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Versions: (draft-gredler-idr-ls-distribution) 00 01 02 03 04 05

Inter-Domain Routing                                          H. Gredler
Internet-Draft                                    Juniper Networks, Inc.
Intended status: Standards Track                               J. Medved
Expires: March 21, 2013                                       S. Previdi
                                                     Cisco Systems, Inc.
                                                               A. Farrel
                                                  Juniper Networks, Inc.
                                                      September 19, 2012


  North-Bound Distribution of Link-State and TE Information using BGP
                   draft-ietf-idr-ls-distribution-00

Abstract

   In a number of environments, a component external to a network is
   called upon to perform computations based on the network topology and
   current state of the connections within the network, including
   traffic engineering information.  This is information typically
   distributed by IGP routing protocols within the network

   This document describes a mechanism by which links state and traffic
   engineering information can be collected from networks and shared
   with external components using the BGP routing protocol.  This is
   achieved using a new BGP Network Layer Reachability Information
   (NLRI) encoding format.  The mechanism is applicable to physical and
   virtual links.  The mechanism described is subject to policy control.

   Applications of this technique include Application Layer Traffic
   Optimization (ALTO) servers, and Path Computation Elements (PCEs).

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this


















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   document are to be interpreted as described in RFC 2119 [RFC2119]

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 21, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Motivation and Applicability . . . . . . . . . . . . . . . . .  5
     2.1.  MPLS-TE with PCE . . . . . . . . . . . . . . . . . . . . .  5
     2.2.  ALTO Server Network API  . . . . . . . . . . . . . . . . .  6
   3.  Carrying Link State Information in BGP . . . . . . . . . . . .  7
     3.1.  TLV Format . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.2.  The Link State NLRI  . . . . . . . . . . . . . . . . . . .  8
       3.2.1.  Node Descriptors . . . . . . . . . . . . . . . . . . . 10
         3.2.1.1.  Local Node Descriptors . . . . . . . . . . . . . . 11
         3.2.1.2.  Remote Node Descriptors  . . . . . . . . . . . . . 11
         3.2.1.3.  Node Descriptor Sub-TLVs . . . . . . . . . . . . . 12
         3.2.1.4.  Router-ID Anchoring Example: ISO Pseudonode  . . . 12
         3.2.1.5.  Router-ID Anchoring Example: OSPFv2 to IS-IS
                   Migration  . . . . . . . . . . . . . . . . . . . . 13
       3.2.2.  Link Descriptors . . . . . . . . . . . . . . . . . . . 13
         3.2.2.1.  Multi Topology ID TLV  . . . . . . . . . . . . . . 14
     3.3.  The LINK_STATE Attribute . . . . . . . . . . . . . . . . . 14
       3.3.1.  Link Attribute TLVs  . . . . . . . . . . . . . . . . . 14

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         3.3.1.1.  MPLS Protocol Mask TLV . . . . . . . . . . . . . . 15
         3.3.1.2.  Metric TLV . . . . . . . . . . . . . . . . . . . . 16
         3.3.1.3.  Shared Risk Link Group TLV . . . . . . . . . . . . 16
         3.3.1.4.  OSPF Specific Link Attribute TLV . . . . . . . . . 17
         3.3.1.5.  IS-IS specific link attribute TLV  . . . . . . . . 17
         3.3.1.6.  Link Area TLV  . . . . . . . . . . . . . . . . . . 18
       3.3.2.  Node Attribute TLVs  . . . . . . . . . . . . . . . . . 18
         3.3.2.1.  Multi Topology Node TLV  . . . . . . . . . . . . . 18
         3.3.2.2.  Node Flag Bits TLV . . . . . . . . . . . . . . . . 19
         3.3.2.3.  OSPF Specific Node Properties TLV  . . . . . . . . 19
         3.3.2.4.  IS-IS Specific Node Properties TLV . . . . . . . . 20
         3.3.2.5.  Area Node TLV  . . . . . . . . . . . . . . . . . . 20
     3.4.  Inter-AS Links . . . . . . . . . . . . . . . . . . . . . . 21
   4.  Link to Path Aggregation . . . . . . . . . . . . . . . . . . . 21
     4.1.  Example: No Link Aggregation . . . . . . . . . . . . . . . 21
     4.2.  Example: ASBR to ASBR Path Aggregation . . . . . . . . . . 22
     4.3.  Example: Multi-AS Path Aggregation . . . . . . . . . . . . 22
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 22
   6.  Manageability Considerations . . . . . . . . . . . . . . . . . 23
     6.1.  Operational Considerations . . . . . . . . . . . . . . . . 23
       6.1.1.  Operations . . . . . . . . . . . . . . . . . . . . . . 23
       6.1.2.  Installation and Initial Setup . . . . . . . . . . . . 23
       6.1.3.  Migration Path . . . . . . . . . . . . . . . . . . . . 23
       6.1.4.  Requirements on Other Protocols and Functional
               Components . . . . . . . . . . . . . . . . . . . . . . 24
       6.1.5.  Impact on Network Operation  . . . . . . . . . . . . . 24
       6.1.6.  Verifying Correct Operation  . . . . . . . . . . . . . 24
     6.2.  Management Considerations  . . . . . . . . . . . . . . . . 24
       6.2.1.  Management Information . . . . . . . . . . . . . . . . 24
       6.2.2.  Fault Management . . . . . . . . . . . . . . . . . . . 24
       6.2.3.  Configuration Management . . . . . . . . . . . . . . . 24
       6.2.4.  Accounting Management  . . . . . . . . . . . . . . . . 24
       6.2.5.  Performance Management . . . . . . . . . . . . . . . . 25
       6.2.6.  Security Management  . . . . . . . . . . . . . . . . . 25
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 25
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 25
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 26

1.  Introduction

   The contents of a Link State Database (LSDB) or a Traffic Engineering
   Database (TED) has the scope of an IGP area.  Some applications, such
   as end-to-end Traffic Engineering (TE), would benefit from visibility
   outside one area or Autonomous System (AS) in order to make better
   decisions.

