path: root/doc/rfc/rfc5376.txt

Network Working Group                                           N. Bitar
Request for Comments: 5376                                       Verizon
Category: Informational                                         R. Zhang
                                                                      BT
                                                               K. Kumaki
                                                           KDDI R&D Labs
                                                           November 2008


                     Inter-AS Requirements for the
        Path Computation Element Communication Protocol (PCECP)

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (c) 2008 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
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   to this document.

Abstract

   Multiprotocol Label Switching Traffic Engineered (MPLS TE) Label
   Switched Paths (LSPs) may be established wholly within an Autonomous
   System (AS) or may cross AS boundaries.

   The Path Computation Element (PCE) is a component that is capable of
   computing constrained paths for (G)MPLS TE LSPs.  The PCE
   Communication Protocol (PCECP) is defined to allow communication
   between Path Computation Clients (PCCs) and PCEs, as well as between
   PCEs.  The PCECP is used to request constrained paths and to supply
   computed paths in response.  Generic requirements for the PCECP are
   set out in "Path Computation Element (PCE) Communication Protocol
   Generic Requirements", RFC 4657.  This document extends those
   requirements to cover the use of PCECP in support of inter-AS MPLS
   TE.





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Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................3
   3. Reference Model .................................................4
      3.1. Scope of Deployment Model ..................................5
   4. Detailed PCECP Requirements for Inter-AS G(MPLS) TE Path
      Computation .....................................................6
      4.1. PCE Communication Protocol Requirements ....................6
           4.1.1. Requirements for Path Computation Requests ..........6
           4.1.2. Requirements for Path Computation Responses .........7
      4.2. Scalability and Performance Considerations .................8
      4.3. Management Considerations ..................................8
      4.4. Confidentiality ............................................9
      4.5. Policy Controls Affecting Inter-AS PCECP ...................9
           4.5.1. Inter-AS PCE Peering Policy Controls ...............10
           4.5.2. Inter-AS PCE Re-Interpretation Policies ............10
   5. Security Considerations ........................................10
      5.1. Use and Distribution of Keys ..............................11
      5.2. Application of Policy .....................................11
      5.3. Confidentiality ...........................................12
      5.4. Falsification of Information ..............................12
   6. Acknowledgments ................................................12
   7. Normative References ...........................................13
   8. Informative References .........................................13


























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1.  Introduction

   [RFC4216] defines the scenarios motivating the deployment of inter-AS
   Multiprotocol Label Switching Traffic Engineering (MPLS TE) and
   specifies the requirements for inter-AS MPLS TE when the ASes are
   under the administration of one Service Provider (SP) or the
   administration of different SPs.

   Three signaling options are defined for setting up an inter-AS TE
   Label Switched Path (LSP):

       1) contiguous TE LSP as documented in [RFC5151];
       2) stitched inter-AS TE LSP discussed in [RFC5150];
       3) nested TE LSP as in [RFC4206].

   [RFC5152] defines mechanisms for the computation of inter-domain TE
   LSPs using network elements along the signaling paths to compute
   per-domain constrained path segments.  The mechanisms in [RFC5152] do
   not guarantee an optimum constrained path across multiple ASes where
   an optimum path for a TE LSP is one that has the smallest cost,
   according to a normalized TE metric (based upon a TE metric or
   Interior Gateway Protocol (IGP) metric adopted in each transit AS)
   among all possible paths that satisfy the LSP TE constraints.

   The Path Computation Element (PCE) [RFC4655] is a component that is
   capable of computing paths for MPLS TE and Generalized Multiprotocol
   Label Switching Protocol ((G)MPLS TE) LSPs.  The requirements for a
   PCE have come from SP demands to compute optimum constrained paths
   across multiple areas and/or domains, and to be able to separate the
   path computation elements from the forwarding elements.

   The PCE Communication Protocol (PCECP) is defined to allow
   communication between Path Computation Clients (PCCs) and PCEs, and
   between PCEs.  The PCECP is used to request (G)MPLS TE paths and to
   supply computed paths in response.  Generic requirements for the
   PCECP are discussed in [RFC4657].  This document provides a set of
   PCECP requirements that are specific to inter-AS (G)MPLS TE path
   computation.

2.  Terminology

   This document adopts the definitions and acronyms defined in Section
   3 of [RFC4216] and Section 2 of [RFC4655].  In addition, we use the
   following terminology:

   ASBR: Autonomous System Border Router (see section 3 of RFC 4216)

   PCECP: PCE Communication Protocol



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   (G)MPLS TE: MPLS or Generalized MPLS Traffic Engineering

   Inter-AS (G)MPLS TE path: An MPLS TE or Generalized MPLS (GMPLS) path
      that traverses two or more ASes.

