





Internet Engineering Task Force (IETF)                       N. Sprecher
Request for Comments: 6669                        Nokia Siemens Networks
Category: Informational                                          L. Fang
ISSN: 2070-1721                                            Cisco Systems
                                                               July 2012


  An Overview of the Operations, Administration, and Maintenance (OAM)
               Toolset for MPLS-Based Transport Networks

Abstract

   This document provides an overview of the Operations, Administration,
   and Maintenance (OAM) toolset for MPLS-based transport networks.  The
   toolset consists of a comprehensive set of fault management and
   performance monitoring capabilities (operating in the data plane)
   that are appropriate for transport networks as required in RFC 5860
   and support the network and services at different nested levels.
   This overview includes a brief recap of the MPLS Transport Profile
   (MPLS-TP) OAM requirements and functions and the generic mechanisms
   created in the MPLS data plane that allow the OAM packets to run
   in-band and share their fate with data packets.  The protocol
   definitions for each of the MPLS-TP OAM tools are defined in separate
   documents (RFCs or Working Group documents), which are referenced by
   this document.

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/rfc6669.










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Copyright Notice

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   publication of this document.  Please review these documents
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   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. Scope ......................................................4
      1.2. Acronyms ...................................................5
   2. Basic OAM Infrastructure Functionality ..........................6
   3. MPLS-TP OAM Functions ...........................................8
      3.1. Continuity Check and Connectivity Verification .............8
           3.1.1. Documents for CC-CV Tools ...........................8
      3.2. Remote Defect Indication ...................................8
           3.2.1. Documents for RDI ...................................9
      3.3. Route Tracing ..............................................9
           3.3.1. Documents for Route Tracing .........................9
      3.4. Alarm Reporting ............................................9
           3.4.1. Documents for Alarm Reporting .......................9
      3.5. Lock Instruct ..............................................9
           3.5.1. Documents for Lock Instruct ........................10
      3.6. Lock Reporting ............................................10
           3.6.1. Documents for Lock Reporting .......................10
      3.7. Diagnostic ................................................10
           3.7.1. Documents for Diagnostic Testing ...................10
      3.8. Packet Loss Measurement ...................................10
           3.8.1. Documents for Packet Loss Measurement ..............11
      3.9. Packet Delay Measurement ..................................11
           3.9.1. Documents for Delay Measurement ....................11
   4. MPLS-TP OAM Documents Guide ....................................12
   5. OAM Toolset Applicability and Utilization ......................13
      5.1. Connectivity Check and Connectivity Verification ..........14
      5.2. Diagnostic Tests and Lock Instruct ........................14
      5.3. Lock Reporting ............................................15
      5.4. Alarm Reporting and Link Down Indication ..................15
      5.5. Remote Defect Indication ..................................16
      5.6. Packet Loss and Delay Measurement .........................17
   6. Security Considerations ........................................18
   7. Acknowledgements ...............................................18
   8. References .....................................................19
      8.1. Normative References ......................................19
      8.2. Informative References ....................................20
   Contributors ......................................................21












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1.  Introduction

1.1.  Scope

   The MPLS Transport Profile (MPLS-TP) architectural framework is
   defined in [RFC5921], and it describes a common set of protocol
   functions that supports the operational models and capabilities
   typical of such transport networks.

   Operations, Administration, and Maintenance (OAM) plays a significant
   role in carrier networks.  It provides methods for fault management
   and performance monitoring in both the transport and service layers,
   in order to improve their ability to support services with guaranteed
   and strict Service Level Agreements (SLAs) while reducing their
   operational costs.

   [RFC5654], in general, and [RFC5860], in particular, define a set of
   requirements for the OAM functionality for MPLS-TP Label Switched
   Paths (LSPs), Pseudowires (PWs), and Sections.

   The OAM solution, developed by the joint IETF and ITU-T MPLS-TP
   project, has three objectives:

   o  The OAM toolset should be developed based on existing MPLS
      architecture, technology, and toolsets.

   o  The OAM operational experience should be similar to that in other
      transport networks.

   o  The OAM toolset developed for MPLS-based transport networks needs
      to be fully interoperable with existing MPLS OAM tools as
      documented in Section 2.1.5. of [RFC5860].

   The MPLS-TP OAM toolset is based on the following existing tools:

   o  LSP ping, as defined in [RFC4379].

   o  Bidirectional Forwarding Detection (BFD), as defined in [RFC5880]
      and refined in [RFC5884].

   o  ITU-T OAM for the Ethernet toolset, as defined in [Y.1731].  This
      has been used as functionality guidelines for the performance
      measurement tools that were not previously supported in MPLS.