   The IETF has defined the Path Computation Element (PCE) [RFC4655] as
   a mechanism for achieving the computation of end-to-end TE paths that
   cross the visibility of more than one TED or which require CPU-
   intensive or coordinated computations.  The IETF has also defined the
   ALTO Server [RFC5693] as an entity that generates an abstracted
   network topology and provides it to network-aware applications.



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   Both a PCE and an ALTO Server need to gather information about the
   topologies and capabilities of the network in order to be able to
   fulfill their function

   This document describes a mechanism by which Link State and TE
   information can be collected from networks and shared with external
   components using the BGP routing protocol [RFC4271].  This is
   achieved using a new BGP Network Layer Reachability Information
   (NLRI) encoding format.  The mechanism is applicable to physical and
   virtual links.  The mechanism described is subject to policy control.

   A router maintains one or more databases for storing link-state
   information about nodes and links in any given area.  Link attributes
   stored in these databases include: local/remote IP addresses, local/
   remote interface identifiers, link metric and TE metric, link
   bandwidth, reservable bandwidth, per CoS class reservation state,
   preemption and Shared Risk Link Groups (SRLG). The router's BGP
   process can retrieve topology from these LSDBs and distribute it to a
   consumer, either directly or via a peer BGP Speaker (typically a
   dedicated Route Reflector), using the encoding specified in this
   document.

   The collection of Link State and TE link state information and its
   distribution to consumers is shown in the following figure.

                        +-----------+
                        | Consumer  |
                        +-----------+
                              ^
                              |
                        +-----------+
                        |    BGP    |               +-----------+
                        |  Speaker  |               | Consumer  |
                        +-----------+               +-----------+
                          ^   ^   ^                       ^
                          |   |   |                       |
          +---------------+   |   +-------------------+   |
          |                   |                       |   |
    +-----------+       +-----------+             +-----------+
    |    BGP    |       |    BGP    |             |    BGP    |
    |  Speaker  |       |  Speaker  |    . . .    |  Speaker  |
    +-----------+       +-----------+             +-----------+
          ^                   ^                         ^
          |                   |                         |
         IGP                 IGP                       IGP

                Figure 1: TE Link State info collection







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   A BGP Speaker may apply configurable policy to the information that
   it distributes.  Thus, it may distribute the real physical topology
   from the LSDB or the TED.  Alternatively, it may create an abstracted
   topology, where virtual, aggregated nodes are connected by virtual
   paths.  Aggregated nodes can be created, for example, out of multiple
   routers in a POP.  Abstracted topology can also be a mix of physical
   and virtual nodes and physical and virtual links.  Furthermore, the
   BGP Speaker can apply policy to determine when information is updated
   to the consumer so that there is reduction of information flow form
   the network to the consumers.  Mechanisms through which topologies
   can be aggregated or virtualized are outside the scope of this
   document

2.  Motivation and Applicability

   This section describes uses cases from which the requirements can be
   derived.

2.1.  MPLS-TE with PCE

   As described in [RFC4655] a PCE can be used to compute MPLS-TE paths
   within a "domain" (such as an IGP area) or across multiple domains
   (such as a multi-area AS, or multiple ASes).

   o  Within a single area, the PCE offers enhanced computational power
      that may not be available on individual routers, sophisticated
      policy control and algorithms, and coordination of computation
      across the whole area.

   o  If a router wants to compute a MPLS-TE path across IGP areas its
      own TED lacks visibility of the complete topology.  That means
      that the router cannot determine the end-to-end path, and cannot
      even select the right exit router (Area Border Router - ABR) for
      an optimal path.  This is an issue for large-scale networks that
      need to segment their core networks into distinct areas, but which
      still want to take advantage of MPLS-TE.

   Previous solutions used per-domain path computation [RFC5152].  The
   source router could only compute the path for the first area because
   the router only has full topological visibility for the first area
   along the path, but not for subsequent areas.  Per-domain path
   computation uses a technique called "loose-hop-expansion" [RFC3209],
   and selects the exit ABR and other ABRs or AS Border Routers (ASBRs)
   using the IGP computed shortest path topology for the remainder of
   the path.  This may lead to sub-optimal paths, makes alternate/back-
   up path computation hard, and might result in no TE path being found
   when one really does exist.







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   The PCE presents a computation server that may have visibility into
   more than one IGP area or AS, or may cooperate with other PCEs to
   perform distributed path computation.  The PCE obviously needs access
   to the TED for the area(s) it serves, but [RFC4655] does not describe
   how this is achieved.  Many implementations make the PCE a passive
   participant in the IGP so that it can learn the latest state of the
   network, but this may be sub-optimal when the network is subject to a
   high degree of churn, or when the PCE is responsible for multiple
   areas.

   The following figure shows how a PCE can get its TED information
   using the mechanism described in this document.

             +----------+                           +---------+
             |  -----   |                           |   BGP   |
             | | TED |<-+-------------------------->| Speaker |
             |  -----   |   TED synchronization     |         |
             |    |     |        mechanism:         +---------+
             |    |     | BGP with Link-State NLRI
             |    v     |
             |  -----   |
             | | PCE |  |
             |  -----   |
             +----------+
                  ^
                  | Request/
                  | Response
                  v
    Service  +----------+   Signaling  +----------+
    Request  | Head-End |   Protocol   | Adjacent |
    -------->|  Node    |<------------>|   Node   |
             +----------+              +----------+

   Figure 2: External PCE node using a TED synchronization mechanism

   The mechanism in this document allows the necessary TED information
   to be collected from the IGP within the network, filtered according
   to configurable policy, and distributed to the PCE as necessary.

