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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: November 22, 2013                                    S. Previdi
                                                     Cisco Systems, Inc.
                                                               A. Farrel
                                                  Juniper Networks, Inc.
                                                                  S. Ray
                                                     Cisco Systems, Inc.
                                                            May 21, 2013


  North-Bound Distribution of Link-State and TE Information using BGP
                   draft-ietf-idr-ls-distribution-03

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 IGP 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
   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-



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   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 November 22, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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




























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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Motivation and Applicability . . . . . . . . . . . . . . . . .  6
     2.1.  MPLS-TE with PCE . . . . . . . . . . . . . . . . . . . . .  6
     2.2.  ALTO Server Network API  . . . . . . . . . . . . . . . . .  8
   3.  Carrying Link State Information in BGP . . . . . . . . . . . .  9
     3.1.  TLV Format . . . . . . . . . . . . . . . . . . . . . . . .  9
     3.2.  The Link State NLRI  . . . . . . . . . . . . . . . . . . . 10
       3.2.1.  Node Descriptors . . . . . . . . . . . . . . . . . . . 13
       3.2.2.  Link Descriptors . . . . . . . . . . . . . . . . . . . 17
       3.2.3.  Prefix Descriptors . . . . . . . . . . . . . . . . . . 18
     3.3.  The LINK_STATE Attribute . . . . . . . . . . . . . . . . . 20
       3.3.1.  Node Attribute TLVs  . . . . . . . . . . . . . . . . . 20
       3.3.2.  Link Attribute TLVs  . . . . . . . . . . . . . . . . . 23
       3.3.3.  Prefix Attribute TLVs  . . . . . . . . . . . . . . . . 27
     3.4.  BGP Next Hop Information . . . . . . . . . . . . . . . . . 30
     3.5.  Inter-AS Links . . . . . . . . . . . . . . . . . . . . . . 31
     3.6.  Router-ID Anchoring Example: ISO Pseudonode  . . . . . . . 31
     3.7.  Router-ID Anchoring Example: OSPFv2 to IS-IS Migration . . 32
   4.  Link to Path Aggregation . . . . . . . . . . . . . . . . . . . 32
     4.1.  Example: No Link Aggregation . . . . . . . . . . . . . . . 33
     4.2.  Example: ASBR to ASBR Path Aggregation . . . . . . . . . . 33
     4.3.  Example: Multi-AS Path Aggregation . . . . . . . . . . . . 34
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 34
   6.  Manageability Considerations . . . . . . . . . . . . . . . . . 34
     6.1.  Operational Considerations . . . . . . . . . . . . . . . . 35
       6.1.1.  Operations . . . . . . . . . . . . . . . . . . . . . . 35
       6.1.2.  Installation and Initial Setup . . . . . . . . . . . . 35
       6.1.3.  Migration Path . . . . . . . . . . . . . . . . . . . . 35
       6.1.4.  Requirements on Other Protocols and Functional
               Components . . . . . . . . . . . . . . . . . . . . . . 35
       6.1.5.  Impact on Network Operation  . . . . . . . . . . . . . 35
       6.1.6.  Verifying Correct Operation  . . . . . . . . . . . . . 36
     6.2.  Management Considerations  . . . . . . . . . . . . . . . . 36
       6.2.1.  Management Information . . . . . . . . . . . . . . . . 36
       6.2.2.  Fault Management . . . . . . . . . . . . . . . . . . . 36
       6.2.3.  Configuration Management . . . . . . . . . . . . . . . 36
       6.2.4.  Accounting Management  . . . . . . . . . . . . . . . . 36
       6.2.5.  Performance Management . . . . . . . . . . . . . . . . 36
       6.2.6.  Security Management  . . . . . . . . . . . . . . . . . 37
   7.  TLV/Sub-TLV Code Points Summary  . . . . . . . . . . . . . . . 37
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 39
   9.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 39
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 39
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 40
     11.2. Informative References . . . . . . . . . . . . . . . . . . 41



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   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 42


















































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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.

   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.












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

                  Figure 1: TE Link State info collection

   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 use 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).




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   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.

   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.















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                +----------+                           +---------+
                |  -----   |                           |   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
   Partition Identifiers (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].

   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



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   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

   This specification contains two parts: definition of a new BGP NLRI
   that describes links, nodes and prefixes comprising IGP link state
   information, and definition of a new BGP path attribute (BGP-LS
   attribute) that carries link, node and prefix properties and
   attributes, such as the link and prefix metric or auxiliary Router-
   IDs of nodes, etc.

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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //                        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



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   preserved and propagated.  In order to compare NLRIs with unknown
   TLVs all TLVs MUST be ordered in ascending order.  If there are more
   TLVs of the same type, then the TLVs MUST be ordered in ascending
   order of the TLV value within the set of TLVs with the same type.
   All TLVs that are not specified as mandatory are considered optional.

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
   node, a link or a prefix.

   All non-VPN link, node and prefix information SHALL be encoded using
   AFI 16388 / SAFI 71.  VPN link, node and prefix information SHALL be
   encoded using AFI 16388 / SAFI 128.

   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 16388 / SAFI 71 and AFI 16388 / SAFI 128 for the VPN flavor.

