    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
   +-+-+-+-+-+-+-+-+
   |Type=SPB-A-OALG| = 30
   +-+-+-+-+-+-+-+-+
   |   Length      |     (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Opaque ECT Algorithm    (4 bytes)            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Opaque ECT Information (variable)            |
   |                  .........................                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: sub-TLV type 30.

   o  Length: Total number of bytes contained in the value field.

   o  ECT-ALGORITHM: ECT-ALGORITHM is advertised when the bridge
      supports a given ECT-ALGORITHM (by OUI/Index) on a given VID.

   o  ECT Information: ECT-ALGORITHM Information of variable length in
      sub-TLV format using new IANA type values as appropriate.

16.  Service Information Extensions

16.1.  SPBM Service Identifier and Unicast Address (SPBM-SI) Sub-TLV

   The SPBM-SI sub-TLV (type 3) is used to introduce service group
   membership on the originating node and/or to advertise an additional
   B-MAC unicast address present on, or reachable by the node.












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    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
   +-+-+-+-+-+-+-+-+
   |Type = SPBM-SI | = 3
   +-+-+-+-+-+-+-+-+
   |   Length      |     (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       B-MAC ADDRESS                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    B-MAC ADDRESS  (6 bytes)   |  Res. |   Base VID (12 bits)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |T|R| Reserved  |                 I-SID  #1                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |T|R| Reserved  |                 I-SID  #2                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            .................
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |T|R| Reserved  |                 I-SID  #n                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: sub-TLV type 3.

   o  Length: Total number of bytes contained in the value field.

   o  B-MAC ADDRESS: a unicast address of this node.  It may be the
      single nodal address, or it may address a port or any other level
      of granularity relative to the node.  In the case where the node
      only has one B-MAC address, this Should be the same as the SYSID
      of the node.  To add multiple B-MACs this TLV MUST be repeated per
      additional B-MAC.

   o  Base VID (12 bits): The Base VID associated with the B-BMAC allows
      the linkage to the ECT-ALGORITHM and SPT Set defined in the SPB-
      Inst sub-TLV.

   o  I-SID #1 .. #n: 24-bit service group membership identifiers.  If
      two nodes have an I-SID in common, intermediate nodes on the
      unique shortest path between them will create forwarding state for
      the related B-MAC addresses and will also construct multicast
      forwarding state using the I-SID and the node's SPSourceID to
      construct a multicast DA as described in IEEE 802.1aq LSB.  Each
      I-SID has a Transmit (T) and Receive (R) bit that indicates if the
      membership is as a transmitter, a receiver, or both (with both
      bits set).  In the case where the Transmit (T) and Receive (R)
      bits are both zero, the I-SID instance is ignored for the purposes
      of distributed multicast computation, but the unicast B-MAC
      address Must be processed and installed at nodes providing transit
      to that address.  If more I-SIDs are associated with a particular



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      B-MAC than can fit in a single sub-TLV, this sub-TLV can be
      repeated with the same B-MAC but with different I-SID values.

   o  Note: When the T bit is not set, an SPB May still multicast to all
      the other receiving members of this I-SID (those advertising with
      their R bits set), by configuring edge replication and serial
      unicast to each member locally.

   The SPBM-SI sub-TLV, when present, MUST be carried within the
   MT-Capability TLV and can occur multiple times in any LSP fragment.

16.2.  SPBV MAC Address (SPBV-ADDR) Sub-TLV

   The SPBV-ADDR sub-TLV is IS-IS sub-TLV type 4.  It Should be used for
   advertisement of Group MAC addresses in SPBV mode.  Unicast MAC
   addresses will normally be distributed by reverse-path learning, but
   carrying them in this TLV is not precluded.  It has the following
   format:

    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
   +-+-+-+-+-+-+-+-+
   | Type=SPBV-ADDR|   = 4            (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |R|R| SR|       SPVID           |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+-+-+-+
   |T|R| Reserved  |      MAC 1 Address              |  (1+6 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+-+-+-+
                            ...
   +-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+-+-+-+
   |T|R| Reserved  |      MAC N Address              |  (1+6 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: sub-TLV type 4.

