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Versions: 00 01                                                         
Inter-Domain Routing                                          H. Gredler
Internet-Draft                                                 J. Medved
Intended status: Standards Track                  Juniper Networks, Inc.
Expires: September 4, 2011                                 March 3, 2011


           Advertising Traffic Engineering Information in BGP
                        draft-gredler-bgp-te-00

Abstract

   This document defines a new Border Gateway Protocol Network Layer
   Reachability Information (BGP NLRI) encoding format that can be used
   to distribute Traffic Engineering (TE) link information.  Links can
   be either physical links connecting physical nodes, or virtual paths
   between physical or abstract nodes.  The TE information is carried
   via the BGP, thereby reusing protocol algorithms, operational
   experience, and administrative processes, such as inter-provider
   peering agreements.

   The BGP protocol carrying Traffic Engineering (TE) information would
   provide a well-defined, uniform, policy-controlled interface from the
   network to outside servers that need to learn the network topology in
   real-time, for example an ALTO Server or a Path Computation Server.
   Having TE information from remote areas and/or Autonomous Systems
   would allow path computation for inter-area and/or inter-AS source-
   routed unicast and multicast tunnels.

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-
   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."



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   This Internet-Draft will expire on September 4, 2011.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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



































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Scope  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Transcoding TE Link Information Into a BGP NLRI  . . . . . . .  5
     3.1.  TLV Format . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.2.  Node anchors . . . . . . . . . . . . . . . . . . . . . . .  7
       3.2.1.  Router-ID Anchoring Example: ISO Pseudonode  . . . . .  8
       3.2.2.  Router-ID Anchoring Example: OSPFv2 to IS-IS
               Migration  . . . . . . . . . . . . . . . . . . . . . .  8
     3.3.  Link Descriptors . . . . . . . . . . . . . . . . . . . . .  8
     3.4.  Link Attributes  . . . . . . . . . . . . . . . . . . . . .  9
       3.4.1.  TE Default Metric TLV  . . . . . . . . . . . . . . . . 10
       3.4.2.  IGP Link Metric TLV  . . . . . . . . . . . . . . . . . 10
       3.4.3.  Shared Risk Link Group TLV . . . . . . . . . . . . . . 11
     3.5.  IGP Area Information . . . . . . . . . . . . . . . . . . . 11
     3.6.  Inter-AS Links . . . . . . . . . . . . . . . . . . . . . . 12
   4.  Link to Path Aggregation . . . . . . . . . . . . . . . . . . . 12
     4.1.  Example: No Link Aggregation . . . . . . . . . . . . . . . 12
     4.2.  Example: ASBR to ASBR Path Aggregation . . . . . . . . . . 13
     4.3.  Example: Multi-AS Path Aggregation . . . . . . . . . . . . 13
   5.  Originating the TED NLRI . . . . . . . . . . . . . . . . . . . 13
   6.  Receiving the TED NLRI . . . . . . . . . . . . . . . . . . . . 14
   7.  Use Cases  . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     7.1.  MPLS TE  . . . . . . . . . . . . . . . . . . . . . . . . . 14
     7.2.  ALTO Server Network API  . . . . . . . . . . . . . . . . . 15
     7.3.  Path Computation Element (PCE) TED Synchronization
           Protocol . . . . . . . . . . . . . . . . . . . . . . . . . 16
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 17
     11.2. Informative References . . . . . . . . . . . . . . . . . . 18
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
















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1.  Introduction

   Today, the contents of the traffic engineering database usually has
   the scope of an IGP area.  There are several use cases that could
   benefit from knowing the topology or Traffic Engineering (TE) data in
   a remote area or Autonomous System, but today no mechanism exists to
   distribute this information beyond an IGP area.  This draft proposes
   to use BGP as the distribution mechanism for traffic engineering data
   between routers in different IGP areas and/or Autonomous Systems.
   The mechanism can also be used to exchange topology and TE data
   between the network and external network-aware applications, such as
   the Alto Servers.

   The Border Gateway Protocol (BGP [RFC4271]) has grown beyond its
   original intention of disseminating IPv4 Inter-domain routing paths.
   A modern BGP implementation can be viewed as a ubiquitous database
   replication mechanism, which allows replication of many different
   state information types across arbitrary distribution graphs.  Its
   built-in loop protection mechanism (AS path, Cluster List attributes)
   enables building of stable and redundant distribution topologies.  In
   addition to IP routing, applications that use BGP for state
   distribution are L2VPN, VPLS, MAC-VPN, Route-target information, and
   Flowspec for firewalling.  Using BGP as a dissemination protocol for
   Traffic Engineering data is a logical consequence.

