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Versions: (draft-chen-ccamp-isis-interas-te-extension) 00 01 02 03 04 RFC 5316

Network working group                                           M. Chen
Internet Draft                                             Renhai Zhang
Category: Standards Track                   Huawei Technologies Co.,Ltd
Created: August 25, 2008                                  Xiaodong Duan
Expires: February 25, 2009                                 China Mobile


    ISIS Extensions in Support of Inter-AS Multiprotocol Label Switching
          (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering

             draft-ietf-ccamp-isis-interas-te-extension-03.txt


Status of this Memo

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   This Internet-Draft will expire on January 25, 2009.

Abstract

   This document describes extensions to the ISIS (ISIS) protocol to
   support Multiprotocol Label Switching (MPLS) and Generalized MPLS
   (GMPLS) Traffic Engineering (TE) for multiple Autonomous Systems
   (ASes). It defines ISIS-TE extensions for the flooding of TE
   information about inter-AS links which can be used to perform inter-
   AS TE path computation.




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   No support for flooding information from within one AS to another AS
   is proposed or defined in this document.

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [RFC2119].

Table of Contents


   1. Introduction.................................................2
   2. Problem Statement............................................3
      2.1. A Note on Non-Objectives................................4
      2.2. Per-Domain Path Determination...........................4
      2.3. Backward Recursive Path Computation.....................6
   3. Extensions to ISIS-TE........................................7
      3.1. Inter-AS Reachability TLV...............................8
      3.2. TE Router ID............................................9
      3.3. Sub-TLV Detail.........................................10
         3.3.1. Remote AS Number Sub-TLV..........................10
         3.3.2. IPv4 Remote ASBR ID Sub-TLV.......................11
         3.3.3. IPv6 Remote ASBR ID Sub-TLV.......................11
         3.3.4. IPv4 TE Router ID sub-TLV.........................12
         3.3.5. IPv6 TE Router ID sub-TLV.........................13
   4. Procedure for Inter-AS TE Links.............................13
      4.1. Origin of Proxied TE Information.......................15
   5. Security Considerations.....................................15
   6. IANA Considerations.........................................16
      6.1. Inter-AS Reachability TLV..............................16
      6.2. Sub-TLVs for the Inter-AS Reachability TLV.............16
      6.3. Sub-TLVs for the IS-IS Router Capability TLV...........17
   7. Acknowledgments.............................................17
   8. References..................................................17
      8.1. Normative References...................................17
      8.2. Informative References.................................18
   Authors' Addresses.............................................19
   Intellectual Property Statement................................19
   Disclaimer of Validity.........................................20
   Copyright Statement............................................20

1. Introduction

   [ISIS-TE] defines extensions to the ISIS protocol [ISIS] to support
   intra-area Traffic Engineering (TE). The extensions provide a way of



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   encoding the TE information for TE-enabled links within the network
   (TE links) and flooding this information within an area. The
   Extended IS Reachability TLV and Traffic Engineering Router ID TLV,
   which are defined in [ISIS-TE], are used to carry such TE
   information. The Extended IS Reachability TLV has several nested
   sub-TLVs which describe the TE attributes for a TE link.

   [ISIS-TE-V3] and [GMPLS-TE] define similar extensions to ISIS [ISIS]
   in support of IPv6 and GMPLS traffic engineering respectively.

   Requirements for establishing Multiprotocol Label Switching (MPLS)
   TE Label Switched Paths (LSPs) that cross multiple Autonomous
   Systems (ASes) are described in [INTER-AS-TE-REQ]. As described in
   [INTER-AS-TE-REQ], a method SHOULD provide the ability to compute a
   path spanning multiple ASes. So a path computation entity that may
   be the head-end Label Switching Router (LSR), an AS Border Router
   (ASBR), or a Path Computation Element (PCE [PCE]) needs to know the
   TE information not only of the links within an AS, but also of the
   links that connect to other ASes.

