Path Computation Element Communication Protocol (PCECP) Specific Requirements for Inter-Area MPLS and GMPLS Traffic Engineering
RFC 4927

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Network Working Group                                 J.-L. Le Roux, Ed.
Request for Comments: 4927                                France Telecom
Category: Informational                                        June 2007

    Path Computation Element Communication Protocol (PCECP) Specific
    Requirements for Inter-Area MPLS and GMPLS Traffic Engineering

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) The IETF Trust (2007).

Abstract

   For scalability purposes, a network may comprise multiple Interior
   Gateway Protocol (IGP) areas.  An inter-area Traffic Engineered Label
   Switched Path (TE-LSP) is an LSP that transits through at least two
   IGP areas.  In a multi-area network, topology visibility remains
   local to a given area, and a head-end Label Switching Router (LSR)
   cannot compute an inter-area shortest constrained path.  One key
   application of the Path Computation Element (PCE)-based architecture
   is the computation of inter-area TE-LSP paths.  The PCE Communication
   Protocol (PCECP) is used to communicate computation requests from
   Path Computation Clients (PCCs) to PCEs, and to return computed paths
   in responses.  This document lists a detailed set of PCECP-specific
   requirements for support of inter-area TE-LSP path computation.  It
   complements the generic requirements for a PCE Communication
   Protocol.

Le Roux                      Informational                      [Page 1]
RFC 4927         PCECP Requirements for MPLS and GMPLS         June 2007

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................3
      2.1. Conventions Used in This Document ..........................4
   3. Motivations for PCE-Based Inter-Area Path Computation ...........4
   4. Detailed Inter-Area Specific Requirements on PCECP ..............5
      4.1. Control and Recording of Area Crossing .....................5
      4.2. Area Recording .............................................6
      4.3. Strict Explicit Path and Loose Path ........................6
      4.4. PCE List Enforcement and Recording in Multiple-PCE
           Computation ................................................6
      4.5. Inclusion of Area IDs in Request ...........................7
      4.6. Area Inclusion/Exclusion ...................................7
      4.7. Inter-Area Diverse Path Computation ........................7
      4.8. Inter-Area Policies ........................................8
      4.9. Loop Avoidance .............................................8
   5. Manageability Considerations ....................................9
   6. Security Considerations .........................................9
   7. Acknowledgments .................................................9
   8. References ......................................................9
      8.1. Normative References .......................................9
      8.2. Informative References ....................................10
   9. Contributors ...................................................10

1.  Introduction

   [RFC4105] lists a set of motivations and requirements for setting up
   TE-LSPs across IGP area boundaries.  These LSPs are called inter-area
   TE-LSPs.  These requirements include the computation of inter-area
   shortest constrained paths with a key guideline being to respect the
   IGP hierarchy concept, and particularly the containment of topology
   information.  The main challenge with inter-area MPLS-TE lies in path
   computation.  Indeed, the head-end LSR cannot compute an explicit
   path across areas, as its topology visibility is limited to its own
   area.

   Inter-area path computation is one of the key applications of the
   PCE-based architecture [RFC4655].  The computation of optimal inter-
   area paths may be achieved using the services of one or more PCEs.

   Such PCE-based inter-area path computation could rely for instance on
   a single multi-area PCE that has the TE database of all the areas in
   the IGP domain and can directly compute an end-to-end constrained
   shortest path.  Alternatively, this could rely on the cooperation
   between PCEs whereby each PCE covers one or more IGP areas and the
   full set of PCEs covers all areas.

Le Roux                      Informational                      [Page 2]
RFC 4927         PCECP Requirements for MPLS and GMPLS         June 2007

   The generic requirements for a PCE Communication Protocol (PCECP),
   which allows a PCC to send path computation requests to a PCE and the
   PCE to send path computation responses to a PCC, are set forth in
   [RFC4657].  The use of a PCE-based approach for inter-area path
   computation implies specific requirements on a PCE Communication