Network Working Group L. Andersson
Request for Comments: 3036 Nortel Networks Inc.
Category: Standards Track P. Doolan
Ennovate Networks
N. Feldman
IBM Corp
A. Fredette
PhotonEx Corp
B. Thomas
Cisco Systems, Inc.
January 2001
LDP Specification
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 (2001). All Rights Reserved.
Abstract
The architecture for Multi Protocol Label Switching (MPLS) is
described in RFC 3031. A fundamental concept in MPLS is that two
Label Switching Routers (LSRs) must agree on the meaning of the
labels used to forward traffic between and through them. This common
understanding is achieved by using a set of procedures, called a
label distribution protocol, by which one LSR informs another of
label bindings it has made. This document defines a set of such
procedures called LDP (for Label Distribution Protocol) by which LSRs
distribute labels to support MPLS forwarding along normally routed
paths.
Andersson, et al. Standards Track [Page 1]
RFC 3036 LDP Specification January 2001
Table of Contents
1 LDP Overview ....................................... 5
1.1 LDP Peers .......................................... 6
1.2 LDP Message Exchange ............................... 6
1.3 LDP Message Structure .............................. 7
1.4 LDP Error Handling ................................. 7
1.5 LDP Extensibility and Future Compatibility ......... 7
1.6 Specification Language ............................. 7
2 LDP Operation ...................................... 8
2.1 FECs ............................................... 8
2.2 Label Spaces, Identifiers, Sessions and Transport .. 9
2.2.1 Label Spaces ....................................... 9
2.2.2 LDP Identifiers .................................... 10
2.2.3 LDP Sessions ....................................... 10
2.2.4 LDP Transport ...................................... 11
2.3 LDP Sessions between non-Directly Connected LSRs ... 11
2.4 LDP Discovery ..................................... 11
2.4.1 Basic Discovery Mechanism .......................... 12
2.4.2 Extended Discovery Mechanism ....................... 12
2.5 Establishing and Maintaining LDP Sessions .......... 13
2.5.1 LDP Session Establishment .......................... 13
2.5.2 Transport Connection Establishment ................. 13
2.5.3 Session Initialization ............................. 14
2.5.4 Initialization State Machine ....................... 17
2.5.5 Maintaining Hello Adjacencies ...................... 20
2.5.6 Maintaining LDP Sessions ........................... 20
2.6 Label Distribution and Management .................. 21
2.6.1 Label Distribution Control Mode .................... 21
2.6.1.1 Independent Label Distribution Control ............. 21
2.6.1.2 Ordered Label Distribution Control ................. 21
2.6.2 Label Retention Mode ............................... 22
2.6.2.1 Conservative Label Retention Mode .................. 22
2.6.2.2 Liberal Label Retention Mode ....................... 22
2.6.3 Label Advertisement Mode ........................... 23
2.7 LDP Identifiers and Next Hop Addresses ............. 23
2.8 Loop Detection ..................................... 24
2.8.1 Label Request Message .............................. 24
2.8.2 Label Mapping Message .............................. 26
2.8.3 Discussion ......................................... 27
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