



Network Working Group                                          D. Fedyk 
Internet Draft                                           Alcatel-Lucent 
Intended status: Standards Track                        P.Ashwood-Smith 
Expires: September 8, 2011                                       Huawei 
                                                                        
                                                          March 8, 2011 
                                      
     IS-IS Extensions Supporting IEEE 802.1aq Shortest Path Bridging 
                      draft-ietf-isis-ieee-aq-05.txt 


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   This Internet-Draft will expire on August 1st 2011. 

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Abstract 

   802.1aq Shortest Path Bridging (SPB) is being 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-multi-point and multi-point-to-multipoint variations. This 
   memo documents the IS-IS changes required to support this IEEE 
   protocol and provides some context and examples. 
    

































 
 
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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...................................12 
      4.7. Data Path SPBV Multicast.................................12 
   5. SPBM Example..................................................12 
   6. SPBV Example..................................................15 
   7. SPB Supported Adjacency types.................................17 
   8. SPB IS-IS adjacency addressing................................17 
   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 sub-TLV.......................24 
   14. Node information extensions..................................25 
      14.1. SPB Instance sub-TLV....................................26 
         14.1.1. SPB Instance Opaque ECT-ALGORITHM sub-TLV..........29 
   15. Adjacency information extensions.............................30 
      15.1. SPB Link Metric sub-TLV.................................30 
         15.1.1. SPB Adjacency Opaque ECT-ALGORITHM sub-TLV.........31 
   16. Service information extensions...............................32 
      16.1. SPBM Service Identifier and Unicast Address sub-TLV.....32 
      16.2. SPBV Mac Address sub-TLV................................33 
   17. Security Considerations......................................35 
   18. IANA Considerations..........................................36 
   19. References...................................................37 
      19.1. Normative References....................................37 
      19.2. Informative References..................................38 
   20. Acknowledgments..............................................38 
   21. Author's Addresses...........................................38 
   22. Intellectual Property Statement..............................39 
   23. Disclaimer of Liability......................................40 
    
 
 
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1. Introduction 

   802.1aq Shortest Path Bridging (SPB) [802.1aq] is being 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-multi-point (E-TREE) and 
   multi-point-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 new terms: 
    
   802.1ad        Provider Bridging (PB) - Q-in-Q encapsulation 
   802.1ah        Provider Backbone Bridges (PBB), 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 
   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 
   C-VLAN         Customer Virtual LAN  
   DA             Destination Address 
 
 
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   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.  
   E-LINE         Bidirectional Logical Connectivity between two UNIs. 
   E-TREE         Asymmetric Logical Connectivity between UNIs. 
   FDB            Filtering Database: {DA/VID}->{next hops} 
   I-SID          Logical Grouping Identifier for E-LAN/LINE/TREE UNIs. 
   LAN            Local Area Network 
   LSDB           Link State Database 
   LSP            Link State Packet 
   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-ISIS        Multi Topology IS-IS as used in [MT] 
   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 
   Q-in-Q         Additional S-VLAN after a C-VLAN (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 
   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 
   SPT            Shortest Path Tree computed by one ECT-ALORITHM 
   SPT Region     A set of SPBs with identical VID usage on their NNIs 
   SPSourceID     20 bit identifier of the source of multicast frames. 
   SPVID          SPBV: a C-VLAN or S-VLAN that identifies the source.   
   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 lower case 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 
   lower case forms with initial capitalization of the conventions in 
   RFC2119 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 which is identical to its SPT. Symmetry and 
   congruency preserve packet ordering and proper fate sharing of OAM 
   flows by the forwarding path. Such modes are fully supported by 
   existing [802.1ag] and [Y.1731] OA&M 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.  

 
 
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   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 
   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 SYS-ID.  

   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 world wide 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 which corresponds to the ECT-ALGORITHM network wide. 

   802.1aq supports membership attributes which are advertised with the 
   I-SID (SPBM) or Group Address (SPBV) that define 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 
 
 
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   congruency and symmetry Must be honored, a single tree may leave 
   some links under utilized. By using different deterministic tie 
   breakers, up to sixteen shortest paths of arbitrary diversity are 
   possible between any pair of nodes. This distributes the traffic on 
   a VLAN basis. 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 not only possible to have different 
   adjacency metrics (or infinite metrics) for SPB adjacencies, 
   distinct from IP or other NLPIDs riding in this IS-IS instance, and 
   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 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-
 
 
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   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 
   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, 
   are used to populate the filtering data bases (FDB). 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 TX bit set but instead Must 
   locally and dynamically construct the appropriate unicast serial 
   replication to all the other receivers (RX) of the same I-SID. 
    