   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 AFI 16388 / SAFI 71 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 VPN AFI 16388 / SAFI 128 NLRI Format

   The 'Total NLRI Length' field contains the cumulative length, in
   octets, of rest of the NLRI not including the NLRI Type field or
   itself.  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: Node NLRI

      Type = 2: Link NLRI

      Type = 3: IPv4 Topology Prefix NLRI

      Type = 4: IPv6 Topology Prefix NLRI

   The Node 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  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Identifier                          |
     |                            (64 bits)                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //                Local Node Descriptors (variable)            //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 7: The Node NLRI format

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




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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
     +-+-+-+-+-+-+-+-+
     |  Protocol-ID  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Identifier                          |
     |                            (64 bits)                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //               Local Node Descriptors (variable)             //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //               Remote Node Descriptors (variable)            //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //                  Link Descriptors (variable)                //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 8: The Link NLRI format

   The IPv4 and IPv6 Prefix NLRIs (NLRI Type = 3 and Type = 4) use the
   same format as 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  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Identifier                          |
     |                            (64 bits)                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //              Local Node Descriptor (variable)               //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //                Prefix Descriptors (variable)                //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 9: The IPv4/IPv6 Topology Prefix NLRI format

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

      Protocol-ID = 0: Unknown, The source of NLRI information could not
      be determined

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

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






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      Protocol-ID = 3: OSPF, The NLRI information has been sourced by
      OSPF

      Protocol-ID = 4: Direct, The NLRI information has been sourced
      from local interface state

      Protocol-ID = 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 [RFC6822] and [RFC6549].  These instances define
   independent "routing universes".  The 64-Bit 'Identifier' field is
   used to identify the "routing universe" where the NLRI belongs.  The
   NLRIs representing IGP objects (nodes, links or prefixes) from the
   same routing universe MUST have the same 'Identifier' value; NLRIs
   with different 'Identifier' values MUST be considered to be from
   different routing universes.  Table Table 1 lists the 'Identifier'
   values that are defined as well-known in this draft.

                   +------------+---------------------+
                   | Identifier | Routing Universe    |
                   +------------+---------------------+
                   |      0     | L3 packet topology  |
                   |      1     | L1 optical topology |
                   +------------+---------------------+

                 Table 1: Well-known Instance Identifiers

   Each Node Descriptor and Link Descriptor consists of one or more TLVs
   described in the following sections.

3.2.1.  Node Descriptors

   Each link is anchored by a pair of Router-IDs that are used by the
   underlying IGP, namely, 48 Bit ISO System-ID for IS-IS and 32 bit
   Router-ID for OSPFv2 and OSPFv3.  An IGP may use one or more
   additional auxiliary Router-IDs, mainly for traffic engineering
   purposes.  For example, IS-IS may have one or more IPv4 and IPv6 TE
   Router-IDs [RFC5305], [RFC6119].  These auxiliary Router-IDs MUST be
   included in the link attribute described in Section Section 3.3.2.

   It is desirable that the Router-ID assignments inside the Node
   Descriptor are globally unique.  However there may be Router-ID
   spaces (e.g.  ISO) where no global registry exists, or worse, Router-
   IDs have been allocated following private-IP RFC 1918 [RFC1918]
   allocation.  We use Autonomous System (AS) Number and BGP-LS
   Identifier in order to disambiguate the Router-IDs, as described in
   Section 3.2.1.1.



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3.2.1.1.  Globally Unique Node/Link/Prefix Identifiers

   One problem that needs to be addressed is the ability to identify an
   IGP node globally (by "global", we mean within the BGP-LS database
   collected by all BGP-LS speakers that talk to each other).  This can
   be expressed through the following two requirements:

   (A) The same node must not be represented by two keys (otherwise one
   node will look like two nodes).

   (B) Two different nodes must not be represented by the same key
   (otherwise, two nodes will look like one node).

   We define an "IGP domain" to be the set of nodes (hence, by extension
   links and prefixes), within which, each node has a unique IGP
   representation by using the combination of Area-ID, Router-ID,
   Protocol, Topology-ID, and Instance ID.  The problem is that BGP may
   receive node/link/prefix information from multiple independent "IGP
   domains" and we need to distinguish between them.  Moreover, we can't
   assume there is always one and only one IGP domain per AS.  During
   IGP transitions it may happen that two redundant IGPs are in place.

   In section Section 3.2.1.4 a set of sub-TLVs is described, which
   allows to specify a flexible key for any given Node/Link information
   such that global uniqueness of the NLRI is ensured.

3.2.1.2.  Local Node Descriptors

   The Local Node Descriptors TLV contains Node Descriptors for the node
   anchoring the local end of the link.  This is a mandatory TLV in all
   three types of NLRIs.  The length of this TLV is variable.  The value
   contains one or more Node Descriptor Sub-TLVs defined in
   Section 3.2.1.4.

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

               Figure 10: Local Node Descriptors TLV format






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3.2.1.3.  Remote Node Descriptors

   The Remote Node Descriptors contains Node Descriptors for the node
   anchoring the remote end of the link.  This is a mandatory TLV for
   link NLRIs.  The length of this TLV is variable.  The value contains
   one or more Node Descriptor Sub-TLVs defined in Section 3.2.1.4.

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

               Figure 11: Remote Node Descriptors TLV format

3.2.1.4.  Node Descriptor Sub-TLVs

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

           +--------------------+-------------------+----------+
           | Sub-TLV Code Point | Description       |   Length |
           +--------------------+-------------------+----------+
           |         512        | Autonomous System |        4 |
           |         513        | BGP-LS Identifier |        4 |
           |         514        | Area-ID           |        4 |
           |         515        | IGP Router-ID     | Variable |
           +--------------------+-------------------+----------+

                     Table 2: Node Descriptor Sub-TLVs

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

   Autonomous System:  opaque value (32 Bit AS Number)

   BGP-LS Identifier:  opaque value (32 Bit ID).  In conjunction with
      ASN, uniquely identifies the BGP-LS domain.  The combination of
      ASN and BGP-LS ID MUST be globally unique.  All BGP-LS speakers
      within an IGP flooding-set (set of IGP nodes within which an LSP/
      LSA is flooded) MUST use the same ASN, BGP-LS ID tuple.  If an IGP
      domain consists of multiple flooding-sets, then all BGP-LS
      speakers within the IGP domain SHOULD use the same ASN, BGP-LS ID
      tuple.  The ASN, BGP Router-ID tuple (which is globally unique
      [RFC6286] ) of one of the BGP-LS speakers within the flooding-set



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      (or IGP domain) may be used for all BGP-LS speakers in that
      flooding-set (or IGP domain).

