Internet DRAFT - draft-fedyk-isis-spb


 Working Group                             Peter Ashwood-Smith 
 Internet-Draft                                      Don Fedyk 
 Date Created: June, 2009                          David Allan 
 Expiration Date:  January, 2010               Jerome Chiabaut 
 Intended Status: Informational                    Nigel Bragg 
           Shortest Path Bridging and Backbone Bridging with IS-IS  
  Status of this Memo 
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  Fedyk et al.                                           [Page 1] 
  Internet Draft     draft-fedyk-isis-spb-00.txt        July 2009 
     Several techniques are being developed which use IS-IS to deliver 
     link state based layer 2 forwarding. The superset of the extensions 
     proposed to IS-IS to allow these capabilities is found in [IS-IS-
     L2].  One technique for layer 2 forwarding is being specified in 
     the IEEE 802.1aq task group, under the over-arching title 
     of "Shortest Path Bridging" (SPB). SPB however only requires a 
     subset of the proposed IS-IS extensions in [IS-IS-L2]. For clarity 
     this informational draft documents only the subset required by SPB. 
     In addition a high level introduction, describing how these TLVs 
     are used is provided for those who do not follow the IEEE work in 
     detail. A reference is also given to the normative IEEE 802.1aq 
     document  The ordering of material in this document follows that of 
     Clause 28 of IEEE 802.1aq, to aid cross-referencing. 
  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]. 
  Table of Contents 
     1.   Terminology..................................................3 
     2.   Introduction.................................................4 
     3.   New TLVs for SPB and SPBB....................................6 
     3.1  Base Vlan-Identifiers sub-TLV................................7 
     3.2  SPB/SPBB Instance sub-TLV....................................8 
     3.3  SPB Link Metric sub-TLV......................................9 
     3.4  The Group MAC Address sub-TLV................................9 
     3.5  The Service Identifier and Unicast Address sub-TLV..........10 
     4.   Security Considerations.....................................10 
     5.   IANA Considerations / ISO Considerations....................10 
     6.   References..................................................11 
     6.1  Normative References........................................11 
     6.2  Informative References......................................11 
     7.   Acknowledgments.............................................12 
     8.   Author's Addresses..........................................12 

  Fedyk et al.                                              [Page 2] 
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  1. Terminology 
     In addition to well understood IS-IS terms, this memo uses 
     terminology from IEEE 802.1 and introduces a few new terms: 
     802.1ah      Provider Backbone Bridges a.k.a. Mac-in-Mac 
     802.1aq      Shortest Path Bridging (SPB)     
     B-DA         Backbone Destination Address in 802.1ah Mac-in-Mac 
     B-MAC        Backbone MAC Address 
     B-SA         Backbone Source address in 802.1ah Mac-in-Mac header 
     B-VID        Backbone VLAN ID in 802.1ah Mac-in-Mac header 
     B-VLAN       Backbone Virtual LAN 
     C-MAC        Customer MAC. Inner MAC in 802.1ah Mac-in-Mac header 
     C-VID        Customer VLAN ID 
     C-VLAN       Customer Virtual LAN  
     DA           Destination Address 
     FIB          Forwarding information base (B-DA/B-VID to next hop(s)) 
     ISID         802.1ah: service membership in datapath(not always=SID) 
     MAC          Media Access Control 
     PBB          Provider Backbone Bridges as specified in 802.1ah 
     M-IS-IS      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] 
     SPSourceID   20 bit nodal identifier used with SID forms mcast DA. 
     PATHID       The unique identifier for a path used for symmetric tie  
     PBB          Provider Backbone Bridge 
     PBT          Provider Backbone Transport 
     SA           Source Address 
     SID          Service Identifier at control plane, groups many ISIDs 
     UNI          User Network Interface: Customer/Backbone attach point 
     VID          VLAN ID  