   o Length: Total number of bytes contained in the value field.  The
      number of MAC address associated with the SPVID is computed by
      (Length - 2)/7.

   o  SR bits (2 bits): The SR bits are the service requirement
      parameter from MMRP.  The service requirement parameters have the
      value 0 (Forward all Groups) and 1 (Forward All Unregistered
      Groups) defined.  However, this attribute May also be missing.  So
      the SR bits are defined as 0 not declared, 1 Forward all Groups,
      and 2 Forward All Unregistered Groups.  The two 'R' reserved bits




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      immediately preceding these SR bits Shall be set to zero when
      originating this sub-TLV and Shall be ignored on receipt.

   o  SPVID (12 bits): The SPVID and by association Base VID and the
      ECT-ALGORITHM and SPT Set that the MAC addresses defined below
      will use.  If the SPVID is not allocated the SPVID Value is 0.
      Note that if the ECT-ALGORITHM in use is spanning tree algorithm
      this value Must be populated with the Base VID and the MAC Must be
      populated.

   o  T bit (1 bit): This is the Transmit allowed bit for a following
      group MAC address.  This is an indication that the Group MAC
      address in the context of the SPVID of the bridge advertising this
      Group MAC Must be installed in the FDB of transit bridges, when
      the bridge computing the trees is on the corresponding ECT-
      ALGORITHM shortest path between the bridge advertising this MAC
      with the T bit set and any receiver of this Group MAC address.  A
      bridge that does not advertise this bit set for a MAC address Must
      Not cause multicast forwarding state to be installed on other
      transit bridges in the network for traffic originating from that
      bridge.

   o  R bit (1 bit): This is the Receive allowed bit for the following
      MAC address.  This is an indication that MAC addresses as the
      receiver Must be populated and installed when the bridge computing
      the trees lies on the corresponding shortest path for this ECT-
      ALGORITHM between this receiver and any transmitter to this MAC
      address.  An entry that does not have this bit set for a Group MAC
      address is prevented from receiving on this Group MAC address
      because transit bridges Must Not install multicast forwarding
      state towards it in their FDBs.

   o  MAC Address (48 bits): The MAC address declares this bridge as
      part of the multicast interest for this destination MAC address.
      Multicast trees can be efficiently constructed for destination by
      populating FDB entries for the subset of the shortest path tree
      that connects the bridges supporting the MAC address.  This
      replaces the function of MMRP for SPTs.  The T and R bits above
      have meaning as specified above.

   The SPBV-ADDR sub-TLV, when present, MUST be carried within the
   MT-Capability TLV and can occur multiple times in any LSP fragment.









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17.  Security Considerations

   This document adds no additional security risks to IS-IS, nor does it
   provide any additional security for IS-IS when used in a configured
   environment or a single-operator domain such as a data center.

   However, this protocol may be used in a zero-configuration
   environment.  Zero configuration may apply to the automatic detection
   and formation of an IS-IS adjacency (forming an NNI port).  Likewise,
   zero configuration may apply to the automatic detection of VLAN-
   tagged traffic and the formation of a UNI port, with resultant I-SID
   advertisements.

   If zero configuration methods are used to autoconfigure NNIs or UNIs,
   there are intrinsic security concerns that should be mitigated with
   authentication procedures for the above cases.  Such procedures are
   beyond the scope of this document and are yet to be defined.

   In addition, this protocol can create significant amounts of
   multicast state when an I-SID is advertised with the T bit set.
   Extra care should be taken to ensure that this cannot be used in a
   denial-of-service attack [RFC4732] in a zero-configuration
   environment.

18.  IANA Considerations

   Note that the NLPID value 0xC1 [RFC6328] used in the IIH PDUs has
   already been assigned by IANA for the purpose of 802.1aq; therefore,
   no further action is required for this code point.

   Since 802.1aq operates within the IS-IS Multi-Topology framework,
   every sub-TLV MUST occur in the context of the proper MT TLV (with
   the exception of the SPB-Metric sub-TLV, which MAY travel in TLV 22
   where its MT ID is unspecified but implied to be 0).  IANA has
   allocated sub-TLVs for three Multi-Topology TLVs per 802.1aq.  These
   are the MT-Port-Cap TLV [RFC6165] used in the IIH, the MT-Capability
   TLV (new) used within the LSP, and finally the MT-ISN TLV [MT] used
   to contain adjacency information within the LSP.