   In this document, a new TLV, which is referred to as the Inter-AS
   Reachability TLV, is defined to advertise inter-AS TE information,
   three new sub-TLVs are defined for inclusion in the Inter-AS
   Reachability TLV to carry the information about the remote AS number
   and remote ASBR ID. The sub-TLVs defined in [ISIS-TE], [ISIS-TE-V3]
   and other documents for inclusion in the Extended IS Reachability
   TLV for describing the TE properties of a TE link are applicable to
   be included in the Inter-AS Reachability TLV for describing the TE
   properties of an inter-AS TE link as well. And two more new sub-TLVs
   are defined for inclusion in the IS-IS Router Capability TLV to
   carry the TE Router ID when TE Router ID needs to reach all routers
   within an entire ISIS routing domain. The extensions are equally
   applicable to IPv4 and IPv6 as identical extensions to [ISIS-TE] and
   [ISIS-TE-V3]. The detailed definitions and procedures are discussed
   in the following sections.

   This document does not propose or define any mechanisms to advertise
   any other extra-AS TE information within ISIS. See Section 2.1 for a
   full list of non-objectives for this work.

2. Problem Statement

   As described in [INTER-AS-TE-REQ], in the case of establishing an
   inter-AS TE LSP traversing multiple ASes, the Path message [RFC3209]
   may include the following elements in the Explicit Route Object (ERO)
   in order to describe the path of the LSP:



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     - a set of AS numbers as loose hops; and/or

     - a set of LSRs including ASBRs as loose hops.

   Two methods for determining inter-AS paths are currently being
   discussed. The per-domain method [PD-PATH] determines the path one
   domain at a time. The backward recursive method [BRPC] uses
   cooperation between PCEs to determine an optimum inter-domain path.
   The sections that follow examine how inter-AS TE link information
   could be useful in both cases.

2.1. A Note on Non-Objectives

   It is important to note that this document does not make any change
   to the confidentiality and scaling assumptions surrounding the use
   of ASes in the Internet. In particular, this document is conformant
   to the requirements set out in [INTER-AS-TE-REQ].

   The following features are explicitly excluded:

     o There is no attempt to distribute TE information from within one
        AS to another AS.

     o There is no mechanism proposed to distribute any form of TE
        reachability information for destinations outside the AS.

     o There is no proposed change to the PCE architecture or usage.

     o TE aggregation is not supported or recommended.

     o There is no exchange of private information between ASes.

     o No ISIS adjacencies are formed on the inter-AS link.

2.2. Per-Domain Path Determination

   In the per-domain method of determining an inter-AS path for an
   MPLS-TE LSP, when an LSR that is an entry-point to an AS receives a
   Path message from an upstream AS with an ERO containing a next hop
   that is an AS number, it needs to find which LSRs (ASBRs) within the
   local AS are connected to the downstream AS so that it can compute a
   TE LSP segment across the local AS to one of those LSRs and forward
   the Path message to it and hence into the next AS. See Figure 1 for
   an example:





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                R1------R3----R5-----R7------R9-----R11
                        |     | \    |      / |
                        |     |  \   |  ----  |
                        |     |   \  | /      |
                R2------R4----R6   --R8------R10----R12
                           :              :
                <-- AS1 -->:<---- AS2 --->:<--- AS3 --->

                  Figure 1: Inter-AS Reference Model

   The figure shows three ASes (AS1, AS2, and AS3) and twelve LSRs (R1
   through R12). R3 and R4 are ASBRs in AS1. R5, R6, R7, and R8 are
   ASBRs in AS2. R9 and R10 are ASBRs in AS3.

   If an inter-AS TE LSP is planned to be established from R1 to R12,
   the AS sequence will be: AS1, AS2, AS3.

   Suppose that the Path message enters AS2 from R3. The next hop in
   the ERO shows AS3, and R5 must determine a path segment across AS2
   to reach AS3. It has a choice of three exit points from AS2 (R6, R7,
   and R8) and it needs to know which of these provide TE connectivity
   to AS3, and whether the TE connectivity (for example, available
   bandwidth) is adequate for the requested LSP.

   Alternatively, if the next hop in the ERO is the entry ASBR for AS3
   (say R9), R5 needs to know which of its exit ASBRs has a TE link
   that connects to R9. Since there may be multiple ASBRs that are
   connected to R9 (both R7 and R8 in this example), R5 also needs to
   know the TE properties of the inter-AS TE links so that it can
   select the correct exit ASBR.

   Once the path message reaches the exit ASBR, any choice of inter-AS
   TE link can be made by the ASBR if not already made by entry ASBR
   that computed the segment.

   More details can be found in the Section 4. of [PD-PATH], which
   clearly points out why advertising of inter-AS links is desired.

