Problem Statement for Layer and Technology Independent OAM in a Multi- Layer Environment

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Operations and Management Area Working Group                       Q. Wu
Internet-Draft                                                 M. Wexler
Intended status: Informational                                    Huawei
Expires: March 20, 2015                                   T. Taylor, Ed.
                                                    PT Taylor Consulting
                                                      September 16, 2014

 Problem Statement for Layer and Technology Independent OAM in a Multi-
                           Layer Environment


   Operations, Administration, and Maintenance (OAM) mechanisms are
   critical building blocks in network operations.  They used for
   service fulfillment assurance, and for service diagnosis,
   troubleshooting, and repair.  The current practice is that many
   technologies rely on their own OAM protocols and procedures that are
   exclusive to a given layer.

   At present, there is little consolidation of OAM in the management
   plane or well-documented inter-layer OAM operation.  Vendors and
   operators dedicate significant resources and effort through the whole
   OAM life-cycle each time a new technology is introduced.  This is
   exacerbated when dealing with integration of OAM into overlay
   networks, which require better OAM visibility since there is no
   method to exchange OAM information between overlay and underlay.

   This document analyzes the problem space for multi-layer OAM in the
   management plane with a focus on layer and technology independent OAM
   management considerations.  It concludes that an attempt to define an
   architecture for consolidated management should be undertaken, and if
   this attempt satisfies key objectives, a gap analysis and a program
   of standardization should follow.

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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on March 20, 2015.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  A Vision of Layer and Technology Independent Management .   4
     1.2.  Looking Forward . . . . . . . . . . . . . . . . . . . . .   5
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  A Preliminary Set Of Objectives . . . . . . . . . . . . . . .   7
   4.  Analysis of the Problem . . . . . . . . . . . . . . . . . . .   8
     4.1.  Argument For Consolidated Management  . . . . . . . . . .   8
     4.2.  Argument For Layer and Technology  Independent Management   9
     4.3.  Detailed Issues . . . . . . . . . . . . . . . . . . . . .  10
       4.3.1.  Strong Technology Dependency For MIB Modules  . . . .  10
       4.3.2.  Issues of Abstraction . . . . . . . . . . . . . . . .  10
       4.3.3.  OAM Interworking Issues . . . . . . . . . . . . . . .  10
       4.3.4.  Multiple (ECMP) Paths OAM Issue . . . . . . . . . . .  11
   5.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .  11
   6.  Considerations For the Work On Architecture . . . . . . . . .  12
     6.1.  What the Architecture Must Define . . . . . . . . . . . .  12
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  14
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     11.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

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1.  Introduction

   Operations, Administration, and Maintenance (OAM, [RFC6291])
   mechanisms are critical tools, used for service assurance,
   fulfillment, or service diagnosis, troubleshooting, and repair, as
   well as supporting functions such as accounting and security
   management.  The key foundations of OAM and its functional roles in
   monitoring and diagnosing the behavior of networks have been studied
   at OSI layers 1, 2 and 3 for many years.

   When operating networks with more than one technology in an overlay
   network, maintenance and troubleshooting are achieved per technology
   and per layer.  As a result, operational processes can be very
   cumbersome.  Stitching together the OAM of adjacent transport
   segments (as defined in Section 2 in one administrative domain is
   often not defined and left to proprietary solutions.

   Current practice, which consists in enabling specific OAM techniques
   for each layer, has shown its limits.  Concretely, we see today a
   large number of layer 1/2/3 OAM protocols being well developed and
   some of them being successfully deployed, but how these OAM protocols
   in each layer can be applied to overlay networks that are using
   different encapsulation protocols so as to provide better OAM
   visibility is still a challenging issue.  When no mechanism is
   defined to exchange performance and liveliness information between
   the underlay and overlay(s) by a coordination system, it is hard, for
   instance, to determine whether a fault originates in higher or lower

   Section 1.1 of [RFC7276] makes the point that each layer in a multi-
   layer architecture has its own OAM protocols.  From this follows the
   basic principle that OAM in the data plane cannot cross layer
   boundaries.  A similar constraint holds for boundaries between
   different transport technologies in the same layer, barring the
   stitching mentioned above.

   One concludes that to simplify OAM and make it more responsive in a
   multi-layer network requires further consolidation in the management
   plane.  The work on management consolidation would benefit from at
   least some new standardization.  A detailed examination of the
   potential scope of the work is left for a gap analysis following
   successful definition of an architecture.