  Fedyk et al.                                              [Page 3] 
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  2. Introduction 
     Shortest Path Bridging (SPB) and Shortest Path Backbone Bridging 
     (SPBB) both apply the [IS-IS] protocol to the utilization of mesh 
     topologies for native Ethernet bridging.  While 802.1aq has the 
     umbrella title of shortest path bridging, this memo adopts the 
     convention of ascribing unique attributes to the terms SPB and SPBB 
     individually; SPB uses an IEEE 802.1Q forwarding paradigm, whilst 
     SPBB extends the FIB population techniques specified in 802.1Qay 
     combined with IEEE 802.1ah [PBB] adaptation.  Both SPB and SPBB 
     forward packets on shortest path trees with minimum path cost as a 
     first order tie-breaker, where for any pair of nodes A and B, the 
     unicast path for A to B is the exact reverse of the path from B to A 
     (reverse path congruency), and all multicast traffic between the two 
     nodes follows the unicast path (multicast and unicast congruency). 
     These are direct extensions to fundamental Ethernet forwarding 
     properties in IEEE bridged networks.  
     In SPB, conventional bridge learning is used to associate (customer) 
     MAC addresses to ports and hence routes through the SPB region.  The 
     source-rooted tree associated with each node is assigned a unique 
     VLAN ID (the SPVID) to identify it. 
     The 802.1ah [PBB] MAC-in-MAC encapsulation used by SPBB permits the 
     isolation of customer Ethernet addressing from backbone Ethernet 
     addressing in the core of a network. This has an important 
     consequence; the association between a customer MAC (C-MAC) and a B-
     MAC to resolve forwarding across the core is required only at the 
     edge of the network. Flooding is only done by the edge adaptation 
     functions to learn which B-MAC reaches a given C-MAC using the 
     normal PBB C-MAC learning behavior, flooding at the C-MAC layer 
     resolving to a service specific multicast tree at the B-MAC layer.  
     A minimum of one B-VID MUST be assigned to each instance of SPBB 
     (IS-IS MT-ID). The B-VID MUST be unique backbone network wide. Two 
     B-VIDs MAY be used by a single SPBB instance (MT-ID) when it is 
     desired to use more than one equal cost shortest path permutation.  
     With Spanning Tree Protocol (STP), Rapid STP or Multiple STP[802.1Q] 
     Ethernet networks use a shared spanning tree (or a small number of 
     shared trees) to route traffic based on the VLAN ID and then on 
     learned MAC addresses. Per service multicast is instantiated as a 
     (*,G) multicast address which is a proper subset of the VID.  
     In order to move from a shared spanning tree to mesh connectivity, 
     SPB and SPBB use one or more broadcast trees per source as a 
     template for per service multicast trees i.e.(S,G).  
     SPB uses the SPVID when flooding, with conventional pruning as C-MAC 
     addresses are learned. 
  Fedyk et al.                                              [Page 4] 
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     SPBB adapts client flooding onto service specific multicast trees 
     instantiated by encoding S,G in the destination MAC address. SPBB 
     therefore uses both B-VID and B-MAC when forwarding.  
     SPBB uses algorithmically constructed addresses for the multicast 
     DA. Multicast addresses are local to a PBB domain. The multicast B-
     MAC DA address constructed for a particular node/service consists of 
     a unique nodal identifier called a SPSourceID (20 bits), combined 
     with the service identifier (SID) (24 bits). Every SPBB node(per 
     SPBB instance/MT-ID) therefore advertises  this unique SPSourceID 
     which can be correlated to the node's ISIS SYSID by all nodes in the 
     SPBB network. 
     In SPB, a VID (called the Base VID) is also defined for 
     interoperation with xSTP regions. This VID identifies the Common and 
     Internal Spanning Tree (CIST) in the Shortest Path Region. It is 
     created as a conventional Spanning Tree within the SPB region, and 
     Group MAC addresses, installed by conventional Ethernet mechanisms, 
     may be supported on this VID. 
     A node performing SPB or SPBB calculations (for a given instance/MT-
     ID) use the IS-IS topology, and link metrics to compute which leaves 
     of each shortest path tree require transit of the local node, and 
     this node can then do pair-wise comparison of services of interest 
     between the root and the leaves to populate the FIB accordingly. The 
     link metrics are forced to be equal in both directions by defaulting 
     to the largest of the two unidirectional metrics specified for a 
     link as seen during the establishment of a standard IS-IS adjacency.  
     A node performing SPB or SPBB for a given MT instance MUST specify 
     the NLPID for SPB and SPBB (IANA allocation 0xC1 pending) in its IS-
     IS hello message. Links that do not support this NLPID for this MT 
     instance must be excluded from the shortest path computations by the 
     given MT instance.  
     Both SPB and SPBB employ a transitive symmetric tie breaking 
     algorithm which chooses deterministically and progressively between 
     equal cost alternatives by ranking the paths according to the sorted 
     list of node identifiers that make up the path. This sorted list of 
     node identifiers (SYSIDs) is called the Path Identifier (PATHID). 
     For SPB, and when only one B-VID is used in SPBB, the tie breaking 
     algorithm will always pick from a set of equal cost shortest path 
     alternatives by choosing the path with the lowest PATHID. Two B-VID 
     instances MAY be used for an SPBB instance, when it will assign the 
     lowest PATHID paths to one B-VID and the highest PATHID paths to the 
     other B-VID. In this manner an SPBB instance will use more of the 
     available paths in a network but will do so by assignment of packets 
     at the head ends to one of different SPBB B-VIDs.  