   This document creates the following TLVs and sub-TLVs within the IIH
   and LSP PDUs MT TLVs as described below.  The '*' indicates new IANA
   assignments (per this document).  Other entries are shown to provide
   context only.

   The MT-Capability TLV is the only TLV that required a new sub-
   registry.  Type value 144 has been assigned, with a starting sub-TLV
   value of 1, and managed by Expert Review.




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      +-----+----+-----------------+--------+------+-------------+
      | PDU |TLV | SUB-TLV         | TYPE   | TYPE | #OCCURRENCE |
      +-----+----+-----------------+--------+------+-------------+
        IIH
             MT-Port-Cap               143
   *               SPB-MCID                    4      1
   *               SPB-Digest                  5      >=0
   *               SPB-B-VID                   6      1

        LSP
   *         MT-Capability             144            >=1
   *               SPB-Inst                    1      1
   *               SPB-I-OALG                  2      >=0
   *               SPBM-SI                     3      >=0
   *               SPBV-ADDR                   4      >=0

             MT-ISN                    222
          or Extended IS Reachability   22
   *               SPB-Metric                 29      1
   *               SPB-A-OALG                 30      >=0

19.  References

19.1.  Normative References

   [802.1aq]  "Standard for Local and Metropolitan Area Networks:
              Virtual Bridges and Virtual Bridged Local Area Networks -
              Amendment 9: Shortest Path Bridging", IEEE P802.1aq, Draft
              4.6, 2012.

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

   [MT]       Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120, February 2008.

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

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

   [RFC6328]  Eastlake 3rd, D., "IANA Considerations for Network Layer
              Protocol Identifiers", BCP 164, RFC 6328, July 2011.



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19.2.  Informative References

   [802.1ag]  "Standard for Local and Metropolitan Area Networks /
              Virtual Bridged Local Area Networks / Amendment 5:
              Connectivity Fault Management", IEEE STD 802.1ag, 2007.

   [MMRP]     "Standard for Local and Metropolitan Area Networks Virtual
              Bridged Local Area Networks - Amendment 07: Multiple
              Registration Protocol", IEEE STD 802.1ak, 2007.

   [PB]       "Standard for Local and Metropolitan Area Networks /
              Virtual Bridged Local Area Networks / Amendment 4:
              Provider Bridges", IEEE STD 802.1ad, 2005.

   [PBB]      "Standard for Local and Metropolitan Area Networks /
              Virtual Bridged Local Area Networks / Amendment 7:
              Provider Backbone Bridges", IEEE STD 802.1ah, 2008.

   [RFC4732]  Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet
              Denial-of-Service Considerations", RFC 4732, December
              2006.

   [Y.1731]   ITU-T, "OAM Functions and Mechanisms for Ethernet based
              networks", ITU-T Y.1731, 2006.

20.  Acknowledgments

   The authors would like to thank Ayan Banerjee, Mick Seaman, Janos
   Farkas, Les Ginsberg, Stewart Bryant , Donald Eastlake, Matthew Bocci
   and Mike Shand for contributions and/or detailed review.





















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Authors' Addresses

   Don Fedyk (editor)
   Alcatel-Lucent
   Groton, MA  01450
   USA
   EMail: Donald.Fedyk@alcatel-lucent.com

   Peter Ashwood-Smith (editor)
   Huawei Technologies Canada Ltd.
   303 Terry Fox Drive, Suite 400
   Kanata, Ontario, K2K 3J1
   CANADA
   EMail: Peter.AshwoodSmith@huawei.com

   Dave Allan
   Ericsson
   300 Holger Way
   San Jose, CA  95134
   USA
   EMail: david.i.allan@ericsson.com

   Nigel Bragg
   Ciena Limited
   Ciena House
   43-51 Worship Street
   London  EC2A 2DX
   UK
   EMail: nbragg@ciena.com

   Paul Unbehagen
   Avaya
   8742 Lucent Boulevard
   Highlands Ranch, CO  80129
   USA
   EMail: unbehagen@avaya.com















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