   This document further argues that in addition to the ability to
   retrieve technology specific information from managed entities when
   following up on problems, consolidated management requires a
   technology independent view of the network and supporting layers.

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   How this view is obtained is a key architectural issue outside the
   scope of the present document.

1.1.  A Vision of Layer and Technology Independent Management

   What follows is based on the assumption of a network supported by a
   strict hierarchy of underlying layers in the data plane.  There may
   be multiple layers at a given level of the OSI layer 1-2-3 hierarchy,
   but that is irrelevant to the vision.

   A management application presents to an user a view of this network
   and its supporting layers that is strictly topological, free of any
   technology specific information.  The user notes a defect along a
   path serving a particular customer.  Looking at the next lower path,
   the user also sees a defect.  Looking the next lower path again,
   there is also a defect.  No lower defect is noted.

   At this point it is appropriate to indicate what the user can see
   along a given path.  The path is divided into one or more segments,
   each spanned by a specific transport technology.  However, as already
   stated, the user does not see any technology specific information.
   Instead, as well as distinguishing the segments, the user can
   identify the managed elements at the beginning and end of each

   To clarify the situation, the user issues an abstract Continuity
   Check command, directed toward the initial managed element of the
   segment in which a fault appears to lie (i.e., in the lowest layer
   where a defect was observed).  By means to be determined by
   architectural choice, this command is converted into a technology-
   specific request which is executed across the selected segment.
   Possible outcomes include:

   1.  The fault could come clear as a result of the test.  The
       immediate problem is solved (and may have affected multiple upper
       paths besides the one of initial interest) and the point at which
       it occurred could be flagged for follow-up maintenance.

   2.  Local craft action to clear the fault is available in timely

   3.  Timely local craft action is not possible, and capacity is
       reallocated on other paths to ensure that service levels are
       maintained.  Note that capacity reallocation can be done based on
       the topological view of the network, still on a layer and
       technology independent basis.

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   In case (2), technology specific management capabilities are likely
   to be required by the craftperson following up on the problem.

1.2.  Looking Forward

   The remainder of this document develops the ideas just stated at a
   greater level of detail.  Section 2 provides terminology that is
   important to the understanding of the rest of the document.
   Section 3 establishes preliminary objectives that are key to
   determining whether a complete program of standardization of
   consolidated management should be undertaken.  Section 4 provides the
   problem analysis.  It is divided into three parts: an argument for
   consolidated management (Section 4.1), an argument for layer and
   technology independent management (Section 4.2), and an examination
   of some more detailed issues.  Section 5 provides the problem
   statement, and Section 6 provides some considerations that should be
   taken into account in the proposed work on architecture.

2.  Terminology

   [RFC6291], cited above, provides the official IETF description of
   Operations, Administration, and Maintenance (OAM) terminology.  For a
   more extensive description of OAM and related terms, see the opening
   sections, but particularly Sections 2.2.1 through 2.2.3, of

   Section 2.2.4 of [RFC7276] introduces the terms data plane, control
   plane, and management plane.

   This document introduces its own interpretation of the following
   terms, which are in wide use but in that general usage present


      A definition of management can be inferred from [RFC6123], which
      in turn refers to [RFC5706].  Unfortunately the latter chose to
      divide operations from management, at least from a documentation
      point of view.  The present document chooses to define management
      as a function that is concerned with all three of operations,
      administration, and maintenance.


      The word "layer" has two potential meanings.  In the first
      instance, it is a topological concept, representing a position in
      a hierarchy of layers.  In the second instance, it refers to OSI
      layers 1, 2 and 3.  Within this document, "layer independent OAM

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      management" as defined below emphasizes the latter meaning when
      talking about independence, but is intended to extend to all
      layers of the hierarchy supporting a given network or overlay (the
      topological view of "layer").

   This document makes use of the following additional terms:

   Layer independent OAM management:

      In a multi-layer network, layer independent OAM management refers
      to OAM in the management plane that can be deployed independently
      of media, data protocols, and routing protocols.  It denotes the
      ability to gather OAM information at the different layers,
      correlate it with layer-specific identifiers and expose it to the
      management application through a unified interface.