  Fedyk et al.                                              [Page 5] 
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  3. New TLVs for SPB and SPBB 
     SPB and SPBB require a subset of the [MT] TLVs. 
     SPB and SPBB inherit the Multi Topology mechanisms from [MT] to 
     allow multiple logical bridging instances to exist within a single 
     IS-IS control instance. Top level TLV's used by SPB and SPBB 
     therefore begin with the Multi Topology Identifier (MT-ID) fields as 
     defined in [MT] and the new sub-TLVs identified here may be used as 
     sub-TLVs of the corresponding new top level Multi Topology TLV's 
     defined in [MT]. 
     In the IEEE the Multiple Spanning tree protocol allowed multiple 
     VIDs to represent a single VLAN. The single "logical" VLAN was 
     identified by a Base VID so that bridges external to the region 
     could have a consistent VID to identify the VLAN.  This concept of a 
     Base VID extends easily to SPB and SPBB.  In this way a Base VID can 
     be used to identify a topology instance and to correlate VIDs that 
     are allocated to a particular shortest path VLAN instance.  
     A Shortest Path Region also has the property that viewed from 
     outside the Region it appears as a single 802.1Q or 802.1ah bridge, 
     irrespective of how the VLAN is implemented.   
     In SPB, each node uses a unique VID as its source identifier (an 
     SPVID), and each SPVID is correlated to a Base VID.  The set of 
     SPVIDs that map to a given Base VID form the SPB region.  In SPBB, 
     this concept is reused however there is a slight modification. A 
     single B-VID maps to a Base VID for all bridges. However multiple B-
     VIDs (currently two) can map to the same Base VID allowing multiple 
     trees within the SPBB VLAN.  A typical use for multiple trees is to 
     instantiate equal cost paths and provide the opportunity to load 
     spread services.  
     A Base VID identifies a traditional spanning tree in both SPB and 
     SPBB that can be used to represent the VLAN for proper bridge 
     behavior when viewed by bridges outside the shortest path region.  
     In essence the VLAN identified by this Base VID can appear as a 
     single bridge allowing proper spanning tree behavior. 
     The following sections introduce the new [MT] TLVs which are used by 
     SPB and SPBB, and give an overview of their use from an SPB and SPBB 

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  3.1 Base Vlan-Identifiers sub-TLV 
     The Base Vlan-Identifier sub-TLV (section 2.3.5 of [IS-IS-L2]) is 
     carried within the Multi Topology aware Port Capability TLV (section 
     2.3 of [IS-IS-L2]), and this is carried in an IIH PDU. 
     The purpose of this sub-TLV is to check for compatible configuration 
     of SPB or SPBB mode of operation and then of SPB or SPBB parameters 
     as bridges form adjacencies, and to prevent adjacency formation when 
     incompatible configurations are detected. 
     In informal terms this requires : 
     -  agreement on the NLPID for SPB and SPBB  
     -  specification of the bridging mode to be used (SPB or SPBB) 
     -  binding of individual VIDs to the Base VID, and specification of 
        the shortest path bridging algorithm to be used for each VID 
     -  use (or not) of auto allocation capability for SPVIDs in SPB and 
        SPSourceIDs in SPBB.  
     It was mentioned earlier that each SPB node is assigned a unique VID 
     (a Shortest Path VID, or SPVID) as its source identifier for all 
     traffic it transmits. The set of SPVIDs, one for each SPB node in 
     the region, are bound to the Base VID, configured to execute a 
     specific tiebreaking algorithm, and collectively provide the 
     shortest path trees to support the VLAN.  A control flag in the sub-
     TLV determines whether the SPVIDs are provisioned, or auto-allocated 
     by the procedure in [801.1aq] 
     In SPB, the Base VID is also used to identify a VLAN providing peer 
     inter-working with other non-SPB bridges outside the SPB Region.  
     This VLAN forms a spanning tree across the region to achieve this. 
     In SPBB, the VID(s) on which forwarding is performed are Region-wide 
     assignments.  At present, the use of one or two VIDs is defined, 
     with the latter capability available for edge-based load spreading 
     using Equal Cost Multiple Trees generated via the symmetric tie-
     breaking variations. 
     Three algorithms are currently available to SPB and SPBB : 
     -  spanning tree algorithm, which constructs a tree which is the 
        same as would be constructed by Spanning Tree Protocol [802.1D] 
     -  shortest path trees, selecting the low PATHID as a tie-breaker 
     -  shortest path trees, selecting the high PATHID as a tie-breaker 