   Note that certain extensions and adjustments have been specified,
   relative to the existing MPLS tools, in order to conform to the
   transport environment and the requirements of MPLS-TP.  However,
   compatibility with the existing MPLS tools has been maintained.



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   This document provides an overview of the MPLS-TP OAM toolset, which
   consists of tools for MPLS-TP fault management and performance
   monitoring.  This overview includes a brief recap of MPLS-TP OAM
   requirements, their functions, and the generic mechanisms used to
   support the MPLS-TP OAM operation.

   The protocol definitions for individual MPLS-TP OAM tools are
   specified in separate RFCs (or Working Group documents), which are
   referenced by this document.

   In addition, this document includes a table that cross-references the
   solution documents of the OAM functionality supported.  Finally, the
   document presents the applicability and utilization of each tool in
   the MPLS-TP OAM toolset.

1.2.  Acronyms

   This document uses the following acronyms:

   ACH     Associated Channel Header
   AIS     Alarm Indication Signal
   BFD     Bidirectional Forwarding Detection
   CC-CV   Continuity Check and Connectivity Verification
   DM      Delay Measurement
   FM      Fault Management
   G-ACh   Generic Associated Channel
   GAL     G-ACh Label
   GMPLS   Generalized Multiprotocol Label Switching
   IANA    Internet Assigned Numbers Authority
   LDI     Link Down Indication
   LKR     Lock Report
   LM      Loss Measurement
   LOC     Loss of Continuity
   LSP     Label Switched Path
   MEP     Maintenance Entity Group End Point
   MEG     Maintenance Entity Group
   MIP     Maintenance Entity Group Intermediate Point
   MPLS    Multiprotocol Label Switching
   MPLS-TP Transport Profile for MPLS
   OAM     Operations, Administration, and Maintenance
   PM      Performance Monitoring
   PW      Pseudowire
   RDI     Remote Defect Indication
   SLA     Service Level Agreement
   TLV     Type, Length, Value
   VCCV    Virtual Circuit Connectivity Verification





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2.  Basic OAM Infrastructure Functionality

   [RFC5860] defines a set of requirements for OAM architecture and
   general principles of operations, which are evaluated below:

   [RFC5860] requires that --

   o  OAM mechanisms in MPLS-TP are independent of the transmission
      media and the client service being emulated by the PW ([RFC5860],
      Section 2.1.2).

   o  MPLS-TP OAM must be able to support both an IP-based and non-IP-
      based environment.  If the network is IP based, i.e., IP routing
      and forwarding are available, then it must be possible to choose
      to make use of IP capabilities.  On the other hand, in
      environments where IP functionality is not available, the OAM
      tools must still be able to operate independent of IP forwarding
      and routing ([RFC5860], Section 2.1.4).  It is required to have
      OAM interoperability between distinct domains materializing the
      environments ([RFC5860], Section 2.1.5).

   o  All OAM protocols support identification information, at least in
      the form of IP addressing structure, and are extensible to support
      additional identification schemes ([RFC5860], Section 2.1.4).

   o  OAM packets and the user traffic are congruent (i.e., OAM packets
      are transmitted in-band) and there is a need to differentiate OAM
      packets from user-plane packets [RFC5860], Section 2.1.3.
      Inherent in this requirement is the principle that full operation
      of the MPLS-TP OAM must be possible independently of the control
      or management plane used to operate the network [RFC5860], Section
      2.1.3.

   o  MPLS-TP OAM supports point-to-point bidirectional PWs, point-to-
      point co-routed bidirectional LSPs, and point-to-point
      bidirectional Sections ([RFC5860], Section 2.1.1).  The
      applicability of particular MPLS-TP OAM functions to point-to-
      point associated bidirectional LSPs, point-to-point unidirectional
      LSPs, and point-to-multipoint LSPs, is described in [RFC5860],
      Section 2.2.  In addition, MPLS-TP OAM supports these LSPs and PWs
      when they span either single or multiple domains ([RFC5860],
      Section 2.1.1).

   o  OAM packets may be directed to an intermediate point of an LSP/PW
      ([RFC5860], Sections 2.2.3, 2.2.4, and 2.2.5).






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   [RFC5860], Section 2.2 recommends that any protocol solution meeting
   one or more functional requirement(s) be the same for PWs, LSPs, and
   Sections.

