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<pre>Network Working Group                                       J. Lang, Ed.
Request for Comments: 4204                                   Sonos, Inc.
Category: Standards Track                                   October 2005


                     <span class="h1">Link Management Protocol (LMP)</span>

Status of This Memo

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

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   For scalability purposes, multiple data links can be combined to form
   a single traffic engineering (TE) link.  Furthermore, the management
   of TE links is not restricted to in-band messaging, but instead can
   be done using out-of-band techniques.  This document specifies a link
   management protocol (LMP) that runs between a pair of nodes and is
   used to manage TE links.  Specifically, LMP will be used to maintain
   control channel connectivity, verify the physical connectivity of the
   data links, correlate the link property information, suppress
   downstream alarms, and localize link failures for
   protection/restoration purposes in multiple kinds of networks.

Table of Contents

   <a href="#section-1">1</a>. Introduction ....................................................<a href="#page-3">3</a>
      <a href="#section-1.1">1.1</a>. Terminology ................................................<a href="#page-5">5</a>
   <a href="#section-2">2</a>. LMP Overview ....................................................<a href="#page-6">6</a>
   <a href="#section-3">3</a>. Control Channel Management ......................................<a href="#page-8">8</a>
      <a href="#section-3.1">3.1</a>. Parameter Negotiation ......................................<a href="#page-9">9</a>
      <a href="#section-3.2">3.2</a>. Hello Protocol ............................................<a href="#page-10">10</a>
   <a href="#section-4">4</a>. Link Property Correlation ......................................<a href="#page-13">13</a>
   <a href="#section-5">5</a>. Verifying Link Connectivity ....................................<a href="#page-15">15</a>
      <a href="#section-5.1">5.1</a>. Example of Link Connectivity Verification .................<a href="#page-18">18</a>
   <a href="#section-6">6</a>. Fault Management ...............................................<a href="#page-19">19</a>
      <a href="#section-6.1">6.1</a>. Fault Detection ...........................................<a href="#page-20">20</a>
      <a href="#section-6.2">6.2</a>. Fault Localization Procedure ..............................<a href="#page-20">20</a>
      <a href="#section-6.3">6.3</a>. Examples of Fault Localization ............................<a href="#page-21">21</a>




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<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