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  3.2 SPB/SPBB Instance sub-TLV 
     The SPB/SPBB Instance sub-TLV (section 2.5.1 of [IS-IS-L2]) is 
     carried within the Multi Topology Aware Capability TLV (section 2.5 
     of [IS-IS-L2]). 
     The purpose of this sub-TLV is to announce configuration and other 
     parameters to the entire SPB or SPBB Region. The instance sub-TLV 
     carries some information elements common to the Base VLAN-
     Identifiers sub-TLV described in the previous section, which are : 
     -  binding of individual VIDs to the Base VID, and specification of 
        the shortest path bridging algorithm to be used for each VID 
     -  use (or not) of auto allocation capability for SPVIDs in SPB and 
        SPSourceIDs in SPBB.   
     The SPB/SPBB Instance sub-TLV carries further information : 
     -  the SPSourceID - the 20 bit network wide unique identifier used 
        in the higher order bits of the SPBB multicast DA for packets 
        originating at this node  
     -  various Spanning Tree parameters for inter-working with non-SPB 
     In SPB, the multicast tree built off each SPB node is uniquely 
     associated with an SPVID which thereby identifies the source.  The 
     required (S,G) trees, and loop avoidance checking, may be directly 
     implemented using this SPVID by standard Ethernet forwarding. The 
     SPVID can be configured from a pool or it can be auto allocated.  
     In SPBB multicast, the same capability is achieved by encoding the 
     service-specific (S,G) tree in the multicast Destination Address. 
     This is achieved by concatenating the PBB Service Identifier with 
     the nodal SPSourceID.  The distribution of SPSourceID therefore 
     allows all SPBB nodes to compute the forwarding state they need to 
     install, based only on topology and service endpoint locations. The 
     computed SPBB multicast DA looks like this: 
        |M/L| A | SPSourceID (20 bit)   |       I-SID (24 bit)      | 
          Where M/L = multicast/local bits 
                     (2 bits - both set to 1) 
                  A = SPSourceID allocation style 
                     (2 bits - both 0 initially) 
                  Figure 1: SPBB multicast MAC address construction 
     The SPSourceID can be provisioned, or auto allocated. 
     The Spanning tree inter-working parameters for SPB comprise : 

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     -  a Spanning tree compatible Bridge identifier, configured exactly 
        as specified in [802.1D].  This allows SPB to build a compatible 
        Spanning tree using link state. 
     -  The Base VID identifies a VLAN capable of covering multiple 
        Regions, SPB and non-SPB.  In SPB, this is known as the Common 
        and Internal Spanning Tree (CIST).  At SPB Region boundaries, the 
        CIST Root Identifier and the CIST External Root Path Cost may be 
        imported from xSTP and flooded by IS-IS as a part of SPB`s 
        Spanning Tree emulation. 
  3.3 SPB Link Metric sub-TLV 
     SPB Link Metric sub-TLV (section 2.6 of [IS-IS-L2]) is carried 
     within the Extended Reachability TLV, or the Multi Topology 
     Intermediate System TLV. 
     The purpose of this sub-TLV is to announce SPB link metrics, in a 
     form which enables SPB to build xSTP compatible Spanning Trees, 
     typically to create the SPB component of the CIST (above) : 
     -  indicates the administrative cost or weight of using a link 
     -  a standard IEEE port identifier used to build a spanning tree 
        associated with this link 
  3.4 The Group MAC Address sub-TLV 
     The Group MAC Address sub-TLV (section 2.2.1 of [IS-IS-L2]) is 
     carried within the Group Address TLV (section 2.2 of [IS-IS-L2]), 
     which is in turn carried within the Multicast Group Level 1 link 
     state PDU. 
     This sub-TLV is used only by SPB.  SPBB builds and installs per-
     service per-source multicast addresses algorithmically, as 
     described earlier, using the SPSourceID and PBB Service Identifier 
     information announced in other sub-TLVs.   
     By default, SPB nodes broadcast traffic to all other nodes in their 
     region.  When inter-working with non-SPB regions over the CIST, 
     multicast group membership may be signaled over the CIST using 
     mechanisms such as MMRP [802.1ak].  The Group MAC Address sub-TLV 
     allows such registrations to be imported and announced by IS-IS. 
     The sub-TLV carries the following information for SPB : 
     -  the VID with which all subsequent MAC addresses are associated 
     -  sets of group records, each consisting of a multicast group 
        address and a list of unicast MAC addresses known to be sources 
        of that group. 