   The following document set addresses the basic requirements listed
   above:

   o  [RFC6371] describes the architectural framework for conformance to
      the basic requirements listed above.  It also defines the basic
      relationships between the MPLS structures, e.g., LSP, PW, and the
      structures necessary for OAM functionality, i.e., the Maintenance
      Entity Group (MEG), its end points, and intermediate points.

   o  [RFC5586] specifies the use of the MPLS-TP in-band control
      channels.  It generalizes the applicability of the PW ACH to MPLS
      LSPs and Sections by defining a Generic Associated Channel
      (G-ACh).  The G-ACh allows control packets to be multiplexed
      transparently over LSPs and Sections similar to that of PW VCCV
      [RFC5085].  The Generic Association Label (GAL) is defined by
      assigning a reserved MPLS label value and is used to identify the
      OAM control packets.  The value of the ACH Channel Type field
      indicates the specific protocol carried on the associated control
      channel.  Each MPLS-TP OAM protocol has an IANA-assigned channel
      type allocated to it.

   [RFC5085] defines an Associated Channel Header (ACH) that provides a
   PW associated control channel between a PW's end points, over which
   OAM and other control messages can be exchanged.  [RFC5586]
   generalizes the PW Associated Channel Header (ACH) to provide common
   in-band control channels also at the LSP and MPLS-TP link levels.
   The G-ACh allows control packets to be multiplexed transparently over
   the same LSP or MPLS-TP link as in PW VCCV.  Multiple control
   channels can exist between end points.

   [RFC5085] also defines a label-based exception mechanism that helps a
   Label Switching Router (LSR) to identify the control packets and
   direct them to the appropriate entity for processing.  The use of
   G-ACh and GAL provides the necessary mechanisms to allow OAM packets
   to run in-band and share their fate with data packets.  It is
   expected that all of the OAM protocols will be used in conjunction
   with this Generic Associated Channel.

   o  [RFC6370] provides an IP-based identifier set for MPLS-TP that can
      be used to identify the transport entities in the network and
      referenced by the different OAM protocols.






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         Note: [MPLS-TP-ITU-Idents] augments that set of identifiers to
         include identifier information in a format used by the ITU-T.
         Other identifier sets may be defined as well.

3.  MPLS-TP OAM Functions

   The following sections discuss the OAM functions that are required in
   [RFC5860] and expanded upon in [RFC6371].

3.1.  Continuity Check and Connectivity Verification

   Continuity Check and Connectivity Verification (CC-CV) are OAM
   operations generally used in tandem and complement each other.  These
   functions are generally run proactively, but may also be used
   on-demand for diagnoses of a specific condition.  [RFC5860] states
   that the function should allow the MEPs to proactively monitor the
   liveliness and connectivity of a transport path (LSP, PW, or a
   Section) between them.  In on-demand mode, this function should
   support monitoring between the MEPs and between a MEP and MIP.  Note
   that as specified in [RFC6371], Sections 3.3 and 3.4, a MEP and a MIP
   can reside in an unspecified location within a node, or in a
   particular interface on a specific side of the forwarding engine.

   [RFC6371] highlights the need for the CC-CV messages to include
   unique identification of the MEG that is being monitored and the MEP
   that originated the message.  The function, both proactively and in
   on-demand mode, needs to be transmitted at regular transmission rates
   pre-configured by the operator.

3.1.1.  Documents for CC-CV Tools

   [RFC6428] defines BFD extensions to support proactive CC-CV
   applications.

   [RFC6426] provides LSP ping extensions that are used to implement
   on-demand connectivity verification.

   Both of these tools will be used within the basic functionality
   framework described in Section 2.

3.2.  Remote Defect Indication

   Remote Defect Indication (RDI) is used by a path end point to report
   that a defect is detected on a bidirectional connection to its peer
   end point.  [RFC5860] points out that this function may be applied to
   a unidirectional LSP only if a return path exists.  [RFC6371] points
   out that this function is associated with the proactive CC-CV
   function.



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3.2.1.  Documents for RDI

   [RFC6428] provides an extension for BFD that includes the RDI
   indication in the BFD format and a specification of how this
   indication is to be used.

3.3.  Route Tracing

   [RFC5860] defines the need for functionality that would allow a path
   end point to identify the intermediate points (if any) and end
   point(s) along the path (LSP, PW, or a Section).  This function would
   be used in on-demand mode.  Normally, this path will be used for
   bidirectional PW, LSP, and Sections; however, unidirectional paths
   may be supported only if a return path exists.

3.3.1.  Documents for Route Tracing

   [RFC6426] specifies that the LSP ping enhancements for MPLS-TP on-
   demand connectivity verification include information on the use of
   LSP ping for route tracing of an MPLS-TP path.