   Area ID:  It is used to identify the 32 Bit area to which the NLRI
      belongs.  Area Identifier allows the different NLRIs of the same
      router to be discriminated.

   IGP Router ID:  opaque value.  This is a mandatory TLV.  For an IS-IS
      non-Pseudonode, this contains 6 octet ISO node-ID (ISO system-ID).
      For an IS-IS Pseudonode corresponding to a LAN, this contains 6
      octet ISO node-ID of the "Designated Intermediate System" (DIS)
      followed by one octet nonzero PSN identifier (7 octet in total).
      For an OSPFv2 or OSPFv3 non-"Pseudonode", this contains 4 octet
      Router-ID.  For an OSPFv2 "Pseudonode" representing a LAN, this
      contains 4 octet Router-ID of the designated router (DR) followed
      by 4 octet IPv4 address of the DR's interface to the LAN (8 octet
      in total).  Similarly, for an OSPFv3 "Pseudonode", this contains 4
      octet Router-ID of the DR followed by 4 octet interface identifier
      of the DR's interface to the LAN (8 octet in total).  The TLV size
      in combination with protocol identifier enables the decoder to
      determine the type of the node.

      There can be at most one instance of each sub-TLV type present in
      any Node Descriptor.  The TLV ordering within a Node descriptor
      MUST be kept in order of increasing numeric value of type.  This
      needs to be done in order to compare NLRIs, even when an
      implementation encounters an unknown sub-TLV.  Using stable
      sorting an implementation can do binary comparison of NLRIs and
      hence allow incremental deployment of new key sub-TLVs.

3.2.1.5.  Multi-Topology ID

   The Multi-Topology ID (MT-ID) TLV carries one or more IS-IS or OSPF
   Multi-Topology IDs for a link, node or prefix.

   Semantics of the IS-IS MT-ID are defined in RFC5120, Section 7.2
   [RFC5120].  Semantics of the OSPF MT-ID are defined in RFC4915,
   Section 3.7 [RFC4915].  If the value in the MT-ID TLV is derived from
   OSPF, then the upper 9 bits MUST be set to 0.  Bits R are reserved,
   SHOULD be set to 0 when originated and ignored on receipt.

   The format of the MT-ID TLV is shown in the following figure.









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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             |          Length=2*n           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |R R R R|  Multi-Topology ID 1  |             ....             //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //             ....             |R R R R|  Multi-Topology ID n  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 12: Multi-Topology ID TLV format

   where Type is 263, Length is 2*n and n is the number of MT-IDs
   carried in the TLV.

   The MT-ID TLV MAY be present in a Link Descriptor, a Prefix
   Descriptor, or in the BGP-LS attribute of a node NLRI.  In Link or
   Prefix Descriptor, only one MT-ID TLV containing only the MT-ID of
   the topology where the link or the prefix belongs is allowed.  In the
   BGP-LS attribute of a node NLRI, one MT-ID TLV containing the array
   of MT-IDs of all topologies where the node belongs can be present.

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 among multiple parallel
   links 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 advertise a half-link
   each, i.e. two link NLRIs are advertised for a given point-to-point
   link.

   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 TLVs are valid as Link Descriptors in the Link NLRI:









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   +-----------+---------------------+---------------+-----------------+
   |  TLV Code | Description         |     IS-IS     | Value defined   |
   |   Point   |                     |  TLV/Sub-TLV  | in:             |
   +-----------+---------------------+---------------+-----------------+
   |    258    | Link Local/Remote   |      22/4     | [RFC5307]/1.1   |
   |           | Identifiers         |               |                 |
   |    259    | IPv4 interface      |      22/6     | [RFC5305]/3.2   |
   |           | address             |               |                 |
   |    260    | IPv4 neighbor       |      22/8     | [RFC5305]/3.3   |
   |           | address             |               |                 |
   |    261    | IPv6 interface      |     22/12     | [RFC6119]/4.2   |
   |           | address             |               |                 |
   |    262    | IPv6 neighbor       |     22/13     | [RFC6119]/4.3   |
   |           | address             |               |                 |
   |    263    | Multi-Topology      |      ---      | Section 3.2.1.5 |
   |           | Identifier          |               |                 |
   +-----------+---------------------+---------------+-----------------+

                       Table 3: Link Descriptor TLVs

3.2.3.  Prefix Descriptors

   The 'Prefix Descriptor' field is a set of Type/Length/Value (TLV)
   triplets.  'Prefix Descriptor' TLVs uniquely identify an IPv4 or IPv6
   Prefix originated by a Node.  The following TLVs are valid as Prefix
   Descriptors in the IPv4/IPv6 Prefix NLRI:

   +--------------+-----------------------+----------+-----------------+
   |   TLV Code   | Description           |  Length  | Value defined   |
   |     Point    |                       |          | in:             |
   +--------------+-----------------------+----------+-----------------+
   |      263     | Multi-Topology        | variable | Section 3.2.1.5 |
   |              | Identifier            |          |                 |
   |      264     | OSPF Route Type       |     1    | Section 3.2.3.1 |
   |      265     | IP Reachability       | variable | Section 3.2.3.2 |
   |              | Information           |          |                 |
   +--------------+-----------------------+----------+-----------------+

                      Table 4: Prefix Descriptor TLVs

3.2.3.1.  OSPF Route Type

   OSPF Route Type is an optional TLV that MAY be present in Prefix
   NLRIs.  It is used to identify the OSPF route-type of the prefix.  It
   is used when an OSPF prefix is advertised in the OSPF domain with
   multiple different route-types.  The Route Type TLV allows to
   discriminate these advertisements.  The format of the OSPF Route Type
   TLV is shown in the following figure.



