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Internet Engineering Task Force (IETF)                             H. LiRequest for Comments: 6423                                  China MobileUpdates:5586                                                 L. MartiniCategory: Standards Track                                   Cisco SystemISSN: 2070-1721                                                    J. He                                                                  Huawei                                                                F. Huang                                                          Alcatel-Lucent                                                           November 2011Using the Generic Associated Channel Label for Pseudowire inthe 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 inRFC 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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6423.Li, et al.                   Standards Track                    [Page 1]

RFC 6423                 Using GAL in MPLS-TP PW           November 2011Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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 Contents1. Introduction ....................................................22. Conventions Used in This Document ...............................22.1. Terminology ................................................33. GAL Usage for MPLS-TP PW ........................................34. Security Considerations .........................................45. Acknowledgments .................................................46. References ......................................................56.1. Normative References .......................................56.2. Informative References .....................................51.  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].2.  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].Li, et al.                   Standards Track                    [Page 2]

RFC 6423                 Using GAL in MPLS-TP PW           November 20112.1.  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 Maintenance3.  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 inSection 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.Li, et al.                   Standards Track                    [Page 3]

RFC 6423                 Using GAL in MPLS-TP PW           November 2011   [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.4.  Security Considerations   There are no further security considerations than those in [RFC5586].5.  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].Li, et al.                   Standards Track                    [Page 4]

RFC 6423                 Using GAL in MPLS-TP PW           November 20116.  References6.1.  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 2009.6.2.  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: lihan@chinamobile.com   Luca Martini   Cisco Systems, Inc.   EMail: lmartini@cisco.com   Jia He   Huawei Technologies Co., Ltd.   EMail: hejia@huawei.com   Feng Huang   Alcatel-Lucent shanghai Bell   EMail: feng.f.huang@alcatel-sbell.com.cnLi, et al.                   Standards Track                    [Page 5]