   Managed entity:

      An architectural concept, an instance of what the management
      function manages.  By definition, a managed entity is capable of
      communicating with the management function in the management

   Local Management Entity (LMgmtE):

      An instance of a management function that is restricted in scope
      to communication with the managed entities associated with a
      specific transport segment in a specific layer.  This term
      includes legacy management entities in an existing network, and
      may include entities of a similar scope if they are defined in a
      consolidated management architecture.

   Consolidated Management Entity (CMgmtE):

      An instance of the management function that is capable of
      communicating with all of the LMgmtEs and/or managed entities in a
      scoped part of the network in order to achieve end-to-end and
      service-level views of network performance and status and initiate
      actions when required.  The phrase "LMgmtEs and/or managed
      entities" allows for the possibility that the target architecture
      allows for direct communication between the CMgmtE and the managed
      entities or alternatively chooses to assume a distributed
      management architecture.  In any case, as discussed in Section 6,
      the CMgmtE will have to communicate with legacy LMgmtEs during the
      transition from the existing to the target architecture.

   Management subsystem:

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      The implementation of the management function in a given network.

   Managed device:

      A network element associated with at least one technology layer
      and one managed entity.

   Transport segment:

      Refers to the portion of a path at a given layer bounded by two
      points between which a specific transport technology is used and
      beyond which either a different technology is used or the path is

   Three-dimensional topology:

      Refers to a three-dimensional view of the topology of the network
      and supporting layers.  The view of paths along a layer comprises
      two dimensions.  The third dimension is provided by the ordered
      hierarchy of layers from bottom to top at any point along a path.
      The three-dimensional topology includes per-path capacity and flow
      information, permitting layer and technology independent
      reallocation of capacity as required.

3.  A Preliminary Set Of Objectives

   Before going further, it is possible to state a preliminary set of
   objectives for this work.  If it does not appear that these can be
   satisfied, there is no point in undertaking further effort.

   As a first objective, the outcome of the work must reduce the time
   required to respond to and mitigate service-affecting events.  The
   ideal result is that the system be able to do so before the customer
   notices a service degradation.  It is possible that satisfaction of
   this objective alone is sufficient to carry on.

   A second objective relates to the business case for the work and is
   more difficult for the IETF to judge but crucial for operators
   attempting to justify changes in their network infrastructure.  It
   should be possible to expect a reduction in life cycle capex and opex
   as a result of making those changes, even taking account of the
   potential costs of abandoning or upgrading existing equipment.  This
   objective may influence work on architecture for consolidated
   management toward minimizing those latter costs (capex).  On the
   positive side, likely savings in craftsperson time implied by the
   first objective are helpful to the business case (opex).

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   At a more detailed level, the outcome of the work must allow
   management to have end-to-end and service-level views of network
   performance, down to the granularity of service instance.  Pre-
   supposing the arguments made in Section 4.2, it must also allow
   management to have a layer and technology independent view of the
   network, at least in the form of the three-dimensional topology, as
   defined in Section 2.

4.  Analysis of the Problem

4.1.  Argument For Consolidated Management

   Multi-layer OAM actually presents two separate but inter-related
   issues.  The first is technology dependency, at the same or different
   layers.  The second is correlation of events between layers.

   OAM mechanisms have a strong technology dependency because each
   technology (or layer) has its best suited OAM tools.  Some of them
   provide rich functionality with one protocol, while the others
   provide each function with a different protocol.  Today a variety of
   OAM tools have been developed by different Standards Development
   Organizations (SDOs) for Optical Transport Network (OTN), Synchronous
   Digital Hierarchy (SDH), Ethernet, MPLS, and IP networks.

   However, orchestrating and coordinating OAM in multi-layer networks
   to provide better network visibility and efficient OAM operations is
   still a challenging issue since no mechanisms are defined, for
   example, to exchange performance and liveliness information between
   different layers.  This means that the required coordination has to
   happen in the management function through communication with the
   managed entities.

   The development of overlay networks, where one network is the client
   of another, adds to the magnitude of the problem.  To take a specific
   example, in the Service Function Chaining (SFC)
   [I.D-ietf-sfc-problem-statement] environment, every Service Function
   (SF) may operate at a different layer and may use a different
   encapsulation scheme.  When taking into account overlay technologies,
   the number of encapsulation options increases even more.

   At this point, it is useful to recall the preliminary objectives
   stated in Section 3.  To achieve end-to-end and service-level views
   of network performance requires that the management function be
   capable of receiving and reacting to related information from every
   transport segment at every layer in the network.  This is a working
   definition of consolidated management.