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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             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Route Type   |
     +-+-+-+-+-+-+-+-+

                   Figure 13: OSPF Route Type TLV Format

   where the Type and Length fields of the TLV are defined in Table 4.
   The OSPF Route Type field values are defined in the OSPF protocol,
   and can be one of the following:

      Intra-Area (0x1)

      Inter-Area (0x2)

      External 1 (0x3)

      External 2 (0x4)

      NSSA 1 (0x5)

      NSSA 2 (0x6)

3.2.3.2.  IP Reachability Information

   The IP Reachability Information is a mandatory TLV that contains one
   IP address prefix (IPv4 or IPv6) originally advertised in the IGP
   topology.  Its purpose is to glue a particular BGP service NLRI vi
   virtue of its BGP next-hop to a given Node in the LSDB.  A router
   SHOULD advertise an IP Prefix NLRI for each of its BGP Next-hops.
   The format of the IP Reachability Information TLV 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Type             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Prefix Length | IP Prefix (variable)                         //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 14: IP Reachability Information TLV Format

   The Type and Length fields of the TLV are defined in Table 4.  The
   following two fields determine the address-family reachability



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   information.  The 'Prefix Length' field contains the length of the
   prefix in bits.  The 'IP Prefix' field contains the most significant
   octets of the prefix; i.e., 1 octet for prefix length 1 up to 8, 2
   octets for prefix length 9 to 16, 3 octets for prefix length 17 up to
   24 and 4 octets for prefix length 25 up to 32, etc.

3.3.  The LINK_STATE Attribute

   This is an optional, non-transitive BGP attribute that is used to
   carry link, node and prefix 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 address-
   families.

3.3.1.  Node Attribute TLVs

   Node attribute TLVs are the TLVs that may be encoded in the BGP-LS
   attribute with a node NLRI.  The following node attribute TLVs are
   defined:

   +--------------+-----------------------+----------+-----------------+
   |   TLV Code   | Description           |   Length | Value defined   |
   |     Point    |                       |          | in:             |
   +--------------+-----------------------+----------+-----------------+
   |      263     | Multi-Topology        | variable | Section 3.2.1.5 |
   |              | Identifier            |          |                 |
   |     1024     | Node Flag Bits        |        1 | Section 3.3.1.1 |
   |     1025     | Opaque Node           | variable | Section 3.3.1.5 |
   |              | Properties            |          |                 |
   |     1026     | Node Name             | variable | Section 3.3.1.3 |
   |     1027     | IS-IS Area Identifier | variable | Section 3.3.1.2 |
   |     1028     | IPv4 Router-ID of     |        4 | [RFC5305]/4.3   |
   |              | Local Node            |          |                 |
   |     1029     | IPv6 Router-ID of     |       16 | [RFC6119]/4.1   |
   |              | Local Node            |          |                 |
   +--------------+-----------------------+----------+-----------------+

                       Table 5: Node Attribute TLVs

3.3.1.1.  Node Flag Bits TLV

   The Node Flag Bits TLV carries a bit mask describing node attributes.
   The value is a variable length bit array of flags, where each bit
   represents a node capability.






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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             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |O|T|E|A| Reserved|
     +-+-+-+-+-+-+-+-+-+

                   Figure 15: Node Flag Bits TLV format

   The bits are defined as follows:

            +----------+-------------------------+-----------+
            |    Bit   | Description             | Reference |
            +----------+-------------------------+-----------+
            |    'O'   | Overload Bit            | [RFC1195] |
            |    'T'   | Attached Bit            | [RFC1195] |
            |    'E'   | External Bit            | [RFC2328] |
            |    'A'   | ABR Bit                 | [RFC2328] |
            | Reserved | Reserved for future use |           |
            +----------+-------------------------+-----------+

                    Table 6: Node Flag Bits Definitions

3.3.1.2.  IS-IS Area Identifier TLV

   An IS-IS node can be part of one or more IS-IS areas.  Each of these
   area addresses is carried in the IS-IS Area Identifier TLV.  If more
   than one Area Addresses are present, multiple TLVs are used to encode
   them.  The IS-IS Area Identifier TLV may be present in the LINK_STATE
   attribute only with the Link State Node 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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //                 Area Identifier (variable)                  //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 16: IS-IS Area Identifier TLV Format

3.3.1.3.  Node Name TLV

   The Node Name TLV is optional.  Its structure and encoding has been
   borrowed from [RFC5301].  The value field identifies the symbolic
   name of the router node.  This symbolic name can be the FQDN for the
   router, it can be a subset of the FQDN, or it can be any string



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   operators want to use for the router.  The use of FQDN or a subset of
   it is strongly recommended.

   The Value field is encoded in 7-bit ASCII.  If a user-interface for
   configuring or displaying this field permits Unicode characters, that
   user-interface is responsible for applying the ToASCII and/or
   ToUnicode algorithm as described in [RFC3490] to achieve the correct
   format for transmission or display.

   Altough [RFC5301] is a IS-IS specific extension, usage of the Node
   Name TLV is possible for all protocols.  How a router derives and
   injects node names for e.g.  OSPF nodes, is outside of the scope of
   this document.

      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 Name (variable)                    //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 17: Node Name format

3.3.1.4.  Local IPv4/IPv6 Router-ID

   The local IPv4/IPv6 Router-ID TLVs are used to describe auxiliary
   Router-IDs that the IGP might be using, e.g., for TE and migration
   purposes like correlating a Node-ID between different protocols.  If
   there is more than one auxiliary Router-ID of a given type, then each
   one is encoded in its own TLV.

3.3.1.5.  Opaque Node Attribute TLV

   The Opaque Node attribute TLV is an envelope that transparently
   carries optional node attribute TLVs advertised by a router.  An
   originating router shall use this TLV for encoding information
   specific to the protocol advertised in the NLRI header Protocol-ID
   field or new protocol extensions to the protocol as advertised in the
   NLRI header Protocol-ID field for which there is no protocol neutral
   representation in the BGP link-state NLRI.  A router for example
   could use this extension in order to advertise the native protocols
   node attribute TLVs, such as the OSPF Router Informational
   Capabilities TLV defined in [RFC4970], or the IGP TE Node Capability
   Descriptor TLV described in [RFC5073].