3.4.  Alarm Reporting

   Alarm Reporting is a function used by an intermediate point of a path
   (LSP or PW) to report to the end points of the path that a fault
   exists on the path.  [RFC6371] states that this may occur as a result
   of a defect condition discovered at a server layer.  The intermediate
   point generates an Alarm Indication Signal (AIS) that continues until
   the fault is cleared.  The consequent action of this function is
   detailed in [RFC6371].

3.4.1.  Documents for Alarm Reporting

   MPLS-TP defines a new protocol to address this functionality that is
   documented in [RFC6427].  This protocol uses all of the basic
   mechanisms detailed in Section 2.

3.5.  Lock Instruct

   The Lock Instruct function is an administrative control tool that
   allows a path end point to instruct its peer end point to lock the
   path (LSP, PW, or Section).  The tool is necessary to support single-
   side provisioning for administrative locking, according to [RFC6371].
   This function is used on-demand.







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3.5.1.  Documents for Lock Instruct

   [RFC6435] describes the details of a new ACH-based protocol format
   for this functionality.

3.6.  Lock Reporting

   Lock Reporting, defined in [RFC5860], is similar to the Alarm
   Reporting function described above.  It is used by an intermediate
   point to notify the end points of a transport path (LSP or PW) that
   an administrative lock condition exists for the transport path.

3.6.1.  Documents for Lock Reporting

   MPLS-TP defines a new protocol to address this functionality that is
   documented in [RFC6427].  This protocol uses all the basic mechanisms
   detailed in Section 2.

3.7.  Diagnostic

   [RFC5860] indicates a need to provide an OAM function that would
   enable conducting different diagnostic tests on a PW, LSP, or
   Section.  [RFC6371] provides two types of specific tests to be used
   through this functionality:

   o  Throughput estimation - allowing the provider to verify the
      bandwidth/throughput of a transport path.  This is an out-of-
      service tool that uses special packets of varying sizes to test
      the actual bandwidth and/or throughput of the path.

   o  Data-plane loopback - this out-of-service tool causes all traffic
      that reaches the target node, either a MEP or MIP, to be looped
      back to the originating MEP.  For targeting MIPs, a co-routed
      bidirectional path is required.

3.7.1.  Documents for Diagnostic Testing

   [RFC6435] describes the details of a new ACH-based protocol format
   for the data-plane loopback functionality.

   The tool for throughput estimation is under study.

3.8.  Packet Loss Measurement

   Packet Loss Measurement is required by [RFC5860] to provide a
   quantification of the packet loss ratio on a transport path.  This is
   the ratio of the number of user packets lost to the total number of
   user packets during a defined time interval.  To employ this



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   function, [RFC6371] defines that the two end points of the transport
   path should exchange counters of messages transmitted and received
   within a time period bounded by loss-measurement messages.  The
   framework warns that there may be small errors in the computation,
   which result from various issues.

3.8.1.  Documents for Packet Loss Measurement

   [RFC6374] describes the protocol formats and procedures for using the
   tool and enabling efficient and accurate measurement of packet loss,
   delay, and throughput in MPLS networks.  [RFC6375] describes a
   profile of the general MPLS loss, delay, and throughput measurement
   techniques that suffice to meet the specific requirements of MPLS-TP.
   Note that the tool logic is based on the behavior of the parallel
   function described in [Y.1731].

3.9.  Packet Delay Measurement

   Packet Delay Measurement is a function that is used to measure the
   one-way or two-way delay of packet transmission between a pair of the
   end points of a path (PW, LSP, or Section), as described in
   [RFC5860], where:

   o  One-way packet delay is the time elapsed from the start of
      transmission of the first bit of the packet by a source node until
      the reception of the last bit of that packet by the destination
      node.

   o  Two-way packet delay is the time elapsed from the start of
      transmission of the first bit of the packet by a source node until
      the reception of the last bit of the loop-backed packet by the
      same source node, when the loopback is performed at the packet's
      destination node.

   [RFC6371] describes how the tool could be used (both in proactive and
   on-demand modes) for either one-way or two-way measurement.  However,
   it warns that the one-way delay option requires precise time
   synchronization between the end points.

3.9.1.  Documents for Delay Measurement

   [RFC6374] describes the protocol formats and procedures for using the
   tool and enabling efficient and accurate measurement of packet loss,
   delay, and throughput in MPLS networks.  [RFC6375] describes a
   profile of the general MPLS loss, delay, and throughput measurement
   techniques that suffices to meet the specific requirements of MPLS-
   TP.  Note that the tool logic is based on the behavior of the
   parallel function described in [Y.1731].