      <a href="#section-6.4">6.4</a>. Channel Activation Indication .............................<a href="#page-22">22</a>
      <a href="#section-6.5">6.5</a>. Channel Deactivation Indication ...........................<a href="#page-23">23</a>
   <a href="#section-7">7</a>. Message_Id Usage ...............................................<a href="#page-23">23</a>
   <a href="#section-8">8</a>. Graceful Restart ...............................................<a href="#page-24">24</a>
   <a href="#section-9">9</a>. Addressing .....................................................<a href="#page-25">25</a>
   <a href="#section-10">10</a>. Exponential Back-off Procedures ...............................<a href="#page-26">26</a>
       <a href="#section-10.1">10.1</a>. Operation ...............................................<a href="#page-26">26</a>
       <a href="#section-10.2">10.2</a>. Retransmission Algorithm ................................<a href="#page-27">27</a>
   <a href="#section-11">11</a>. LMP Finite State Machines .....................................<a href="#page-28">28</a>
       <a href="#section-11.1">11.1</a>. Control Channel FSM .....................................<a href="#page-28">28</a>
       <a href="#section-11.2">11.2</a>. TE Link FSM .............................................<a href="#page-32">32</a>
       <a href="#section-11.3">11.3</a>. Data Link FSM ...........................................<a href="#page-34">34</a>
   <a href="#section-12">12</a>. LMP Message Formats ...........................................<a href="#page-38">38</a>
       <a href="#section-12.1">12.1</a>. Common Header ...........................................<a href="#page-39">39</a>
       <a href="#section-12.2">12.2</a>. LMP Object Format .......................................<a href="#page-41">41</a>
       <a href="#section-12.3">12.3</a>. Parameter Negotiation Messages ..........................<a href="#page-42">42</a>
       <a href="#section-12.4">12.4</a>. Hello Message (Msg Type = 4) ............................<a href="#page-43">43</a>
       <a href="#section-12.5">12.5</a>. Link Verification Messages ..............................<a href="#page-43">43</a>
       <a href="#section-12.6">12.6</a>. Link Summary Messages ...................................<a href="#page-47">47</a>
       <a href="#section-12.7">12.7</a>. Fault Management Messages ...............................<a href="#page-49">49</a>
   <a href="#section-13">13</a>. LMP Object Definitions ........................................<a href="#page-50">50</a>
       <a href="#section-13.1">13.1</a>. CCID (Control Channel ID) Class .........................<a href="#page-50">50</a>
       <a href="#section-13.2">13.2</a>. NODE_ID Class ...........................................<a href="#page-51">51</a>
       <a href="#section-13.3">13.3</a>. LINK_ID Class ...........................................<a href="#page-52">52</a>
       <a href="#section-13.4">13.4</a>. INTERFACE_ID Class ......................................<a href="#page-53">53</a>
       <a href="#section-13.5">13.5</a>. MESSAGE_ID Class ........................................<a href="#page-54">54</a>
       <a href="#section-13.6">13.6</a>. CONFIG Class ............................................<a href="#page-55">55</a>
       <a href="#section-13.7">13.7</a>. HELLO Class .............................................<a href="#page-56">56</a>
       <a href="#section-13.8">13.8</a>. BEGIN_VERIFY Class ......................................<a href="#page-56">56</a>
       <a href="#section-13.9">13.9</a>. BEGIN_VERIFY_ACK Class ..................................<a href="#page-58">58</a>
       <a href="#section-13.10">13.10</a>. VERIFY_ID Class ........................................<a href="#page-59">59</a>
       <a href="#section-13.11">13.11</a>. TE_LINK Class ..........................................<a href="#page-59">59</a>
       <a href="#section-13.12">13.12</a>. DATA_LINK Class ........................................<a href="#page-61">61</a>
       <a href="#section-13.13">13.13</a>. CHANNEL_STATUS Class ...................................<a href="#page-65">65</a>
       <a href="#section-13.14">13.14</a>. CHANNEL_STATUS_REQUEST Class ...........................<a href="#page-68">68</a>
       <a href="#section-13.15">13.15</a>. ERROR_CODE Class .......................................<a href="#page-70">70</a>
   <a href="#section-14">14</a>. References ....................................................<a href="#page-71">71</a>
       <a href="#section-14.1">14.1</a>. Normative References ....................................<a href="#page-71">71</a>
       <a href="#section-14.2">14.2</a>. Informative References ..................................<a href="#page-72">72</a>
   <a href="#section-15">15</a>. Security Considerations .......................................<a href="#page-73">73</a>
       <a href="#section-15.1">15.1</a>. Security Requirements ...................................<a href="#page-73">73</a>
       <a href="#section-15.2">15.2</a>. Security Mechanisms .....................................<a href="#page-74">74</a>
   <a href="#section-16">16</a>. IANA Considerations ...........................................<a href="#page-76">76</a>
   <a href="#section-17">17</a>. Acknowledgements ..............................................<a href="#page-83">83</a>
   <a href="#section-18">18</a>. Contributors ..................................................<a href="#page-83">83</a>






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<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>

   Networks are being developed with routers, switches, crossconnects,
   dense wavelength division multiplexed (DWDM) systems, and add-drop
   multiplexors (ADMs) that use a common control plane, e.g.,
   Generalized MPLS (GMPLS), to dynamically allocate resources and to
   provide network survivability using protection and restoration
   techniques.  A pair of nodes may have thousands of interconnects,
   where each interconnect may consist of multiple data links when
   multiplexing (e.g., Frame Relay DLCIs at Layer 2, time division
   multiplexed (TDM) slots or wavelength division multiplexed (WDM)
   wavelengths at Layer 1) is used.  For scalability purposes, multiple
   data links may be combined into a single traffic-engineering (TE)
   link.

   To enable communication between nodes for routing, signaling, and
   link management, there must be a pair of IP interfaces that are
   mutually reachable.  We call such a pair of interfaces a control
   channel.  Note that "mutually reachable" does not imply that these
   two interfaces are (directly) connected by an IP link; there may be
   an IP network between the two.  Furthermore, the interface over which
   the control messages are sent/received may not be the same interface
   over which the data flows.  This document specifies a link management
   protocol (LMP) that runs between a pair of nodes and is used to
   manage TE links and verify reachability of the control channel.  For
   the purposes of this document, such nodes are considered "LMP
   neighbors" or simply "neighboring nodes".

   In GMPLS, the control channels between two adjacent nodes are no
   longer required to use the same physical medium as the data links
   between those nodes.  For example, a control channel could use a
   separate virtual circuit, wavelength, fiber, Ethernet link, an IP
   tunnel routed over a separate management network, or a multi-hop IP
   network.  A consequence of allowing the control channel(s) between
   two nodes to be logically or physically diverse from the associated
   data links is that the health of a control channel does not
   necessarily correlate to the health of the data links, and vice-
   versa.  Therefore, a clean separation between the fate of the control
   channel and data links must be made.  New mechanisms must be
   developed to manage the data links, both in terms of link
   provisioning and fault management.