2.2.  ALTO Server Network API

   An ALTO Server [RFC5693] is an entity that generates an abstracted
   network topology and provides it to network-aware applications over a
   web service based API. Example applications are p2p clients or
   trackers, or CDNs.  The abstracted network topology comes in the form
   of two maps: a Network Map that specifies allocation of prefixes to
   PIDs, and a Cost Map that specifies the cost between PIDs listed in
   the Network Map.  For more details, see [I-D.ietf-alto-protocol].






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   ALTO abstract network topologies can be auto-generated from the
   physical topology of the underlying network.  The generation would
   typically be based on policies and rules set by the operator.  Both
   prefix and TE data are required: prefix data is required to generate
   ALTO Network Maps, TE (topology) data is required to generate ALTO
   Cost Maps.  Prefix data is carried and originated in BGP, TE data is
   originated and carried in an IGP. The mechanism defined in this
   document provides a single interface through which an ALTO Server can
   retrieve all the necessary prefix and network topology data from the
   underlying network.  Note an ALTO Server can use other mechanisms to
   get network data, for example, peering with multiple IGP and BGP
   Speakers.

   The following figure shows how an ALTO Server can get network
   topology information from the underlying network using the mechanism
   described in this document.

   +--------+
   | Client |<--+
   +--------+   |
                |    ALTO    +--------+     BGP with    +---------+
   +--------+   |  Protocol  |  ALTO  | Link-State NLRI |   BGP   |
   | Client |<--+------------| Server |<----------------| Speaker |
   +--------+   |            |        |                 |         |
                |            +--------+                 +---------+
   +--------+   |
   | Client |<--+
   +--------+

        Figure 3: ALTO Server using network topology information

3.  Carrying Link State Information in BGP

   Two parts: a new BGP NLRI that describes links and nodes comprising
   IGP link state information, and a new BGP path attribute that carries
   link and node properties and attributes, such as the link metric or
   node properties.

3.1.  TLV Format

   Information in the new link state NLRIs and attributes is encoded in
   Type/Length/Value triplets.  The TLV format is shown in Figure 4.

    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             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |





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   |                         Value (variable)                      |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          Figure 4: TLV format

   The Length field defines the length of the value portion in octets
   (thus a TLV with no value portion would have a length of zero). The
   TLV is not padded to four-octet alignment; Unrecognized types are
   ignored.

3.2.  The Link State NLRI

   The MP_REACH and MP_UNREACH attributes are BGP's containers for
   carrying opaque information.  Each Link State NLRI describes either a
   single node or link.

   All link and node information SHALL be encoded using a TBD AFI / SAFI
   1 or SAFI 128 header into those attributes.  SAFI 1 SHALL be used for
   Internet routing (Public) and SAFI 128 SHALL be used for VPN routing
   (Private) applications.

   In order for two BGP speakers to exchange Link-State NLRI, they MUST
   use BGP Capabilities Advertisement to ensure that they both are
   capable of properly processing such NLRI.  This is done as specified
   in [RFC4760], by using capability code 1 (multi-protocol BGP), with
   an AFI of TBD and an SAFI of 1 or 128.

   The format of the Link State NLRI is shown in the following figure.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            NLRI Type          |     Total NLRI Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                   Link-State NLRI (variable)                  |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 5: Link State SAFI 1 NLRI 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            NLRI Type          |     Total NLRI Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                       Route Distinguisher                     +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                   Link-State NLRI (variable)                  |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 6: Link State SAFI 128 NLRI Format

   The 'Total NLRI Length' field contains the cumulative length of all
   the TLVs in the NLRI. For VPN applications it also includes the
   length of the Route Distinguisher.

   The 'NLRI Type' field can contain one of the following values:

      Type = 1: Link NLRI, contains link descriptors and link attributes

      Type = 2: Node NLRI, contains node attributes

   The Link NLRI (NLRI Type = 1) is shown in the following figure.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Protocol-ID  |    Reserved   |       Instance Identifier     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Local Node Descriptors (variable)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Remote Node Descriptors (variable)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Link Descriptors (variable)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 7: The Link NLRI format

   The Node NLRI (NLRI Type = 2) is shown in the following figure.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Protocol-ID  |    Reserved   |       Instance Identifier     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Local Node Descriptors (variable)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 8: The Node NLRI format

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   The 'Protocol-ID' field can contain one of the following values:

      Type = 0: Unknown, The source of NLRI information could not be
      determined

      Type = 1: IS-IS Level 1, The NLRI information has been sourced by
      IS-IS Level 1

      Type = 2: IS-IS Level 2, The NLRI information has been sourced by
      IS-IS Level 2

      Type = 3: OSPF, The NLRI information has been sourced by OSPF

      Type = 4: Direct, The NLRI information has been sourced from local
      interface state

      Type = 5: Static, The NLRI information has been sourced by static
      configuration

   Both OSPF and IS-IS may run multiple routing protocol instances over
   the same link.  See [I-D.ietf-isis-mi] and [RFC6549].  The 'Instance
   Identifier' field identifies the protocol instance.

   Each Node Descriptor and Link Descriptor consists of one or more TLVs
   described in the following sections.  The sender of an UPDATE message
   MUST order the TLVs within a Node Descriptor or a Link Descriptor in
   ascending order of TLV type."

3.2.1.  Node Descriptors

   Each link gets anchored by at least a pair of router-IDs.  Since
   there are many Router-IDs formats (32 Bit IPv4 router-ID, 56 Bit ISO
   Node-ID and 128 Bit IPv6 router-ID) a link may be anchored by more
   than one Router-ID pair.  The set of Local and Remote Node
   Descriptors describe which Protocols Router-IDs will be following to
   "anchor" the link described by the "Link attribute TLVs".  There must
   be at least one "like" router-ID pair of a Local Node Descriptors and
   a Remote Node Descriptors per-protocol.  If a peer sends an illegal
   combination in this respect, then this is handled as an NLRI error,
   described in [RFC4760].














