Inter-AS Requirements for the Path Computation Element Communication Protocol (PCECP)
draft-ietf-pce-interas-pcecp-reqs-06

Network Working Group                                        Nabil Bitar
Internet Draft                                                   Verizon
Intended Status: Informational                             Raymond Zhang
Created: May 7, 2008                                                  BT
Expires: October 7, 2008                                    Kenji Kumaki
                                                        KDDI Corporation

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

               draft-ietf-pce-interas-pcecp-reqs-06.txt

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

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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.

Table of Contents

   1. Introduction....................................................2
   2. Terminology.....................................................3
   3. Reference Model.................................................4
   3.1 Scope of Deployment Model......................................5
   4. Detailed PCEP Requirements for Inter-AS 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 PCEP........................9
   4.5.1 Inter-AS PCE Peering Policy Controls.........................9
   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...............................................11
   5.4 Falsification of Information..................................12
   6. IANA Considerations............................................12
   7. Acknowledgments................................................12
   8. Authors' Addresses.............................................12
   9. Normative References...........................................13
   10. Informative References........................................13

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
   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
   Label Switched Paths (LSPs) using network elements along the
   signaling paths to compute per-domain constrained path segments. The

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   mechanisms in [RFC5152] do not guarantee an optimum constrained path
   across multiple ASes where an optimum path for an 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 Multiprotcol
   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 (PCEP) is defined to allow
   communication between Path Computation Clients (PCCs) and PCEs, and
   between PCEs. The PCEP is used to request (G)MPLS TE paths and to
   supply computed paths in response. Generic requirements for the
   PCEP are discussed in [RFC4657]. This document provides a set of
   PCEP 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:

   PCEP: PCE Communication Protocol

   Inter-AS (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.

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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.

   Let's follow a scenario that illustrates the interaction among PCCs,
   inter-AS PCEs and intra-AS PCEs as shown 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 scope of
   this document, that R7 is an inter-AS route and that it needs to
   contact its Inter-AS PCE1 to compute the path. R1, as a PCC, sends a
   PCEP 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 PCEP path computation request
   to PCE2. Inter-AS PCE2, in turn, sends a PCEP 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
   PCEP 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 PCEP path computation request to PCE3 to compute the path
   segment across AS3, starting at ASBR7 and terminating at R7. PCE3
   returns a PCEP path computation response to PCE2 with the path
   segment ASBR7-R7. PCE2 then return 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, and
   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. That is, for PCCs to communicate path
   computation requests for inter-AS (G)MPLS TE path to a PCE, and for
   the PCE to respond. It also includes the requirements for PCEs to
   communicate inter-AS path computation requests and responses.

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              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

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 PCEP-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
   PCEP relationships between ASes are limited to at most n-squared
   where n is the number of peering PCEs in the various ASes
   (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 PCEP 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.

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4. Detailed PCEP Requirements for Inter-AS Computation

   This section discusses detailed PCEP 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 perations than to intra-provider
   operations.

4.1. PCE Communication Protocol Requirements

   Requirements specific to inter-AS PCEP 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 PCEP 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, PCEP 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 as mandatory or non-mandatory to be on the (G)MPLS TE path.

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

   4. A PCEP 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 SRLG failure using 1:1 detours
      or facility backup. It MUST be possible to request protection
      across all ASes or across specific ASes.

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   6. PCEP 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 PCEP 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 PCEP responses
   for path computation:

   1. A PCEP 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 PCEP 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, PCEP SHOULD allow the
      PCE to notify the requester of that fact as an error in a path
      computation response.

   4. A PCEP path computation 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.

   5. A PCEP 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 PCEP 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.

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4.2. Scalability and Performance Considerations

   PCEP 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:
      - number of PCCs within the scope of an inter-AS PCE
      - number of intra-AS PCEs within the scope of an inter-AS PCE
      - 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 PCEP management. This
   document addresses new requirements that apply to inter-AS
   operations.