   A router maintains a database for storing Traffic Engineering related
   data and link information.  The Traffic Engineering Database (TED) is
   populated by a link-state IGP routing protocol that supports TE
   extensions: IS-IS or OSPF.  The TED can be seen as a protocol-neutral
   representation of links in the area.  Link attributes stored in the
   TED are: local/remote IP addresses, local/remote interface indices,
   metric, link bandwidth, reservable bandwidth, per CoS class
   reservation state, preemption and Shared Risk Link Groups (SRLG).
   The router's BGP process can retrieve the TE data from the TED
   database and distribute it to peer BGP Speakers using the encoding
   specified in this draft.

   A BGP Speaker may distribute the real physical topology from the TED,
   or 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.

   Consumers of the TE data are peer routers in other areas either in
   the router's own AS or in remote ASes, or entities outside the
   network that may need network and/or TE data to optimize their
   behavior.



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2.  Scope

   The scope of TED NLRI are the static attributes / metrics of a path
   between two routers.  The path can be a physical link or multiple
   links aggregated into a path.  Dynamic data, such as dynamic
   bandwidth or delay metrics, is out of scope of this draft.


3.  Transcoding TE Link Information Into a BGP NLRI

   The MP_REACH and MP_UNREACH attributes are BGP's containers for
   carrying opaque information.  Each TED NLRI describes a single link
   anchored by at least a pair of router-IDs.  Since there are many
   Router-IDs formats (32 Bit IPv4 router-ID, 56 Bit ISO Node-ID and 128
   Bit IPv6 router-ID) a link may be anchored by more than one Router-ID
   pair.  The anchoring Router-IDs are carried in the Node Anchor TLVs.

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

   In order for two BGP speakers to exchange TE 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 (multiprotocol BGP), with an
   AFI of TBD and an SAFI of 1 or 128.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Total Link Length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Node Anchors (variable)                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Link Descriptors (variable)                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Link Attributes (variable)                  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 1: TED SAFI 1 NLRI Format










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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Total Link Length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                       Route Distinguisher                     +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Node Anchors (variable)                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Link Descriptors (variable)                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Link Attributes (variable)                  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 2: TED SAFI 128 NLRI Format

   The 'Total Link Length" field contains the cumulative length of all
   the TLVs, describing the Node Anchors, Link descriptors and Link
   Attributes.  For VPN applications it also includes the length of the
   Route Distinguisher.

3.1.  TLV Format

   The Node anchor, Link descriptor and Link attribute fields are
   described using a set of Type/Length/Value triplets.  The format of
   each TLV is shown in Figure 3

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Type             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                         Value (variable)                      |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Figure 3: TLV format

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






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3.2.  Node anchors

   The set of Node Anchor TLVs describes which Protocols Router-IDs will
   be following to "anchor" the link described by the "Link attribute
   TLVs".  There must be at least one "like" router-ID pair per-
   protocol.  If a peer sends an illegal combination in this respect,
   then this is handled as an NLRI error, described in [RFC4760].

               +------+--------------------------+--------+
               | Type | Description              | Length |
               +------+--------------------------+--------+
               |  256 | Local Autonomous System  |      4 |
               |  257 | Local IPv4 Router-ID     |      4 |
               |  258 | Local IPv6 Router-ID     |     16 |
               |  259 | Local ISO Node-ID        |      7 |
               |  260 | Remote Autonomous System |      4 |
               |  261 | Remote IPv4 Router-ID    |      4 |
               |  262 | Remote IPv6 Router-ID    |     16 |
               |  263 | Remote ISO Node-ID       |      7 |
               +------+--------------------------+--------+

                         Table 1: Node Anchor TLVs

   Local IPv4 Router ID:  opaque value (can be an IPv4 address or an 32
      Bit router ID)

   Remote IPv4 Router ID:  opaque value (can be an IPv4 address or 32
      Bit router ID)

   Local IPv6 Router ID:  opaque value (can be an IPv6 address or 128
      Bit router ID)

   Remote IPv6 Router ID:  opaque value (can be an IPv6 address or 128
      Bit router ID)

   Local ISO Node ID:  ISO node-ID (6 octets ISO system-ID plus PSN
      octet)

