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RFC 7276

Informational
Pages: 53
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An Overview of Operations, Administration, and Maintenance (OAM) Tools

Part 1 of 3, p. 1 to 17
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Internet Engineering Task Force (IETF)                        T. Mizrahi
Request for Comments: 7276                                       Marvell
Category: Informational                                      N. Sprecher
ISSN: 2070-1721                             Nokia Solutions and Networks
                                                           E. Bellagamba
                                                                Ericsson
                                                           Y. Weingarten
                                                               June 2014


                             An Overview of
        Operations, Administration, and Maintenance (OAM) Tools

Abstract

   Operations, Administration, and Maintenance (OAM) is a general term
   that refers to a toolset for fault detection and isolation, and for
   performance measurement.  Over the years, various OAM tools have been
   defined for various layers in the protocol stack.

   This document summarizes some of the OAM tools defined in the IETF in
   the context of IP unicast, MPLS, MPLS Transport Profile (MPLS-TP),
   pseudowires, and Transparent Interconnection of Lots of Links
   (TRILL).  This document focuses on tools for detecting and isolating
   failures in networks and for performance monitoring.  Control and
   management aspects of OAM are outside the scope of this document.
   Network repair functions such as Fast Reroute (FRR) and protection
   switching, which are often triggered by OAM protocols, are also out
   of the scope of this document.

   The target audience of this document includes network equipment
   vendors, network operators, and standards development organizations.
   This document can be used as an index to some of the main OAM tools
   defined in the IETF.  At the end of the document, a list of the OAM
   toolsets and a list of the OAM functions are presented as a summary.

Page 2 
Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see 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/rfc7276.

Copyright Notice

   Copyright (c) 2014 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.

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Table of Contents

   1. Introduction ....................................................4
      1.1. Background .................................................5
      1.2. Target Audience ............................................6
      1.3. OAM-Related Work in the IETF ...............................6
      1.4. Focusing on the Data Plane .................................7
   2. Terminology .....................................................8
      2.1. Abbreviations ..............................................8
      2.2. Terminology Used in OAM Standards .........................10
           2.2.1. General Terms ......................................10
           2.2.2. Operations, Administration, and Maintenance ........10
           2.2.3. Functions, Tools, and Protocols ....................11
           2.2.4. Data Plane, Control Plane, and Management Plane ....11
           2.2.5. The Players ........................................12
           2.2.6. Proactive and On-Demand Activation .................13
           2.2.7. Connectivity Verification and Continuity Checks ....14
           2.2.8. Connection-Oriented vs. Connectionless
                  Communication ......................................15
           2.2.9. Point-to-Point vs. Point-to-Multipoint Services ....16
           2.2.10. Failures ..........................................16
   3. OAM Functions ..................................................17
   4. OAM Tools in the IETF - A Detailed Description .................18
      4.1. IP Ping ...................................................18
      4.2. IP Traceroute .............................................19
      4.3. Bidirectional Forwarding Detection (BFD) ..................20
           4.3.1. Overview ...........................................20
           4.3.2. Terminology ........................................20
           4.3.3. BFD Control ........................................20
           4.3.4. BFD Echo ...........................................21
      4.4. MPLS OAM ..................................................21
           4.4.1. LSP Ping ...........................................21
           4.4.2. BFD for MPLS .......................................22
           4.4.3. OAM for Virtual Private Networks (VPNs) over MPLS ..23
      4.5. MPLS-TP OAM ...............................................23
           4.5.1. Overview ...........................................23
           4.5.2. Terminology ........................................24
           4.5.3. Generic Associated Channel .........................25
           4.5.4. MPLS-TP OAM Toolset ................................25
                  4.5.4.1. Continuity Check and Connectivity
                           Verification ..............................26
                  4.5.4.2. Route Tracing .............................26
                  4.5.4.3. Lock Instruct .............................27
                  4.5.4.4. Lock Reporting ............................27
                  4.5.4.5. Alarm Reporting ...........................27
                  4.5.4.6. Remote Defect Indication ..................27
                  4.5.4.7. Client Failure Indication .................27