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4.  MPLS-TP OAM Documents Guide

   The complete MPLS-TP OAM protocol suite is covered by a small set of
   existing IETF documents.  This set of documents may be expanded in
   the future to cover additional OAM functionality.  In order to allow
   the reader to understand this set of documents, a cross-reference of
   the existing documents (RFCs or Working Group documents) for the
   initial phase of the specification of MPLS-based transport networks
   is provided below.

   [RFC5586] provides a specification of the basic structure of protocol
   messages for in-band data-plane OAM in an MPLS environment.

   [RFC6370] provides definitions of different formats that may be used
   within OAM protocol messages to identify the network elements of an
   MPLS-based transport network.

   The following table (Table 1) provides the summary of proactive MPLS-
   TP OAM Fault Management toolset functions, the associated
   tool/protocol, and the corresponding RFCs in which they are defined.

  +--------------------------+-------------------------------+---------+
  | OAM Functions            | OAM Tools/Protocols           | RFCs    |
  +--------------------------+-------------------------------+---------+
  | Continuity Check and     | Bidirectional Forwarding      |[RFC6428]|
  | Connectivity             | Detection (BFD)               |         |
  | Verification             |                               |         |
  +--------------------------+-------------------------------+---------+
  | Remote Defect Indication | Flag in Bidirectional         |[RFC6428]|
  | (RDI)                    | Forwarding Detection (BFD)    |         |
  |                          | message                       |         |
  +--------------------------+-------------------------------+---------+
  | Alarm Indication Signal  | G-ACh-based AIS message       |[RFC6427]|
  | (AIS)                    |                               |         |
  +--------------------------+-------------------------------+---------+
  | Link Down Indication     | Flag in AIS message           |[RFC6427]|
  | (LDI)                    |                               |         |
  +--------------------------+-------------------------------+---------+
  | Lock Reporting (LKR)     | G-ACh-based LKR message       |[RFC6427]|
  |                          |                               |         |
  +--------------------------+-------------------------------+---------+

             Table 1.  Proactive Fault Management OAM Toolset








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   The following table (Table 2) provides an overview of the on-demand
   MPLS-TP OAM Fault Management toolset functions, the associated
   tool/protocol, and the corresponding RFCs in which they are defined.

  +------------------------+---------------------------------+---------+
  | OAM Functions          | OAM Tools/Protocols             |  RFCs   |
  +------------------------+---------------------------------+---------+
  | Connectivity           | LSP Ping                        |[RFC6426]|
  | Verification           |                                 |         |
  +------------------------+---------------------------------+---------+
  | Lock Instruct (LI)     | (1) G-ACh-based Loopback,       |[RFC6426]|
  |                        | (2) Lock Instruct (LI)          |         |
  +------------------------+---------------------------------+---------+
  | Lock Report (LKR)      | Flag in AIS message             |[RFC6426]|
  |                        |                                 |         |
  +------------------------+---------------------------------+---------+

             Table 2.  On Demand Fault Management OAM Toolset

   The following table (Table 3) provides the Performance Monitoring
   Functions, the associated tool/protocol definitions, and the
   corresponding RFCs in which they are defined.

   +----------------------+--------------------------+-----------------+
   | OAM Functions        | OAM Tools/Protocols      | RFCs            |
   +----------------------+--------------------------+-----------------+
   | Packet Loss          | G-ACh-based LM & DM      | [RFC6374]       |
   | Measurement (LM)     | query messages           | [RFC6375]       |
   +----------------------+--------------------------+-----------------+
   | Packet Delay         | G-ACh-based LM & DM      | [RFC6374]       |
   | Measurement (DM)     | query messages           | [RFC6375]       |
   +----------------------+--------------------------+-----------------+
   | Throughput           | derived from Loss        | [RFC6374]       |
   | Measurement          | Measurement              | [RFC6375]       |
   +----------------------+--------------------------+-----------------+
   | Delay Variation      | derived from Delay       | [RFC6374]       |
   | Measurement          | Measurement              | [RFC6375]       |
   +----------------------+--------------------------+-----------------+

               Table 3.  Performance Monitoring OAM Toolset

5.  OAM Toolset Applicability and Utilization

   The following subsections present the MPLS-TP OAM toolset from the
   perspective of the specified protocols and identifies the required
   functionality that is supported by the particular protocol.