   Remote ISO Node ID:  ISO node-ID (6 octets ISO system-ID plus PSN
      octet)

   It is desirable that the Router-ID assignments inside the Node anchor
   are globally unique.  However there may be router-ID spaces (e.g.
   ISO) where not even a global registry exists, or worse, Router-IDs
   have been allocated following private-IP RFC 1918 [RFC1918]
   allocation.  In order to disambiguate the Router-IDs the local and
   remote Autonomous System number TLVs of the anchor nodes may be
   included in the NLRI.  The Local and Remote Autonomous System TLVs



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   are 4 octets wide as described in [RFC4893]. 2-octet AS Numbers shall
   be expanded to 4-octet AS Numbers by zeroing the two MSB octets.

3.2.1.  Router-ID Anchoring Example: ISO Pseudonode

   IS-IS Pseudonodes are a good example for the variable Router-ID
   anchoring.  Consider Figure 4.  This represents a Broadcast LAN
   between a pair of routers.  The "real" (=non pseudonode) routers have
   both an IPv4 Router-ID and IS-IS Node-ID.  The pseudonode does not
   have an IPv4 Router-ID.  Two unidirectional links (Node1, Pseudonode
   1) and (Pseudonode 1, Node 2) are being generated.

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

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

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

                        Figure 4: IS-IS Pseudonodes

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

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

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

3.3.  Link Descriptors

   The 'Link Descriptor' field is a set of Type/Length/Value (TLV)
   triplets.  The format of each TLV is shown in Figure 3.  The 'Link
   descriptor' TLVs uniquely identify a link between a pair of anchor
   Routers.

   The encoding of 'Link Descriptor' TLVs, i.e. the Codepoints in



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   'Type', and the 'Length' and 'Value' fields are the same as defined
   in [RFC5305], [RFC5307], and [RFC6119] for sub-TLVs in the Extended
   IS reachability TLV.  The Codepoints are in the IANA Protocol
   Registry for IS-IS, sub-TLV Codepoints for TLV 22, [IANA-ISIS].
   Although the encodings for 'Link Descriptor' TLVs were originally
   defined for IS-IS, the TLVs can carry data sourced either by IS-IS or
   OSPF.

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

     +------+-------------------------------+------------------------+
     | Type | Description                   | Defined in:            |
     +------+-------------------------------+------------------------+
     |   4  | Link Local/Remote Identifiers | [RFC5307], Section 1.1 |
     |   6  | IPv4 interface address        | [RFC5305], Section 3.2 |
     |   8  | IPv4 neighbor address         | [RFC5305], Section 3.3 |
     |  12  | IPv6 interface address        | [RFC6119], Section 4.2 |
     |  13  | IPv6 neighbor address         | [RFC6119], Section 4.3 |
     +------+-------------------------------+------------------------+

                       Table 2: Link Descriptor TLVs

3.4.  Link Attributes

   The 'Link Attributes' field is a set of Type/Length/Value (TLV)
   triplets.  The format of each TLV is shown in Figure 3.

   For Codepoints < 255, the encoding of 'Link Attributes' TLVs, i.e.
   the Codepoints in 'Type', and the 'Length' and 'Value' fields are the
   same as defined in [RFC5305], [RFC5307], and [RFC6119] for sub-TLVs
   in the Extended IS reachability TLV.  The Codepoints are in the IANA
   Protocol Registry for IS-IS, sub-TLV Codepoints for TLV 22,
   [IANA-ISIS].  Although the encodings for 'Link Attributes' TLVs were
   originally defined for IS-IS, the TLVs can carry data sourced either
   by IS-IS or OSPF.

   For Codepoints > 255, the encoding of 'Link Attributes' TLVs is
   described in subsequent sections.

   The following link attribute TLVs are valid in the TED NLRI:











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    +-------+--------------------------------+------------------------+
    |  Type | Description                    | Defined in:            |
    +-------+--------------------------------+------------------------+
    |   3   | Administrative group (color)   | [RFC5305], Section 3.1 |
    |   9   | Maximum link bandwidth         | [RFC5305], Section 3.3 |
    |   10  | Max. reservable link bandwidth | [RFC5305], Section 3.5 |
    |   11  | Unreserved bandwidth           | [RFC5305], Section 3.6 |
    |   20  | Link Protection Type           | [RFC5307], Section 1.2 |
    | 64512 | TE Default Metric              | Section 3.4.1          |
    | 64513 | IGP Link Metric                | Section 3.4.2          |
    | 64514 | Shared Risk Link Group         | Section 3.4.3          |
    +-------+--------------------------------+------------------------+