   Among the tasks that LMP accomplishes is checking that the grouping
   of links into TE links, as well as the properties of those links, are
   the same at both end points of the links -- this is called "link
   property correlation".  Also, LMP can communicate these link
   properties to the IGP module, which can then announce them to other




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   nodes in the network.  LMP can also tell the signaling module the
   mapping between TE links and control channels.  Thus, LMP performs a
   valuable "glue" function in the control plane.

   Note that while the existence of the control network (single or
   multi-hop) is necessary for enabling communication, it is by no means
   sufficient.  For example, if the two interfaces are separated by an
   IP network, faults in the IP network may result in the lack of an IP
   path from one interface to another, and therefore an interruption of
   communication between the two interfaces.  On the other hand, not
   every failure in the control network affects a given control channel,
   hence the need for establishing and managing control channels.

   For the purposes of this document, a data link may be considered by
   each node that it terminates on as either a 'port' or a 'component
   link', depending on the multiplexing capability of the endpoint on
   that link; component links are multiplex capable, whereas ports are
   not multiplex capable.  This distinction is important since the
   management of such links (including, for example, resource
   allocation, label assignment, and their physical verification) is
   different based on their multiplexing capability.  For example, a
   Frame Relay switch is able to demultiplex an interface into virtual
   circuits based on DLCIs; similarly, a SONET crossconnect with OC-192
   interfaces may be able to demultiplex the OC-192 stream into four
   OC-48 streams.  If multiple interfaces are grouped together into a
   single TE link using link bundling [<a href="./rfc4201" title="&quot;Link Bundling in MPLS Traffic Engineering (TE)&quot;">RFC4201</a>], then the link resources
   must be identified using three levels: Link_Id, component interface
   Id, and label identifying virtual circuit, timeslot, etc.  Resource
   allocation happens at the lowest level (labels), but physical
   connectivity happens at the component link level.  As another
   example, consider the case where an optical switch (e.g., PXC)
   transparently switches OC-192 lightpaths.  If multiple interfaces are
   once again grouped together into a single TE link, then link bundling
   [<a href="./rfc4201" title="&quot;Link Bundling in MPLS Traffic Engineering (TE)&quot;">RFC4201</a>] is not required and only two levels of identification are
   required: Link_Id and Port_Id.  In this case, both resource
   allocation and physical connectivity happen at the lowest level
   (i.e., port level).

   To ensure interworking between data links with different multiplexing
   capabilities, LMP-capable devices SHOULD allow sub-channels of a
   component link to be locally configured as (logical) data links.  For
   example, if a Router with 4 OC-48 interfaces is connected through a
   4:1 MUX to a cross-connect with OC-192 interfaces, the cross-connect
   should be able to configure each sub-channel (e.g., STS-48c SPE if
   the 4:1 MUX is a SONET MUX) as a data link.






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<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   LMP is designed to support aggregation of one or more data links into
   a TE link (either ports into TE links, or component links into TE
   links).  The purpose of forming a TE link is to group/map the
   information about certain physical resources (and their properties)
   into the information that is used by Constrained SPF for the purpose
   of path computation, and by GMPLS signaling.

<span class="h3"><a class="selflink" id="section-1.1" href="#section-1.1">1.1</a>.  Terminology</span>

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [<a href="./rfc2119" title="&quot;Key words for use in RFCs to Indicate Requirement Levels&quot;">RFC2119</a>].

   The reader is assumed to be familiar with the terminology in
   [<a href="./rfc3471" title="&quot;Generalized MPLS - Signaling Functional Description&quot;">RFC3471</a>], [<a href="./rfc4202" title="&quot;Routing Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)&quot;">RFC4202</a>], and [<a href="./rfc4201" title="&quot;Link Bundling in MPLS Traffic Engineering (TE)&quot;">RFC4201</a>].

   Bundled Link:

      As defined in [<a href="./rfc4201" title="&quot;Link Bundling in MPLS Traffic Engineering (TE)&quot;">RFC4201</a>], a bundled link is a TE link such that,
      for the purpose of GMPLS signaling, a combination of &lt;link
      identifier, label&gt; is not sufficient to unambiguously identify the
      appropriate resources used by an LSP.  A bundled link is composed
      of two or more component links.

   Control Channel:

      A control channel is a pair of mutually reachable interfaces that
      are used to enable communication between nodes for routing,
      signaling, and link management.

   Component Link:

      As defined in [<a href="./rfc4201" title="&quot;Link Bundling in MPLS Traffic Engineering (TE)&quot;">RFC4201</a>], a component link is a subset of resources
      of a TE Link such that (a) the partition is minimal, and (b)
      within each subset a label is sufficient to unambiguously identify
      the appropriate resources used by an LSP.