   To enable R5 to make the correct choice of exit ASBR the following
   information is needed:

     o List of all inter-AS TE links for the local AS.

     o TE properties of each inter-AS TE link.





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     o AS number of the neighboring AS connected to by each inter-AS TE
        link.

     o Identity (TE Router ID) of the neighboring ASBR connected to by
        each inter-AS TE link.

   In GMPLS networks further information may also be required to select
   the correct TE links as defined in [GMPLS-TE].

   The example above shows how this information is needed at the entry
   point ASBRs for each AS (or the PCEs that provide computation
   services for the ASBRs), but this information is also needed
   throughout the local AS if path computation function is fully
   distributed among LSRs in the local AS, for example to support LSPs
   that have start points (ingress nodes) within the AS.

2.3. Backward Recursive Path Computation

   Another scenario using PCE techniques has the same problem. [BRPC]
   defines a PCE-based TE LSP computation method (called Backward
   Recursive Path Computation) to compute optimal inter-domain
   constrained MPLS-TE or GMPLS LSPs. In this path computation method,
   a specific set of traversed domains (ASes) are assumed to be
   selected before computation starts. Each downstream PCE in domain(i)
   returns to its upstream neighbor PCE in domain(i-1) a multipoint-to-
   point tree of potential paths. Each tree consists of the set of
   paths from all Boundary Nodes located in domain(i) to the
   destination where each path satisfies the set of required
   constraints for the TE LSP (bandwidth, affinities, etc.).

   So a PCE needs to select Boundary Nodes (that is, ASBRs) that
   provide connectivity from the upstream AS. In order that the tree of
   paths provided by one PCE to its neighbor can be correlated, the
   identities of the ASBRs for each path need to be referenced, so the
   PCE must know the identities of the ASBRs in the remote AS reached
   by any inter-AS TE link, and, in order that it provides only
   suitable paths in the tree, the PCE must know the TE properties of
   the inter-AS TE links. See the following figure as an example:










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                   PCE1<------>PCE2<-------->PCE3
                   /       :             :
                  /        :             :
                R1------R3----R5-----R7------R9-----R11
                        |     | \    |      / |
                        |     |  \   |  ----  |
                        |     |   \  | /      |
                R2------R4----R6   --R8------R10----R12
                           :              :
                <-- AS1 -->:<---- AS2 --->:<--- AS3 --->

            Figure 2: BRPC for Inter-AS Reference Model

   The figure shows three ASes (AS1, AS2, and AS3), three PCEs (PCE1,
   PCE2, and PCE3), and twelve LSRs (R1 through R12). R3 and R4 are
   ASBRs in AS1. R5, R6, R7, and R8 are ASBRs in AS2. R9 and R10 are
   ASBRs in AS3. PCE1, PCE2, and PCE3 cooperate to perform inter-AS
   path computation and are responsible for path segment computation
   within their own domain(s).

   If an inter-AS TE LSP is planned to be established from R1 to R12,
   the traversed domains are assumed to be selected: AS1->AS2->AS3, and
   the PCE chain is: PCE1->PCE2->PCE3. First, the path computation
   request originated from the PCC (R1) is relayed by PCE1 and PCE2
   along the PCE chain to PCE3, then PCE3 begins to compute the path
   segments from the entry boundary nodes that provide connection from
   AS2 to the destination (R12). But, to provide suitable path segments,
   PCE3 must determine which entry boundary nodes provide connectivity
   to its upstream neighbor AS (identified by its AS number), and must
   know the TE properties of the inter-AS TE links. In the same way,
   PCE2 also needs to determine the entry boundary nodes according to
   its upstream neighbor AS and the inter-AS TE link capabilities.

   Thus, to support Backward Recursive Path Computation the same
   information listed in Section 2.2 is required. The AS number of the
   neighboring AS connected to by each inter-AS TE link is particularly
   important.

3. Extensions to ISIS-TE

   Note that this document does not define mechanisms for distribution
   of TE information from one AS to another, does not distribute any
   form of TE reachability information for destinations outside the AS,
   does not change the PCE architecture or usage, does not suggest or
   recommend any form of TE aggregation, and does not feed private
   information between ASes. See Section 2.1.