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                  4.5.4.8. Performance Monitoring ....................28
                           4.5.4.8.1. Packet Loss Measurement (LM) ...28
                           4.5.4.8.2. Packet Delay Measurement (DM) ..28
      4.6. Pseudowire OAM ............................................29
           4.6.1. Pseudowire OAM Using Virtual Circuit
                  Connectivity Verification (VCCV) ...................29
           4.6.2. Pseudowire OAM Using G-ACh .........................30
           4.6.3. Attachment Circuit - Pseudowire Mapping ............30
      4.7. OWAMP and TWAMP ...........................................31
           4.7.1. Overview ...........................................31
           4.7.2. Control and Test Protocols .........................32
           4.7.3. OWAMP ..............................................32
           4.7.4. TWAMP ..............................................33
      4.8. TRILL .....................................................33
   5. Summary ........................................................34
      5.1. Summary of OAM Tools ......................................34
      5.2. Summary of OAM Functions ..................................37
      5.3. Guidance to Network Equipment Vendors .....................38
   6. Security Considerations ........................................38
   7. Acknowledgments ................................................39
   8. References .....................................................39
      8.1. Normative References ......................................39
      8.2. Informative References ....................................39
   Appendix A. List of OAM Documents ................................ 46
      A.1. List of IETF OAM Documents ............................... 46
      A.2. List of Selected Non-IETF OAM Documents .................. 50

1.  Introduction

   "OAM" is a general term that refers to a toolset for detecting,
   isolating, and reporting failures, and for monitoring network
   performance.

   There are several different interpretations of the "OAM" acronym.
   This document refers to Operations, Administration, and Maintenance,
   as recommended in Section 3 of [OAM-Def].

   This document summarizes some of the OAM tools defined in the IETF in
   the context of IP unicast, MPLS, MPLS Transport Profile (MPLS-TP),
   pseudowires, and TRILL.

   This document focuses on tools for detecting and isolating failures
   and for performance monitoring.  Hence, this document focuses on the
   tools used for monitoring and measuring the data plane; control and
   management aspects of OAM are outside the scope of this document.
   Network repair functions such as Fast Reroute (FRR) and protection
   switching, which are often triggered by OAM protocols, are also out
   of the scope of this document.

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1.1.  Background

   OAM was originally used in traditional communication technologies
   such as E1 and T1, evolving into Plesiochronous Digital Hierarchy
   (PDH) and then later into Synchronous Optical Network / Synchronous
   Digital Hierarchy (SONET/SDH).  ATM was probably the first technology
   to include inherent OAM support from day one, while in other
   technologies OAM was typically defined in an ad hoc manner after the
   technology was already defined and deployed.  Packet-based networks
   were traditionally considered unreliable and best effort.  As packet-
   based networks evolved, they have become the common transport for
   both data and telephony, replacing traditional transport protocols.
   Consequently, packet-based networks were expected to provide a
   similar "carrier grade" experience, and specifically to support more
   advanced OAM functions, beyond ICMP and router hellos, that were
   traditionally used for fault detection.

   As typical networks have a multi-layer architecture, the set of OAM
   protocols similarly take a multi-layer structure; each layer has its
   own OAM protocols.  Moreover, OAM can be used at different levels of
   hierarchy in the network to form a multi-layer OAM solution, as shown
   in the example in Figure 1.

   Figure 1 illustrates a network in which IP traffic between two
   customer edges is transported over an MPLS provider network.  MPLS
   OAM is used at the provider level for monitoring the connection
   between the two provider edges, while IP OAM is used at the customer
   level for monitoring the end-to-end connection between the two
   customer edges.

           |<-------------- Customer-level OAM -------------->|
                 IP OAM (Ping, Traceroute, OWAMP, TWAMP)

                        |<- Provider-level OAM ->|
                            MPLS OAM (LSP Ping)

     +-----+       +----+                        +----+       +-----+
     |     |       |    |========================|    |       |     |
     |     |-------|    |          MPLS          |    |-------|     |
     |     |  IP   |    |                        |    |  IP   |     |
     +-----+       +----+                        +----+       +-----+
     Customer     Provider                      Provider      Customer
       Edge         Edge                          Edge          Edge

                  Figure 1: Example of Multi-layer OAM

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1.2.  Target Audience

   The target audience of this document includes:

   o  Standards development organizations - Both IETF working groups and
      non-IETF organizations can benefit from this document when
      designing new OAM protocols, or when looking to reuse existing OAM
      tools for new technologies.

   o  Network equipment vendors and network operators can use this
      document as an index to some of the common IETF OAM tools.