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5.1.  Connectivity Check and Connectivity Verification

   Proactive Continuity Check and Connectivity Verification (CC-CV)
   functions are used to detect loss of continuity (LOC) and unintended
   connectivity between two MEPs.  Loss of connectivity, mis-merging,
   mis-connectivity, or unexpected Maintenance Entity Group End Points
   (MEPs) can be detected using the CC-CV tools.  See Sections 3.1, 3.2,
   3.3 in this document for CC-CV protocol references.

   The CC-CV tools are used to support MPLS-TP fault management,
   performance management, and protection switching.  Proactive CC-CV
   control packets are sent by the source MEP to the sink MEP.  The
   sink-MEP monitors the arrival of the CC-CV control packets and
   detects the defect.  For bidirectional transport paths, the CC-CV
   protocol is usually transmitted simultaneously in both directions.

   The transmission interval of the CC-CV control packets can be
   configured.  For example:

   o  3.3 ms is the default interval for protection switching.

   o  100 ms is the default interval for performance monitoring.

   o  1 s is the default interval for fault management.

5.2.  Diagnostic Tests and Lock Instruct

   [RFC6435] describes a protocol that provides a mechanism to Lock and
   Unlock traffic (e.g., data and control traffic or specific OAM
   traffic) at a specific LSR on the path of the MPLS-TP LSP to allow
   loopback of the traffic to the source.

   These diagnostic functions apply to associated bidirectional MPLS-TP
   LSPs, including MPLS-TP LSPs, bidirectional RSVP-Traffic Engineering
   (RSVP-TE) tunnels (which is relevant for the MPLS-TP dynamic control-
   plane option with GMPLS), and single-segment and multi-segment
   Pseudowires.  [RFC6435] provides the protocol definition for
   diagnostic tests functions.

   [RFC6435] defines a mechanism where a lock instruction is sent by a
   management application to both ends of a point-to-point LSP,
   requesting them to take the LSP out-of-service.  When an end point
   gets the management request, it locks the LSP and sends a Lock
   Instruct message to the other end of the LSP.  The Lock Instruct
   message is carried in a Generic ACH message and is sent periodically.
   The time between successive messages is no longer than the value set
   in the Refresh Timer field of the Lock Instruct message.  An LSP end
   point keeps the LSP locked while it is either receiving the periodic



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   Lock Instruct messages or has an in-force lock instruction from the
   management application.

   Note that since the management application will receive a management
   plane response from both ends of the LSP confirming that the LSP has
   been locked, there is no requirement for the Lock Instruct message to
   have a response.  Therefore, [RFC6435] does not define a Lock
   Instruct response message.

   The loopback operations include:

   o  Lock: take an LSP out of service for maintenance.

   o  Unlock: Restore a previously locked LSP to service.

   o  Set_Full_Loopback and Set_OAM_Loopback.

   o  Unset_Full_Loopback and Set_OAM_Loopback.

   Operators can use the loopback mode to test the connectivity or
   performance (loss, delay, delay variation, and throughput) of a given
   LSP up to a specific node on the path of the LSP.

5.3.  Lock Reporting

   The Lock Report (LKR) function is used to communicate to the MEPS of
   the client (sub-)layer MEPs the administrative locking of a server
   (sub-)layer MEP, and consequential interruption of data traffic
   forwarding in the client layer.  See Section 3.6 in this document for
   Lock Reporting protocol references.

   When an operator is taking the LSP out of service for maintenance or
   another operational reason, using the LKR function can help to
   distinguish the condition as administrative locking from a defect
   condition.

   The Lock Report function may also serve the purpose of alarm
   suppression in the MPLS-TP network above the level at which the Lock
   has occurred.  The receipt of an LKR message may be treated as the
   equivalent of the loss of continuity at the client layer.

5.4.  Alarm Reporting and Link Down Indication

   Alarm Indication Signal (AIS) message is used to suppress alarms
   following detection of defect conditions at the server (sub-)layer.
   When the Link Down Indication (LDI) is set, the AIS message may be
   used to trigger recovery mechanisms.




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   When a server MEP detects the failure, it asserts LOC or signal fail,
   which sets the flag up to generate an OAM packet with the AIS
   message.  The AIS message is forwarded to the downstream sink MEP in
   the client layer.  This enables the client layer to suppress the
   generation of secondary alarms.

   An LDI flag is defined in the AIS message.  The LDI flag is set in
   the AIS message in response to detecting a fatal failure in the
   server layer.  Receipt of an AIS message with this flag set may be
   interpreted by a MEP as an indication of signal fail at the client
   layer.

   The protocols for AIS and LDI are defined in [RFC6427].