   Intra-AS (G)MPLS TE path: An MPLS TE or GMPLS path that is confined
      to a single AS.  It may traverse one or more IGP areas.

   Intra-AS PCE: A PCE responsible for computing (G)MPLS TE paths
      remaining within a single AS.

   Inter-AS PCE: A PCE responsible for computing inter-AS (G)MPLS paths
      or path segments, possibly by cooperating with intra-AS PCEs.

   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.

3.  Reference Model

   Figure 1 depicts the reference model for PCEs in an inter-AS
   application.  We refer to two types of PCE functions in this
   document: inter-AS PCEs and intra-AS PCEs.  Inter-AS PCEs perform the
   procedures needed for inter-AS (G)MPLS TE path computation while
   intra-AS PCEs perform the functions needed for intra-AS (G)MPLS TE
   path computation.

              Inter-AS       Inter-AS              Inter-AS
        PCC <-->PCE1<--------->PCE2<---------------->PCE3
         ::      ::             ::                    ::
         ::      ::             ::                    ::
         R1----ASBR1====ASBR3---R3---ASBR5====ASBR7---R5---R7
         |       |        |            |        |           |
         |       |        |            |        |           |
         R2----ASBR2====ASBR4---R4---ASBR6====ASBR8---R6---R8
                                ::
                                ::
                             Intra-AS
                                PCE

         <==AS1==>        <=====AS2=====>       <====AS3====>

          Figure 1: Inter- and Intra-AS PCE Reference Model

   Let's follow a scenario that illustrates the interaction among PCCs,
   inter-AS PCEs, and intra-AS PCEs, as shown in Figure 1.  R1 in AS1
   wants to setup a (G)MPLS TE path, call it LSP1, with certain
   constraints to R7 in AS3.  R1 determines, using mechanisms out of the



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   scope of this document, that R7 is an inter-AS route and that R1
   (itself) needs to contact its Inter-AS PCE1 to compute the path.  R1,
   as a PCC, sends a PCECP path computation request to PCE1.  PCE1
   determines that R7 is reachable via AS2 and that PCE2 is the PCE to
   ask for path computation across AS2.  PCE1 sends a PCECP path
   computation request to PCE2.  Inter-AS PCE2, in turn, sends a PCECP
   path computation request to Intra-AS PCE R4 to compute a path within
   AS2 (in certain cases, the same router such as R3 can assume both
   inter-AS and intra-AS path computation functions).  R4 may for
   instance return a PCECP path computation response to PCE2 with ASBR3
   as the entry point to AS2 from AS1 and ASBR7 as the exit point to
   AS3.  PCE2 then sends a PCECP path computation request to PCE3 to
   compute the path segment across AS3, starting at ASBR7 and
   terminating at R7.  PCE3 returns a PCECP path computation response to
   PCE2 with the path segment ASBR7-R7.  PCE2 then returns path ASBR3-
   ASBR5-ASBR7-R7 to PCE1, which, in turn, returns path ASBR1-ASBR3-
   ASBR5-ASBR7-R7 to PCC R1.

   As described in the above scenario, in general, a PCC may contact an
   inter-AS PCE to request the computation of an inter-AS path.  That
   PCE may supply the path itself or may solicit the services of other
   PCEs, which may themselves be inter-AS PCEs, or may be intra-AS PCEs
   with the responsibility for computing path segments within just one
   AS.

   This document describes the PCE Communication Protocol requirements
   for inter-AS path computation, i.e., for PCCs to communicate path
   computation requests for inter-AS (G)MPLS TE paths to PCEs, and for
   the PCEs to respond.  It also includes the requirements for PCEs to
   communicate inter-AS path computation requests and responses.

3.1.  Scope of Deployment Model

   All attempts to predict future deployment scopes within the Internet
   have proven fruitless.  Nevertheless, it may be helpful to provide
   some discussion of the scope of the inter-AS deployment model as
   envisioned at the time of writing.

