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A Per-Domain Path Computation Method for Establishing Inter-Domain Traffic Engineering (TE) Label Switched Paths (LSPs)
RFC 5152

Networking Working Group                                JP. Vasseur, Ed.
Request for Comments: 5152                           Cisco Systems, Inc.
Category: Standards Track                               A. Ayyangar, Ed.
                                                        Juniper Networks
                                                                R. Zhang
                                                                      BT
                                                           February 2008

   A Per-Domain Path Computation Method for Establishing Inter-Domain
          Traffic Engineering (TE) Label Switched Paths (LSPs)

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This document specifies a per-domain path computation technique for
   establishing inter-domain Traffic Engineering (TE) Multiprotocol
   Label Switching (MPLS) and Generalized MPLS (GMPLS) Label Switched
   Paths (LSPs).  In this document, a domain refers to a collection of
   network elements within a common sphere of address management or path
   computational responsibility such as Interior Gateway Protocol (IGP)
   areas and Autonomous Systems.

   Per-domain computation applies where the full path of an inter-domain
   TE LSP cannot be or is not determined at the ingress node of the TE
   LSP, and is not signaled across domain boundaries.  This is most
   likely to arise owing to TE visibility limitations.  The signaling
   message indicates the destination and nodes up to the next domain
   boundary.  It may also indicate further domain boundaries or domain
   identifiers.  The path through each domain, possibly including the
   choice of exit point from the domain, must be determined within the
   domain.

Vasseur, et al.             Standards Track                     [Page 1]
RFC 5152          Path Comp. for Inter-Domain TE LSPs      February 2008

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................3
      2.1. Requirements Language ......................................4
   3. General Assumptions .............................................4
      3.1. Common Assumptions .........................................4
      3.2. Example of Topology for the Inter-Area TE Case .............6
      3.3. Example of Topology for the Inter-AS TE Case ...............7
   4. Per-Domain Path Computation Procedures ..........................8
      4.1. Example with an Inter-Area TE LSP .........................11
           4.1.1. Case 1: T0 Is a Contiguous TE LSP ..................11
           4.1.2. Case 2: T0 Is a Stitched or Nested TE LSP ..........12
      4.2. Example with an Inter-AS TE LSP ...........................13
           4.2.1. Case 1: T1 Is a Contiguous TE LSP ..................13
           4.2.2. Case 2: T1 Is a Stitched or Nested TE LSP ..........14
   5. Path Optimality/Diversity ......................................14
   6. Reoptimization of an Inter-Domain TE LSP .......................15
      6.1. Contiguous TE LSPs ........................................15
      6.2. Stitched or Nested (non-contiguous) TE LSPs ...............16
      6.3. Path Characteristics after Reoptimization .................17
   7. Security Considerations ........................................17
   8. Acknowledgements ...............................................18
   9. References .....................................................18
      9.1. Normative References ......................................18
      9.2. Informative References ....................................18

1.  Introduction

   The requirements for inter-domain Traffic Engineering (inter-area and
   inter-AS TE) have been developed by the Traffic Engineering Working
   Group and have been stated in [RFC4105] and [RFC4216].  The framework
   for inter-domain MPLS Traffic Engineering has been provided in
   [RFC4726].

   Some of the mechanisms used to establish and maintain inter-domain TE
   LSPs are specified in [RFC5151] and [RFC5150].

   This document exclusively focuses on the path computation aspects and
   defines a method for establishing inter-domain TE LSPs where each
   node in charge of computing a section of an inter-domain TE LSP path
   is always along the path of such a TE LSP.

   When the visibility of an end-to-end complete path spanning multiple
   domains is not available at the Head-end LSR (the LSR that initiated
   the TE LSP), one approach described in this document consists of

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