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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             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //               Opaque node attributes (variable)             //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 18: Opaque Node attribute format

3.3.2.  Link Attribute TLVs

   Link attribute TLVs are TLVs that may be encoded in the BGP-LS
   attribute with a link NLRI.  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:

   +------------+---------------------+--------------+-----------------+
   |  TLV Code  | Description         |     IS-IS    | Defined in:     |
   |    Point   |                     |  TLV/Sub-TLV |                 |
   +------------+---------------------+--------------+-----------------+
   |    1028    | IPv4 Router-ID of   |    134/---   | [RFC5305]/4.3   |
   |            | Local Node          |              |                 |
   |    1029    | IPv6 Router-ID of   |    140/---   | [RFC6119]/4.1   |
   |            | Local Node          |              |                 |
   |    1030    | IPv4 Router-ID of   |    134/---   | [RFC5305]/4.3   |
   |            | Remote Node         |              |                 |
   |    1031    | IPv6 Router-ID of   |    140/---   | [RFC6119]/4.1   |
   |            | Remote Node         |              |                 |
   |    1088    | Administrative      |     22/3     | [RFC5305]/3.1   |
   |            | group (color)       |              |                 |
   |    1089    | Maximum link        |     22/9     | [RFC5305]/3.3   |
   |            | bandwidth           |              |                 |
   |    1090    | Max. reservable     |     22/10    | [RFC5305]/3.5   |
   |            | link bandwidth      |              |                 |
   |    1091    | Unreserved          |     22/11    | [RFC5305]/3.6   |
   |            | bandwidth           |              |                 |
   |    1092    | TE Default Metric   |     22/18    | [RFC5305]/3.7   |




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   |    1093    | Link Protection     |     22/20    | [RFC5307]/1.2   |
   |            | Type                |              |                 |
   |    1094    | MPLS Protocol Mask  |      ---     | Section 3.3.2.2 |
   |    1095    | Metric              |      ---     | Section 3.3.2.3 |
   |    1096    | Shared Risk Link    |      ---     | Section 3.3.2.4 |
   |            | Group               |              |                 |
   |    1097    | Opaque link         |      ---     | Section 3.3.2.5 |
   |            | attribute           |              |                 |
   |    1098    | Link Name attribute |      ---     | Section 3.3.2.6 |
   +------------+---------------------+--------------+-----------------+

                       Table 7: Link Attribute TLVs

3.3.2.1.  IPv4/IPv6 Router-ID

   The local/remote IPv4/IPv6 Router-ID TLVs are used to describe
   auxiliary Router-IDs that the IGP might be using, e.g., for TE
   purposes.  All auxiliary Router-IDs of both the local and the remote
   node MUST be included in the link attribute of each link NLRI.  If
   there are more than one auxiliary Router-ID of a given type, then
   multiple TLVs are used to encode them.

3.3.2.2.  MPLS Protocol Mask TLV

   The MPLS Protocol TLV 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|  Reserved |
     +-+-+-+-+-+-+-+-+

                       Figure 19: MPLS Protocol TLV

   The following bits are defined:











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   +------------+------------------------------------------+-----------+
   |     Bit    | Description                              | Reference |
   +------------+------------------------------------------+-----------+
   |     'L'    | Label Distribution Protocol (LDP)        | [RFC5036] |
   |     'R'    | Extension to RSVP for LSP Tunnels        | [RFC3209] |
   |            | (RSVP-TE)                                |           |
   | 'Reserved' | Reserved for future use                  |           |
   +------------+------------------------------------------+-----------+

                   Table 8: MPLS Protocol Mask TLV Codes

3.3.2.3.  Metric TLV

   The IGP Metric TLV carries the metric for this link.  The length of
   this TLV is variable, depending on the metric width of the underlying
   protocol.  IS-IS small metrics have a length of 1 octet (the two most
   significant bits are ignored).  OSPF metrics have a length of two
   octects.  IS-IS wide-metrics have a length of three 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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //      IGP Link Metric (variable length)      //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 20: Metric TLV format

3.3.2.4.  Shared Risk Link Group TLV

   The Shared Risk Link Group (SRLG) TLV 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 21.  The length of this TLV is 4 *
   (number of SRLG values).














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

               Figure 21: 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].  In Link State NLRI both IPv4 and IPv6 SRLG
   information are carried in a single TLV.

3.3.2.5.  Opaque Link Attribute TLV

   The Opaque link attribute TLV is an envelope that transparently
   carries optional link atrribute TLVs advertised by a router.  An
   originating router shall use this TLV for encoding information
   specific to the protocol advertised in the NLRI header Protocol-ID
   field or new protocol extensions to the protocol as advertised in the
   NLRI header Protocol-ID field 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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //                Opaque link attributes (variable)            //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 22: Opaque link attribute format

3.3.2.6.  Link Name TLV

   The Link Name TLV is optional.  The value field identifies the
   symbolic name of the router link.  This symbolic name can be the FQDN
   for the link, it can be a subset of the FQDN, or it can be any string
   operators want to use for the link.  The use of FQDN or a subset of
   it is strongly recommended.




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   The Value field is encoded in 7-bit ASCII.  If a user-interface for
   configuring or displaying this field permits Unicode characters, that
   user-interface is responsible for applying the ToASCII and/or
   ToUnicode algorithm as described in [RFC3490] to achieve the correct
   format for transmission or display.

   How a router derives and injects link names is outside of the scope
   of this document.