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   It is desirable that the Router-ID assignments inside the Node anchor
   are globally unique.  However there may be router-ID spaces (e.g.
   ISO) where not even a global registry exists, or worse, Router-IDs
   have been allocated following private-IP RFC 1918 [RFC1918]
   allocation.  In order to disambiguate the Router-IDs the local and
   remote Autonomous System number TLVs of the anchor nodes may be
   included in the NLRI. If the anchor node's AS is a member of an AS
   Confederation ([RFC5065]), then the Autonomous System number TLVs
   contains the confederations' AS Confederation Identifier and the
   Member-AS TLV is included in the NLRI. The Local and Remote
   Autonomous System TLVs are 4 octets wide as described in [RFC4893].
   2-octet AS Numbers SHALL be expanded to 4-octet AS Numbers by zeroing
   the two MSB octets.

3.2.1.1.  Local Node Descriptors

   The Local Node Descriptors TLV (Type 256) contains Node Descriptors
   for the node anchoring the local end of the link.  The length of this
   TLV is variable.  The value contains one or more Node Descriptor Sub-
   TLVs defined in Section 3.2.1.3.

    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             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |               Node Descriptor Sub-TLVs (variable)             |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 9: Local Node Descriptors TLV format

3.2.1.2.  Remote Node Descriptors

   The Remote Node Descriptors TLV (Type 257) contains Node Descriptors
   for the node anchoring the remote end of the link.  The length of
   this TLV is variable.  The value contains one or more Node Descriptor
   Sub-TLVs defined in Section 3.2.1.3.

    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             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |               Node Descriptor Sub-TLVs (variable)             |







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   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 10: Remote Node Descriptors TLV format

3.2.1.3.  Node Descriptor Sub-TLVs

   The Node Descriptor Sub-TLV type codepoints and lengths are listed in
   the following table:

                 +------+-------------------+--------+
                 | Type | Description       | Length |
                 +------+-------------------+--------+
                 | 258  | Autonomous System |      4 |
                 | 259  | Member-AS         |      4 |
                 | 260  | IPv4 Router-ID    |      5 |
                 | 261  | IPv6 Router-ID    |     17 |
                 | 262  | ISO Node-ID       |      7 |
                 +------+-------------------+--------+

                   Table 1: Node Descriptor Sub-TLVs

   The TLV values in Node Descriptor Sub-TLVs are defined as follows:

   Autonomous System: opaque value (32 Bit AS ID)

   Member-AS: opaque value (32 Bit AS ID); only included if the node is
      in an AS confederation.

   IPv4 Router ID: opaque value (can be an IPv4 address or an 32 Bit
      router ID) followed by a LAN-ID octet in case LAN "Pseudonode"
      information gets advertised.  The PSN octet must be zero for non-
      LAN "Pseudonodes".

   IPv6 Router ID: opaque value (can be an IPv6 address or 128 Bit
      router ID) followed by a LAN-ID octet in case LAN "Pseudonode"
      information gets advertised.  The PSN octet must be zero for non-
      LAN "Pseudonodes".

   ISO Node ID: ISO node-ID (6 octets ISO system-ID) followed by a PSN
      octet in case LAN "Pseudonode" information gets advertised.  The
      PSN octet must be zero for non-LAN "Pseudonodes".

3.2.1.4.  Router-ID Anchoring Example: ISO Pseudonode

   IS-IS Pseudonodes are a good example for the variable Router-ID
   anchoring.  Consider Figure 11. This represents a Broadcast LAN
   between a pair of routers.  The "real" (=non pseudonode) routers have
   both an IPv4 Router-ID and IS-IS Node-ID. The pseudonode does not
   have an IPv4 Router-ID. Two unidirectional links (Node1, Pseudonode
   1) and (Pseudonode 1, Node 2) are being generated.




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   The NRLI for (Node1, Pseudonode1) encodes local IPv4 router-ID, local
   ISO node-ID and remote ISO node-id)

   The NLRI for (Pseudonode1, Node2) encodes a local ISO node-ID, remote
   IPv4 router-ID and remote ISO node-id.

   +-----------------+    +-----------------+    +-----------------+
   |      Node1      |    |   Pseudonode 1  |    |      Node2      |
   |1921.6800.1001.00|--->|1921.6800.1001.02|--->|1921.6800.1002.00|
   |   192.168.1.1   |    |                 |    |   192.168.1.2   |
   +-----------------+    +-----------------+    +-----------------+

                      Figure 11: IS-IS Pseudonodes

3.2.1.5.  Router-ID Anchoring Example: OSPFv2 to IS-IS Migration

   Migrating gracefully from one IGP to another requires congruent
   operation of both routing protocols during the migration period.  The
   target protocol (IS-IS) supports more router-ID spaces than the
   source (OSPFv2) protocol.  When advertising a point-to-point link
   between an OSPFv2-only router and an OSPFv2 and IS-IS enabled router
   the following link information may be generated.  Note that the IS-IS
   router also supports the IPv6 traffic engineering extensions RFC 6119
   [RFC6119] for IS-IS.

   The NRLI encodes local IPv4 router-id, remote IPv4 router-id, remote
   ISO node-id and remote IPv6 node-id.

3.2.2.  Link Descriptors

   The 'Link Descriptor' field is a set of Type/Length/Value (TLV)
   triplets.  The format of each TLV is shown in Section 3.1.  The 'Link
   descriptor' TLVs uniquely identify a link between a pair of anchor
   Routers.  A link described by the Link descriptor TLVs actually is a
   "half-link", a unidirectional representation of a logical link.  In
   order to fully describe a single logical link two originating routers
   need to advertise a half-link each, i.e.  two link NLRIs will be
   advertised.

