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Multiprotocol Label Switching Architecture
RFC 3031

Document type: RFC - Proposed Standard (January 2001; Errata)
Updated by RFC 6790, RFC 6178
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

IETF State: (None)
Consensus: Unknown
Document shepherd: No shepherd assigned

IESG State: RFC 3031 (Proposed Standard)
Responsible AD: (None)
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Network Working Group                                           E. Rosen
Request for Comments: 3031                           Cisco Systems, Inc.
Category: Standards Track                                 A. Viswanathan
                                                  Force10 Networks, Inc.
                                                               R. Callon
                                                  Juniper Networks, Inc.
                                                            January 2001

               Multiprotocol Label Switching Architecture

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

   This document specifies the architecture for Multiprotocol Label
   Switching (MPLS).

Table of Contents

   1          Specification  ......................................   3
   2          Introduction to MPLS  ...............................   3
   2.1        Overview  ...........................................   4
   2.2        Terminology  ........................................   6
   2.3        Acronyms and Abbreviations  .........................   9
   2.4        Acknowledgments  ....................................   9
   3          MPLS Basics  ........................................   9
   3.1        Labels  .............................................   9
   3.2        Upstream and Downstream LSRs  .......................  10
   3.3        Labeled Packet  .....................................  11
   3.4        Label Assignment and Distribution  ..................  11
   3.5        Attributes of a Label Binding  ......................  11
   3.6        Label Distribution Protocols  .......................  11
   3.7        Unsolicited Downstream vs. Downstream-on-Demand  ....  12
   3.8        Label Retention Mode  ...............................  12
   3.9        The Label Stack  ....................................  13
   3.10       The Next Hop Label Forwarding Entry (NHLFE)  ........  13
   3.11       Incoming Label Map (ILM)  ...........................  14

Rosen, et al.               Standards Track                     [Page 1]
RFC 3031                   MPLS Architecture                January 2001

   3.12       FEC-to-NHLFE Map (FTN)  .............................  14
   3.13       Label Swapping  .....................................  15
   3.14       Scope and Uniqueness of Labels  .....................  15
   3.15       Label Switched Path (LSP), LSP Ingress, LSP Egress  .  16
   3.16       Penultimate Hop Popping  ............................  18
   3.17       LSP Next Hop  .......................................  20
   3.18       Invalid Incoming Labels  ............................  20
   3.19       LSP Control: Ordered versus Independent  ............  20
   3.20       Aggregation  ........................................  21
   3.21       Route Selection  ....................................  23
   3.22       Lack of Outgoing Label  .............................  24
   3.23       Time-to-Live (TTL)  .................................  24
   3.24       Loop Control  .......................................  25
   3.25       Label Encodings  ....................................  26
   3.25.1     MPLS-specific Hardware and/or Software  .............  26
   3.25.2     ATM Switches as LSRs  ...............................  26
   3.25.3     Interoperability among Encoding Techniques  .........  28
   3.26       Label Merging  ......................................  28
   3.26.1     Non-merging LSRs  ...................................  29
   3.26.2     Labels for Merging and Non-Merging LSRs  ............  30
   3.26.3     Merge over ATM  .....................................  31
   3.26.3.1   Methods of Eliminating Cell Interleave  .............  31
   3.26.3.2   Interoperation: VC Merge, VP Merge, and Non-Merge  ..  31
   3.27       Tunnels and Hierarchy  ..............................  32
   3.27.1     Hop-by-Hop Routed Tunnel  ...........................  32
   3.27.2     Explicitly Routed Tunnel  ...........................  33
   3.27.3     LSP Tunnels  ........................................  33
   3.27.4     Hierarchy: LSP Tunnels within LSPs  .................  33
   3.27.5     Label Distribution Peering and Hierarchy  ...........  34
   3.28       Label Distribution Protocol Transport  ..............  35
   3.29       Why More than one Label Distribution Protocol?  .....  36
   3.29.1     BGP and LDP  ........................................  36

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