      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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //                     Link Name (variable)                    //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 23: Link Name format

3.3.3.  Prefix Attribute TLVs

   Prefixes are learned from the IGP topology (IS-IS or OSPF) with a set
   of IGP attributes (such as metric, route tags, etc.) that MUST be
   reflected into the LINK_STATE attribute.  This section describes the
   different attributes related to the IPv4/IPv6 prefixes.  Prefix
   Attributes TLVs SHOULD be used when advertising NLRI types 3 and 4
   only.  The following attributes TLVs are defined:

   +---------------+----------------------+----------+-----------------+
   |    TLV Code   | Description          |   Length | Reference       |
   |     Point     |                      |          |                 |
   +---------------+----------------------+----------+-----------------+
   |      1152     | IGP Flags            |        1 | Section 3.3.3.1 |
   |      1153     | Route Tag            |      4*n | Section 3.3.3.2 |
   |      1154     | Extended Tag         |      8*n | Section 3.3.3.3 |
   |      1155     | Prefix Metric        |        4 | Section 3.3.3.4 |
   |      1156     | OSPF Forwarding      |        4 | Section 3.3.3.5 |
   |               | Address              |          |                 |
   |      1157     | Opaque Prefix        | variable | Section 3.3.3.6 |
   |               | Attribute            |          |                 |
   +---------------+----------------------+----------+-----------------+

                      Table 9: Prefix Attribute TLVs








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3.3.3.1.  IGP Flags TLV

   IGP Flags TLV contains IS-IS and OSPF flags and bits originally
   assigned to the prefix.  The IGP Flags TLV is encoded as follows:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Type             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |D|   Reserved  |
     +-+-+-+-+-+-+-+-+

                      Figure 24: IGP Flag TLV format

   The value field contains bits defined according to the table below:

            +----------+--------------------------+-----------+
            |    Bit   | Description              | Reference |
            +----------+--------------------------+-----------+
            |    'D'   | IS-IS Up/Down Bit        | [RFC5305] |
            | Reserved | Reserved for future use. |           |
            +----------+--------------------------+-----------+

                    Table 10: IGP Flag Bits Definitions

3.3.3.2.  Route Tag

   Route Tag TLV carries original IGP TAGs (IS-IS [RFC5130] or OSPF) of
   the prefix and is encoded as follows:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Type             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //                    Route Tags (one or more)                 //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 25: IGP Route TAG TLV format

   Length is a multiple of 4.

   The value field contains one or more Route Tags as learned in the IGP
   topology.






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3.3.3.3.  Extended Route Tag

   Extended Route Tag TLV carries IS-IS Extended Route TAGs of the
   prefix [RFC5130] and is encoded as follows:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Type             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //                Extended Route Tag (one or more)             //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 26: Extended IGP Route TAG TLV format

   Length is a multiple of 8.

   The 'Extended Route Tag' field contains one or more Extended Route
   Tags as learned in the IGP topology.

3.3.3.4.  Prefix Metric TLV

   Prefix Metric TLV carries the metric of the prefix as known in the
   IGP topology [RFC5305].  The attribute is mandatory and can only
   appear once.

      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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Metric                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 27: Prefix Metric TLV Format

   Length is 4.

3.3.3.5.  OSPF Forwarding Address TLV

   OSPF Forwarding Address TLV [RFC2328] carries the OSPF forwarding
   address as known in the original OSPF advertisement.  Forwarding
   address can be either IPv4 or IPv6.








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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             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //                Forwarding Address (variable)                //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 28: OSPF Forwarding Address TLV Format

   Length is 4 for an IPv4 forwarding address an 16 for an IPv6
   forwarding address.

3.3.3.6.  Opaque Prefix Attribute TLV

   The Opaque Prefix attribute TLV is an envelope that transparently
   carries optional prefix attribute TLVs advertised by a router.  An
   originating router shall use this TLV for encoding information
   specific to the protocol advertised in the NLRI header Protocol-ID
   field or new protocol extensions to the protocol as advertised in the
   NLRI header Protocol-ID field for which there is no protocol neutral
   representation in the BGP link-state NLRI.

   The format of the TLV is as follows:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Type             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //              Opaque Prefix Attributes  (variable)           //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 29: Opaque Prefix Attribute TLV Format

   Type is as specified in Table 9 and Length is variable.

3.4.  BGP Next Hop Information

   BGP link-state information for both IPv4 and IPv6 networks can be
   carried over either an IPv4 BGP session, or an IPv6 BGP session.  If
   IPv4 BGP session is used, then the next hop in the MP_REACH_NLRI
   SHOULD be an IPv4 address.  Similarly, if IPv6 BGP session is used,
   then the next hop in the MP_REACH_NLRI SHOULD be an IPv6 address.
   Usually the next hop will be set to the local end-point address of
   the BGP session.  The next hop address MUST be encoded as described
   in [RFC4760].  The length field of the next hop address will specify
   the next hop address-family.  If the next hop length is 4, then the



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   next hop is an IPv4 address; if the next hop length is 16, then it is
   a global IPv6 address and if the next hop length is 32, then there is
   one global IPv6 address followed by a link-local IPv6 address.  The
   link-local IPv6 address should be used as described in [RFC2545].
   For VPN SAFI, as per custom, an 8 byte route-distinguisher set to all
   zero is prepended to the next hop.

   The BGP Next Hop attribute is used by each BGP-LS speaker to validate
   the NLRI it receives.  However, this specification doesn't mandate
   any rule regarding the re-write of the BGP Next Hop attribute.

3.5.  Inter-AS Links

   The main source of TE information is the IGP, which is not active on
   inter-AS links.  In some cases, the IGP may have information of
   inter-AS links ([RFC5392], [RFC5316]).  In other cases, for injecting
   a non-IGP enabled link into the BGP link-state RIB, an implementation
   MUST support configuration of either 'Static' or 'Direct' links.

3.6.  Router-ID Anchoring Example: ISO Pseudonode

   Encoding of a broadcast LAN in IS-IS provides a good example of how
   Router-IDs are encoded.  Consider Figure 30.  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.  Node1 is the DIS for
   the LAN.  Two unidirectional links (Node1, Pseudonode 1) and
   (Pseudonode1, Node2) are being generated.