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   In this document, for the advertisement of inter-AS TE links, a new
   TLV, which is referred to as the Inter-AS Reachability TLV, is
   defined and three new sub-TLVs are defined for inclusion in the
   Inter-AS Reachability TLV to carry the information about the
   neighboring AS number and the remote ASBR ID of an inter-AS link.
   The sub-TLVs defined in [ISIS-TE], [ISIS-TE-V3] and other documents
   for inclusion in the Extended IS Reachability TLV are applicable to
   be included in the Inter-AS Reachability TLV for inter-AS TE links
   advertisement. And another two new sub-TLVs are defined for
   inclusion in the IS-IS Router Capability TLV to carry the TE Router
   ID when the TE Router ID is needed to reach all routers within an
   entire ISIS routing domain.

   While some of the TE information of an inter-AS TE link may be
   available within the AS from other protocols, in order to avoid any
   dependency on where such protocols are processed, this mechanism
   carries all the information needed for the required TE operations.

3.1. Inter-AS Reachability TLV

   The Inter-AS Reachability TLV has type 141 (which needs to be
   confirmed by IANA see Section 6.1), it contains a data structure
   consisting of:

      4 octets of Router ID
      3 octets of default metric
      1 octet of control information, consisting of:
         1 bit of flooding-scope information (S bit)
         1 bit of up/down information (D bit)
         6 bits reserved
      1 octet of length of sub-TLVs
      0-246 octets of sub-TLVs
         where each sub-TLV consists of a sequence of:
           1 octet of sub-type
           1 octet of length of the value field of the sub-TLV
           0-244 octets of value

   Compare to the Extended Reachability TLV which is defined in [ISIS-
   TE], the Inter-AS Reachability TLV replaces the "7 octets of System
   ID and Pseudonode Number" field with a "4 octets of Router ID" field
   and introduces an extra "control information" field which is
   consisted of a flooding-scope bit (S bit), a up/down bit (D bit) and
   6 reserved bits.

   The Router ID field of the Inter-AS Reachability TLV is four octets
   in length, which contains the Router ID of the router who generates



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   the Inter-AS Reachability TLV. The Router ID MUST be unique within
   the ISIS area. If the router generates Inter-AS Reachability TLV
   with entire ISIS routing domain flooding scope, then the Router ID
   MUST also be unique within the entire ISIS routing domain. The
   Router ID could be used to indicate the source of the Inter-AS
   Reachability TLV.

   The flooding procedures for Inter-AS Reachability TLV are identical
   to the flooding procedures for the GNINFO TLV which are defined in
   the Section 4 of [GENINFO]. These procedures have been previously
   discussed in [ISIS-CAP]. The flooding-scope bit (S bit) SHOULD be
   set to 0 if the flooding scope is to be limited to within the single
   IGP area to which the ASBR belongs, or MAY be set to 1 if the
   information is intended to reach all routers (including area border
   routers, ASBRs, and PCEs) in the entire ISIS routing domain. The
   choice between the use of 0 or 1 is an AS-wide policy choice, and
   configuration control SHOULD be provided in ASBR implementations
   that supports the advertisement of inter-AS TE links.

   The sub-TLVs which are defined in [ISIS-TE], [ISIS-TE-V3] and other
   documents for describing the TE properties of an TE link are also
   applicable to be carried in the Inter-AS Reachability TLV to
   describe the TE properties of an Inter-AS TE link. Apart from these
   sub-TLVs, three new sub-TLVs are defined for inclusion in the Inter-
   AS Reachability TLV in this document:

   Sub-TLV type   Length  Name
   ------------    ------  ---------------------------
             23        4   Remote AS number
             24        4   IPv4 Remote ASBR Identifier
             25       16   IPv6 Remote ASBR Identifier

   The detailed definitions of the three new sub-TLVs are described in
   Section 3.3.

3.2. TE Router ID

   The IPv4 TE Router ID TLV (type 134) and IPv6 TE Router ID TLV (type
   140), which are defined in [ISIS-TE] and [ISIS-TE-V3] respectively,
   only have area flooding-scope, when performing inter-AS TE, the TE
   Router ID MAY be needed to reach all routers within an entire ISIS
   routing domain, and it MUST have the same flooding scope as the
   Inter-AS Reachability TLV does.