   Fault OAM messages are generated by intermediate nodes where an LSP
   is switched and propagated to the end points (MEPs).

   From a practical point of view, when both proactive Continuity Check
   functions and LDI are used, one may consider running the proactive
   Continuity Check functions at a slower rate (e.g., longer BFD hello
   intervals), and reply on LDI to trigger fast protection switch over
   upon failure detection in a given LSP.

5.5.  Remote Defect Indication

   The Remote Defect Indication (RDI) function enables an end point to
   report to its peer end point that a fault or defect condition is
   detected on the PW, LSP, or Section.

   The RDI OAM function is supported by the use of BFD control packets
   [RFC6428].  RDI is only used for bidirectional connections and is
   associated with proactive CC-CV activation.

   When an end point (MEP) detects a signal failure condition, it sets
   the flag up by setting the diagnostic field of the BFD control packet
   to a particular value to indicate the failure condition on the
   associated PW, LSP, or Section.  Additionally, the BFD control packet
   is transmitted with the failure flag up to the other end point (its
   peer MEP).

   The RDI function can be used to facilitate protection switching by
   synchronizing the two end points when unidirectional failure occurs
   and is detected by one end.








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5.6.  Packet Loss and Delay Measurement

   The packet loss and delay measurement toolset enables operators to
   measure the quality of the packet transmission over a PW, LSP, or
   Section.  Section 3.8 in this document defines the protocols for
   packet loss measurement, and Section 3.9 defines the protocols for
   packet delay measurement.

   The loss and delay protocols have the following characteristics and
   capabilities:

   o  They support the measurement of packet loss, delay, and throughput
      over Label Switched Paths (LSPs), Pseudowires, and MPLS Sections.

   o  The same LM and DM protocols can be used for both
      continuous/proactive and selective/on-demand measurements.

   o  The LM and DM protocols use a simple query/response model for
      bidirectional measurement that allows a single node -- the querier
      -- to measure the loss or delay in both directions.

   o  The LM and DM protocols use query messages for unidirectional loss
      and delay measurement.  The measurement can either be carried out
      at the downstream node(s), or at the querier if an out-of-band
      return path is available.

   o  The LM and DM protocols do not require that the transmit-and-
      receive interfaces be the same when performing bidirectional
      measurement.

   o  The LM supports test-message-based measurement (i.e., inferred
      mode) as well as measurement based on data-plane counters (i.e.,
      direct mode).

   o  The LM protocol supports both 32-bit and 64-bit counters.

   o  The LM protocol supports measurement in terms of both packet
      counts and octet counts; although for simplicity, only packet
      counters are currently included in the MPLS-TP profile.

   o  The LM protocol can be used to measure channel throughput as well
      as packet loss.

   o  The DM protocol supports varying the measurement message size in
      order to measure delays associated with different packet sizes.

   o  The DM protocol uses IEEE 1588 timestamps [IEEE1588] by default
      but also supports other timestamp formats, such as NTP.



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6.  Security Considerations

   This document, as an overview of MPLS OAM tools, does not by itself
   raise any particular security considerations.

   The general security considerations are provided in [RFC5920] and
   [MPLS-TP-SEC].  Security considerations for each function within the
   OAM toolset have been recorded in each document that specifies a
   particular functionality.

   In general, OAM is always an area where the security risk is high.
   For example, confidential information may be intercepted by attackers
   to gain access to networks; therefore, authentication, authorization,
   and encryption must be enforced to prevent security breaches.

   It is also important to strictly follow operational security
   procedures.  For example, in the case of MPLS-TP static provisioning,
   the operator interacts directly with the Network Management System
   (NMS) and devices, and it is critical in order to prevent human
   errors and malicious attacks.

   Since MPLS-TP OAM uses G-ACh, the security risks and mitigations
   described in [RFC5085] also apply here.  In short, messages on the
   G-ACh could be intercepted, or false G-ACh packets could be inserted.

   Additionally, DoS attacks can be mounted by flooding G-ACh messages
   to peer devices.  To mitigate this type of attack, throttling
   mechanisms or rate limits can be used.  For more details, please see
   [RFC5085].

7.  Acknowledgements

   The authors would like to thank the MPLS-TP experts from both the
   IETF and ITU-T for their helpful comments.  In particular, we would
   like to thank Loa Andersson and the Area Directors for their
   suggestions and enhancements to the text.

   Thanks to Tom Petch for useful comments and discussions.

   Thanks to Rui Costa for his review and comments, which helped improve
   this document.