   Data Link:

      A data link is a pair of interfaces that are used to transfer user
      data.  Note that in GMPLS, the control channel(s) between two
      adjacent nodes are no longer required to use the same physical
      medium as the data links between those nodes.

   Link Property Correlation:

      This is a procedure to correlate the local and remote properties
      of a TE link.



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   Multiplex Capability:

      The ability to multiplex/demultiplex a data stream into sub-rate
      streams for switching purposes.

   Node_Id:

      For a node running OSPF, the LMP Node_Id is the same as the
      address contained in the OSPF Router Address TLV.  For a node
      running IS-IS and advertising the TE Router ID TLV, the Node_Id is
      the same as the advertised Router ID.

   Port:

      An interface that terminates a data link.

   TE Link:

      As defined in [<a href="./rfc4202" title="&quot;Routing Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)&quot;">RFC4202</a>], a TE link is a logical construct that
      represents a way to group/map the information about certain
      physical resources (and their properties) that interconnect LSRs
      into the information that is used by Constrained SPF for the
      purpose of path computation, and by GMPLS signaling.

   Transparent:

      A device is called X-transparent if it forwards incoming signals
      from input to output without examining or modifying the X aspect
      of the signal.  For example, a Frame Relay switch is network-layer
      transparent; an all-optical switch is electrically transparent.

<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>.  LMP Overview</span>

   The two core procedures of LMP are control channel management and
   link property correlation.  Control channel management is used to
   establish and maintain control channels between adjacent nodes.  This
   is done using a Config message exchange and a fast keep-alive
   mechanism between the nodes.  The latter is required if lower-level
   mechanisms are not available to detect control channel failures.
   Link property correlation is used to synchronize the TE link
   properties and verify the TE link configuration.

   LMP requires that a pair of nodes have at least one active bi-
   directional control channel between them.  Each direction of the
   control channel is identified by a Control Channel Id (CC_Id), and
   the two directions are coupled together using the LMP Config message
   exchange.  Except for Test messages, which may be limited by the




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<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   transport mechanism for in-band messaging, all LMP packets are run
   over UDP with an LMP port number.  The link level encoding of the
   control channel is outside the scope of this document.

   An "LMP adjacency" is formed between two nodes when at least one bi-
   directional control channel is established between them.  Multiple
   control channels may be active simultaneously for each adjacency;
   control channel parameters, however, MUST be individually negotiated
   for each control channel.  If the LMP fast keep-alive is used over a
   control channel, LMP Hello messages MUST be exchanged over the
   control channel.  Other LMP messages MAY be transmitted over any of
   the active control channels between a pair of adjacent nodes.  One or
   more active control channels may be grouped into a logical control
   channel for signaling, routing, and link property correlation
   purposes.

   The link property correlation function of LMP is designed to
   aggregate multiple data links (ports or component links) into a TE
   link and to synchronize the properties of the TE link.  As part of
   the link property correlation function, a LinkSummary message
   exchange is defined.  The LinkSummary message includes the local and
   remote Link_Ids, a list of all data links that comprise the TE link,
   and various link properties.  A LinkSummaryAck or LinkSummaryNack
   message MUST be sent in response to the receipt of a LinkSummary
   message indicating agreement or disagreement on the link properties.

   LMP messages are transmitted reliably using Message_Ids and
   retransmissions.  Message_Ids are carried in MESSAGE_ID objects.  No
   more than one MESSAGE_ID object may be included in an LMP message.
   For control-channel-specific messages, the Message_Id is within the
   scope of the control channel over which the message is sent.  For
   TE-link-specific messages, the Message_Id is within the scope of the
   LMP adjacency.  The value of the Message_Id is monotonically
   increasing and wraps when the maximum value is reached.

   In this document, two additional LMP procedures are defined: link
   connectivity verification and fault management.  These procedures are
   particularly useful when the control channels are physically diverse
   from the data links.  Link connectivity verification is used for data
   plane discovery, Interface_Id exchange (Interface_Ids are used in
   GMPLS signaling, either as port labels or component link identifiers,
   depending on the configuration), and physical connectivity
   verification.  This is done by sending Test messages over the data
   links and TestStatus messages back over the control channel.  Note
   that the Test message is the only LMP message that must be
   transmitted over the data link.  The ChannelStatus message exchange
   is used between adjacent nodes for both the suppression of downstream
   alarms and the localization of faults for protection and restoration.