   It is expected that most, if not all, inter-AS PCECP-based
   communications will be between PCEs operating in the cooperative PCE
   model described in [RFC4655].  Clearly, in this model, the requesting
   PCE acts as a PCC for the purpose of issuing a path computation
   request, but nevertheless, the requesting node fills the wider role
   of a PCE in its own AS.  It is currently considered unlikely that a
   PCC (for example, a normal Label Switching Router) will make a path
   computation request to a PCE outside its own AS.  This means that the
   PCECP relationships between ASes are limited to at most n squared
   (n^2), where n is the number of peering PCEs in the various ASes



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   (considered to be no greater than 100 in [RFC4657]).  In practice,
   however, it is likely that only a few PCEs in one AS will be
   designated for PCECP communications with a PCE in an adjacent AS, and
   each of these will only have a few PCEs in the adjacent AS to choose
   from.  A deployment model might place the PCEs as co-resident with
   the ASBRs, resulting in a manageable scaling of the PCE-PCE
   relationships.  Scaling considerations (Section 4.2), manageability
   considerations (Section 4.3), and security considerations (Section 5)
   should be examined in the light of these deployment expectations.

4.  Detailed PCECP Requirements for Inter-AS G(MPLS) TE Path Computation

   This section discusses detailed PCECP requirements for inter-AS
   (G)MPLS TE LSPs.  Depending on the deployment environment, some or
   all of the requirements described here may be utilized.
   Specifically, some requirements are more applicable to inter-
   provider inter-AS (G)MPLS TE operations than to intra-provider
   operations.

4.1.  PCE Communication Protocol Requirements

   Requirements specific to inter-AS PCECP path computation requests and
   responses are discussed in the following sections.

4.1.1.  Requirements for Path Computation Requests

   The following are inter-AS specific requirements for PCECP requests
   for path computation:

   1. [RFC4657] states the requirement for a priority level to be
      associated with each path computation request.  This document does
      not change that requirement.  However, PCECP should include a
      mechanism that enables an inter-AS PCE to inform the requesting
      inter-AS PCE of a change in the request priority level that may
      have resulted from the application of a local policy.

   2. A path computation request by an inter-AS PCE or a PCC to another
      inter-AS PCE MUST be able to specify the sequence of ASes and/or
      ASBRs across the network by providing ASBRs and/or ASes as hops in
      the desired path of the TE LSP to the destination.  For instance,
      an inter-AS PCE MUST be able to specify to the inter-AS PCE
      serving the neighboring AS a preferred ASBR for exiting to that AS
      and reach the destination.  That is, where multiple ASBRs exist,
      the requester MUST be able to indicate a preference for one of
      them.  The PCE must be able to indicate whether the specified ASBR
      or AS is mandatory or non-mandatory on the (G)MPLS TE path.





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   3. PCECP MUST allow a requester to provide a list of ASes and/or
      ASBRs to be excluded from the computed path.

   4. A PCECP path computation request from one inter-AS PCE to another
      MUST include the AS number of the requesting AS to enable the
      correct application of local policy at the second inter-AS PCE.

   5. A path computation request from a PCC to an inter-AS PCE or an
      inter-AS PCE to another MUST be able to specify the need for
      protection against node, link, or Shared Risk Link Group (SRLG)
      failure using 1:1 detours or facility backup.  It MUST be possible
      to request protection across all ASes or across specific ASes.

   6. PCECP MUST support the disjoint path requirements as specified in
      [RFC4657].  In addition, it MUST allow the specification of AS-
      diversity for the computation of a set of two or more paths.

   7. A PCECP path computation request message MUST be able to identify
      the scope of diversified path computation to be end-to-end (i.e.,
      between the endpoints of the (G)MPLS TE tunnel) or to be limited
      to a specific AS.

4.1.2.  Requirements for Path Computation Responses

   The following are inter-AS specific requirements for PCECP responses
   for path computation:

   1. A PCECP path computation response from one inter-AS PCE to another
      MUST be able to include both ASBRs and ASes in the computed path
      while preserving path segment and topology confidentiality.

   2. A PCECP path computation response from one inter-AS PCE to the
      requesting inter-AS PCE MUST be able to carry an identifier for a
      path segment it computes to preserve path segment and topology
      confidentiality.  The objective of the identifier is to be
      included in the TE LSP signaling, whose mechanism is out of scope
      of this document, to be used for path expansion during LSP
      signaling.

   3. If a constraint for a desired ASBR (see Section 4.1.1, requirement
      2) cannot be satisfied by a PCE, PCECP SHOULD allow the PCE to
      notify the requester of that fact as an error in a path
      computation response.

   4. A PCECP path computation response from an inter-AS PCE to a
      requesting inter-AS PCE or a PCC MUST be able to carry a
      cumulative inter-AS path cost.  Path cost normalization across
      ASes is out of scope of this document.