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   A key issue with "management consolidation" is that it may include a
   requirement for management to interact with every technology used in
   the network on a per-technology basis either initially or when it has
   to follow up on detected problems by collecting detailed information.
   It is an architectural challenge beyond the scope of this document to
   determine whether consolidated management then becomes an aggregation
   of local managers of legacy type tied together by a coordination
   function, or whether simplifications are possible.

4.2.  Argument For Layer and Technology Independent Management

   The argument for consolidated management to have a layer and
   technology independent view of the network and supporting layers is
   two-pronged.  The first argument is fairly straightforward and
   initially independent of architectural considerations.  Some
   management functions are concerned solely with the topology of the
   network and supporting layers as represented by the three-dimensional
   topology defined in Section 2.  These include network optimization,
   efficient enforcement of Traffic Engineering (TE) techniques
   including assurance of path diversity in one layer and over the
   complete hierarchy of layers, and fine-grained tweaking.  Even in
   this case management action may require interaction with the managed
   elements at a technology-specific level, barring an alternative
   architectural solution.

   The second argument for a layer and technology independent view
   involves considerably more substance than the first one.  The three-
   dimensional topology would be a starting point for this view, but in
   addition it would include an abstracted view of service-affecting or
   potentially service-affecting events, identified by layer and
   reporting managed device.  This allows management to correlate events
   in different layers and identify the devices from which it must seek
   further information or to which it must direct other requests,
   without being burdened with excess information.  The intention is to
   ease root cause analysis and improve the ability to maintain end-to-
   end and service-level visibility.

   Where this second version of a technology independent view is created
   is an architectural issue, beyond the scope of the present document.
   One possibility is that the work is all done in the "consolidated
   management" function, in which case the latter just becomes an
   aggregation of legacy technology-specific managers tied together by a
   coordination function, as mentioned above.  A contrasting possibility
   is that the managed devices also support the abstraction, with a view
   to minimizing the amount of technology specific information and
   management actions the management function has to support.

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4.3.  Detailed Issues

4.3.1.  Strong Technology Dependency For MIB Modules

   OAM protocols rely heavily on the specific network technology they
   are associated with.  For example, ICMPv6 [RFC4443] and LSP Ping
   [RFC4379] provide the same OAM functionality, path discovery, for
   IPv6 and MPLS Label Switched Path (LSP) technologies respectively.

   SNMP MIB modules to manage these protocols were developed on a per
   OAM protocol basis.  As a result, there was little reuse of MIB
   modules for other existing OAM protocols.  To the extent that
   management operations are being redesigned in terms of YANG modules
   [RFC6020] over NETCONF [RFC6241], the opportunity exists to use the
   concept of layer and technology independent abstraction to extract
   the reusable parts, simplifying the work on the remainder.

4.3.2.  Issues of Abstraction

   In a multi-layer network, OAM functions are enabled at different
   layers and OAM information needs to be gathered from various layers
   independently.  Without multi-layer OAM in place, it is hard for
   management applications to understand what information (e.g.,
   Context, OAM functionalities) at different layers stands for and have
   a unified view of OAM information at different layers.  A mechanism
   is required to provide this information to management.

   The challenge is to abstract in a way that retains in the management
   plane as much useful information as possible while filtering the data
   that is not needed.  An important part of this effort is a clear
   understanding of what information is actually needed.  There is a
   close relationship between this issue and the issue already
   identified in the previous section.

4.3.3.  OAM Interworking Issues

   When multiple layer OAMs are used in the different parts of the
   network, two layer OAMs interworking at the boundaries need to be

   o  How one layer OAM in given part of the network interworks with
      another layer OAM in another part of the network operated by the
      same administrative entity through a consolidated management
      interface? e.g., E-LMI used in UNI interworks with Ethernet link
      OAM used on an IEEE 802.3 link in the same domain?

   o  How one layer OAM interworks with another layer OAM in the same
      part of the network through a conssolidated management interface?

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      e.g., Ethernet OAM interworks with MPLS OAM in the same part of
      the network?  In this case, Ethernet OAM and MPLS OAM are both
      supported by the same two managed devices in communication.