   [ISIS-CAP] defines a generic advertisement mechanism for ISIS which
   allows a router to advertise its capabilities within an ISIS area or



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   an entire ISIS routing domain. And [ISIS-CAP] also points out that
   TE Router ID is candidate to be carried in the IS-IS Router
   Capability TLV when performing inter-area TE.

   This document uses such mechanism for TE Router ID advertisement
   when the TE Router ID is needed to reach all routers within an
   entire ISIS Routing domain. Two new sub-TLVs are defined for
   inclusion in the IS-IS Router Capability TLV to carry the IPv4 and
   IPv6 TE Router ID respectively:

   Sub-TLV type   Length  Name
   ------------    ------  -----------------
             11        4   IPv4 TE Router ID
             12       16   IPv6 TE Router ID


   The Detailed definitions of the two new sub-TLVs are described in
   Section 3.3.

3.3. Sub-TLV Detail

3.3.1. Remote AS Number Sub-TLV

   A new sub-TLV, the Remote AS Number sub-TLV is defined for inclusion
   in the Inter-AS Reachability TLV when advertising inter-AS links.
   The Remote AS Number sub-TLV specifies the AS number of the
   neighboring AS to which the advertised link connects.

   The Remote AS number sub-TLV is TLV type 23 (which needs to be
   confirmed by IANA see Section 6.2), and is four octets in length.
   The format 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            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Remote AS Number                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Remote AS number field has 4 octets. When only two octets are
   used for the AS number, as in current deployments, the left (high-
   order) two octets MUST be set to zero. The Remote AS Number Sub-TLV
   MUST be included when a router advertises an inter-AS TE link.





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3.3.2. IPv4 Remote ASBR ID Sub-TLV

   A new sub-TLV, which is referred to as the IPv4 Remote ASBR ID sub-
   TLV, is defined for inclusion in the Inter-AS Reachability TLV when
   advertising inter-AS links. The IPv4 Remote ASBR ID sub-TLV
   specifies the IPv4 identifier of the remote ASBR to which the
   advertised inter-AS link connects. This could be any stable and
   routable IPv4 address of the remote ASBR. Use of the TE Router ID as
   specified in the Traffic Engineering Router ID TLV [ISIS-TE] is
   RECOMMENDED.

   The IPv4 Remote ASBR ID sub-TLV is TLV type 24 (which needs to be
   confirmed by IANA see Section 6.2), and is four octets in length.
   The format of the IPv4 Remote ASBR ID sub-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            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Remote ASBR ID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The IPv4 Remote ASBR ID sub-TLV MUST be included if the neighboring
   ASBR has an IPv4 address. If the neighboring ASBR does not have an
   IPv4 address (not even an IPv4 TE Router ID), the IPv6 Remote ASBR
   ID sub-TLV MUST be included instead. An IPv4 Remote ASBR ID sub-TLV
   and IPv6 Remote ASBR ID sub-TLV MAY both be present in an Extended
   IS Reachability TLV.

3.3.3. IPv6 Remote ASBR ID Sub-TLV

   A new sub-TLV, which is referred to as the IPv6 Remote ASBR ID sub-
   TLV, is defined for inclusion in the Inter-AS Reachability TLV when
   advertising inter-AS links. The IPv6 Remote ASBR ID sub-TLV
   specifies the IPv6 identifier of the remote ASBR to which the
   advertised inter-AS link connects. This could be any stable and
   routable IPv6 address of the remote ASBR. Use of the TE Router ID as
   specified in the IPv6 Traffic Engineering Router ID TLV [ISIS-TE-V3]
   is RECOMMENDED.

   The IPv6 Remote ASBR ID sub-TLV is TLV type 25 (which needs to be
   confirmed by IANA see Section 6.2), and is sixteen octets in length.
   The format of the IPv6 Remote ASBR ID sub-TLV is as follows:





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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Remote ASBR ID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Remote ASBR ID (continued)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Remote ASBR ID (continued)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Remote ASBR ID (continued)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The IPv6 Remote ASBR ID sub-TLV MUST be included if the neighboring
   ASBR has an IPv6 address. If the neighboring ASBR does not have an
   IPv6 address, the IPv4 Remote ASBR ID sub-TLV MUST be included
   instead. An IPv4 Remote ASBR ID sub-TLV and IPv6 Remote ASBR ID sub-
   TLV MAY both be present in an Extended IS Reachability TLV.