  Fedyk et al.                                              [Page 9] 
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  3.5 The Service Identifier and Unicast Address sub-TLV 
     The Service Identifier and Unicast Address sub-TLV (section 2.5.2 of 
     [IS-IS-L2]) is carried within the Multi Topology Aware Capability 
     TLV (section 2.5 of [IS-IS-L2]). 
     The purpose of this sub-TLV is to announce service group membership 
     (using the PBB Service Identifier or I-SID) on the originating node, 
     also to advertise an additional B-MAC unicast address present on or 
     reachable by the node.  It is applicable to SPBB only. 
     This sub-TLV carries: 
     -  the unicast B-MAC address which must be used to send to the set 
        of PBB I-SIDs announced in the sub-TLV, and which this node will 
        use as its source B-MAC when transmitting these I-SIDs 
     -  the unicast VID which must be used to send to the set of PBB I-
        SIDs announced in the sub-TLV, and which this node will use when 
        transmitting these I-SIDs 
     -  a list of PBB I-SIDs and their transmit and receive properties. 
     Announcement of I-SIDs in this way allows all SPBB nodes to see all 
     service endpoints, and allows nodes not terminating a particular 
     service to algorithmically determine the per-service per-source 
     forwarding state which they must install if they lie on the shortest 
     path between two or more service end-points. 
     The advertisement of the B-MAC unicast address to be used to reach 
     the set of services allows different granularities of addressing to 
     be used within the SPBB node, without compromising inter-working 
     between nodes of different types.  It also has application in some 
     resiliency schemes. 
  4. Security Considerations 
     This document adds no additional security risks to IS-IS. 
     SPBB assumes that the link state bridged subnetwork consists of 
     trusted devices and that the UNI ports to the domain are untrusted. 
     Care is required to ensure untrusted access to the trusted domain 
     does not occur.  
  5. IANA Considerations / ISO Considerations 
     See the subset of [IS-IS-L2] cited by this document and also the 
     NLPID assignments requested by [NLPID]. 

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  6. References 
  6.1  Normative References 
     [RFC2119]    Bradner, S., "Key words for use in RFCs to Indicate 
                  Requirement Levels", BCP 14, RFC 2119, March 1997.  
     [MT]         Multi Topology (MT) Routing in Intermediate System to 
                  Intermediate Systems (IS-ISs), 
                  RFC 5120, February 2008 
     [802.1D]     "IEEE draft Standard for Local and Metropolitan  
                  Networks, Media Access Control (MAC) Bridges", 
                  IEEE 802.D June 2004  
     [802.1aq]    "IEEE draft Standard for Local and Metropolitan  
                  Networks, Virtual Bridged Local Area Networks,  
                  Amendment 9: Shortest Path Bridging",  
                  IEEE 802.1aq D2.0, June 2009 
     [802.1ak]    "IEEE Standard for Local and Metropolitan Networks, 
                  Virtual Bridged Local Area Networks, Amendment 7: 
                  Multiple Registration Protocol" 
                  IEEE Std 802.1ak - 2007 amendment to IEEE 802.Q - 2005  
     [PBB]        "IEEE Standard for Local and Metropolitan  
                  Networks, Virtual Bridged Local Area Networks,  
                  Amendment 7: Provider Backbone Bridges"  
                  IEEE Std 802.1ah - 2008 amendment to IEEE 802.Q - 2005 
     [IS-IS-L2]   Extensions to IS-IS for Layer-2 Systems, IETF,  
                  Internet Draft, draft-ietf-isis-layer2-00.txt,  
                  Work in Progress, June 2009 
     [NLPID]      IANA Considerations for NLPIDs, IETF,  
                  Internet Draft, Draft-eastlake-nlpid-iana-
                  Work in Progress, June 23, 2009 
  6.2  Informative References 
     [IS-IS]      ISO/IEC 10589:2002, "Intermediate system to  
                  Intermediate system routing information exchange 
                  protocol" ISO/IEC 
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  7. Acknowledgments 
     The authors would like to thank Antonela Paraschiv, Daniel Joyal, 
     Paul Unbehagen and Gautam Khera for their detailed review of this 
  8. Author's Addresses 
     Don Fedyk 
     220 Hayden Road 
     Groton, MA, USA 
     Peter Ashwood-Smith 
     Huawei Technologies Canada 
     411 Leggget Drive, Suite 503 
     Kanata, Ontario, K2k3C9, Canada 
     Nigel Bragg 
     Nortel Networks 
     London Road, Harlow, 
     Essex  CM17 9NA,  UK 
     David Allan 
     Nortel Networks 
     3500 Carling Ave. 
     Ottawa, ON, Canada 
     Jerome Chiabaut 
     Nortel Networks 
     3500 Carling Ave. 
     Ottawa, ON, Canada 
     K1Y 4H7 

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