   In these cases, mapping and notifications of defect states between
   different layer OAMs is required at the boundary nodes of the two
   parts of the network [RFC6310] [RFC7023]
   [I-D.ietf-l2vpn-vpws-iw-oam].  Management must provide the
   interworking function to establish dynamic mapping and translation,
   supervise defects, and suppress alarms.  [Issue for debate.  The
   original text from draft-ww-oamwg provides for a separate
   interworking function.  To me, that violates the concept of
   consolidated management.  Maybe this is a case of local versus
   consolidated management as discussed in Section 6 -- PTT as
   individual contributor]

4.3.4.  Multiple (ECMP) Paths OAM Issue

   Network devices typically use fields in the MAC or IP header or MPLS
   header and perform hash computations (e.g., 5-tuple hash consisting
   of IP protocol, source address, destination address, source port, and
   destination port) on these packet header fields to classify packets
   into flows and select the forwarding path for the flow among multiple
   equal cost paths, ECMP becomes more important when network overlay,
   service chain technology are introduced, e.g., in case of multi-
   instances of the same service function is invoked for a given chain
   to provide redundancy, how 5-tuple hash is used based on contents in
   the outer headers and inner encapsulated packet.

   Multiple path OAM requires that Connectivity Check and Continuity
   Check must follow the same path as the data traffic (e.g., TCP
   traffic and UDP traffic).  Overlay encapsulation allows OAM data to
   piggyback packets, in the way record route is used in IPv4 options.
   However, there is no standard way to exercise end to end continuity
   and connectivity verification that covers all of ECMP paths in the IP
   networks.  Such a standard is desirable.

5.  Problem Statement

   OAM functions are used heavily during service and network life-cycle.
   Today, OAM management requires expertise due to technology dependency
   despite the similarity in functions (adding to CAPEX and OPEX).
   Troubleshooting is cumbersome due to protocol variety and lack of
   multi- layer OAM.  This requires expertise and long troubleshooting
   cycles (OPEX).  Last but not least, today's various management
   interfaces make it difficult to accept and introduce new protocols
   and technologies

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   There is value in attempting to define an architecture for
   consolidated management that may reasonably be argued to meet the
   objectives stated in Section 3.  If this attempt succeeds, it can be
   followed up with a gap analysis, which in turn will define a further
   program of standardization.

   At the detailed level, Section 4.3.1 and Section 4.3.2 deal with the
   matter of abstraction and its relationship to the specification of
   YANG modules.  This is work beyond the initial definition of
   architecture and awaits justification and prioritization by the gap
   analysis.  A similar consideration relates to the solution to the
   ECMP problem.

   The remaining issue is the OAM interworking issue identified in
   Section 4.3.3.  This is architectural in nature, and should be
   addressed by the proposed work on architecture.

6.  Considerations For the Work On Architecture

   Definition of an architecture for consolidated management is beyond
   the scope of the present document.  This section instead provides
   considerations that should be taken into account when defining such
   an architecture.

6.1.  What the Architecture Must Define

   This section is a discussion in the nature of a very general use case
   rather than a discussion of functions and entities.  However, as a
   preliminary remark, the architecture must be thought through for all
   five of the FCAPS areas (fault, configuration, accounting,
   performance, and security management).  RFC 5706 Section 3, while
   nominally directed to protocol design, reviews operational issues
   associated with each of these areas.

   To begin with, previous analysis (Section 4.2) has indicated that the
   CMgmtE Section 2 needs to work with a view of network topology that
   is layer and technology independent in order to achieve the
   objectives stated in Section 3.  Two questions immediately come to
   mind: where is this view prepared, taking account of the limited
   processing power of network devices in particular, and what model is
   used to present the topology to the CMgmtE?  Of course, these
   questions are evaded if the architecture makes the CMgmtE responsible
   for creating the abstracted topology from data gathered from the
   LMgmtEs and/or managed entities Section 2 within its scope.

   Note that from the end-to-end point of view multiple network
   topologies will typically exist in the network at one time, possibly
   down to the granularity of a service instance.  The relationship of

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   the scope of a CMgmtE to the set of available topologies is subject
   to the condition that it has end-to-end and service-level views of
   all paths between the endpoints within its scope, and is otherwise

   The CMgmtE must be aware of all of the LMgmtEs and/or managed
   entities within its scope.  The architecture must define how the
   CMgmtE identifies the correct sequence of these entities along a path
   in a given layer, and similarly, must identify the correct ordering
   of layers from bottom to top.  In effect, the CMgmtE requires a
   three-dimensional topological view of the data plane maintenance
   infrastructure.  Entity identification may be implicit in this work.
   Note that management actions may alter this topology (e.g., for
   routine maintenance or installation of new equipment).