   The format and semantics of the 'value' fields in most 'Link
   Descriptor' TLVs correspond to the format and semantics of value
   fields in IS-IS Extended IS Reachability sub-TLVs, defined in
   [RFC5305], [RFC5307] and [RFC6119].  Although the encodings for 'Link
   Descriptor' TLVs were originally defined for IS-IS, the TLVs can
   carry data sourced either by IS-IS or OSPF.

   The following link descriptor TLVs are valid in the Link NLRI:








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   +--------+--------------------+-----------------+-------------------+
   |  Type  | Description        |  IS-IS TLV/Sub- | Value defined in: |
   |        |                    |       TLV       |                   |
   +--------+--------------------+-----------------+-------------------+
   |  263   | Link Local/Remote  |       22/4      | [RFC5307]/1.1     |
   |        | Identifiers        |                 |                   |
   |  264   | IPv4 interface     |       22/6      | [RFC5305]/3.2     |
   |        | address            |                 |                   |
   |  265   | IPv4 neighbor      |       22/8      | [RFC5305]/3.3     |
   |        | address            |                 |                   |
   |  266   | IPv6 interface     |      22/12      | [RFC6119]/4.2     |
   |        | address            |                 |                   |
   |  267   | IPv6 neighbor      |      22/13      | [RFC6119]/4.3     |
   |        | address            |                 |                   |
   |  268   | Multi Topology ID  |       ---       | Section 3.2.2.1   |
   +--------+--------------------+-----------------+-------------------+

                     Table 2: Link Descriptor TLVs

3.2.2.1.  Multi Topology ID TLV

   The Multi Topology ID TLV (Type 268) carries the Multi Topology ID
   for this link.  The semantics of the Multi Topology ID are defined in
   RFC5120, Section 7.2 [RFC5120], and the OSPF Multi Topology ID),
   defined in RFC4915, Section 3.7 [RFC4915].  If the value in the Multi
   Topology ID TLV is derived from OSPF, then the upper 9 bits of the
   Multi Topology ID are set to 0.

    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             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |R R R R|   Multi Topology ID   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 12: Multi Topology ID TLV format

3.3.  The LINK_STATE Attribute

   This is an optional non-transitive BGP attribute that is used to
   carry link and node link-state parameters and attributes.  It is
   defined as a set of Type/Length/Value (TLV) triplets, described in
   the following section.  This attribute SHOULD only be included with
   Link State NLRIs.  This attribute MUST be ignored for all other NLRI
   types.

3.3.1.  Link Attribute TLVs






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   Each 'Link Attribute' is a Type/Length/Value (TLV) triplet formatted
   as defined in Section 3.1. The format and semantics of the 'value'
   fields in some 'Link Attribute' TLVs correspond to the format and
   semantics of value fields in IS-IS Extended IS Reachability sub-TLVs,
   defined in [RFC5305] and [RFC5307].  Other 'Link Attribute' TLVs are
   defined in this document.  Although the encodings for 'Link
   Attribute' TLVs were originally defined for IS-IS, the TLVs can carry
   data sourced either by IS-IS or OSPF.

   The following 'Link Attribute' TLVs are are valid in the LINK_STATE
   attribute:

   +------+----------------------+-----------------+-------------------+
   | Type | Description          |  IS-IS TLV/Sub- | Defined in:       |
   |      |                      |       TLV       |                   |
   +------+----------------------+-----------------+-------------------+
   | 269  | Administrative group |       22/3      | [RFC5305]/3.1     |
   |      | (color)              |                 |                   |
   | 270  | Maximum link         |       22/9      | [RFC5305]/3.3     |
   |      | bandwidth            |                 |                   |
   | 271  | Max. reservable link |      22/10      | [RFC5305]/3.5     |
   |      | bandwidth            |                 |                   |
   | 272  | Unreserved bandwidth |      22/11      | [RFC5305]/3.6     |
   | 273  | Link Protection Type |      22/20      | [RFC5307]/1.2     |
   | 274  | MPLS Protocol Mask   |       ---       | Section 3.3.1.1   |
   | 275  | Metric               |       ---       | Section 3.3.1.2   |
   | 276  | Shared Risk Link     |       ---       | Section 3.3.1.3   |
   |      | Group                |                 |                   |
   | 277  | OSPF specific link   |       ---       | Section 3.3.1.4   |
   |      | attribute            |                 |                   |
   | 278  | IS-IS Specific Link  |       ---       | Section 3.3.1.5   |
   |      | Attribute            |                 |                   |
   | 279  | Area ID              |       ---       | Section 3.3.1.6   |
   +------+----------------------+-----------------+-------------------+

                      Table 3: Link Attribute TLVs

3.3.1.1.  MPLS Protocol Mask TLV

   The MPLS Protocol TLV (Type 274) carries a bit mask describing which
   MPLS signaling protocols are enabled.  The length of this TLV is 1.
   The value is a bit array of 8 flags, where each bit represents an
   MPLS Protocol capability.

    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             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |L R            |




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   +-+-+-+-+-+-+-+-+

                      Figure 13: MPLS Protocol TLV

   The following bits are defined:

   +-----+---------------------------------------------+-----------+
   | Bit | Description                                 | Reference |
   +-----+---------------------------------------------+-----------+
   |  0  | Label Distribution Protocol (LDP)           | [RFC5036] |
   |  1  | Extension to RSVP for LSP Tunnels (RSVP-TE) | [RFC3209] |
   | 2-7 | Reserved for future use                     |           |
   +-----+---------------------------------------------+-----------+

                 Table 4: MPLS Protocol Mask TLV Codes

3.3.1.2.  Metric TLV

   The IGP Metric TLV (Type 275) carries the metric for this link.  The
   length of this TLV is 3.  If the length of the metric from which the
   IGP Metric value is derived is less than 3 (e.g.  for OSPF link
   metrics or non-wide IS-IS metric), then the upper bits of the TLV are
   set to 0.