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<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   For LMP link connectivity verification, the Test message is
   transmitted over the data links.  For X-transparent devices, this
   requires examining and modifying the X aspect of the signal.  The LMP
   link connectivity verification procedure is coordinated using a
   BeginVerify message exchange over a control channel.  To support
   various aspects of transparency, a Verify Transport Mechanism is
   included in the BeginVerify and BeginVerifyAck messages.  Note that
   there is no requirement that all data links must lose their
   transparency simultaneously; but, at a minimum, it must be possible
   to terminate them one at a time.  There is also no requirement that
   the control channel and TE link use the same physical medium;
   however, the control channel MUST be terminated by the same two
   control elements that control the TE link.  Since the BeginVerify
   message exchange coordinates the Test procedure, it also naturally
   coordinates the transition of the data links in and out of the
   transparent mode.

   The LMP fault management procedure is based on a ChannelStatus
   message exchange that uses the following messages: ChannelStatus,
   ChannelStatusAck, ChannelStatusRequest, and ChannelStatusResponse.
   The ChannelStatus message is sent unsolicited and is used to notify
   an LMP neighbor about the status of one or more data channels of a TE
   link.  The ChannelStatusAck message is used to acknowledge receipt of
   the ChannelStatus message.  The ChannelStatusRequest message is used
   to query an LMP neighbor for the status of one or more data channels
   of a TE Link.  The ChannelStatusResponse message is used to
   acknowledge receipt of the ChannelStatusRequest message and indicate
   the states of the queried data links.

<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>.  Control Channel Management</span>

   To initiate an LMP adjacency between two nodes, one or more bi-
   directional control channels MUST be activated.  The control channels
   can be used to exchange control-plane information such as link
   provisioning and fault management information (implemented using a
   messaging protocol such as LMP, proposed in this document), path
   management and label distribution information (implemented using a
   signaling protocol such as RSVP-TE [<a href="./rfc3209" title="&quot;RSVP-TE: Extensions to RSVP for LSP Tunnels&quot;">RFC3209</a>]), and network topology
   and state distribution information (implemented using traffic
   engineering extensions of protocols such as OSPF [<a href="./rfc3630" title="&quot;Traffic Engineering (TE) Extensions to OSPF Version 2&quot;">RFC3630</a>] and IS-IS
   [<a href="./rfc3784" title="&quot;Intermediate System to Intermediate System (IS-IS) Extensions for Traffic Engineering (TE)&quot;">RFC3784</a>]).

   For the purposes of LMP, the exact implementation of the control
   channel is not specified; it could be, for example, a separate
   wavelength or fiber, an Ethernet link, an IP tunnel through a
   separate management network, or the overhead bytes of a data link.
   Each node assigns a node-wide, unique, 32-bit, non-zero integer
   control channel identifier (CC_Id).  This identifier comes from the



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   same space as the unnumbered interface Id.  Furthermore, LMP packets
   are run over UDP with an LMP port number.  Thus, the link level
   encoding of the control channel is not part of the LMP specification.

   To establish a control channel, the destination IP address on the far
   end of the control channel must be known.  This knowledge may be
   manually configured or automatically discovered.  Note that for in-
   band signaling, a control channel could be explicitly configured on a
   particular data link.  In this case, the Config message exchange can
   be used to dynamically learn the IP address on the far end of the
   control channel.  This is done by sending the Config message with the
   unicast IP source address and the multicast IP destination address
   (224.0.0.1 or ff02::1).  The ConfigAck and ConfigNack messages MUST
   be sent to the source IP address found in the IP header of the
   received Config message.

   Control channels exist independently of TE links and multiple control
   channels may be active simultaneously between a pair of nodes.
   Individual control channels can be realized in different ways; one
   might be implemented in-fiber while another one may be implemented
   out-of-fiber.  As such, control channel parameters MUST be negotiated
   over each individual control channel, and LMP Hello packets MUST be
   exchanged over each control channel to maintain LMP connectivity if
   other mechanisms are not available.  Since control channels are
   electrically terminated at each node, it may be possible to detect
   control channel failures using lower layers (e.g., SONET/SDH).

   There are four LMP messages that are used to manage individual
   control channels.  They are the Config, ConfigAck, ConfigNack, and
   Hello messages.  These messages MUST be transmitted on the channel to
   which they refer.  All other LMP messages may be transmitted over any
   of the active control channels between a pair of LMP adjacent nodes.

   In order to maintain an LMP adjacency, it is necessary to have at
   least one active control channel between a pair of adjacent nodes
   (recall that multiple control channels can be active simultaneously
   between a pair of nodes).  In the event of a control channel failure,
   alternate active control channels can be used and it may be possible
   to activate additional control channels as described below.

