Allocating and Retiring Special-Purpose MPLS Labels
RFC 7274

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Internet Engineering Task Force (IETF)                       K. Kompella
Request for Comments: 7274                              Juniper Networks
Updates: 3032, 3038, 3209, 3811, 4182, 4928, 5331,          L. Andersson
         5586, 5921, 5960, 6391, 6478, 6790                       Huawei
Category: Standards Track                                      A. Farrel
ISSN: 2070-1721                                         Juniper Networks
                                                               June 2014

          Allocating and Retiring Special-Purpose MPLS Labels

Abstract

   Some MPLS labels have been allocated for specific purposes.  A block
   of labels (0-15) has been set aside to this end; these labels are
   commonly called "reserved labels".  They will be called "special-
   purpose labels" in this document.

   As there are only 16 of these special-purpose labels, caution is
   needed in the allocation of new special-purpose labels; yet, at the
   same time, forward progress should be allowed when one is called for.

   This memo defines new procedures for the allocation and retirement of
   special-purpose labels, as well as a method to extend the special-
   purpose label space and a description of how to handle extended
   special-purpose labels in the data plane.  Finally, this memo renames
   the IANA registry for special-purpose labels to "Special-Purpose MPLS
   Label Values" and creates a new registry called the "Extended
   Special-Purpose MPLS Label Values" registry.

   This document updates a number of previous RFCs that use the term
   "reserved label".  Specifically, this document updates RFCs 3032,
   3038, 3209, 3811, 4182, 4928, 5331, 5586, 5921, 5960, 6391, 6478, and
   6790.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7274.

Kompella, et al.             Standards Track                    [Page 1]
RFC 7274               Special-Purpose MPLS Labels             June 2014

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................3
      1.1. Conventions Used in This Document ..........................3
   2. Questions .......................................................3
   3. Answers .........................................................4
      3.1. Extended Special-Purpose MPLS Label Values .................5
      3.2. Process for Retiring Special-Purpose Labels ................6
   4. Updated RFCs ....................................................7
   5. IANA Considerations .............................................8
   6. Security Considerations .........................................8
   7. Acknowledgments .................................................9
   8. References ......................................................9
      8.1. Normative References .......................................9
      8.2. Informative References ....................................10

Kompella, et al.             Standards Track                    [Page 2]
RFC 7274               Special-Purpose MPLS Labels             June 2014

1.  Introduction

   The MPLS Label Stack Encoding specification [RFC3032] defined four
   special-purpose label values (0 to 3) and set aside values 4 through
   15 for future use.  These labels have special significance in both
   the control and the data plane.  Since then, three further values
   have been allocated (values 7, 13, and 14 in [RFC6790], [RFC5586],
   and [RFC3429], respectively), leaving nine unassigned values from the
   original space of sixteen.

   While the allocation of three out of the remaining twelve special-
   purpose label values in the space of about 12 years is not in itself
   a cause for concern, the scarcity of special-purpose labels is.
   Furthermore, many of the special-purpose labels require special