    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             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  IGP Link Metric              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 14: Metric TLV format

3.3.1.3.  Shared Risk Link Group TLV

   The Shared Risk Link Group (SRLG) TLV (Type 276) carries the Shared
   Risk Link Group information (see Section 2.3, "Shared Risk Link Group
   Information", of [RFC4202]). It contains a data structure consisting
   of a (variable) list of SRLG values, where each element in the list
   has 4 octets, as shown in Figure 15. The length of this TLV is 4 *
   (number of SRLG values).

    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             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Shared Risk Link Group Value                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          ............                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Shared Risk Link Group Value                 |


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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 15: Shared Risk Link Group TLV format

   Note that there is no SRLG TLV in OSPF-TE. In IS-IS the SRLG
   information is carried in two different TLVs: the IPv4 (SRLG) TLV
   (Type 138) defined in [RFC5307], and the IPv6 SRLG TLV (Type 139)
   defined in [RFC6119].  Since the Link State NLRI uses variable
   Router-ID anchoring, both IPv4 and IPv6 SRLG information can be
   carried in a single TLV.

3.3.1.4.  OSPF Specific Link Attribute TLV

   The OSPF specific link attribute TLV (Type 277) is an envelope that
   transparently carries optional link properties TLVs advertised by an
   OSPF router.  The value field contains one or more optional OSPF link
   attribute TLVs.  An originating router shall use this TLV for
   encoding information specific to the OSPF protocol or new OSPF
   extensions for which there is no protocol neutral representation in
   the BGP link-state NLRI.

    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             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |            OSPF specific link attributes (variable)           |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 16: OSPF specific link attribute format

3.3.1.5.  IS-IS specific link attribute TLV

   The IS-IS specific link attribute TLV (Type 278) is an envelope that
   transparently carries optional link properties TLVs advertised by an
   IS-IS router.  The value field contains one or more optional IS-IS
   link attribute TLVs.  An originating router shall use this TLV for
   encoding information specific to the IS-IS protocol or new IS-IS
   extensions for which there is no protocol neutral representation in
   the BGP link-state NLRI.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+









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   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |           IS-IS specific link attributes (variable)           |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 17: IS-IS specific link attribute format

3.3.1.6.  Link Area TLV

   The Area TLV (Type 279) carries the Area ID which is assigned on this
   link.  If a link is present in more than one Area then several
   occurrences of this TLV may be generated.  Since only the OSPF
   protocol carries the notion of link specific areas, the Area ID has a
   fixed length of 4 octets.

    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             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Area ID                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 18: Link Area TLV format

3.3.2.  Node Attribute TLVs

   The following node attribute TLVs are defined:

          +------+--------------------------------+----------+
          | Type | Description                    |   Length |
          +------+--------------------------------+----------+
          | 280  | Multi Topology                 |        2 |
          | 281  | Node Flag Bits                 |        1 |
          | 282  | OSPF Specific Node Properties  | variable |
          | 283  | IS-IS Specific Node Properties | variable |
          | 284  | Node Area ID                   | variable |
          +------+--------------------------------+----------+

                      Table 5: Node Attribute TLVs

3.3.2.1.  Multi Topology Node TLV

   The Multi Topology TLV (Type 280) carries the Multi Topology ID and
   topology specific flags for this node.  The format and semantics of
   the 'value' field in the Multi Topology TLV is defined in RFC5120,







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   Section 7.1 [RFC5120].  If the value in the Multi Topology TLV is
   derived from OSPF, then the upper 9 bits of the Multi Topology ID and
   the 'O' and 'A' bits are set to 0.

    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             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |O A R R|   Multi Topology ID   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 19: Multi Topology Node TLV format

3.3.2.2.  Node Flag Bits TLV

   The Node Flag Bits TLV (Type 281) carries a bit mask describing node
   attributes.  The value is a bit array of 8 flags, where each bit
   represents an MPLS Protocol capability.

    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             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Flags     |
   +-+-+-+-+-+-+-+-+

                  Figure 20: Node Flag Bits TLV format

   The bits are defined as follows:

                   +-----+--------------+-----------+
                   | Bit | Description  | Reference |
                   +-----+--------------+-----------+
                   |  0  | Overload Bit | [RFC1195] |
                   |  1  | Attached Bit | [RFC1195] |
                   |  2  | External Bit | [RFC2328] |
                   |  3  | ABR Bit      | [RFC2328] |
                   +-----+--------------+-----------+

                  Table 6: Node Flag Bits Definitions

3.3.2.3.  OSPF Specific Node Properties TLV

   The OSPF Specific Node Properties TLV (Type 282) is an envelope that









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   transparently carries optional node properties TLVs advertised by an
   OSPF router.  The value field contains one or more optional OSPF node
   property TLVs, such as the OSPF Router Informational Capabilities TLV
   defined in [RFC4970], or the OSPF TE Node Capability Descriptor TLV
   described in [RFC5073].  An originating router shall use this TLV for
   encoding information specific to the OSPF protocol or new OSPF
   extensions for which there is no protocol neutral representation in
   the BGP link-state NLRI.