3.3.4. IPv4 TE Router ID sub-TLV

   The IPv4 TE Router ID sub-TLV is TLV type 11 (which needs to be
   confirmed by IANA see Section 6.3), and is four octets in length.
   The format of the IPv4 TE Router ID sub-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            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       TE Router ID                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   When the TE Router ID is needed to reach all routers within an
   entire ISIS routing domain, the IS-IS Router Capability TLV MUST be
   included in its LSP. And if an ASBR supports Traffic Engineering for
   IPv4, the IPv4 TE Router ID sub-TLV MUST be included if the ASBR has
   an IPv4 TE Router ID. If the ASBR does not have an IPv4 TE Router ID,
   the IPv6 TE Router sub-TLV MUST be included instead. An IPv4 TE
   Router ID sub-TLV and IPv6 TE Router ID sub-TLV MAY both be present
   in an IS-IS Router Capability TLV.







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3.3.5. IPv6 TE Router ID sub-TLV

   The IPv6 TE Router ID sub-TLV is TLV type 12 (which needs to be
   confirmed by IANA see Section 6.3), and is four octets in length.
   The format of the IPv6 TE Router ID sub-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            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       TE Router ID                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       TE Router ID   (continued)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       TE Router ID   (continued)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       TE Router ID   (continued)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   When the TE Router ID is needed to reach all routers within an
   entire ISIS routing domain, the IS-IS Router Capability TLV MUST be
   included in its LSP. And if an ASBR supports Traffic Engineering for
   IPv6, the IPv6 TE Router ID sub-TLV MUST be included if the ASBR has
   an IPv6 TE Router ID. If the ASBR does not have an IPv6 TE Router ID,
   the IPv4 TE Router sub-TLV MUST be included instead. An IPv4 TE
   Router ID sub-TLV and IPv6 TE Router ID sub-TLV MAY both be present
   in an IS-IS Router Capability TLV.

4. Procedure for Inter-AS TE Links

   When TE is enabled on an inter-AS link and the link is up, the ASBR
   SHOULD advertise this link using the normal procedures for ISIS-TE
   [ISIS-TE]. When either the link is down or TE is disabled on the
   link, the ASBR SHOULD withdraw the advertisement. When there are
   changes to the TE parameters for the link (for example, when the
   available bandwidth changes) the ASBR SHOULD re-advertise the link,
   but the ASBR MUST take precautions against excessive re-
   advertisements.

   Hellos MUST NOT be exchanged over the inter-AS link, and
   consequently, an ISIS adjacency MUST NOT be formed.

   The information advertised comes from the ASBR's knowledge of the TE
   capabilities of the link, the ASBR's knowledge of the current status




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   and usage of the link, and configuration at the ASBR of the remote
   AS number and remote ASBR TE Router ID.

   Legacy routers receiving an advertisement for an inter-AS TE link
   are able to ignore it because they do not know the new TLV and sub-
   TLVs that are defined in Section 3 in this document. They will
   continue to flood the LSP, but will not attempt to use the
   information received.

   In the current operation of ISIS TE the LSRs at each end of a TE
   link emit LSAs describing the link. The databases in the LSRs then
   have two entries (one locally generated, the other from the peer)
   that describe the different 'directions' of the link.  This enables
   CSPF to do a two-way check on the link when performing path
   computation and eliminate it from consideration unless both
   directions of the link satisfy the required constraints.

   In the case we are considering here (i.e., of a TE link to another
   AS) there is, by definition, no IGP peering and hence no bi-
   directional TE link information. In order for the CSPF route
   computation entity to include the link as a candidate path, we have
   to find a way to get LSAs describing its (bidirectional) TE
   properties into the TE database.

   This is achieved by the ASBR advertising, internally to its AS,
   information about both directions of the TE link to the next AS. The
   ASBR will normally generate a LSA describing its own side of a link;
   here we have it 'proxy' for the ASBR at the edge of the other AS and
   generate an additional LSA that describes that devices 'view' of the
   link.

   Only some essential TE information for the link needs to be
   advertised; i.e., the Interface Address, the Remote AS number and
   the Remote ASBR ID of an inter-AS TE link.

