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MPLS Label Stack Encoding
RFC 3032

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

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IESG State: RFC 3032 (Proposed Standard)
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Network Working Group                                           E. Rosen
Request for Comments: 3032                                     D. Tappan
Category: Standards Track                                    G. Fedorkow
                                                     Cisco Systems, Inc.
                                                              Y. Rekhter
                                                        Juniper Networks
                                                            D. Farinacci
                                                                   T. Li
                                                  Procket Networks, Inc.
                                                                A. Conta
                                                  TranSwitch Corporation
                                                            January 2001

                       MPLS Label Stack Encoding

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

   "Multi-Protocol Label Switching (MPLS)" [1] requires a set of
   procedures for augmenting network layer packets with "label stacks",
   thereby turning them into "labeled packets".  Routers which support
   MPLS are known as "Label Switching Routers", or "LSRs".  In order to
   transmit a labeled packet on a particular data link, an LSR must
   support an encoding technique which, given a label stack and a
   network layer packet, produces a labeled packet.  This document
   specifies the encoding to be used by an LSR in order to transmit
   labeled packets on Point-to-Point Protocol (PPP) data links, on LAN
   data links, and possibly on other data links as well.  On some data
   links, the label at the top of the stack may be encoded in a
   different manner, but the techniques described here MUST be used to
   encode the remainder of the label stack.  This document also
   specifies rules and procedures for processing the various fields of
   the label stack encoding.

Rosen, et al.               Standards Track                     [Page 1]
RFC 3032               MPLS Label Stack Encoding            January 2001

Table of Contents

    1      Introduction  ...........................................  2
    1.1    Specification of Requirements  ..........................  3
    2      The Label Stack  ........................................  3
    2.1    Encoding the Label Stack  ...............................  3
    2.2    Determining the Network Layer Protocol  .................  5
    2.3    Generating ICMP Messages for Labeled IP Packets  ........  6
    2.3.1  Tunneling through a Transit Routing Domain  .............  7
    2.3.2  Tunneling Private Addresses through a Public Backbone  ..  7
    2.4    Processing the Time to Live Field  ......................  8
    2.4.1  Definitions  ............................................  8
    2.4.2  Protocol-independent rules  .............................  8
    2.4.3  IP-dependent rules  .....................................  9
    2.4.4  Translating Between Different Encapsulations  ...........  9
    3      Fragmentation and Path MTU Discovery  ................... 10
    3.1    Terminology  ............................................ 11
    3.2    Maximum Initially Labeled IP Datagram Size  ............. 12
    3.3    When are Labeled IP Datagrams Too Big?  ................. 13
    3.4    Processing Labeled IPv4 Datagrams which are Too Big  .... 13
    3.5    Processing Labeled IPv6 Datagrams which are Too Big  .... 14
    3.6    Implications with respect to Path MTU Discovery  ........ 15
    4      Transporting Labeled Packets over PPP  .................. 16
    4.1    Introduction  ........................................... 16
    4.2    A PPP Network Control Protocol for MPLS  ................ 17
    4.3    Sending Labeled Packets  ................................ 18
    4.4    Label Switching Control Protocol Configuration Options  . 18
    5      Transporting Labeled Packets over LAN Media  ............ 18
    6      IANA Considerations  .................................... 19
    7      Security Considerations  ................................ 19
    8      Intellectual Property  .................................. 19
    9      Authors' Addresses  ..................................... 20
   10      References  ............................................. 22

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