    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             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |            OSPF specific node properties (variable)           |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 21: OSPF specific Node property format

3.3.2.4.  IS-IS Specific Node Properties TLV

   The IS-IS Router Specific Node Properties TLV (Type 283) is an
   envelope that transparently carries optional node specific TLVs
   advertised by an IS-IS router.  The value field contains one or more
   optional IS-IS node property TLVs, such as the IS-IS TE Node
   Capability Descriptor TLV described in [RFC5073].  An originating
   router shall use this TLV for encoding information specific to the
   IS-IS protocol or new IS-IS extensions for which there is no protocol
   neutral representation in the BGP link-state NLRI.

    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             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |           IS-IS specific node properties (variable)           |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 22: IS-IS specific Node property format

3.3.2.5.  Area Node TLV

   The Area TLV (Type 284) carries the Area ID which is assigned to this
   node.  If a node is present in more than one Area then several
   occurrences of this TLV may be generated.  Since only the IS-IS
   protocol carries the notion of per-node areas, the Area ID has a





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   variable length of 1 to 20 octets.

    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             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                       Area ID (variable)                      |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 23: Area Node TLV format

3.4.  Inter-AS Links

   The main source of TE information is the IGP, which is not active on
   inter-AS links.  In order to inject a non-IGP enabled link into the
   BGP link-state RIB an implementation must support configuration of
   static links.

4.  Link to Path Aggregation

   Distribution of all links available in the global Internet is
   certainly possible, however not desirable from a scaling and privacy
   point of view.  Therefore an implementation may support link to path
   aggregation.  Rather than advertising all specific links of a domain,
   an ASBR may advertise an "aggregate link" between a non-adjacent pair
   of nodes.  The "aggregate link" represents the aggregated set of link
   properties between a pair of non-adjacent nodes.  The actual methods
   to compute the path properties (of bandwidth, metric) are outside the
   scope of this document.  The decision whether to advertise all
   specific links or aggregated links is an operator's policy choice.
   To highlight the varying levels of exposure, the following deployment
   examples shall be discussed.

4.1.  Example: No Link Aggregation

   Consider Figure 24. Both AS1 and AS2 operators want to protect their
   inter-AS {R1,R3}, {R2, R4} links using RSVP-FRR LSPs.  If R1 wants to
   compute its link-protection LSP to R3 it needs to "see" an alternate
   path to R3. Therefore the AS2 operator exposes its topology.  All BGP
   TE enabled routers in AS1 "see" the full topology of AS and therefore
   can compute a backup path.  Note that the decision if the direct link
   between {R3, R4} or the {R4, R5, R3) path is used is made by the
   computing router.









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       AS1   :   AS2
             :
        R1-------R3
         |   :   | \
         |   :   |  R5
         |   :   | /
        R2-------R4
             :
             :

                     Figure 24: no-link-aggregation

4.2.  Example: ASBR to ASBR Path Aggregation

   The brief difference between the "no-link aggregation" example and
   this example is that no specific link gets exposed.  Consider Figure
   25. The only link which gets advertised by AS2 is an "aggregate" link
   between R3 and R4. This is enough to tell AS1 that there is a backup
   path.  However the actual links being used are hidden from the
   topology.

       AS1   :   AS2
             :
        R1-------R3
         |   :   |
         |   :   |
         |   :   |
        R2-------R4
             :
             :

                    Figure 25: asbr-link-aggregation

4.3.  Example: Multi-AS Path Aggregation

   Service providers in control of multiple ASes may even decide to not
   expose their internal inter-AS links.  Consider Figure 26. Rather
   than exposing all specific R3 to R6 links, AS3 is modeled as a single
   node which connects to the border routers of the aggregated domain.

       AS1   :   AS2   :   AS3
             :         :
        R1-------R3-----
         |   :         : \
         |   :         :   vR0
         |   :         : /
        R2-------R4-----
             :         :
             :         :

                    Figure 26: multi-as-aggregation

5.  IANA Considerations

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   This document requests a code point from the registry of Address
   Family Numbers.

   This document requests a code point from the BGP Path Attributes
   registry.

   This document requests creation of a new registry for node anchor,
   link descriptor and link attribute TLVs.  Values 0-255 are reserved.
   Values 256-65535 will be used for Codepoints.  The registry will be
   initialized as shown in Table 2 and Table 3. Allocations within the
   registry will require documentation of the proposed use of the
   allocated value and approval by the Designated Expert assigned by the
   IESG (see [RFC5226]).

   Note to RFC Editor: this section may be removed on publication as an
   RFC.

6.  Manageability Considerations

   This section is structured as recommended in [RFC5706].

6.1.  Operational Considerations

6.1.1.  Operations

   Existing BGP operation procedures apply.  No new operation procedures
   are defined in this document.  It shall be noted that the NLRI
   information present in this document purely carries application level
   data that have no immediate corresponding forwarding state impact.
   As such, any churn in reachability information has different impact
   than regular BGP update which needs to chaange forwarding state for
   an entire router.  Furthermore it is anticipated that distribution of
   this NLRI will be handled by dedicated route-reflectors providing a
   level of isolation and fault-containment between different NLRI
   types.

6.1.2.  Installation and Initial Setup

   Configuration parameters defined in Section 6.2.3 SHOULD be
   initialized to the following default values:

   o  The Link-State NLRI capability is turned off for all neighbors.

   o  The maximum rate at which Link State NLRIs will be advertised/
      withdrawn from neighbors is set to 200 updates per second.

6.1.3.  Migration Path

   The proposed extension is only activated between BGP peers after
   capability negotiation.  Moreover, the extensions can be turned on/
   off an individual peer basis (see Section 6.2.3), so the extension
   can be gradually rolled out in the network.


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6.1.4.  Requirements on Other Protocols and Functional Components

   The protocol extension defined in this document does not put new
   requirements on other protocols or functional components.

6.1.5.  Impact on Network Operation

   Frequency of Link-State NLRI updates could interfere with regular BGP
   prefix distribution.  A network operator MAY use a dedicated Route-
   Reflector infrastructure to distribute Link-State NLRIs.