   The link NRLI of (Node1, Pseudonode1) is encoded as follows: the IGP
   Router-ID TLV of the local node descriptor is 6 octets long
   containing ISO-ID of Node1, 1920.0000.2001; the IGP Router-ID TLV of
   the remote node descriptor is 7 octets long containing the ISO-ID of
   Pseudonode1, 1920.0000.2001.02.  The BGP-LS attribute of this link
   contains one local IPv4 Router-ID TLV (TLV type 1028) containing
   192.0.2.1, the IPv4 Router-ID of Node1.

   The link NRLI of (Pseudonode1.  Node2) is encoded as follows: the IGP
   Router-ID TLV of the local node descriptor is 7 octets long
   containing the ISO-ID of Pseudonode1, 1920.0000.2001.02; the IGP
   Router-ID TLV of the remote node descriptor is 6 octets long
   containing ISO-ID of Node2, 1920.0000.2002.  The BGP-LS attribute of
   this link contains one remote IPv4 Router-ID TLV (TLV type 1030)
   containing 192.0.2.2, the IPv4 Router-ID of Node2.







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     +-----------------+    +-----------------+    +-----------------+
     |      Node1      |    |   Pseudonode1   |    |      Node2      |
     |1920.0000.2001.00|--->|1920.0000.2001.02|--->|1920.0000.2002.00|
     |     192.0.2.1   |    |                 |    |     192.0.2.2   |
     +-----------------+    +-----------------+    +-----------------+

                       Figure 30: IS-IS Pseudonodes

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

   Graceful migration from one IGP to another requires coordinated
   operation of both protocols during the migration period.  Such a
   coordination requires identifying a given physical link in both IGPs.
   The IPv4 Router-ID provides that "glue" which is present in the node
   descriptors of the OSPF link NLRI and in the link attribute of the
   IS-IS link NLRI.

   Consider a point-to-point link between two routers, A and B, that
   initially were OSPFv2-only routers and then IS-IS is enabled on them.
   Node A has IPv4 Router-ID and ISO-ID; node B has IPv4 Router-ID, IPv6
   Router-ID and ISO-ID.  Each protocol generates one link NLRI for the
   link (A, B), both of which are carried by BGP-LS.  The OSPFv2 link
   NLRI for the link is encoded with the IPv4 Router-ID of nodes A and B
   in the local and remote node descriptors, respectively.  The IS-IS
   link NLRI for the link is encoded with the ISO-ID of nodes A and B in
   the local and remote node descriptors, respectively.  In addition,
   the BGP-LS attribute of the IS-IS link NLRI contains the the TLV type
   1028 containing the IPv4 Router-ID of node A; TLV type 1030
   containing the IPv4 Router-ID of node B and TLV type 1031 containing
   the IPv6 Router-ID of node B. In this case, by using IPv4 Router-ID,
   the link (A, B) can be identified in both IS-IS and OSPF protocol.


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 are discussed.




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4.1.  Example: No Link Aggregation

   Consider Figure 31.  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.

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

                      Figure 31: 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 32.  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 32: ASBR link aggregation








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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 33.  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 33: Multi-AS aggregation


5.  IANA Considerations

   This document requests a code point from the registry of Address
   Family Numbers.  As per early allocation procedure this is AFI 16388.

   This document requests a code point from the registry of Subsequent
   Address Family Numbers.  As per early allocation procedure this is
   SAFI 71.

   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 11.  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].




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6.1.  Operational Considerations

6.1.1.  Operations

   Existing BGP operational procedures apply.  No new operation
   procedures are defined in this document.  It is noted that the NLRI
   information present in this document purely carries application level
   data that has no immediate corresponding forwarding state impact.  As
   such, any churn in reachability information has different impact than
   regular BGP updates which need to change 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.

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.





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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
   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.

   An implementation SHOULD allow the operator to configure a 64-bit
   instance ID.

   An implementation SHOULD allow the operator to configure a pair of
   ASN and BGP-LS identifier per flooding set the node participates in.

6.2.4.  Accounting Management

   Not Applicable.

6.2.5.  Performance Management

   An implementation SHOULD provide the following statistics:





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   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.  TLV/Sub-TLV Code Points Summary

   This section contains the global table of all TLVs/Sub-TLVs defined
   in this document.
































