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Removing a Restriction on the use of MPLS Explicit NULL (RFC4182)

IP.com Disclosure Number: IPCOM000127661D
Original Publication Date: 2005-Sep-01
Included in the Prior Art Database: 2005-Sep-08
Document File: 8 page(s) / 14K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

E. Rosen: AUTHOR

Abstract

The label stack encoding for Multi-protocol Label Switching (MPLS) defines a reserved label value known as "IPv4 Explicit NULL" and a reserved label value known as "IPv6 Explicit NULL". Previously, these labels were only legal when they occurred at the bottom of the MPLS label stack. This restriction is now removed, so that these label values may legally occur anywhere in the stack.

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Network Working Group                                           E. Rosen
Request for Comments: 4182                           Cisco Systems, Inc.
Updates: 3032                                             September 2005
Category: Standards Track


        Removing a Restriction on the use of MPLS Explicit NULL

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 (2005).

Abstract

   The label stack encoding for Multi-protocol Label Switching (MPLS)
   defines a reserved label value known as "IPv4 Explicit NULL" and a
   reserved label value known as "IPv6 Explicit NULL".  Previously,
   these labels were only legal when they occurred at the bottom of the
   MPLS label stack.  This restriction is now removed, so that these
   label values may legally occur anywhere in the stack.

   This document updates RFC 3032.

Table of Contents

   1. Introduction ....................................................2
   2. Detail of Change ................................................2
   3. Reasons for Change ..............................................3
   4. Deployment Considerations .......................................5
   5. Security Considerations .........................................5
   6. Acknowledgments .................................................5
   7. Normative References ............................................5
   8. Informative References ..........................................5


Rosen                       Standards Track                     [Page 1]
RFC 4182       Removing a Restriction on the use of MPLS  September 2005


1.  Introduction

   RFC 3032 defines a reserved label value known as "IPv4 Explicit NULL"
   and a reserved label value known as "IPv6 Explicit NULL" [RFC3032].
   It states that these label values are only legal at the bottom of the
   MPLS label stack.  However, no reason is given for this restriction.

   It has turned out that in practice there are some situations in which
   it is useful to send MPLS packets that have Explicit NULL occur
   somewhere other than at that bottom of the label stack.  While the
   intended semantics are obvious enough, the fact that such packets are
   gratuitously declared by RFC 3032 to be illegal has made it difficult
   to handle these situations in an interoperable manner.

   This document updates RFC 3032 by removing the unnecessary
   restriction, so that the tw...