RFC6423

Internet Engineering Task Force (IETF) H. Li Request for Comments: 6423 China Mobile Updates: 5586 L. Martini Category: Standards Track Cisco System ISSN: 2070-1721 J. He

                                                              Huawei
                                                            F. Huang
                                                      Alcatel-Lucent
                                                       November 2011

  Using the Generic Associated Channel Label for Pseudowire in
              the MPLS Transport Profile (MPLS-TP)

Abstract

This document describes the requirements for using the Generic Associated Channel Label (GAL) in pseudowires (PWs) in MPLS Transport Profile (MPLS-TP) networks, and provides an update to the description of GAL usage in RFC 5586 by removing the restriction that is imposed on using GAL for PWs, especially in MPLS-TP environments.

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/rfc6423.

Copyright Notice

Copyright (c) 2011 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.

Introduction

RFC5586 generalizes the Associated Channel mechanism of RFC5085 to be used for Sections, Label Switched Paths (LSPs), and Pseudowires (PWs) in MPLS networks. RFC5085 defines the Associated Channel Header (ACH), and RFC5586 generalizes this for use as the Generic Associated Channel (G-ACh).

RFC5586 defines a generalized label-based exception mechanism using the Generic Associated Channel Label (GAL) to work together with the ACH for use with LSPs but prohibits GAL usage with PWs.

This document removes the restriction imposed by RFC5586.

Conventions Used in This Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119.

Terminology

ACH Associated Channel Header

CW Control Word

G-ACh Generic Associated Channel

GAL Generic Associated Channel Label

MPLS-TP MPLS Transport Profile

OAM Operation, Administration, and Maintenance

GAL Usage for MPLS-TP PW

According to the MPLS-TP requirements document RFC5654, it is necessary that MPLS-TP mechanisms and capabilities be able to interoperate with the existing IETF MPLS RFC3031 and IETF PWE3 RFC3985 architectures as appropriate. RFC5586 differentiates between the usage of the GAL with PWs in MPLS and MPLS-TP environments in Section 4.2 as follows:

  In MPLS-TP, the GAL MUST be used with packets on a G-ACh on LSPs,
  Concatenated Segments of LSPs, and with Sections, and MUST NOT be
  used with PWs.

This indicates that the GAL can be used for MPLS-TP LSPs and Sections, but not for PWs in an MPLS-TP network.

However, there is no restriction imposed on the usage of the GAL in MPLS PWs, which is described immediately afterwards in the same section (Section 4.2) of RFC5586:

  However, in other MPLS environments, this document places no
  restrictions on where the GAL may appear within the label stack or
  its use with PWs.

The inconsistency between the usage of the GAL with MPLS PWs and MPLS-TP PWs may cause unnecessary implementation differences and is in disagreement with the MPLS-TP requirements.

Therefore, this document specifies that the GAL can be used with packets on a G-ACh on LSPs, Concatenated Segments of LSPs, Sections, and PWs in both MPLS and MPLS-TP environments without discrimination.

RFC5586 is updated by removing the restrictions on using GAL for PW as follows:

- Section 1 (Introduction) in RFC5586, the original text:

     The GAL mechanism is defined to work together with the ACH for
     LSPs and MPLS Sections.

  is replaced by:

     The GAL mechanism is defined to work together with the ACH for
     LSPs and MPLS Sections, and for PWs.

- Section 4.2. (GAL Applicability and Usage) in RFC5586, the

  original text:

     In MPLS-TP, the GAL MUST be used with packets on a G-ACh on
     LSPs, Concatenated Segments of LSPs, and with Sections, and
     MUST NOT be used with PWs.  It MUST always be at the bottom of
     the label stack (i.e., S bit set to 1).  However, in other MPLS
     environments, this document places no restrictions on where the
     GAL may appear within the label stack or its use with PWs.

  is replaced by:

     In MPLS-TP, the GAL MUST be used with packets on a G-ACh on
     LSPs, Concatenated Segments of LSPs, and with Sections, and MAY
     be used with PWs.  The presence of a GAL indicates that an ACH
     immediately follows the MPLS label stack.

Security Considerations

There are no further security considerations than those in RFC5586.

Acknowledgments

The authors would like to thank Luyuan Fang, Adrian Farrel, Haiyan Zhang, Guanghui Sun, Italo Busi, and Matthew Bocci for their contributions to this work.

The authors would also like to thank the authors of RFC5586 and people who were involved in the development of RFC5586.

References

Normative References

RFC2119 Bradner, S., "Key words for use in RFCs to Indicate

         Requirement Levels", BCP 14, RFC 2119, March 1997

RFC3031 Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol

         Label Switching Architecture", RFC 3031, January 2001.

RFC3985 Bryant, S., Ed., and P. Pate, Ed., "Pseudo Wire Emulation

         Edge-to-Edge (PWE3) Architecture", RFC 3985, March 2005.

RFC5586 Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,

         "MPLS Generic Associated Channel", RFC 5586, June 2009.

Informative References

RFC5085 Nadeau, T., Ed., and C. Pignataro, Ed., "Pseudowire Virtual

         Circuit Connectivity Verification (VCCV): A Control Channel
         for Pseudowires", RFC 5085, December 2007.

RFC5654 Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,

         Sprecher, N.,and S. Ueno, "Requirements of an MPLS
         Transport Profile", RFC 5654, September 2009.

Authors' Addresses

Han Li China Mobile Communications Corporation EMail: [email protected]

Luca Martini Cisco Systems, Inc. EMail: [email protected]

Jia He Huawei Technologies Co., Ltd. EMail: [email protected]

Feng Huang Alcatel-Lucent shanghai Bell EMail: [email protected]