   Routers or PCEs that are capable of processing advertisements of
   inter-AS TE links SHOULD NOT use such links to compute paths that
   exit an AS to a remote ASBR and then immediately re-enter the AS
   through another TE link. Such paths would constitute extremely rare
   occurrences and SHOULD NOT be allowed except as the result of
   specific policy configurations at the router or PCE computing the
   path.







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4.1. Origin of Proxied TE Information

   Section 4 describes how to an ASBR advertises TE link information as
   a proxy for its neighbor ASBR, but does not describe where this
   information comes from.

   Although the source of this information is outside the scope of this
   document, it is possible that it will be a configuration requirement
   at the ASBR, as are other, local, properties of the TE link. Further,
   where BGP is used to exchange IP routing information between the
   ASBRs, a certain amount of additional local configuration about the
   link and the remote ASBR is likely to be available.

   We note further that it is possible, and may be operationally
   advantageous, to obtain some of the required configuration
   information from BGP. Whether and how to utilize these possibilities
   is an implementation matter.

5. Security Considerations

   The protocol extensions defined in this document are relatively
   minor and can be secured within the AS in which they are used by the
   existing ISIS security mechanisms.

   There is no exchange of information between ASes, and no change to
   the ISIS security relationship between the ASes. In particular,
   since no ISIS adjacency is formed on the inter-AS links, there is no
   requirement for ISIS security between the ASes.

   Some of the information included in these new advertisements (e.g.,
   the remote AS number and the remote ASBR ID) is obtained manually
   from a neighboring administration as part of commercial relationship.
   The source and content of this information should be carefully
   checked before it is entered as configuration information at the
   ASBR responsible for advertising the inter-AS TE links.

   It is worth noting that in the scenario we are considering a Border
   Gateway Protocol (BGP) peering may exist between the two ASBRs and
   this could be used to detect inconsistencies in configuration (e.g.,
   the administration that originally supplied the information may be
   lying, or some manual mis-configurations or mistakes are made by the
   operators). For example, if a different remote AS number is received
   in a BGP OPEN [BGP] from that locally configured into ISIS-TE, as we
   describe here, then local policy SHOULD be applied to determine
   whether to alert the operator to a potential mis-configuration or to
   suppress the ISIS advertisement of the inter-AS TE link. Note,



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   further, that if BGP is used to exchange TE information as described
   in Section 4.1, the inter-AS BGP session SHOULD be secured using
   mechanisms as described in [BGP] to provide authentication and
   integrity checks.

6. IANA Considerations

   IANA is requested to make the following allocations from registries
   under its control.

6.1. Inter-AS Reachability TLV

   This document defines the following new ISIS TLV type, described in
   Section 3.4, that needs to be registered in the ISIS TLV code-point
   registry:

              Type        Description              IIH   LSP   SNP
              ----        ----------------------   ---   ---   ---
               141        Inter-AS reachability     n     y     n
                                information


6.2. Sub-TLVs for the Inter-AS Reachability TLV

   This document defines the following new sub-TLV types, described in
   Sections 3.3.1, 3.3.2 and 3.3.3, of top-level TLV 141 (see section
   6.1 above) that need to be registered in the ISIS sub-TLV registry
   for TLV 141, note that these three new sub-TLVs SHOULD NOT appear in
   TLV 22 (or TLV 222) and MUST be ignored in TLV 22 (or TLV 222):

      Type        Description                        Length
      ----        ------------------------------   --------
        23        Remote AS number                        4
        24        IPv4 Remote ASBR Identifier             4
        25        IPv6 Remote ASBR Identifier            16

   As described above in Section 3.1, the sub-TLVs which are defined in
   [ISIS-TE], [ISIS-TE-V3] and other documents for describing the TE
   properties of an TE link are applicable to describe an inter-AS TE
   link and MAY be included in the Inter-AS Reachability TLV when
   adverting inter-AS TE links. So, these sub-TLVs need to be
   registered in the ISIS sub-TLV registry for TLV 141. And in order to
   simplify the registration, we suggest using the same registry value
   as they are registered in the ISIS sub-TLV registry for TLV 22.





