LDP State Machine
RFC 3215

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Network Working Group                                         C. Boscher
Request for Comments: 3215                                     P. Cheval
Category: Informational                                          Alcatel
                                                                   L. Wu
                                                                   Cisco
                                                                 E. Gray
                                                               Sandburst
                                                            January 2002

                           LDP State Machine

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 Internet Society (2002).  All Rights Reserved.

Abstract

   This document provides state machine tables for ATM (Asynchronous
   Transfer Mode) switch LSRs.  In the current LDP specification, there
   is no state machine specified for processing LDP messages. We think
   that defining a common state machine is very important for
   interoperability between different LDP and CR-LDP implementations.

   We begin in section 1 by defining a list of terminologies.  Then in
   section 2, we propose two sets of state machine tables for ATM switch
   LSRs that use downstream-on-demand mode, one method can be used for
   non-vc merge capable ATM LSRs, while the other one can be used for
   the vc-merge capable ATM LSRs.  In section 3, we provides a state
   machine for downstream unsolicited mode ATM LSRs.

   We focus on the LDP state machines and the associated control blocks
   used for establishing and maintaining LSPs.  We do not describe state
   machines for the "LDP controller" that is in charge of LDP session
   initialization, address mapping messages management, routing
   interface, etc. that is defined in the LDP specification.

   Even though the state machines in this document are specific for
   ATM-LSR, they can be easily adapted for other types of LSRs.

Boscher, et al.              Informational                      [Page 1]
RFC 3215                   LDP State Machine                January 2002

Table Of Contents

   1. Terminology ...................................................  4
   2. State Machine for Downstream-on-Demand Mode ...................  4
   2.1 An LSR's Behavior in the Case of a Next Hop Change ...........  4
   2.2. ATM Switch LSR with No VC-merge Capability ..................  5
   2.2.1 LSP Control Block ..........................................  5
   2.2.2 States .....................................................  7
   2.2.3 Events .....................................................  8
   2.2.4 State Transitions ..........................................  9
   2.2.5 State Machine .............................................. 10
   2.2.5.1 State -- "IDLE" .......................................... 10
   2.2.5.2 State -- "RESPONSE_AWAITED" .............................. 13
   2.2.5.3 State -- "ESTABLISHED" ................................... 16
   2.2.5.4 State -- "RELEASE_AWAITED" ............................... 21
   2.2.6 Handling the Next Hop Change ............................... 23
   2.2.6.1 Next Hop Trigger Control Block ........................... 24
   2.2.6.2 States ................................................... 24
   2.2.6.3 Events ................................................... 24
   2.2.6.4 State Transition for next hop change ..................... 25
   2.2.6.5 State Machine ............................................ 25
   2.2.6.5.1 State -- "IDLE" ........................................ 25
   2.2.6.5.2 State -- "NEW_NH_RETRY" ................................ 27
   2.2.6.5.3 State -- "NEW_NH_RESPONSE_AWAITED" ..................... 28
   2.2.7 LDP Related Message Handling ............................... 29
   2.3. ATM Switch LSR with VC-merge ................................ 31
   2.3.1 VC-merge ................................................... 31
   2.3.2 Control Block .............................................. 31
   2.3.3   State Machines for Downstream-on-demand Mode ............. 34
   2.3.3.1 State of the Upstream LSP Control Block's State Machine
           for Downstream-on-demand Mode ............................ 34
   2.3.3.2 Events of the Upstream LSP Control Block's State Machine
           for Downstream-on-demand Mode ............................ 35
   2.3.3.3 State Transitions of the Upstream LSP Control Block's State
           Machine for Downstream-on-demand Mode .................... 36
   2.3.3.4 Upstream LSP Control Block's State Machine
           for Downstream-on-demand Mode ............................ 37
   2.3.3.4.1 State -- "IDLE" ........................................ 37
   2.3.3.4.2 State -- "RESPONSE_AWAITED" ............................ 39
   2.3.3.4.3 State -- "ESTABLISHED" ................................. 42