Assignment of the 'OAM Alert Label' for Multiprotocol Label Switching Architecture (MPLS) Operation and Maintenance (OAM) Functions
RFC 3429

Document Type RFC - Informational (November 2002; No errata)
Was draft-ohta-mpls-label-value (individual in sub area)
Last updated 2013-03-02
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Network Working Group                                            H. Ohta
Request for Comments: 3429                                           NTT
Category: Informational                                    November 2002

                Assignment of the 'OAM Alert Label' for
           Multiprotocol Label Switching Architecture (MPLS)
              Operation and Maintenance (OAM) Functions

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This document describes the assignment of one of the reserved label
   values defined in RFC 3032 (MPLS label stack encoding) to the
   'Operation and Maintenance (OAM) Alert Label' that is used by user-
   plane Multiprotocol Label Switching Architecture (MPLS) OAM functions
   for identification of MPLS OAM packets.

1. Introduction

   This document describes the assignment of one of the reserved label
   values defined in RFC 3032 (MPLS label stack encoding [2]) to the
   'OAM Alert Label' that is used by user-plane MPLS OAM functions for
   identification of MPLS OAM packets as described in the ITU-T
   Recommendation Y.1711 [1] (on MPLS OAM functions).

2. OAM functions

   MPLS OAM (Operation and Maintenance) functions provide necessary
   tools for network operators to operate and maintain the networks.
   MPLS OAM functionality is required at the MPLS layer, and more
   specifically at each MPLS level, independent of OAM functionality
   provided by the lower layers (SONET/SDH, etc.).  The objectives of
   the OAM functions include the following:

   -  Defect and failure detection: Defect/failures affecting the
      transport of user information are detected by continuous or
      periodic checking.  As a result, maintenance event information or
      appropriate alarms will be produced.

Ohta                         Informational                      [Page 1]
RFC 3429           OAM Alert Label for OAM Functions       November 2002

   -  Reporting the defect/failure information: Defect information is
      given to other management entities (e.g., Operation Support
      System) in order to provide the appropriate indications to the
      maintenance staff for maintaining the Quality of Service (QoS)
      level offered to customers.

   -  Defect/failure localization: Determination by internal or external
      test systems of a failed entity is performed if defect information
      is insufficient.

   -  Performance monitoring: Performance (packet losses, transfer
      delay, bit errors, etc.) of the user information transport is
      measured in order to estimate the transport integrity.

3. OAM Packet Identification

   The user-plane MPLS OAM mechanisms as described in the ITU-T
   Recommendation Y.1711 [1] uses a special label called 'OAM Alert
   Label' to differentiate OAM packets from the normal user packets.
   One of the reserved label values defined in RFC 3032 (MPLS label
   stack encoding [2]) is assigned to 'OAM Alert Label'.  A value of 14
   is used for this purpose.

4. MPLS OAM work in ITU-T SG13

   ITU-T Study Group 13, Question 3/13 is progressing work on user-plane
   MPLS OAM and has produced the following documents:

   (1) Recommendation Y.1710 (Requirements for OAM functionality for
       MPLS networks) [3]

   (2) Corrigendum 1 to Recommendation Y.1710 [4]

   (3) Recommendation Y.1711 (OAM mechanisms for MPLS networks) [1]

   (4) Draft Recommendation Y.1720 (Protection switching for MPLS
       networks) [6] relies on OAM mechanisms in Y.1711, under last call
       as of Nov. 2002.

5. Considerations on penultimate hop popping (PHP)

   In response to concerns raised during IETF meetings and in related
   discussions, this section provides an explanation on how MPLS OAM
   functions defined in ITU-T Recommendation Y.1711 [1] are applied to
   MPLS networks where PHP is in effect.

Ohta                         Informational                      [Page 2]
RFC 3429           OAM Alert Label for OAM Functions       November 2002

5.1 Scope of ITU-T Recommendation Y.1711

   The scope of ITU-T Recommendation Y.1711 includes application to both
   non-PHP and PHP cases as quoted below [1].

   "1 Scope
   This Recommendation provides mechanisms for user-plane OAM (Operation
   and Maintenance) functionality in MPLS networks according to the
   requirements and principles given in Recommendation Y.1710.  OAM
   functions specified in this Recommendation can be applied to both
   non-PHP and PHP cases unless otherwise stated.  The current version
   of this recommendation is designed primarily to support
   point-to-point and multipoint-to-point explicit routed LSPs
   (ER-LSPs)."

5.2 Applicability of MPLS OAM to PHP

   There are two cases where PHP is used:

   Case 1: The ultimate node is an MPLS LSR, and implements both MPLS
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