<span class="h3"><a class="selflink" id="section-3.1" href="#section-3.1">3.1</a>.  Parameter Negotiation</span>

   Control channel activation begins with a parameter negotiation
   exchange using Config, ConfigAck, and ConfigNack messages.  The
   contents of these messages are built using LMP objects, which can be
   either negotiable or non-negotiable (identified by the N bit in the
   object header).  Negotiable objects can be used to let LMP peers




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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-10" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   agree on certain values.  Non-negotiable objects are used for the
   announcement of specific values that do not need, or do not allow,
   negotiation.

   To activate a control channel, a Config message MUST be transmitted
   to the remote node, and in response, a ConfigAck message MUST be
   received at the local node.  The Config message contains the Local
   Control Channel Id (CC_Id), the sender's Node_Id, a Message_Id for
   reliable messaging, and a CONFIG object.  It is possible that both
   the local and remote nodes initiate the configuration procedure at
   the same time.  To avoid ambiguities, the node with the higher
   Node_Id wins the contention; the node with the lower Node_Id MUST
   stop transmitting the Config message and respond to the Config
   message it received.  If the Node_Ids are equal, then one (or both)
   nodes have been misconfigured.  The nodes MAY continue to retransmit
   Config messages in hopes that the misconfiguration is corrected.
   Note that the problem may be solved by an operator changing the
   Node_Ids on one or both nodes.

   The ConfigAck message is used to acknowledge receipt of the Config
   message and express agreement on ALL of the configured parameters
   (both negotiable and non-negotiable).

   The ConfigNack message is used to acknowledge receipt of the Config
   message, indicate which (if any) non-negotiable CONFIG objects are
   unacceptable, and to propose alternate values for the negotiable
   parameters.

   If a node receives a ConfigNack message with acceptable alternate
   values for negotiable parameters, the node SHOULD transmit a Config
   message using these values for those parameters.

   If a node receives a ConfigNack message with unacceptable alternate
   values, the node MAY continue to retransmit Config messages in hopes
   that the misconfiguration is corrected.  Note that the problem may be
   solved by an operator changing parameters on one or both nodes.

   In the case where multiple control channels use the same physical
   interface, the parameter negotiation exchange is performed for each
   control channel.  The various LMP parameter negotiation messages are
   associated with their corresponding control channels by their node-
   wide unique identifiers (CC_Ids).

<span class="h3"><a class="selflink" id="section-3.2" href="#section-3.2">3.2</a>.  Hello Protocol</span>

   Once a control channel is activated between two adjacent nodes, the
   LMP Hello protocol can be used to maintain control channel
   connectivity between the nodes and to detect control channel



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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-11" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   failures.  The LMP Hello protocol is intended to be a lightweight
   keep-alive mechanism that will react to control channel failures
   rapidly so that IGP Hellos are not lost and the associated link-state
   adjacencies are not removed unnecessarily.

<span class="h4"><a class="selflink" id="section-3.2.1" href="#section-3.2.1">3.2.1</a>.  Hello Parameter Negotiation</span>

   Before sending Hello messages, the HelloInterval and
   HelloDeadInterval parameters MUST be agreed upon by the local and
   remote nodes.  These parameters are exchanged in the Config message.
   The HelloInterval indicates how frequently LMP Hello messages will be
   sent, and is measured in milliseconds (ms).  For example, if the
   value were 150, then the transmitting node would send the Hello
   message at least every 150 ms.  The HelloDeadInterval indicates how
   long a device should wait to receive a Hello message before declaring
   a control channel dead, and is measured in milliseconds (ms).

   The HelloDeadInterval MUST be greater than the HelloInterval, and
   SHOULD be at least 3 times the value of HelloInterval.  If the fast
   keep-alive mechanism of LMP is not used, the HelloInterval and
   HelloDeadInterval parameters MUST be set to zero.

   The values for the HelloInterval and HelloDeadInterval should be
   selected carefully to provide rapid response time to control channel
   failures without causing congestion.  As such, different values will
   likely be configured for different control channel implementations.
   When the control channel is implemented over a directly connected
   link, the suggested default values for the HelloInterval is 150 ms
   and for the HelloDeadInterval is 500 ms.

   When a node has either sent or received a ConfigAck message, it may
   begin sending Hello messages.  Once it has sent a Hello message and
   received a valid Hello message (i.e., with expected sequence numbers;
   see <a href="#section-3.2.2">Section 3.2.2</a>), the control channel moves to the up state.  (It
   is also possible to move to the up state without sending Hellos if
   other methods are used to indicate bi-directional control-channel
   connectivity.  For example, indication of bi-directional connectivity
   may be learned from the transport layer.)  If, however, a node
   receives a ConfigNack message instead of a ConfigAck message, the
   node MUST not send Hello messages and the control channel SHOULD NOT
   move to the up state.  See <a href="#section-11.1">Section 11.1</a> for the complete control
   channel FSM.