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   5. A PCECP path computation response from an inter-AS PCE to a PCC
      SHOULD be able to carry the intra-AS cost of the path segment
      within the PCC AS.

   6. A PCECP path computation response MUST be able to identify
      diversified paths for the same (G)MPLS TE LSP.  End-to-end (i.e.,
      between the two endpoints of the (G)MPLS TE tunnel) disjoint paths
      are paths that do not share nodes, links, or SRLGs except for the
      LSP head-end and tail-end.  In cases where diversified path
      segments are desired within one or more ASes, the disjoint path
      segments may share only the ASBRs of the first AS and the ASBR of
      the last AS across these ASes.

4.2.  Scalability and Performance Considerations

   PCECP design for use in the inter-AS case SHOULD consider the
   following criteria:

   -  PCE message processing load.
   -  Scalability as a function of the following parameters:
      o  number of PCCs within the scope of an inter-AS PCE
      o  number of intra-AS PCEs within the scope of an inter-AS PCE
      o  number of peering inter-AS PCEs per inter-AS PCE
   -  Added complexity caused by inter-AS features.

4.3.  Management Considerations

   [RFC4657] specifies generic requirements for PCECP management.  This
   document specifies new requirements that apply to inter-AS
   operations.

   The PCECP MIB module MUST provide objects to control the behavior of
   PCECP in inter-AS applications.  These objects include the ASes
   within the scope of an inter-AS PCE, inter-AS PCEs in neighboring
   ASes to which the requesting PCE will or will not communicate,
   confidentiality, and policies.

   The built-in diagnostic tools MUST enable failure detection and
   status checking of PCC/PCE-PCE PCECP.  Diagnostic tools include
   statistics collection on the historical behavior of PCECP as
   specified in [RFC4657], but additionally it MUST be possible to
   analyze these statistics on a neighboring AS basis (i.e., across the
   inter-AS PCEs that belong to a neighboring AS).

   The MIB module MUST support trap functions when thresholds are
   crossed or when important events occur as stated in [RFC4657].  These
   thresholds SHOULD be specifiable per neighbor AS as well as per peer
   inter-AS PCE, and traps should be accordingly generated.



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   Basic liveliness detection for PCC/PCE-PCE PCECP is described in
   [RFC4657].  The PCECP MIB module SHOULD allow control of liveliness
   check behavior by providing a liveliness message frequency MIB
   object, and this frequency object SHOULD be specified per inter-AS
   PCE peer.  In addition, there SHOULD be a MIB object that specifies
   the dead-interval as a multiplier of the liveliness message frequency
   so that if no liveliness message is received within that time from an
   inter-AS PCE, the inter-AS PCE is declared unreachable.

4.4.  Confidentiality

   Confidentiality mainly applies to inter-provider (inter-AS) PCE
   communication.  It is about protecting the information exchanged
   between PCEs and about protecting the topology information within an
   SP's network.  Confidentiality rules may also apply among ASes owned
   by a single SP.  Each SP will in most cases designate some PCEs for
   inter-AS (G)MPLS TE path computation within its own administrative
   domain and some other PCEs for inter-provider inter-AS (G)MPLS TE
   path computation.  Among the inter-provider-scoped inter-AS PCEs in
   each SP domain, there may also be a subset of the PCEs specifically
   enabled for path computation across a specific set of ASes of
   different peer SPs.

   PCECP MUST allow an SP to hide from other SPs the set of hops within
   its own ASes that are traversed by an inter-AS inter-provider TE LSP
   (c.f., Section 5.2.1 of [RFC4216]).  In a multi-SP administrative
   domain environment, SPs may want to hide their network topologies for
   security or commercial reasons.  Thus, for each inter-AS TE LSP path
   segment an inter-AS PCE computes, it may return to the requesting
   inter-AS PCE an inter-AS TE LSP path segment from its own ASes
   without detailing the explicit intra-AS hops.  As stated earlier,
   PCECP responses SHOULD be able to carry path-segment identifiers that
   replace the details of that path segment.  The potential use of that
   identifier for path expansion, for instance, during LSP signaling is
   out of scope of this document.

4.5.  Policy Controls Affecting Inter-AS PCECP

   Section 5.2.2 of [RFC4216] discusses the policy control requirements
   for inter-AS RSVP-TE signaling at the AS boundaries for the
   enforcement of interconnect agreements, attribute/parameter
   translation and security hardening.