   When an unknown customer unicast or a multicast frame arrives at an 
   SPBM User to Network Interface (UNI) port which 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 RX 
   (receive) attribute set. This RX/I-SID pair is found in the SPBM 
   Service Identifier and Unicast Address 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 
 
 
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   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 TX bit set. 
     
   Broadcast, unknown unicast or multicast frames arriving at an SPBM 
   UNI port are encapsulated with a B-DA multicast address which 
   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) which 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]  |  ISID [16:23] | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |  ISID [8:15]  |   ISID [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 a SPBM constructed 
      multicast DA. 

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



 
 
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   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 sub-TLV. The 
      value SPSourceID = 0 has special significance; it is advertised 
      by an SPBM node which 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]).  

   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 a SPBV UNI port VID 
   translation (or VID encapsulation for un-tagged 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 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 
 
 
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   check 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 

   Conversely when a packet for a known DA arrives at a SPBV UNI port 
   VID translation (or VID encapsulation for un-tagged Frames) with the 
   corresponding SPVID for this VLAN and ingress SPB 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.  

4.7. Data Path SPBV Multicast 

   C-DA multicast addresses May be advertised from SPBV UNI ports. 
   These may be configured or learned through MMRP. The MMRP protocol 
   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 following 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 show at the end of the UNI ports as i1. 
     











 
 
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                        +----+           +----+ 
                        | :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 } 
    
   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 who's DA contains its SPSourceID (in the 
   example the last 20 bits of the B-MAC) and the I-SID 1 and sends to 
   interface 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/OO. 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. 
    



 
 
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          +-------+-------------------+------+-----------------+ 
          | 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. 
    
          +-------+-------------------+------+-----------------+ 
          | 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 2, 3 and 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/{2, 3 and 5}. This can be seen in 
   the first multicast entry in Figure 4. 
    

 
 
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   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 or S-TAG and the MAC addresses SA,DA are reverse-path learned, 
   as in traditional bridging. 
     
                        +----+           +----+ 
                        | :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 (Shortest Path Tree) for this ECT-ALGORITHM is 
   therefore (described as a sequence of unidirectional paths): 
    
 
 
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          { 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 a FDB which 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 shared VLAN learning (SVL) exists between these SPVIDs, 
   because they are all associated with BASE VID = 100, which defines 
   the VLAN being bridged. 
 
          +-------+-------------------+------+-----------------+ 
          | 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) 
    


 
 
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7. SPB Supported Adjacency types 

   IS-IS for SPB currently only supports P2P 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 
   anyway change the state machinery or packet formats of IS-IS but 
   simply 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 but 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 either within an IS-IS level 1, or an 
   ISIS level 2. As a result, the TLVs specified here MAY propagate 
   either in 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 TLV's Should Not be leaked 
   between level 1 and level 2. 

11. Shortest Path Default Tie Breaking  

   (ECT-ALGORITHM = 00-80-C2-01) 

 
 
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   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 node's 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 the lower 6 bytes are the node's SYSID. 
    
   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  

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





 
 
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        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 xor's with all 0's is just the same as the 
   default algorithm described above 00-80-C2-01, while ECT-MASK{0x02} 
   since it xor's with a mask of all 1's 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. 
    
   To support many other tie breaking mechanisms in the future two 
   opaque ECT TLV's 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 for 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 [NLPID] 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 
   TLV's they receive over such adjacencies. 
 
 
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   IEEE 802.1aq augments the normal IIH PDU with three new TLV's 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 PDU's carry a digest of all the used 
   VIDs (on the NNI's) referred to as the SPB-MCID TLV which uses a 
   common and compact encoding taken 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 MTIDS) 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 sub-TLV.  

    

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.  












 
 
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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=SPB-MCID  | = 6 
   +-+-+-+-+-+-+-+-+ 
   |   Length      |    (1 byte) 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                           MCID (51 Bytes)                     | 
   |                           ...............                     | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                     Aux   MCID (51 Bytes)                     | 
   |                           ...............                     | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
    
   o  Type: sub-TLV Type = 6 (Pending IANA). 

   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. 

   The SPB MCID sub-TLV is carried within the MT-Port-Cap TLV [LAYER2] 
   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 [LAYER2] 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 
 
 
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   probability) that the topology view between two SPBs is 
   synchronized, and 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 are common. 
   The digest is therefore a summarized means of determining agreement 
   between nodes on database commonality, and hence infer 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. [802.1aq] section 28.2 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| = 7 
   +-+-+-+-+-+-+-+-+ 
   |   Length      | (1 byte) 
   +-----+-+---+---+ 
   | Res |V| A | D | (1 byte) 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |               Agreement Digest (Length - 1)                   | 
   |                            ...............                    | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
    
   o  Type: sub-TLV Type = 7 (Pending IANA). 

   o  Length: The size of the value.  

   o  V - agreed digest valid bit. See [802.1aq] Sec 28.2. 