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   +-----------+---------------------+---------------+-----------------+
   |  TLV Code | Description         |   IS-IS TLV/  | Value defined   |
   |   Point   |                     |    Sub-TLV    | in:             |
   +-----------+---------------------+---------------+-----------------+
   |    256    | Local Node          |      ---      | Section 3.2.1.2 |
   |           | Descriptors         |               |                 |
   |    257    | Remote Node         |      ---      | Section 3.2.1.3 |
   |           | Descriptors         |               |                 |
   |    258    | Link Local/Remote   |      22/4     | [RFC5307]/1.1   |
   |           | Identifiers         |               |                 |
   |    259    | IPv4 interface      |      22/6     | [RFC5305]/3.2   |
   |           | address             |               |                 |
   |    260    | IPv4 neighbor       |      22/8     | [RFC5305]/3.3   |
   |           | address             |               |                 |
   |    261    | IPv6 interface      |     22/12     | [RFC6119]/4.2   |
   |           | address             |               |                 |
   |    262    | IPv6 neighbor       |     22/13     | [RFC6119]/4.3   |
   |           | address             |               |                 |
   |    263    | Multi-Topology ID   |      ---      | Section 3.2.1.5 |
   |    264    | OSPF Route Type     |      ---      | Section 3.2.3   |
   |    265    | IP Reachability     |      ---      | Section 3.2.3   |
   |           | Information         |               |                 |
   |    512    | Autonomous System   |      ---      | Section 3.2.1.4 |
   |    513    | BGP-LS Identifier   |      ---      | Section 3.2.1.4 |
   |    514    | Area ID             |      ---      | Section 3.2.1.4 |
   |    515    | IGP Router-ID       |      ---      | Section 3.2.1.4 |
   |    1024   | Node Flag Bits      |      ---      | Section 3.3.1.1 |
   |    1025   | Opaque Node         |      ---      | Section 3.3.1.5 |
   |           | Properties          |               |                 |
   |    1026   | Node Name           |    variable   | Section 3.3.1.3 |
   |    1027   | IS-IS Area          |    variable   | Section 3.3.1.2 |
   |           | Identifier          |               |                 |
   |    1028   | IPv4 Router-ID of   |    134/---    | [RFC5305]/4.3   |
   |           | Local Node          |               |                 |
   |    1029   | IPv6 Router-ID of   |    140/---    | [RFC6119]/4.1   |
   |           | Local Node          |               |                 |
   |    1030   | IPv4 Router-ID of   |    134/---    | [RFC5305]/4.3   |
   |           | Remote Node         |               |                 |
   |    1031   | IPv6 Router-ID of   |    140/---    | [RFC6119]/4.1   |
   |           | Remote Node         |               |                 |
   |    1088   | Administrative      |      22/3     | [RFC5305]/3.1   |
   |           | group (color)       |               |                 |
   |    1089   | Maximum link        |      22/9     | [RFC5305]/3.3   |
   |           | bandwidth           |               |                 |
   |    1090   | Max. reservable     |     22/10     | [RFC5305]/3.5   |
   |           | link bandwidth      |               |                 |
   |    1091   | Unreserved          |     22/11     | [RFC5305]/3.6   |
   |           | bandwidth           |               |                 |



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   |    1092   | TE Default Metric   |     22/18     | [RFC5305]/3.7   |
   |    1093   | Link Protection     |     22/20     | [RFC5307]/1.2   |
   |           | Type                |               |                 |
   |    1094   | MPLS Protocol Mask  |      ---      | Section 3.3.2.2 |
   |    1095   | Metric              |      ---      | Section 3.3.2.3 |
   |    1096   | Shared Risk Link    |      ---      | Section 3.3.2.4 |
   |           | Group               |               |                 |
   |    1097   | Opaque link         |      ---      | Section 3.3.2.5 |
   |           | attribute           |               |                 |
   |    1098   | Link Name attribute |      ---      | Section 3.3.2.6 |
   |    1152   | IGP Flags           |      ---      | Section 3.3.3.1 |
   |    1153   | Route Tag           |      ---      | [RFC5130]       |
   |    1154   | Extended Tag        |      ---      | [RFC5130]       |
   |    1155   | Prefix Metric       |      ---      | [RFC5305]       |
   |    1156   | OSPF Forwarding     |      ---      | [RFC2328]       |
   |           | Address             |               |                 |
   |    1157   | Opaque Prefix       |      ---      | Section 3.3.3.6 |
   |           | Attribute           |               |                 |
   +-----------+---------------------+---------------+-----------------+

             Table 11: Summary Table of TLV/Sub-TLV Codepoints


8.  Security Considerations

   Procedures and protocol extensions defined in this document do not
   affect the BGP security model.  See
   [I-D.ietf-karp-routing-tcp-analysis] for details.

   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.


9.  Contributors

   We would like to thank Robert Varga for the significant contribution
   he gave to this document.


10.  Acknowledgements

   We would like to thank Nischal Sheth, 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, Steven Luong, Tamas Mondal, Waqas Alam,
   Vipin Kumar, Naiming Shen, Balaji Rajagopalan and Yakov Rekhter for



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   their comments.


11.  References

11.1.  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.

   [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.

   [RFC2545]  Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol
              Extensions for IPv6 Inter-Domain Routing", RFC 2545,
              March 1999.

   [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.

   [RFC3490]  Faltstrom, P., Hoffman, P., and A. Costello,
              "Internationalizing Domain Names in Applications (IDNA)",
              RFC 3490, March 2003.

   [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.

   [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.



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   [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.

   [RFC5130]  Previdi, S., Shand, M., and C. Martin, "A Policy Control
              Mechanism in IS-IS Using Administrative Tags", RFC 5130,
              February 2008.

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

   [RFC5301]  McPherson, D. and N. Shen, "Dynamic Hostname Exchange
              Mechanism for IS-IS", RFC 5301, October 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.

   [RFC6286]  Chen, E. and J. Yuan, "Autonomous-System-Wide Unique BGP
              Identifier for BGP-4", RFC 6286, June 2011.

   [RFC6822]  Previdi, S., Ginsberg, L., Shand, M., Roy, A., and D.
              Ward, "IS-IS Multi-Instance", RFC 6822, December 2012.

11.2.  Informative References

   [I-D.ietf-alto-protocol]
              Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
              draft-ietf-alto-protocol-13 (work in progress),
              September 2012.

   [I-D.ietf-karp-routing-tcp-analysis]
              Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP and MSDP Issues According to KARP Design
              Guide", draft-ietf-karp-routing-tcp-analysis-07 (work in
              progress), April 2013.

   [RFC4655]  Farrel, A., Vasseur, J., 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.



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              Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 4970, July 2007.

   [RFC5073]  Vasseur, J. and J. 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.

   [RFC5316]  Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in
              Support of Inter-Autonomous System (AS) MPLS and GMPLS
              Traffic Engineering", RFC 5316, December 2008.

   [RFC5392]  Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in
              Support of Inter-Autonomous System (AS) MPLS and GMPLS
              Traffic Engineering", RFC 5392, January 2009.

   [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
   Rome  00142
   Italy

   Email: sprevidi@cisco.com


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

   Email: afarrel@juniper.net


   Saikat Ray
   Cisco Systems, Inc.
   170, West Tasman Drive
   San Jose, CA  95134
   US

   Email: sairay@cisco.com

















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