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MPLS Generic Associated Channel
RFC 5586

Network Working Group                                      M. Bocci, Ed.
Request for Comments: 5586                             M. Vigoureux, Ed.
Updates: 3032, 4385, 5085                                 Alcatel-Lucent
Category: Standards Track                                 S. Bryant, Ed.
                                                           Cisco Systems
                                                               June 2009

                    MPLS Generic Associated Channel

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (c) 2009 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 in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Abstract

   This document generalizes the applicability of the pseudowire (PW)
   Associated Channel Header (ACH), enabling the realization of a
   control channel associated to MPLS Label Switched Paths (LSPs) and
   MPLS Sections in addition to MPLS pseudowires.  In order to identify
   the presence of this Associated Channel Header in the label stack,
   this document also assigns one of the reserved MPLS label values to
   the Generic Associated Channel Label (GAL), to be used as a label
   based exception mechanism.

Bocci, et al.               Standards Track                     [Page 1]
RFC 5586                     G-ACh and GAL                     June 2009

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Objectives . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.2.  Scope  . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.3.  Requirements Language and Terminology  . . . . . . . . . .  5
   2.  Generic Associated Channel Header  . . . . . . . . . . . . . .  5
     2.1.  Definition . . . . . . . . . . . . . . . . . . . . . . . .  6
     2.2.  Allocation of Channel Types  . . . . . . . . . . . . . . .  6
   3.  ACH TLVs . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1.  ACH TLV Payload Structure  . . . . . . . . . . . . . . . .  7
     3.2.  ACH TLV Header . . . . . . . . . . . . . . . . . . . . . .  8
     3.3.  ACH TLV Object . . . . . . . . . . . . . . . . . . . . . .  8
   4.  Generalized Exception Mechanism  . . . . . . . . . . . . . . .  9
     4.1.  Relationship with Existing MPLS OAM Alert Mechanisms . . .  9
     4.2.  GAL Applicability and Usage  . . . . . . . . . . . . . . . 10
       4.2.1.  GAL Processing . . . . . . . . . . . . . . . . . . . . 10
     4.3.  Relationship with RFC 3429 . . . . . . . . . . . . . . . . 13
   5.  Compatibility  . . . . . . . . . . . . . . . . . . . . . . . . 14
   6.  Congestion Considerations  . . . . . . . . . . . . . . . . . . 15
   7.  Major Contributing Authors . . . . . . . . . . . . . . . . . . 15
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 15
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 17
     11.2. Informative References . . . . . . . . . . . . . . . . . . 18

Bocci, et al.               Standards Track                     [Page 2]
RFC 5586                     G-ACh and GAL                     June 2009

1.  Introduction

   There is a need for Operations, Administration, and Maintenance (OAM)
   mechanisms that can be used for fault detection, diagnostics,
   maintenance, and other functions on a pseudowire (PW) and a Label
   Switched Path (LSP).  These functions can be used between any two
   Label Edge Routers (LERs)/Label Switching Router (LSRs) or
   Terminating Provider Edge routers (T-PEs)/Switching Provider Edge
   routers (S-PEs) along the path of an LSP or PW, respectively
   [MPLS-TP].  Some of these functions can be supported using existing
   tools such as Virtual Circuit Connectivity Verification (VCCV)
   [RFC5085], Bidirectional Forwarding Detection for MPLS LSPs (BFD-
   MPLS) [BFD-MPLS], LSP-Ping [RFC4379], or BFD-VCCV [BFD-VCCV].
   However, a requirement has been indicated to augment this set of

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