   It should be noted that some background in OAM is necessary in order
   to understand and benefit from this document.  Specifically, the
   reader is assumed to be familiar with the term "OAM" [OAM-Def], the
   motivation for using OAM, and the distinction between OAM and network
   management [OAM-Mng].

1.3.  OAM-Related Work in the IETF

   This memo provides an overview of the different sets of OAM tools
   defined by the IETF.  The set of OAM tools described in this memo are
   applicable to IP unicast, MPLS, pseudowires, MPLS Transport Profile
   (MPLS-TP), and TRILL.  While OAM tools that are applicable to other
   technologies exist, they are beyond the scope of this memo.

   This document focuses on IETF documents that have been published as
   RFCs, while other ongoing OAM-related work is outside the scope.

   The IETF has defined OAM protocols and tools in several different
   contexts.  We roughly categorize these efforts into a few sets of
   OAM-related RFCs, listed in Table 1.  Each set defines a logically
   coupled set of RFCs, although the sets are in some cases intertwined
   by common tools and protocols.

   The discussion in this document is ordered according to these sets
   (the acronyms and abbreviations are listed in Section 2.1).

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                        +--------------+------------+
                        | Toolset      | Transport  |
                        |              | Technology |
                        +--------------+------------+
                        |IP Ping       | IPv4/IPv6  |
                        +--------------+------------+
                        |IP Traceroute | IPv4/IPv6  |
                        +--------------+------------+
                        |BFD           | generic    |
                        +--------------+------------+
                        |MPLS OAM      | MPLS       |
                        +--------------+------------+
                        |MPLS-TP OAM   | MPLS-TP    |
                        +--------------+------------+
                        |Pseudowire OAM| Pseudowires|
                        +--------------+------------+
                        |OWAMP and     | IPv4/IPv6  |
                        |TWAMP         |            |
                        +--------------+------------+
                        |TRILL OAM     | TRILL      |
                        +--------------+------------+

                Table 1: OAM Toolset Packages in the IETF Documents

   This document focuses on OAM tools that have been developed in the
   IETF.  A short summary of some of the significant OAM standards that
   have been developed in other standard organizations is presented in
   Appendix A.2.

1.4.  Focusing on the Data Plane

   OAM tools may, and quite often do, work in conjunction with a control
   plane and/or management plane.  OAM provides instrumentation tools
   for measuring and monitoring the data plane.  OAM tools often use
   control-plane functions, e.g., to initialize OAM sessions and to
   exchange various parameters.  The OAM tools communicate with the
   management plane to raise alarms, and often OAM tools may be
   activated by the management plane (as well as by the control plane),
   e.g., to locate and localize problems.

   The considerations of the control-plane maintenance tools and the
   functionality of the management plane are out of scope for this
   document, which concentrates on presenting the data-plane tools that
   are used for OAM.  Network repair functions such as Fast Reroute
   (FRR) and protection switching, which are often triggered by OAM
   protocols, are also out of the scope of this document.

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   Since OAM protocols are used for monitoring the data plane, it is
   imperative for OAM tools to be capable of testing the actual data
   plane with as much accuracy as possible.  Thus, it is important to
   enforce fate-sharing between OAM traffic that monitors the data plane
   and the data-plane traffic it monitors.

