Update of the Pseudowire Control-Word Negotiation Mechanism
RFC 6723

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Internet Engineering Task Force (IETF)                       L. Jin, Ed.
Request for Comments: 6723                                           ZTE
Updates: 4447, 6073                                          R. Key, Ed.
Category: Standards Track                                         Huawei
ISSN: 2070-1721                                                S. Delord
                                                          Alcatel-Lucent
                                                               T. Nadeau
                                                                 Juniper
                                                              S. Boutros
                                                     Cisco Systems, Inc.
                                                          September 2012

      Update of the Pseudowire Control-Word Negotiation Mechanism

Abstract

   The control-word negotiation mechanism specified in RFC 4447 has a
   problem when a PE (Provider Edge) changes the preference for the use
   of the control word from NOT PREFERRED to PREFERRED.  This document
   updates RFC 4447 and RFC 6073 by adding the Label Request message to
   resolve this control-word negotiation issue for single-segment and
   multi-segment pseudowires.

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/rfc6723.

Jin, et al.                  Standards Track                    [Page 1]
RFC 6723             Update of PW C-Bit Negotiation       September 2012

Copyright Notice

   Copyright (c) 2012 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  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Conventions Used in This Document . . . . . . . . . . . . . . . 3
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Control-Word Renegotiation by Label Request Message . . . . . . 4
     4.1.  Control-Word Renegotiation for Multi-Segment PW . . . . . . 5
     4.2.  Control-Word Renegotiation Use Case . . . . . . . . . . . . 5
   5.  Backward Compatibility  . . . . . . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . 7
   9.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Appendix A.  Updated Diagram of C-Bit Handling Procedures . . . . . 8

1.  Introduction

   The control-word negotiation mechanism specified in [RFC4447],
   Section 6.2, encounters a problem when a PE changes the preference
   for the use of the control word from NOT PREFERRED to PREFERRED.
   [RFC4447] specifies that if both endpoints prefer the use of the
   control word, then the pseudowire control word should be used.
   However, in the case where a PE changes its preference from NOT
   PREFERRED to PREFERRED and both ends of the PW (pseudowire) PE have
   the use of control word set as PREFERRED, an incorrect negotiated
   result of the control word as "not used" occurs.  This document
   updates the control-word negotiation mechanism in [RFC4447] by adding
   a Label Request message to resolve this negotiation issue for single-
   segment PW.  Multi-segment PW in [RFC6073] inherits the control-word
   negotiation mechanism in [RFC4447], and this document updates
   [RFC6073] by adding the processing of Label Request message on the

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RFC 6723             Update of PW C-Bit Negotiation       September 2012

   S-PE (Switching Provider Edge).  When the PE changes the preference
   for the use of control word from PREFERRED to NOT PREFERRED, it
   should follow [RFC4447], and there is no problem.

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",