 
 
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   o  A (2 bits) The Agreement Number 0-3 which aligns with BPDUs 
      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 
      BPDUs 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 13.1), and so all SPB instances will contain the 
      same set of nodes. The size and exact procedure for computing the 
      Agreement Digest is defined in section 28.2 of [802.1aq]. 

   The SPB Digest sub-TLV is carried within the MT-Port-Cap TLV 
   [LAYER2] (with the MT-ID value 0) which in turn is carried in an IIH 
   PDU.  
    
 
 
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   When supported, this sub-TLV MUST be carried on every IIH between 
   SPB neighbors, not just when a Digest changes. 
    
   When one peer supports this TLV and the other does not, loop 
   prevention by digest agreement Must Not be done by either side. 
 
13.3. SPB Base VLAN-Identifiers 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 [LAYER2] 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| = 8 
   +-+-+-+-+-+-+-+-+ 
   |   Length      |    (1 byte) 
   +-+-+-+-+-+-+-+-+-----------------------------------------------+ 
   |      ECT - VID Tuple (1)  (6 bytes)                           | 
   +---------------------------------+-----------------------------+ 
   |      ...                        | ECT-VID Tuple(2) (6 bytes)  |      
   +---------------------------------+-----------------------------+ 
   |                          .....                                | 
   +---------------------------------------------------------------+ 
   |                          .....                                | 
   |                          .....                                | 
   +---------------------------------------------------------------+ 
    
    
   o  Type: sub-TLV Type = 8 (Pending IANA). 

   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: 








 
 
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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 
    
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                     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. 

   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 Instance 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 Base VLAN-Identifier sub-TLV is carried within the MT-Port-
   Cap TLV [LAYER2] 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 ... ) 

 
 
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   The format of this TLV is identical in its first 2 bytes to all 
   current MT TLV's 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. 

14.1.  SPB Instance sub-TLV 

   The SPB Instance sub-TLV gives the SPSourceID for this node/topology 
   instance.  This is the 20 bit value that is used in the formation of 
   multicast DA addresses 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 MUST be declared under a separate MT-
   Topology 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)              | 
   |                  ...........................                  | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
 
 
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      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 (Pending IANA). 

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

   o  CIST Root Identifier (64-bits)The CIST Root Identifier is for SPB 
      interworking with RSTP and 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 is configured exactly as specified in IEEE802 
      [802.1D]. 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 pre-defined ECT tie 
      breaker algorithms. 

   o  V bit (1-Bit) The V bit (SPBM) indicates this SPSourceID is auto 
      allocated(27.11).  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 and 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. 


 
 
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   o  The SPSourceID is a 20 bit value used to construct multicast DA's 
      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-ALGORITMM (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. 

   o  M-Bit (1-bit) The M-bit indicates if this is SPBM or SPBV mode. 
      When cleared the mode is SPBV and when set the mode is SPBM.  

   o  A 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.  







 
 
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   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 world wide 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. 

14.1.1. SPB Instance Opaque ECT-ALGORITHM 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 / 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 which uses nodal data to break ties and 
   one which uses link data to break ties, this 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 Instance 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 which 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)            | 
   |                   .......................                     | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
 
 
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   o  Type: sub-TLV Type 2 (Pending IANA). 

   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. 

15. Adjacency information extensions  

15.1. SPB Link Metric sub-TLV 

   The SPB Link Metric sub-TLV (type = 12) occurs within the Multi 
   Topology Intermediate System TLV (type 222) or within the Extended 
   IS Reachability TLV (type 22).  If this sub TLV is not present for 
   an ISIS 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| = 12 
   +-+-+-+-+-+-+-+-+ 
   |   Length      |     (1 byte) 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |       SPB-LINK-METRIC                         |   (3 bytes) 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   | Num of ports    |     (1 byte) 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |     Port  Identifier          |   ( 2 bytes) 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
   o  Type: sub-TLV Type 12 (Pending IANA). 

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








 
 
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   o  SPB-LINK-METRIC indicates 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 is the number of ports associated with this link. 

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

15.1.1. SPB Adjacency Opaque ECT-ALGORITHM sub-TLV 

   There are multiple ECT algorithms defined for SPB, however for the 
   future additional algorithms may be defined.  The SPB Adjacency 
   Opaque ECT-ALGORITHM 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| = 13 
   +-+-+-+-+-+-+-+-+ 
   |   Length      |     (1 byte) 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                  Opaque ECT Algorithm    (4 bytes)            | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                  Opaque ECT Information (variable)            | 
   |                  .........................                    | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
   o  Type: sub-TLV Type = 13 (PENDING IANA). 

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

   The SPBM Service Identifier and Unicast Address 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. 
    