2.  Terminology

2.1.  Abbreviations

   ACH      Associated Channel Header

   AIS      Alarm Indication Signal

   ATM      Asynchronous Transfer Mode

   BFD      Bidirectional Forwarding Detection

   CC       Continuity Check

   CC-V     Continuity Check and Connectivity Verification

   CV       Connectivity Verification

   DM       Delay Measurement

   ECMP     Equal-Cost Multipath

   FEC      Forwarding Equivalence Class

   FRR      Fast Reroute

   G-ACh    Generic Associated Channel

   GAL      Generic Associated Channel Label

   ICMP     Internet Control Message Protocol

   L2TP     Layer 2 Tunneling Protocol

   L2VPN    Layer 2 Virtual Private Network

   L3VPN    Layer 3 Virtual Private Network

   LCCE     L2TP Control Connection Endpoint

   LDP      Label Distribution Protocol

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   LER      Label Edge Router

   LM       Loss Measurement

   LSP      Label Switched Path

   LSR      Label Switching Router

   ME       Maintenance Entity

   MEG      Maintenance Entity Group

   MEP      MEG End Point

   MIP      MEG Intermediate Point

   MP       Maintenance Point

   MPLS     Multiprotocol Label Switching

   MPLS-TP  MPLS Transport Profile

   MTU      Maximum Transmission Unit

   OAM      Operations, Administration, and Maintenance

   OWAMP    One-Way Active Measurement Protocol

   PDH      Plesiochronous Digital Hierarchy

   PE       Provider Edge

   PSN      Public Switched Network

   PW       Pseudowire

   PWE3     Pseudowire Emulation Edge-to-Edge

   RBridge  Routing Bridge

   RDI      Remote Defect Indication

   SDH      Synchronous Digital Hierarchy

   SONET    Synchronous Optical Network

   TRILL    Transparent Interconnection of Lots of Links

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   TTL      Time To Live

   TWAMP    Two-Way Active Measurement Protocol

   VCCV     Virtual Circuit Connectivity Verification

   VPN      Virtual Private Network

2.2.  Terminology Used in OAM Standards

2.2.1.  General Terms

   A wide variety of terms is used in various OAM standards.  This
   section presents a comparison of the terms used in various OAM
   standards, without fully quoting the definition of each term.

   An interesting overview of the term "OAM" and its derivatives is
   presented in [OAM-Def].  A thesaurus of terminology for MPLS-TP terms
   is presented in [TP-Term], which provides a good summary of some of
   the OAM-related terminology.

2.2.2.  Operations, Administration, and Maintenance

   The following definition of OAM is quoted from [OAM-Def]:

   The components of the "OAM" acronym (and provisioning) are defined as
   follows:

   o  Operations - Operation activities are undertaken to keep the
      network (and the services that the network provides) up and
      running.  It includes monitoring the network and finding problems.
      Ideally these problems should be found before users are affected.

   o  Administration - Administration activities involve keeping track
      of resources in the network and how they are used.  It includes
      all the bookkeeping that is necessary to track networking
      resources and the network under control.

   o  Maintenance - Maintenance activities are focused on facilitating
      repairs and upgrades -- for example, when equipment must be
      replaced, when a router needs a patch for an operating system
      image, or when a new switch is added to a network.  Maintenance
      also involves corrective and preventive measures to make the
      managed network run more effectively, e.g., adjusting device
      configuration and parameters.

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2.2.3.  Functions, Tools, and Protocols

   OAM Function

      An OAM function is an instrumentation measurement type or
      diagnostic.

      OAM functions are the atomic building blocks of OAM, where each
      function defines an OAM capability.

      Typical examples of OAM functions are presented in Section 3.

   OAM Protocol

      An OAM protocol is a protocol used for implementing one or more
      OAM functions.

      The OWAMP-Test [OWAMP] is an example of an OAM protocol.

   OAM Tool

      An OAM tool is a specific means of applying one or more OAM
      functions.

      In some cases, an OAM protocol *is* an OAM tool, e.g., OWAMP-Test.
      In other cases, an OAM tool uses a set of protocols that are not
      strictly OAM related; for example, Traceroute (Section 4.2) can be
      implemented using UDP and ICMP messages, without using an OAM
      protocol per se.

