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This is a modified version of the Internet RFC suitable for machine-translating. Original version is available here: RFC6423
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PROPOSED STANDARD
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.
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RFC 6423                 Using GAL in MPLS-TP PW           November 2011
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.

Table of Contents

1. Introduction ....................................................2
2. Conventions Used in This Document ...............................2
2.1. Terminology ................................................3
3. GAL Usage for MPLS-TP PW ........................................3
4. Security Considerations .........................................4
5. Acknowledgments .................................................4
6. References ......................................................5
6.1. Normative References .......................................5
6.2. Informative References .....................................5
1.  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].
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RFC 6423                 Using GAL in MPLS-TP PW           November 2011
2.1.  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 Maintenance
3.  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:
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RFC 6423                 Using GAL in MPLS-TP PW           November 2011
- 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].
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RFC 6423                 Using GAL in MPLS-TP PW           November 2011
6.  References

6.1.  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.cn





Li, et al. Standards Track [Page 5]

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