    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  |                  ISID  #1                     |  
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |T|R| Reserved  |                  ISID  #2                     | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
                            ................. 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |T|R| Reserved  |                  ISID  #n                     |  
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
     

   o  Type: sub-TLV Type = 3 (Pending IANA)  

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





 
 
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   o  B-MAC ADDRESS is a unicast address of this node.  It may be 
      either the single nodal address, or 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 SYS-ID 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 this 
      allows the linkage to the ECT-Algorithm and SPT Set defined in 
      the SPB Instance sub-TLV. 

    

   o  ISID #1 .. #N are 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 which indicates if the 
      membership is as a Transmitter/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 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 receive 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 Service Identifier 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 sub-TLV 

   The SPBV MAC Address (SPBV-MAC-ADDR) sub-TLV is IS-IS sub-TLV type 4 
   (PENDING IANA).  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 : 


 
 
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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=SPBV-ADDR|   = 4            (1 byte) 
   +-+-+-+-+-+-+-+-+ 
   |   Length      |                  (1 byte) 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |R|R|S-R|       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, set to 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  S-R 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 
      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. 








 
 
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   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 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-MAC-ADDR sub-TLV, when present, MUST be carried within the 
   MT-Capability TLV and can occur multiple times in any LSP fragment. 
    
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 ISID 
   advertisements. 
    
 
 
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   If zero configuration methods are used to auto configure 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 ISID is advertised with the TX 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 [NLPID] 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 Link Metric sub-TLV which MAY travel in TLV 
   22 where its MT-ID is unspecified but implied to be 0). There are 
   three Multi Topology TLV's in which 802.1aq requests allocation of 
   sub-TLV's. These are the MT-Port-Cap TLV [LAYER2] used in the IIH, 
   the MT-Capability TLV (new) used within the LSP and finally the MT-
   Intermediate-System TLV [MT] used to contain adjacency information 
   within the LSP. 
    
   This document creates the following TLVs & sub-TLV's within the IIH 
   and LSP PDUs MT TLV's as described below. The '*' indicates IANA 
   action is required. Other entries are shown to provide context only. 
   A '?' next to a number indicates a requested but of course not 
   necessarily the final assigned value. 
    
   The MT-Capability TLV is the only TLV requiring a new sub-registry. 
   Type value 144 (TBD) is requested, 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               147? 
   *               SPB-MCID                    6?     1   
   *               SPB-Digest                  7?     >=0 
   *               SPB-B-VID                   8?     1 
    
        LSP 
   *         MT-Capability             144? 
   *               SPB-Inst                    1?     1 
   *               SPB-I-OALG                  2?     >=0 
   *               SPBM-SI                     3?     >=0 
   *               SPBV-ADDR                   4?     >=0 
    
             MT-Intermediate-System    222 
          or Extended IS Reachability   22 
   *               SPB-Metric                 12?     1 
   *               SPB-A-OALG                 13?     >=0 
    
    
19. References 

19.1. Normative References 

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

   [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]      M-ISIS: Multi Topology (MT) Routing in Intermediate System 
             to Intermediate Systems (IS-ISs), RFC 5120, February 2008. 

    

   [802.1aq] "Standard for Local and Metropolitan Area Networks / 
             Virtual Bridged Local Area Networks / Amendment: Shortest 
             Path Bridging, IEEE P802.1aq  Draft 3.6", 2011. 

   [NLPID]   www.ietf.org/id/draft-eastlake-nlpid-iana-considerations-
             04.txt 

 
 
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   [LAYER2]   www.ietf.org/id/draft-ietf-isis-layer2-09.txt. 

 

19.2. Informative References 

    

   [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. 

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

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

   [RFC4732] Handley, M., Ed, "Internet Denial-of-Service 
             Considerations", RFC 4732, November 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. 
    
   This document was prepared using 2-Word-v2.0.template.dot. 
    
21. Author's Addresses 

   Don Fedyk 
   Alcatel-Lucent 
   Groton, MA, 01450, USA 
   Email: Donald.Fedyk@alcatel-lucent.com 
    
 
 
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   Peter Ashwood-Smith 
   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  
   Email: david.i.allan@ericsson.com 
    
   Nigel Bragg 
   Ciena Limited, 
   Ciena House 
   43-51 Worship Street   
   London  EC2A 2DX 
   Email: nbragg@ciena.com 
    
   Paul Unbehagen 
   Alcatel-Lucent 
   8742 Lucent Boulevard 
   Highlands Ranch, CO 80129, USA 
   Email: Paul.Unbehagen@alcatel-lucent.com 
    
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   The IETF invites any interested party to bring to its attention any 
   copyrights, patents or patent applications, or other proprietary 
   rights that may cover technology that may be required to implement 

 
 
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   any standard or specification contained in an IETF Document. Please 
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   This document and the information contained herein are provided on 
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