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8.  References

8.1.  Normative References

   [RFC4379]  Kompella, K. and G. Swallow, "Detecting Multi-Protocol
              Label Switched (MPLS) Data Plane Failures", RFC 4379,
              February 2006.

   [RFC5085]  Nadeau, T., Ed., and C. Pignataro, Ed., "Pseudowire
              Virtual Circuit Connectivity Verification (VCCV): A
              Control Channel for Pseudowires", RFC 5085, December 2007.

   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
              "MPLS Generic Associated Channel", RFC 5586, June 2009.

   [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.

   [RFC5860]  Vigoureux, M., Ed., Ward, D., Ed., and M. Betts, Ed.,
              "Requirements for Operations, Administration, and
              Maintenance (OAM) in MPLS Transport Networks", RFC 5860,
              May 2010.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, June 2010.

   [RFC5884]  Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
              "Bidirectional Forwarding Detection (BFD) for MPLS Label
              Switched Paths (LSPs)", RFC 5884, June 2010.

   [RFC5921]  Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
              L., and L. Berger, "A Framework for MPLS in Transport
              Networks", RFC 5921, July 2010.

   [RFC6370]  Bocci, M., Swallow, G., and E. Gray, "MPLS Transport
              Profile (MPLS-TP) Identifiers", RFC 6370, September 2011.

   [RFC6371]  Busi, I., Ed., and D. Allan, Ed., "Operations,
              Administration, and Maintenance Framework for MPLS-Based
              Transport Networks", RFC 6371, September 2011.

   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS Networks", RFC 6374, September 2011.

   [RFC6375]  Frost, D., Ed., and S. Bryant, Ed., "A Packet Loss and
              Delay Measurement Profile for MPLS-Based Transport
              Networks", RFC 6375, September 2011.



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   [RFC6426]  Gray, E., Bahadur, N., Boutros, S., and R. Aggarwal, "MPLS
              On-Demand Connectivity Verification and Route Tracing",
              RFC 6426, November 2011.

   [RFC6427]  Swallow, G., Ed., Fulignoli, A., Ed., Vigoureux, M., Ed.,
              Boutros, S., and D. Ward, "MPLS Fault Management
              Operations, Administration, and Maintenance (OAM)", RFC
              6427, November 2011.

   [RFC6428]  Allan, D., Ed., Swallow Ed., G., and J. Drake Ed.,
              "Proactive Connectivity Verification, Continuity Check,
              and Remote Defect Indication for the MPLS Transport
              Profile", RFC 6428, November 2011.

   [RFC6435]  Boutros, S., Ed., Sivabalan, S., Ed., Aggarwal, R., Ed.,
              Vigoureux, M., Ed., and X. Dai, Ed., "MPLS Transport
              Profile Lock Instruct and Loopback Functions", RFC 6435,
              November 2011.

8.2.  Informative References

   [IEEE1588] IEEE, "1588-2008 IEEE Standard for a Precision Clock
              Synchronization Protocol for Networked Measurement and
              Control Systems", March 2008.

   [MPLS-TP-ITU-Idents]
              Winter, R., van Helvoort, H., and M. Betts, "MPLS-TP
              Identifiers Following ITU-T Conventions", Work in
              Progress, March 2012.

   [MPLS-TP-SEC]
              Fang, L., Niven-Jenkins, B., and S. Mansfield, "MPLS-TP
              Security Framework", Work in Progress, March 2012.

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, July 2010.

   [Y.1731]   International Telecommunications Union - Standardization,
              "OAM functions and mechanisms for Ethernet based
              networks", ITU Y.1731, May 2006.











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Contributors

   Elisa Bellagamba   Ericsson
   Yaacov Weingarten  Nokia Siemens Networks
   Dan Frost          Cisco
   Nabil Bitar        Verizon
   Raymond Zhang      Alcatel Lucent
   Lei Wang           Telenor
   Kam Lee Yap        XO Communications
   John Drake         Juniper
   Yaakov Stein       RAD
   Anamaria Fulignoli Ericsson
   Italo Busi         Alcatel Lucent
   Huub van Helvoort  Huawei
   Thomas Nadeau      Computer Associate
   Henry Yu           TW Telecom
   Mach Chen          Huawei
   Manuel Paul        Deutsche Telekom

Authors' Addresses

   Nurit Sprecher
   Nokia Siemens Networks
   3 Hanagar St. Neve Ne'eman B
   Hod Hasharon, 45241
   Israel

   EMail: nurit.sprecher@nsn.com


   Luyuan Fang
   Cisco Systems
   111 Wood Avenue South
   Iselin, NJ 08830
   USA

   EMail: lufang@cisco.com














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