                       Table 3: Link Attribute TLVs

3.4.1.  TE Default Metric TLV

   The TE Default Metric TLV (Type 64512) carries the TE Default metric
   for this link.  This TLV corresponds to the IS-IS TE Default metric
   sub-TLV (Type 18), defined in RFC5305, Section 3.7 [RFC5305], and the
   OSPF TE Metric sub-TLV (Type 5), defined in RFC3630, Section 2.5.5
   [RFC3630].  If the value in the TE Default metric TLV is derived from
   IS-IS TE Default Metric, then the upper 8 bits of this TLV are set to
   0.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Type             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         TE Default Metric                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 5: TE Default metric TLV format

3.4.2.  IGP Link Metric TLV

   The IGP Metric TLV (Type 64513) carries the IGP metric for this link.
   This attribute is only present if the IGP link metric is different
   from the TE Default Metric (Type 18).  The length of this TLV is 3.
   If the length of the IGP link metric from which the IGP Metric value
   is derived is less than 3 (e.g. for OSPF link metrics or non-wide
   IS-IS metric), then the upper bits of the TLV are set to 0.








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

                   Figure 6: IGP Link Metric TLV format

3.4.3.  Shared Risk Link Group TLV

   The Shared Risk Link Group (SRLG) TLV (Type 64514) 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 7.  The length of this TLV is 4 *
   (number of SRLG values).

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Type             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  Shared Risk Link Group Value                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          ............                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  Shared Risk Link Group Value                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 7: Shared Risk Link Group TLV format

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

3.5.  IGP Area Information

   IGP Area information can be carried in BGP communities.  An
   implementation should support configuration that maps IGP areas to
   BGP communities.






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3.6.  Inter-AS Links

   The main source of TE information is the IGP, which is not active on
   inter-AS links.  In order to inject a non-IGP enabled link into the
   traffic-engineering database (TED) an implementation must support
   configuration of static TE links.


4.  Link to Path Aggregation

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

4.1.  Example: No Link Aggregation

   Consider Figure 8.  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 8: no-link-aggregation






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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 9.  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 9: asbr-link-aggregation

4.3.  Example: Multi-AS Path Aggregation

   Service providers in control of multiple-ASes may even decide to not
   expose their internal inter-AS links.  Consider Figure 10.  Rather
   than exposing all specific R3 to R6 links, AS3 is modeled as a single
   node which connects to the border routers of the aggregated domain.

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

                      Figure 10: multi-as-aggregation


5.  Originating the TED NLRI

   A BGP Speaker must be configured to originate TED NLRIs.  Usually
   export of the TED database into BGP is enabled on ASBRs and ABRs.

   The BGP Speaker shall throttle the rate of TED NLRI updates.  An
   implementation shall provide a configuration attribute for the



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   interval between updates.  The minimum interval between updates is 30
   seconds.


6.  Receiving the TED NLRI

   This section describes the processing of TED NLRIs at the receiving
   BGP Speaker.

   TE attributes for a link received from an IGP have higher priority
   than TED NLRIs received via BGP.  Multiple BGP Speakers may advertise
   the same TED NLRI; the receiving BGP Speaker can individually choose
   the source BGP Speaker for each NLRI.

   The AS_PATH attribute is used both for loop detection and for NLRI
   selection: the TED NLRI with shorter AS_PATH length is preferred.
   The Community and Extended Community path attributes are stored in
   the RIB and may be used in operator-defined policies.  Communities
   can also be used to encode the IGP Area information.  All other path
   attributes are ignored.


7.  Use Cases

7.1.  MPLS TE

   If a router wants to compute a MPLS TE path across IGP areas TED
   lacks visibility of the complete topology.  This is an issue for
   large scale networks that need to segment their core networks into
   distinct areas because inter-area TE cannot get deployed there.
   Current solutions for inter area TE only compute the path for the
   first area.  The router only has full topological visibility for the
   first area along the path, but not for subsequent areas.  The best
   practice is to use a technique called "loose-hop-expansion" which
   uses the IGP computed shortest path topology for the remainder of the
   path.  Therefore no non-SPF based path setup is possible across
   areas.  This has disadvantages for path protection and path
   engineering applications, as shown in Figure 11.