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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-12" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h4"><a class="selflink" id="section-3.2.2" href="#section-3.2.2">3.2.2</a>.  Fast Keep-alive</span>

   Each Hello message contains two sequence numbers: the first sequence
   number (TxSeqNum) is the sequence number for the Hello message being
   sent and the second sequence number (RcvSeqNum) is the sequence
   number of the last Hello message received from the adjacent node over
   this control channel.

   There are two special sequence numbers.  TxSeqNum MUST NOT ever be 0.
   TxSeqNum = 1 is used to indicate that the sender has just started or
   has restarted and has no recollection of the last TxSeqNum that was
   sent.  Thus, the first Hello sent has a TxSeqNum of 1 and an RxSeqNum
   of 0.  When TxSeqNum reaches (2^32)-1, the next sequence number used
   is 2, not 0 or 1, as these have special meanings.

   Under normal operation, the difference between the RcvSeqNum in a
   Hello message that is received and the local TxSeqNum that is
   generated will be at most 1.  This difference can be more than one
   only when a control channel restarts or when the values wrap.

   Since the 32-bit sequence numbers may wrap, the following expression
   may be used to test if a newly received TxSeqNum value is less than a
   previously received value:

   If ((int) old_id - (int) new_id &gt; 0) {
      New value is less than old value;
   }

   Having sequence numbers in the Hello messages allows each node to
   verify that its peer is receiving its Hello messages.  By including
   the RcvSeqNum in Hello packets, the local node will know which Hello
   packets the remote node has received.

   The following example illustrates how the sequence numbers operate.
   Note that only the operation at one node is shown, and alternative
   scenarios are possible:

   1) After completing the configuration stage, Node A sends Hello
      messages to Node B with {TxSeqNum=1;RcvSeqNum=0}.

   2) Node A receives a Hello from Node B with {TxSeqNum=1;RcvSeqNum=1}.
      When the HelloInterval expires on Node A, it sends Hellos to Node
      B with {TxSeqNum=2;RcvSeqNum=1}.

   3) Node A receives a Hello from Node B with {TxSeqNum=2;RcvSeqNum=2}.
      When the HelloInterval expires on Node A, it sends Hellos to Node
      B with {TxSeqNum=3;RcvSeqNum=2}.




<span class="grey">Lang                        Standards Track                    [Page 12]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-13" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h4"><a class="selflink" id="section-3.2.3" href="#section-3.2.3">3.2.3</a>.  Control Channel Down</span>

   To allow bringing a control channel down gracefully for
   administration purposes, a ControlChannelDown flag is available in
   the Common Header of LMP packets.  When data links are still in use
   between a pair of nodes, a control channel SHOULD only be taken down
   administratively when there are other active control channels that
   can be used to manage the data links.

   When bringing a control channel down administratively, a node MUST
   set the ControlChannelDown flag in all LMP messages sent over the
   control channel.  The node that initiated the control channel down
   procedure may stop sending Hello messages after HelloDeadInterval
   seconds have passed, or if it receives an LMP message over the same
   control channel with the ControlChannelDown flag set.

   When a node receives an LMP packet with the ControlChannelDown flag
   set, it SHOULD send a Hello message with the ControlChannelDown flag
   set and move the control channel to the down state.

<span class="h4"><a class="selflink" id="section-3.2.4" href="#section-3.2.4">3.2.4</a>.  Degraded State</span>

   A consequence of allowing the control channels to be physically
   diverse from the associated data links is that there may not be any
   active control channels available while the data links are still in
   use.  For many applications, it is unacceptable to tear down a link
   that is carrying user traffic simply because the control channel is
   no longer available; however, the traffic that is using the data
   links may no longer be guaranteed the same level of service.  Hence,
   the TE link is in a Degraded state.

   When a TE link is in the Degraded state, routing and signaling SHOULD
   be notified so that new connections are not accepted and the TE link
   is advertised with no unreserved resources.

<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>.  Link Property Correlation</span>

   As part of LMP, a link property correlation exchange is defined for
   TE links using the LinkSummary, LinkSummaryAck, and LinkSummaryNack
   messages.  The contents of these messages are built using LMP
   objects, which can be either negotiable or non-negotiable (identified
   by the N flag in the object header).  Negotiable objects can be used
   to let both sides agree on certain link parameters.  Non-negotiable
   objects are used for announcement of specific values that do not
   need, or do not allow, negotiation.