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      Type        Description
      ----        ------------------------------
         3        Administrative group (color)       [ISIS-TE]
         4        Link Local/Remote Identifiers      [GMPLS-TE]
         6        IPv4 interface address             [ISIS-TE]
         9        Maximum link bandwidth             [ISIS-TE]
        10        Reservable link bandwidth          [ISIS-TE]
        11        Unreserved bandwidth               [ISIS-TE]
        12        IPv6 Interface Address             [ISIS-TE-V3]
        18        TE Default metric                  [ISIS-TE]
        19        Link-attributes                    [RFC5029]
        20        Link Protection Type               [GMPLS-TE]
        21        Interface Switching Capability Descriptor [GMPLS-TE]
        22        Bandwidth Constraints              [RFC4124]

   Because sub-TLVs defined for TLV 22 can be advertised in the Inter-
   AS Reachability TLV, the new sub-TLVs defined in this document
   SHOULD NOT conflict with existing and/or future sub-TLV definitions
   for TLV 22. Therefore the new sub-TLVs MUST be defined from a sub-
   TLV registry which is shared by these two TLVs.

6.3. Sub-TLVs for the IS-IS Router Capability TLV

   This document defines the following new sub-TLV types, described in
   Sections 3.3.4 and 3.3.5, of top-level TLV 242 (which is defined in
   [ISIS-CAP]) that need to be registered in the ISIS sub-TLV registry
   for TLV 242:

      Type        Description                        Length
      ----        ------------------------------   --------
        11        IPv4 TE Router ID                       4
        12        IPv6 TE Router ID                      16


7. Acknowledgments

   The authors would like to thank Adrian Farrel, Jean-Louis Le Roux,
   Christian Hopps, and Les Ginsberg for their review and comments on
   this document.

8. References

8.1. Normative References

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



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   [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.

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

   [ISIS-CAP] Vasseur, J.P. et al., "IS-IS extensions for advertising
             router information", RFC 4971, July 2007.

8.2. Informative References

   [INTER-AS-TE-REQ] Zhang and Vasseur, "MPLS Inter-AS Traffic
             Engineering Requirements", RFC4216, November 2005.

   [PD-PATH] Ayyangar, A., Vasseur, JP., and Zhang, R., "A Per-domain
             path computation method for establishing Inter-domain",
             RFC 5152, February 2008.

   [BRPC] JP. Vasseur, Ed., R. Zhang, N. Bitar, JL. Le Roux, "A
             Backward Recursive PCE-based Computation (BRPC) procedure
             to compute shortest inter-domain Traffic Engineering Label
             Switched Paths", draft-ietf-pce-brpc, (work in progress)

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

   [ISIS-TE] Smit, H. and T. Li, "Intermediate System to Intermediate
             System (IS-IS) Extensions for Traffic Engineering (TE)",
             RFC 3784, June 2004.

   [ISIS-TE-V3] Harrison, J., Berger, J., and Bartlett, M., "IPv6
             Traffic Engineering in IS-IS", draft-ietf-isis-ipv6-te,
             {work in progress}.

   [GMPLS-TE] K.Kompella and Y.Rekhter, "IS-IS Extensions in Support of
             Generalized Multi-Protocol Label Switching", RFC 4205,
             October 2005.

   [BGP] Rekhter, Li, Hares, "A Border Gateway Protocol 4 (BGP-4)",
             RFC4271, January 2006.

   [RFC5029] Vasseur, JP., and Previdi, S., "Definition of an IS-IS
             Link Attribute Sub-TLV", RFC5029, September 2007.





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   [RFC4124] Le Faucheur, F. "Protocol Extensions for Support of
             Diffserv-aware MPLS Traffic Engineering", RFC 4124, June
             2005.

   [GENINFO] L. Ginsberg., S. Previdi., and M. Shand., "Advertising
             Generic Information in IS-IS", draft-ietf-isis-genapp,
             (work in progress).



Authors' Addresses

   Mach(Guoyi) Chen
   Huawei Technologies Co.,Ltd
   KuiKe Building, No.9 Xinxi Rd.,
   Hai-Dian District
   Beijing, 100085
   P.R. China

   Email: mach@huawei.com


   Renhai Zhang
   Huawei Technologies Co.,Ltd
   KuiKe Building, No.9 Xinxi Rd.,
   Hai-Dian District
   Beijing, 100085
   P.R. China

   Email: zhangrenhai@huawei.com


   Xiaodong Duan
   China Mobile
   53A,Xibianmennei Ave,Xunwu District
   Beijing, China

   Email: duanxiaodong@chinamobile.com


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