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   ...............................  ...................................
   :          Area 51            :  :             Area 0              :
   :             +--------+     +--------+     +--------+             :
   :   ************************************************************   :
   :   * +-------|   R1   |-----|  ABR1  |-----|   R3   |-------+ *   :
   :   * | ########       |     |      # |     |        |       | *   :
   :   * | #     +--------+     +----|-#-+     +--------+       | *   :
   : +-*-|-#-+                   :  :| #                    +---|-*-+ :
   : | *   # |                   :  :| #                    |     * | :
   : |   S # |                   :  :| #                    |   D   | :
   : |     # |                   :  :| #                    |       | :
   : +---|-#-+                   :  :| #                    +---|---+ :
   :     | #     +--------+     +----|-#-+     +--------+       |     :
   :     | ############################# |     |        |       |     :
   :     +-------|   R2   |-----|  ABR2  |-----|   R4   |-------+     :
   :             |        |     |        |     |        |             :
   :             +--------+     +--------+     +--------+             :
   :                             :  :                                 :
   :.............................:  :.................................:

                                ......
      ****  Primary LSP         :    : Area Boundary
      ####  Bypass LSP          :....:

                   Figure 11: MPLS TE Bypass LSP problem

   Router S sets up an RSVP LSP from S to D. Although it has only
   visibility into Area 51, the LSP setup ultimately succeeds, as
   shortest path first routing from ABR1 onwards routes the RSVP message
   towards destination D. What does not work is to setup a Link
   Protection bypass LSP protection for the R1 to ABR1 link as shown in
   the figure.  The problem is that the TE database at Router R1 does
   not have path visibility of the link between ABR1 and ABR2, such that
   it can compute the Link Bypass LSP.

7.2.  ALTO Server Network API

   An ALTO Server 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: the network map that specifies allocation of prefixes to PIDs,
   and the cost map that specifies the cost between the PIDs.  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



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   prefix and TE data are required: prefix data is required to generate
   the network maps, TE (topology) data is required to generate the cost
   maps.  Prefix data is carried and originated in BGP, TE data is
   originated and carried in an IGP.  Without BGP TE NLRI the ALTO
   Server would have to peer with both BGP Speakers and IGP in multiple
   areas and/or ASes to obtain all the necessary network topology data.
   The BGP TE NLRI allows for a single interface between the network and
   the ALTO Server.

7.3.  Path Computation Element (PCE) TED Synchronization Protocol

   RFC4655, Section 5.2, Figure 2 [RFC4655] describes a Path Computation
   Element (PCE) which synchronizes its traffic engineering database
   (TED) by use of a routing protocol.  This memo describes the first
   standardized protocol for PCE to learn about inter-AS or inter-area
   TE information.


8.  IANA Considerations

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

   This document requests creation of a new registry for node anchor,
   link descriptor and link attribute TLVs.  The range of Codepoints in
   the registry is 0-65535.  Values 0-255 will shadow Codepoints of the
   IANA Protocol Registry for IS-IS, sub-TLV Codepoints for TLV 22.
   Values 256-65535 will be used for Codepoints that are specific to the
   BGP TE NLRI.  The registry will be initialized as shown in Table 2
   and Table 3.  Allocations within the registry will require
   documentation of the proposed use of the allocated value and approval
   by the Designated Expert assigned by the IESG (see [RFC5226]).

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


9.  Security Considerations

   This draft does not affect the BGP security model.


10.  Acknowledgements

   We would like to thank Alia Atlas, David Ward, John Scudder, Kaliraj
   Vairavakkalai, Nischal Sheth and Yakov Rekhter from Juniper Networks,
   Inc. and Richard Woundy from Comcast for their invaluable input and
   comments.



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11.  References

11.1.  Normative References

   [IANA-ISIS]
              "IS-IS TLV Codepoint, Sub-TLVs for TLV 22", <http://
              www.iana.org/assignments/isis-tlv-codepoints/
              isis-tlv-codepoints.xml#isis-tlv-codepoints-3>.

   [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.

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              September 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.

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

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

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

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

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

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




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

11.2.  Informative References

   [I-D.ietf-alto-protocol]
              Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
              draft-ietf-alto-protocol-06 (work in progress),
              October 2010.


Authors' Addresses

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

   Email: hannes@juniper.net


   Jan Medved
   Juniper Networks, Inc.
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089
   US

   Email: jmedved@juniper.net






















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