Fault Tolerance for the Label Distribution Protocol (LDP)
RFC 3479

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Network Working Group                                     A. Farrel, Ed.
Request for Comments: 3479                          Movaz Networks, Inc.
Category: Standards Track                                  February 2003

       Fault Tolerance for the Label Distribution Protocol (LDP)

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.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

IESG Note

   This specification includes procedures for failure detection and
   failover for a TCP connection carrying MPLS LDP control traffic, so
   that it can be switched to a new TCP connection.  It does not provide
   a general approach to using multiple TCP connections to provide this
   kind of fault tolerance.  The specification lacks adequate guidance
   for the timer and retry value choices related to the TCP connection
   fault tolerance procedures.  The specification should not serve as a
   model for TCP connection fault tolerance design for any future
   document, and users are advised to test configurations based on this
   specification very carefully for problems such as premature
   failovers.

Abstract

   Multiprotocol Label Switching (MPLS) systems will be used in core
   networks where system downtime must be kept to an absolute minimum.
   Many MPLS Label Switching Routers (LSRs) may, therefore, exploit
   Fault Tolerant (FT) hardware or software to provide high availability
   of the core networks.

   The details of how FT is achieved for the various components of an FT
   LSR, including Label Distribution Protocol (LDP), the switching
   hardware and TCP, are implementation specific.  This document
   identifies issues in the LDP specification in RFC 3036, "LDP
   Specification", that make it difficult to implement an FT LSR using
   the current LDP protocols, and defines enhancements to the LDP
   specification to ease such FT LSR implementations.

Farrel                      Standards Track                     [Page 1]
RFC 3479              Fault Tolerance for the LDP          February 2003

   The issues and extensions described here are equally applicable to
   RFC 3212, "Constraint-Based LSP Setup Using LDP" (CR-LDP).

Table of Contents

   1. Conventions and Terminology used in this document..........3
   2. Contributing Authors.......................................4
   3. Introduction...............................................4
      3.1. Fault Tolerance for MPLS..............................4
      3.2. Issues with LDP.......................................5
   4. Overview of LDP FT Enhancements............................7
      4.1. Establishing an FT LDP Session........................8
           4.1.1 Interoperation with Non-FT LSRs.................8
      4.2. TCP Connection Failure................................9
           4.2.1 Detecting TCP Connection Failures...............9
           4.2.2 LDP Processing after Connection Failure.........9
      4.3. Data Forwarding During TCP Connection Failure........10
      4.4. FT LDP Session Reconnection..........................10
      4.5. Operations on FT Labels..............................11
      4.6. Check-Pointing.......................................11
           4.6.1 Graceful Termination...........................12
      4.7. Label Space Depletion and Replenishment..............13
      4.8. Tunneled LSPs........................................13
   5. FT Operations.............................................14
      5.1. FT LDP Messages......................................14
           5.1.1 Sequence Numbered FT Label Messages............14
           5.1.2 FT Address Messages............................15
           5.1.3 Label Resources Available Notifications........15
      5.2. FT Operation ACKs....................................17
      5.3. Preservation of FT State.............................17
      5.4. FT Procedure After TCP Failure.......................19
           5.4.1 FT LDP Operations During TCP Failure...........20
      5.5. FT Procedure After TCP Re-connection.................21
           5.5.1 Re-Issuing FT Messages.........................22
   6. Check-Pointing Procedures.................................22
      6.1 Check-Pointing with the Keepalive Message.............23
      6.2 Quiesce and Keepalive.................................23
   7. Changes to Existing Messages..............................24
      7.1. LDP Initialization Message...........................24
      7.2. LDP Keepalive Messages...............................25
      7.3. All Other LDP Session Messages.......................25
   8. New Fields and Values.....................................26