   This section discusses those policy control requirements that are
   similar to what are discussed in section 5.2.2 of [RFC4216] for
   PCECP.  Please note that SPs may still require policy controls during





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   signaling of TE LSPs to enforce their bilateral or multilateral
   agreements at AS boundaries, but signaling is out of scope for this
   document.

4.5.1.  Inter-AS PCE Peering Policy Controls

   An inter-AS PCE sends path computation requests to its neighboring
   inter-AS PCEs, and an inter-AS PCE that receives such a request
   enforces policies applicable to the sender of the request.  These
   policies may include rewriting some of the parameters or rejecting
   requests based on parameter values.  Such policies may be applied for
   PCEs belonging to different SPs or to PCEs responsible for ASes
   within a single SP administrative domain.  Parameters that might be
   subject to policy include bandwidth, setup/holding priority, Fast
   Reroute request, Differentiated Services Traffic Engineering (DS-TE)
   Class Type (CT), and others as specified in section 5.2.2.1 of
   [RFC4216].

   For path computation requests that are not compliant with locally
   configured policies, PCECP SHOULD enable a PCE to send an error
   message to the requesting PCC or PCE indicating that the request has
   been rejected because a specific parameter did not satisfy the local
   policy.

4.5.2.  Inter-AS PCE Re-Interpretation Policies

   Each SP may have different definitions in its use of, for example,
   DS-TE TE classes.  An inter-AS PCE receiving a path computation
   request needs to interpret the parameters and constraints and adapt
   them to the local environment.  Specifically, a request constructed
   by a PCC or PCE in one AS may have parameters and constraints that
   should be interpreted differently or translated by the receiving PCE
   that is in a different AS.  A list of signaling parameters subject to
   policy re-interpretation at AS borders can be found in section
   5.2.2.2 of [RFC4216], and the list for path computation request
   parameters and constraints is the same.  In addition, the transit SPs
   along the inter-AS TE path may be GMPLS transport providers, which
   may require re-interpretation of MPLS-specific PCECP path computation
   request objects in order to enable path computation over a GMPLS
   network or vice versa.

5.  Security Considerations

   The PCECP is a communications protocol for use between potentially
   remote entities (PCCs and PCEs) over an IP network.  Security
   concerns arise in order to protect the PCC, PCE, and the information
   they exchange.  [RFC4758] specifies requirements on the PCECP to
   protect against spoofing, snooping, and DoS attacks.  That document



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   is concerned with general protocol requirements applicable to the
   basic use of the PCECP.  This document is specific to the application
   of the PCE architecture in an inter-AS environment, and so it is
   appropriate to highlight the security considerations that apply in
   that environment.

   Security requirements that exist within a single administrative
   domain become critical in the multi-AS case when the control of IP
   traffic and access to the network may leave the authority of a single
   administration.

5.1.  Use and Distribution of Keys

   How the participants in a PCECP session discover each other and the
   need for the session is out of scope of this document.  It may be
   through configuration or automatic discovery.  However, when a PCECP
   session is established, the PCECP speakers MUST have mechanisms to
   authenticate each other's identities and validate the data they
   exchange.  They also SHOULD have mechanisms to protect the data that
   they exchange via encryption.  Such mechanisms usually require the
   use of keys, and so the PCECP MUST describe techniques for the
   exchange and use of security keys.  Where inter-AS PCE discovery is
   used, and PCECP security is required, automated key distribution
   mechanisms MUST also be used.  Since such key exchange must
   (necessarily) operate over an AS boundary, proper consideration needs
   to be given to how inter-AS key exchanges may be carried out and how
   the key exchange, itself, may be secured.  Key distribution
   mechanisms MUST be defined with consideration of [RFC4107].  Where a
   PCECP session is configured between a pair of inter-AS PCEs, a
   security key may be manually set for that session.

5.2.  Application of Policy

   Policy forms an important part of the operation of PCEs in an inter-
   AS environment as described in Section 4.5, especially when ASes are
   administrated by different SPs.  A wider discussion of the
   application of policy to the PCE architecture can be found in
   [PCE-POLICY].

   Policy may also form part of the security model for the PCECP and may
   be particularly applicable to inter-AS path computation requests.  A
   fundamental element of the application of policy at a PCE is the
   identity of the requesting PCC/PCE.  This makes the use of
   authentication described in Section 5.1 particularly important.
   Where policy information is exchanged as part of the computation
   request and/or response, the policy object is transparent to the
   PCECP being delivered un-inspected and unmodified to the policy
   component of a PCE or PCC.  Therefore, the policy components are



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   responsible for protecting (for example, encrypting) the policy
   information and using additional identification and authentication if
   a higher level of validation is required than is provided by the base
   protocol elements of the PCECP.