2.2.4.  Data Plane, Control Plane, and Management Plane

   Data Plane

      The data plane is the set of functions used to transfer data in
      the stratum or layer under consideration [ITU-Terms].

      The data plane is also known as the forwarding plane or the user
      plane.

   Control Plane

      The control plane is the set of protocols and mechanisms that
      enable routers to efficiently learn how to forward packets towards
      their final destination (based on [Comp]).

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   Management Plane

      The term "Management Plane", as described in [Mng], is used to
      describe the exchange of management messages through management
      protocols (often transported by IP and by IP transport protocols)
      between management applications and the managed entities such as
      network nodes.

   Data Plane vs. Control Plane vs. Management Plane

      The distinction between the planes is at times a bit vague.  For
      example, the definition of "Control Plane" above may imply that
      OAM tools such as ping, BFD, and others are in fact in the control
      plane.

      This document focuses on tools used for monitoring the data plane.
      While these tools could arguably be considered to be in the
      control plane, these tools monitor the data plane, and hence it is
      imperative to have fate-sharing between OAM traffic that monitors
      the data plane and the data-plane traffic it monitors.

      Another potentially vague distinction is between the management
      plane and control plane.  The management plane should be seen as
      separate from, but possibly overlapping with, the control plane
      (based on [Mng]).

2.2.5.  The Players

   An OAM tool is used between two (or more) peers.  Various terms are
   used in IETF documents to refer to the players that take part in OAM.
   Table 2 summarizes the terms used in each of the toolsets discussed
   in this document.

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        +--------------------------+---------------------------+
        | Toolset                  | Terms                     |
        +--------------------------+---------------------------+
        | Ping / Traceroute        |- Host                     |
        | ([ICMPv4], [ICMPv6],     |- Node                     |
        |  [TCPIP-Tools])          |- Interface                |
        |                          |- Gateway                  |
        + ------------------------ + ------------------------- +
        | BFD [BFD]                |- System                   |
        + ------------------------ + ------------------------- +
        | MPLS OAM [MPLS-OAM-FW]   |- LSR                      |
        + ------------------------ + ------------------------- +
        | MPLS-TP OAM [TP-OAM-FW]  |- End Point - MEP          |
        |                          |- Intermediate Point - MIP |
        + ------------------------ + ------------------------- +
        | Pseudowire OAM [VCCV]    |- PE                       |
        |                          |- LCCE                     |
        + ------------------------ + ------------------------- +
        | OWAMP and TWAMP          |- Host                     |
        | ([OWAMP], [TWAMP])       |- End system               |
        + ------------------------ + ------------------------- +
        | TRILL OAM [TRILL-OAM]    |- RBridge                  |
        +--------------------------+---------------------------+

                  Table 2: Maintenance Point Terminology

2.2.6.  Proactive and On-Demand Activation

   The different OAM tools may be used in one of two basic types of
   activation:

   Proactive

      Proactive activation - indicates that the tool is activated on a
      continual basis, where messages are sent periodically, and errors
      are detected when a certain number of expected messages are not
      received.

   On-demand

      On-demand activation - indicates that the tool is activated
      "manually" to detect a specific anomaly.

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2.2.7.  Connectivity Verification and Continuity Checks

   Two distinct classes of failure management functions are used in OAM
   protocols: Connectivity Verification and Continuity Checks.  The
   distinction between these terms is defined in [MPLS-TP-OAM] and is
   used similarly in this document.

   Continuity Check

      Continuity Checks are used to verify that a destination is
      reachable, and are typically sent proactively, though they can be
      invoked on-demand as well.

   Connectivity Verification

      A Connectivity Verification function allows Alice to check whether
      she is connected to Bob or not.  It is noted that while the CV
      function is performed in the data plane, the "expected path" is
      predetermined in either the control plane or the management plane.
      A Connectivity Verification (CV) protocol typically uses a CV
      message, followed by a CV reply that is sent back to the
      originator.  A CV function can be applied proactively or
      on-demand.