   The next issue is how the CMgmtE and the other entities discover each
   other.  Bound up in this is the issue of trust.  This bootstrapping
   problem is a hard one, constantly recurring in IETF work but never
   yet solved.  The architecture work will have to come to its own
   conclusions on this topic.

   Where correlation of events from different layers and transport
   segments is done is not an issue.  By definition it can be done only
   by the CMgmtE.  The architecture must decide whether the necessary
   data gathering is done as required or continuously.

   As a final point, the architecture must specify how an existing
   network evolves from legacy operation to the target architecture.
   The existing network will have LMgmtEs in place.  The question is
   whether the CMgmtE simply replaces them or communicates with them.
   If it simply replaces them, the architecture must define (in an
   operational considerations section) how testing of the new management
   configuration takes place before cutover.  Considerations of data
   continuity during cutover should also be addressed.

   The above is not an exhaustive list of considerations, but should
   give a good start to the architectural work.

7.  Security Considerations

   The architectural work must include work on the security architecture
   of the whole system.  Beyond that, potential future work on
   individual interfaces must include the appropriate security
   mechanisms within the architectural framework.  The present document
   cannot be more specific by its nature.

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8.  IANA Considerations

   This document does not require any action from IANA.

9.  Contributors

   In the understanding of the Editor, the following individuals (listed
   in alphabetical order by last name) contributed text to or strongly
   influenced the development of versions of draft-ww-opsawg-multi-
   layer-oam, from which this document was derived:

   o  Sam Aldrin, Huawei USA;

   o  Mohamed Boucadair, France

   o  Huub van Helvoort, Hai Gaoming BV;

   o  Tom Herbert, Google;

   o  Pradeep Jain, Nuage Networks;

   o  Daniel King, Olddog Consulting;

   o  Greg Mirsky, Ericsson;

   o  Dan Romascanu, Avaya;

   o  Ravi Shekhar, Juniper.

10.  Acknowledgements

   The authors would like to thank Jan Lindblad, Tissa Senevirathne,
   Yuji Tochio, Ignas Bagdonas, Eric Osborne, Rob Shakir, Georgis
   Karagiannis, Melinda Shore and Jouni Korhonen for their reviews and

11.  References

11.1.  Normative References

   [RFC6291]  Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
              D., and S. Mansfield, "Guidelines for the Use of the "OAM"
              Acronym in the IETF", BCP 161, RFC 6291, June 2011.

   [RFC7276]  Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
              Weingarten, "An Overview of Operations, Administration,
              and Maintenance (OAM) Tools", RFC 7276, June 2014.

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11.2.  Informative References

              Aissaoui, M., Busschbach, P., Allan, D., Morrow, M., and
              T. Nadeau, "OAM Procedures for VPWS Interworking", draft-
              ietf-l2vpn-vpws-iw-oam-04 (work in progress), March 2014.

              Quinn, P., Guichard, J., and S. Surendra, "Network Service
              Chaining Problem Statement (Work in progress)", ID draft-
              ietf-sfc-problem-statement, August 2014.

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

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

   [RFC5706]  Harrington, D., "Guidelines for Considering Operations and
              Management of New Protocols and Protocol Extensions", RFC
              5706, November 2009.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

   [RFC6123]  Farrel, A., "Inclusion of Manageability Sections in Path
              Computation Element (PCE) Working Group Drafts", RFC 6123,
              February 2011.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)", RFC
              6241, June 2011.

   [RFC6310]  Aissaoui, M., Busschbach, P., Martini, L., Morrow, M.,
              Nadeau, T., and Y(J). Stein, "Pseudowire (PW) Operations,
              Administration, and Maintenance (OAM) Message Mapping",
              RFC 6310, July 2011.

   [RFC7023]  Mohan, D., Bitar, N., Sajassi, A., DeLord, S., Niger, P.,
              and R. Qiu, "MPLS and Ethernet Operations, Administration,
              and Maintenance (OAM) Interworking", RFC 7023, October

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Authors' Addresses

   Qin Wu
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012


   Mishael Wexler
   Riesstr. 25
   Munich  80992


   T. Taylor (editor)
   PT Taylor Consulting


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