   Distribution of Link-State NLRIs SHOULD be limited to a single admin
   domain, which can consist of multiple areas within an AS or multiple
   ASes.

6.1.6.  Verifying Correct Operation

   Existing BGP procedures apply.  In addition, an implementation SHOULD
   allow an operator to:

   o  List neighbors with whom the Speaker is exchanging Link-State
      NLRIs

6.2.  Management Considerations

6.2.1.  Management Information

6.2.2.  Fault Management

   TBD.

6.2.3.  Configuration Management

   An implementation SHOULD allow the operator to specify neighbors to
   which Link-State NLRIs will be advertised and from which Link-State
   NLRIs will be accepted.

   An implementation SHOULD allow the operator to specify the maximum
   rate at which Link State NLRIs will be advertised/withdrawn from
   neighbors

   An implementation SHOULD allow the operator to specify the maximum
   rate at which Link State NLRIs will be accepted from neighbors

   An implementation SHOULD allow the operator to specify the maximum
   number of Link State NLRIs stored in router's RIB.

   An implementation SHOULD allow the operator to create abstracted
   topologies that are advertised to neighbors; Create different
   abstractions for different neighbors.

6.2.4.  Accounting Management


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   Not Applicable.

6.2.5.  Performance Management

   An implementation SHOULD provide the following statistics:

   o  Total number of Link-State NLRI updates sent/received

   o  Number of Link-State NLRI updates sent/received, per neighbor

   o  Number of errored received Link-State NLRI updates, per neighbor

   o  Total number of locally originated Link-State NLRIs

6.2.6.  Security Management

   An operator SHOULD define ACLs to limit inbound updates as follows:

   o  Drop all updates from Consumer peers

7.  Security Considerations

   Procedures and protocol extensions defined in this document do not
   affect the BGP security model.

   A BGP Speaker SHOULD NOT accept updates from a Consumer peer.

   An operator SHOULD employ a mechanism to protect a BGP Speaker
   against DDOS attacks from Consumers.

8.  Acknowledgements

   We would like to thank Nischal Sheth for contributions to this
   document.

   We would like to thank Alia Atlas, David Ward, Derek Yeung, Murtuza
   Lightwala, John Scudder, Kaliraj Vairavakkalai, Les Ginsberg, Liem
   Nguyen, Manish Bhardwaj, Mike Shand, Peter Psenak, Rex Fernando,
   Richard Woundy, Robert Varga, Saikat Ray, Steven Luong, Tamas Mondal,
   Waqas Alam, and Yakov Rekhter for their comments.

9.  References

9.1.  Normative References

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, December 1990.

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets", BCP
              5, RFC 1918, February 1996.



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

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, December 2001.

   [RFC4202]  Kompella, K. and Y. Rekhter, "Routing Extensions in
              Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4202, October 2005.

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760, January
              2007.

   [RFC4893]  Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
              Number Space", RFC 4893, May 2007.

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC
              4915, June 2007.

   [RFC5036]  Andersson, L., Minei, I., and B. Thomas, "LDP
              Specification", RFC 5036, October 2007.

   [RFC5065]  Traina, P., McPherson, D., and J. Scudder, "Autonomous
              System Confederations for BGP", RFC 5065, August 2007.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120, February 2008.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, October 2008.

   [RFC5307]  Kompella, K. and Y. Rekhter, "IS-IS Extensions in Support
              of Generalized Multi-Protocol Label Switching (GMPLS)",
              RFC 5307, October 2008.

   [RFC6119]  Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic
              Engineering in IS-IS", RFC 6119, February 2011.

9.2.  Informative References


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   [I-D.ietf-alto-protocol]
              Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
              Internet-Draft draft-ietf-alto-protocol-11, March 2012.

   [I-D.ietf-isis-mi]
              Roy, A., Ward, D., Ginsberg, L., Shand, M., and S.
              Previdi, "IS-IS Multi-Instance", Internet-Draft draft-
              ietf-isis-mi-06, February 2012.

   [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
              Computation Element (PCE)-Based Architecture", RFC 4655,
              August 2006.

   [RFC4970]  Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S.
              Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 4970, July 2007.

   [RFC5073]  Vasseur, J.P. and J.L. Le Roux, "IGP Routing Protocol
              Extensions for Discovery of Traffic Engineering Node
              Capabilities", RFC 5073, December 2007.

   [RFC5152]  Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain
              Path Computation Method for Establishing Inter-Domain
              Traffic Engineering (TE) Label Switched Paths (LSPs)", RFC
              5152, February 2008.

   [RFC5693]  Seedorf, J. and E. Burger, "Application-Layer Traffic
              Optimization (ALTO) Problem Statement", RFC 5693, October
              2009.

   [RFC5706]  Harrington, D., "Guidelines for Considering Operations and
              Management of New Protocols and Protocol Extensions", RFC
              5706, November 2009.

   [RFC6549]  Lindem, A., Roy, A., and S. Mirtorabi, "OSPFv2 Multi-
              Instance Extensions", RFC 6549, March 2012.

Authors' Addresses

   Hannes Gredler
   Juniper Networks, Inc.
   1194 N. Mathilda Ave.
   Sunnyvale, CA 94089
   US

   Email: hannes@juniper.net








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   Jan Medved
   Cisco Systems, Inc.
   170, West Tasman Drive
   San Jose, CA 95134
   US

   Email: jmedved@cisco.com


   Stefano Previdi
   Cisco Systems, Inc.
   Via Del Serafico, 200
   Roma 00142
   Italy

   Email: sprevidi@cisco.com


   Adrian Farrel
   Juniper Networks, Inc.
   1194 N. Mathilda Ave.
   Sunnyvale, CA 94089
   US

   Email: afarrel@juniper.net




























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