LDP Extension for Inter-Area Label Switched Paths (LSPs)
RFC 5283

Document Type RFC - Proposed Standard (July 2008; Errata)
Last updated 2013-03-02
Replaces draft-decraene-mpls-ldp-interarea
Stream IETF
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Stream WG state WG Document
Consensus Unknown
Document shepherd No shepherd assigned
IESG IESG state RFC 5283 (Proposed Standard)
Telechat date
Responsible AD Ross Callon
Send notices to mpls-chairs@ietf.org, draft-ietf-mpls-ldp-interarea@ietf.org
Network Working Group                                        B. Decraene
Request for Comments: 5283                                   JL. Le Roux
Category: Standards Track                                 France Telecom
                                                                I. Minei
                                                  Juniper Networks, Inc.
                                                               July 2008

        LDP Extension for Inter-Area 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

   To facilitate the establishment of Label Switched Paths (LSPs) that
   would span multiple IGP areas in a given Autonomous System (AS), this
   document describes a new optional Longest-Match Label Mapping
   Procedure for the Label Distribution Protocol (LDP).

   This procedure allows the use of a label if the Forwarding
   Equivalence Class (FEC) Element matches an entry in the Routing
   Information Base (RIB).  Matching is defined by an IP longest-match
   search and does not mandate an exact match.

Table of Contents

   1. Introduction ....................................................2
   2. Conventions Used in This Document ...............................2
   3. Terminology .....................................................2
   4. Problem Statement ...............................................3
   5. Longest-Match Label Mapping Message Procedure ...................4
   6. Application Examples ............................................6
      6.1. Inter-Area LSPs ............................................6
      6.2. Use of Static Routes .......................................7
   7. Caveats for Deployment ..........................................8
      7.1. Deployment Considerations ..................................8
      7.2. Routing Convergence Time Considerations ....................8
   8. Security Considerations .........................................9
   9. References ......................................................9
      9.1. Normative References .......................................9
      9.2. Informative References .....................................9
   10. Acknowledgments ...............................................11

Decraene, et al.            Standards Track                     [Page 1]
RFC 5283           LDP Extension for Inter-Area LSPs           July 2008

1.  Introduction

   Link state Interior Gateway Protocols (IGPs) such as OSPF [OSPFv2]
   and IS-IS [IS-IS] allow the partition of an autonomous system into
   areas or levels so as to increase routing scalability within a
   routing domain.

   However, [LDP] recommends that the IP address of the FEC Element
   should *exactly* match an entry in the IP Routing Information Base
   (RIB).  According to [LDP], section 3.5.7.1 ("Label Mapping Messages
   Procedures"):

      An LSR [Label Switching Router] receiving a Label Mapping message
      from a downstream LSR for a Prefix SHOULD NOT use the label for
      forwarding unless its routing table contains an entry that exactly
      matches the FEC Element.

   Therefore, MPLS LSPs between Label Edge Routers (LERs) in different
   areas/levels are not set up unless the specific (e.g., /32 for IPv4)
   loopback addresses of all the LERs are redistributed across all
   areas.

   The problem statement is discussed in section 4.  Then, in section 5
   we extend the Label Mapping Procedure defined in [LDP] so as to
   support the setup of contiguous inter-area LSPs while maintaining IP
   prefix aggregation on the ABRs.  This consists of allowing for
   longest-match-based Label Mapping.

2.  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 [RFC2119].

3.  Terminology

   IGP Area: OSPF Area or IS-IS level

   ABR: OSPF Area Border Router or IS-IS L1/L2 router

   LSP: Label Switched Path

   Intra-area LSP: LSP that does not traverse any IGP area boundary.

   Inter-area LSP: LSP that traverses at least one IGP area boundary.

Decraene, et al.            Standards Track                     [Page 2]
RFC 5283           LDP Extension for Inter-Area LSPs           July 2008
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