   The PCEP MIB module MUST provide objects to control the behavior of
   PCEP in inter-AS applications.  They 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 PCEP. Diagnostic tools include
   statistics collection on the historical behavior of PCEP as
   specified in [RFC4657], but additionally it MUST be possible to
   analyze this 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.

   Basic liveliness detection for PCC/PCE-PCE PCEP is described in
   [RFC4657]. The  PCEP 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.

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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.

   PCEP 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, PCEP 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 PCEP

   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
   PCEP. Please note that SPs may still require policy controls during
   signaling of TE LSPs to enforce their bilateral or multi-lateral
   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

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   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, PCEP 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 PCEP path computation
   request objects to enable path computation over a GMPLS network or
   vice versa.

5. Security Considerations

   The PCEP 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 and PCE, and the
   information they exchange. [RFC4758] specifies requirements on the
   PCEP to protect against spoofing, snooping, and DoS attacks. That
   document is concerned with general protocol requirements applicable
   to the basic use of the PCEP. 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.

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5.1. Use and Distribution of Keys

   How the participants in a PCEP 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 PCEP
   session is established, the PCEP speakers MUST have mechanisms to
   authenticate each other's identities and validate the data the
   exchange.  They also SHOULD have mechanisms protect the data that
   they exchange via encryption. Such mechanisms usually require the
   use of keys, and so the PCEP MUST describe techniques for the
   exchange and use of security keys. Where inter-AS PCE discovery is
   used, and PCEP 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 PCEP
   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 PCEP 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
   PCEP being delivered un-inspected and unmodified to the policy
   component of a PCE or PCC. Therefore, the policy components are
   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 PCEP.

5.3. Confidentiality

   The PCEP 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

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   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 PCEP 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
   PCEP, 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. IANA Considerations

   This document makes no requests for IANA action.

7. 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.

8. Authors' Addresses

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

   Kenji Kumaki
   KDDI Corporation
   Garden Air Tower
   Iidabashi, Chiyoda-ku,
   Tokyo 102-8460, JAPAN
   Phone: +81-3-6678-3103
   Email: ke-kumaki@kddi.com

Bitar, Zhang, and Kumaki   Inter-AS Requirements for PCEP      [Page 12]
Internet Draft draft-ietf-pce-interas-pecp-reqs-06              May 2008

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

9. Normative References

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

   [RFC4216] Zhang. R., and Vasseur, JP., "MPLS Inter-AS Traffic
             Engineering Requirements", RFC 4216, November 2005.

   [RFC4655] Farrel, A.. Vasseur, JP., and Ash, J., "A Path Computation
             Element (PCE)-Based Architecture", RFC 4755, August 2006.

   [RFC4657] Ash, J., Le Roux, JL., et al., "PCE Communication Protocol
             Generic Requirements", RFC 4657, September 2006.

10. Informative References

   [BRPC]    Vasseur, JP., et. al, "A Backward Recursive PCE-based
             Computation (BRPC) Procedure To Compute Shortest
             Constrained Inter-domain Traffic Engineering Label Switched
             paths", draft-ietf-pce-brpc, work in progress.

   [RFC4206] Kompella, K., and Rekhter, Y., "Label switched Paths(LSP)
             Hierarchy with Generalized MPLS TE", RFC4206, October 2005.

   [RFC4758] Mystroem, 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 Farrel, A.,
             "Label Switched Path Stitching with Generalized MPLS
             Traffic Engineering (GMPLS TE)", RFC 5150, February 2008.

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

   [RFC5152] Vasseur, JP., Ayyangar, A.,  and Zhang, R., "A Per-domain
             path computation method for Establishing Inter-domain
             Traffic Engineering (TE) Label Switched Paths (LSPs)", RFC
             5152, February 2008.

Bitar, Zhang, and Kumaki   Inter-AS Requirements for PCEP      [Page 13]
Internet Draft draft-ietf-pce-interas-pecp-reqs-06              May 2008

   [PCE-POLICY] Bryskin, I., Berger, L. and Ash, J., "Policy-Enabled
             Path Computation Framework", draft-ietf-pce-policy-enabled-
             path-comp, work in progress.

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