      Connectivity Verification tools often perform path verification as
      well, allowing Alice to verify that messages from Bob are received
      through the correct path, thereby verifying not only that the two
      MPs are connected, but also that they are connected through the
      expected path, allowing detection of unexpected topology changes.

      Connectivity Verification functions can also be used for checking
      the MTU of the path between the two peers.

      Connectivity Verification and Continuity Checks are considered
      complementary mechanisms and are often used in conjunction with
      each other.

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2.2.8.  Connection-Oriented vs. Connectionless Communication

   Connection-Oriented

      In connection-oriented technologies, an end-to-end connection is
      established (by a control protocol or provisioned by a management
      system) prior to the transmission of data.

      Typically a connection identifier is used to identify the
      connection.  In connection-oriented technologies, it is often the
      case (although not always) that all packets belonging to a
      specific connection use the same route through the network.

   Connectionless

      In connectionless technologies, data is typically sent between end
      points without prior arrangement.  Packets are routed
      independently based on their destination address, and hence
      different packets may be routed in a different way across the
      network.

   Discussion

      The OAM tools described in this document include tools that
      support connection-oriented technologies, as well as tools for
      connectionless technologies.

      In connection-oriented technologies, OAM is used to monitor a
      *specific* connection; OAM packets are forwarded through the same
      route as the data traffic and receive the same treatment.  In
      connectionless technologies, OAM is used between a source and
      destination pair without defining a specific connection.
      Moreover, in some cases, the route of OAM packets may differ from
      the one of the data traffic.  For example, the connectionless IP
      Ping (Section 4.1) tests the reachability from a source to a given
      destination, while the connection-oriented LSP Ping (Section
      4.4.1) is used for monitoring a specific LSP (connection) and
      provides the capability to monitor all the available paths used by
      an LSP.

      It should be noted that in some cases connectionless protocols are
      monitored by connection-oriented OAM protocols.  For example,
      while IP is a connectionless protocol, it can be monitored by BFD
      (Section 4.3), which is connection oriented.

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2.2.9.  Point-to-Point vs. Point-to-Multipoint Services

   Point-to-point (P2P)

      A P2P service delivers data from a single source to a single
      destination.

   Point-to-multipoint (P2MP)

      A P2MP service delivers data from a single source to a one or more
      destinations (based on [Signal]).

      An MP2MP service is a service that delivers data from more than
      one source to one or more receivers (based on [Signal]).

      Note: the two definitions for P2MP and MP2MP are quoted from
      [Signal].  Although [Signal] describes a specific case of P2MP and
      MP2MP that is MPLS-specific, these two definitions also apply to
      non-MPLS cases.

   Discussion

      The OAM tools described in this document include tools for P2P
      services, as well as tools for P2MP services.

      The distinction between P2P services and P2MP services affects the
      corresponding OAM tools.  A P2P service is typically simpler to
      monitor, as it consists of a single pair of endpoints.  P2MP and
      MP2MP services present several challenges.  For example, in a P2MP
      service, the OAM mechanism not only verifies that each of the
      destinations is reachable from the source but also verifies that
      the P2MP distribution tree is intact and loop-free.

2.2.10.  Failures

   The terms "Failure", "Fault", and "Defect" are used interchangeably
   in the standards, referring to a malfunction that can be detected by
   a Connectivity Verification or a Continuity Check.  In some
   standards, such as 802.1ag [IEEE802.1Q], there is no distinction
   between these terms, while in other standards each of these terms
   refers to a different type of malfunction.

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   The terminology used in IETF MPLS-TP OAM is based on the ITU-T
   terminology, which distinguishes between these three terms in
   [ITU-T-G.806] as follows:

   Fault

   The term "Fault" refers to an inability to perform a required action,
   e.g., an unsuccessful attempt to deliver a packet.

   Defect

   The term "Defect" refers to an interruption in the normal operation,
   such as a consecutive period of time where no packets are delivered
   successfully.

   Failure

   The term "Failure" refers to the termination of the required
   function.  While a Defect typically refers to a limited period of
   time, a failure refers to a long period of time.



(page 17 continued on part 2)

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