5.3.  Confidentiality

   The PCECP MUST provide a mechanism to preserve the confidentiality of
   path segments computed by a PCE in one AS and provided in a
   computation response to another AS.

   Furthermore, a PCE SHOULD be provided with a mechanism to mask its
   identity such that its presence in the path computation chain in a
   cooperative PCE model (such as described in [BRPC]) cannot be derived
   from the computed path.  This will help to protect the PCE from
   targeted attacks.  Clearly, such confidentiality does not extend to
   the PCECP peer (i.e., a PCC or another PCE) that invokes the PCE with
   a path computation request.

5.4.  Falsification of Information

   In the PCE architecture, when PCEs cooperate, one PCE may return a
   path computation result that is composed of multiple path segments,
   each computed by a different PCE.  In the inter-AS case, each PCE may
   belong to a different administrative domain, and the source PCC might
   not know about the downstream PCEs, nor fully trust them.  Although
   it is possible and RECOMMENDED to establish a chain of trust between
   PCEs, this might not always be possible.  In this case, it becomes
   necessary to guard against a PCE changing the information provided by
   another downstream PCE.  Some mechanism MUST be available in the
   PCECP, and echoed in the corresponding signaling, that allows an AS
   to verify that the signaled path conforms to the path segment
   computed by the local PCE and returned on the path computation
   request.

6.  Acknowledgments

   We would like to thank Adrian Farrel, Jean-Philippe Vasseur, and Jean
   Louis Le Roux for their useful comments and suggestions.  Pasi Eronen
   and Sandy Murphy provided valuable early Security Directorate
   reviews.  Adrian Farrel re-wrote the Security Considerations section.










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7.  Normative References

   [RFC4107]    Bellovin, S. and R. Housley, "Guidelines for
                Cryptographic Key Management", BCP 107, RFC 4107, June
                2005.

   [RFC4216]    Zhang, R., Ed., and J.-P. Vasseur, Ed., "MPLS Inter-
                Autonomous System (AS) Traffic Engineering (TE)
                Requirements", RFC 4216, November 2005.

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

   [RFC4657]    Ash, J., Ed., and J. Le Roux, Ed., "Path Computation
                Element (PCE) Communication Protocol Generic
                Requirements", RFC 4657, September 2006.

8.  Informative References

   [BRPC]       Vasseur, JP., Zhang, R., Bitar, N., and JL. Le Roux, "A
                Backward Recursive PCE-based Computation (BRPC)
                Procedure To Compute Shortest Constrained Inter-domain
                Traffic Engineering Label Switched paths", Work in
                Progress, April 2008.

   [RFC4206]    Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
                Hierarchy with Generalized Multi-Protocol Label
                Switching (GMPLS) Traffic Engineering (TE)", RFC 4206,
                October 2005.

   [RFC4758]    Nystroem, M., "Cryptographic Token Key Initialization
                Protocol (CT-KIP) Version 1.0 Revision 1", RFC 4758,
                November 2006.

   [RFC5150]    Ayyangar, A., Kompella, K., Vasseur, JP., and A. Farrel,
                "Label Switched Path Stitching with Generalized
                Multiprotocol Label Switching Traffic Engineering (GMPLS
                TE)", RFC 5150, February 2008.

   [RFC5151]    Farrel, A., Ed., Ayyangar, A., and JP. Vasseur, "Inter-
                Domain MPLS and GMPLS Traffic Engineering -- Resource
                Reservation Protocol-Traffic Engineering (RSVP-TE)
                Extensions", RFC 5151, February 2008.







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RFC 5376            Inter-AS Requirements for PCECP        November 2008


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

   [PCE-POLICY] Bryskin, I., Papadimitriou, D., Berger, L., and J. Ash,
                "Policy-Enabled Path Computation Framework", Work in
                Progress, October 2007.

Authors' Addresses

   Nabil Bitar
   Verizon
   117 West Street
   Waltham, MA 02451 USA
   EMail: nabil.n.bitar@verizon.com

   Kenji Kumaki
   KDDI R&D Laboratories, Inc.
   2-1-15 Ohara Fujimino
   Saitama 356-8502, JAPAN
   EMail: ke-kumaki@kddi.com

   Raymond Zhang
   BT
   2160 E. Grand Ave.
   El Segundo, CA 90245 USA
   EMail: Raymond.zhang@bt.com























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