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<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   Each TE link has an identifier (Link_Id) that is assigned at each end
   of the link.  These identifiers MUST be the same type (i.e, IPv4,
   IPv6, unnumbered) at both ends.  If a LinkSummary message is received
   with different local and remote TE link types, then a LinkSummaryNack
   message MUST be sent with Error Code "Bad TE Link Object".
   Similarly, each data link is assigned an identifier (Interface_Id) at
   each end.  These identifiers MUST also be the same type at both ends.
   If a LinkSummary message is received with different local and remote
   Interface_Id types, then a LinkSummaryNack message MUST be sent with
   Error Code "Bad Data Link Object".

   Link property correlation SHOULD be done before the link is brought
   up and MAY be done any time a link is up and not in the Verification
   process.

   The LinkSummary message is used to verify for consistency the TE and
   data link information on both sides.  Link Summary messages are also
   used (1) to aggregate multiple data links (either ports or component
   links) into a TE link; (2) to exchange, correlate (to determine
   inconsistencies), or change TE link parameters; and (3) to exchange,
   correlate (to determine inconsistencies), or change Interface_Ids
   (either Port_Ids or component link identifiers).

   The LinkSummary message includes a TE_LINK object followed by one or
   more DATA_LINK objects.  The TE_LINK object identifies the TE link's
   local and remote Link_Id and indicates support for fault management
   and link verification procedures for that TE link.  The DATA_LINK
   objects are used to characterize the data links that comprise the TE
   link.  These objects include the local and remote Interface_Ids, and
   may include one or more sub-objects further describing the properties
   of the data links.

   If the LinkSummary message is received from a remote node, and the
   Interface_Id mappings match those that are stored locally, then the
   two nodes have agreement on the Verification procedure (see <a href="#section-5">Section</a>
   <a href="#section-5">5</a>) and data link identification configuration.  If the verification
   procedure is not used, the LinkSummary message can be used to verify
   agreement on manual configuration.

   The LinkSummaryAck message is used to signal agreement on the
   Interface_Id mappings and link property definitions.  Otherwise, a
   LinkSummaryNack message MUST be transmitted, indicating which
   Interface mappings are not correct and/or which link properties are
   not accepted.  If a LinkSummaryNack message indicates that the
   Interface_Id mappings are not correct and the link verification
   procedure is enabled, the link verification process SHOULD be
   repeated for all mismatched, free data links; if an allocated data
   link has a mapping mismatch, it SHOULD be flagged and verified when



<span class="grey">Lang                        Standards Track                    [Page 14]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-15" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   it becomes free.  If a LinkSummaryNack message includes negotiable
   parameters, then acceptable values for those parameters MUST be
   included.  If a LinkSummaryNack message is received and includes
   negotiable parameters, then the initiator of the LinkSummary message
   SHOULD send a new LinkSummary message.  The new LinkSummary message
   SHOULD include new values for the negotiable parameters.  These
   values SHOULD take into account the acceptable values received in the
   LinkSummaryNack message.

   It is possible that the LinkSummary message could grow quite large
   due to the number of DATA LINK objects.  An LMP implementation SHOULD
   be able to fragment when transmitting LMP messages, and MUST be able
   to re-assemble IP fragments when receiving LMP messages.

<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>.  Verifying Link Connectivity</span>

   In this section, an optional procedure is described that may be used
   to verify the physical connectivity of the data links and dynamically
   learn (i.e., discover) the TE link and Interface_Id associations.
   The procedure SHOULD be done when establishing a TE link, and
   subsequently, on a periodic basis for all unallocated (free) data
   links of the TE link.

   Support for this procedure is indicated by setting the "Link
   Verification Supported" flag in the TE_LINK object of the LinkSummary
   message.

   If a BeginVerify message is received and link verification is not
   supported for the TE link, then a BeginVerifyNack message MUST be
   transmitted with Error Code indicating, "Link Verification Procedure
   not supported for this TE Link."

   A unique characteristic of transparent devices is that the data is
   not modified or examined during normal operation.  This
   characteristic poses a challenge for validating the connectivity of
   the data links and establishing the label mappings.  Therefore, to
   ensure proper verification of data link connectivity, it is required
   that, until the data links are allocated for user traffic, they must
   be opaque (i.e., lose their transparency).  To support various
   degrees of opaqueness (e.g., examining overhead bytes, terminating
   the IP payload, etc.) and, hence, different mechanisms to transport
   the Test messages, a Verify Transport Mechanism field is included in
   the BeginVerify and BeginVerifyAck messages.

   There is no requirement that all data links be terminated
   simultaneously; but, at a minimum, the data links MUST be able to be
   terminated one at a time.  Furthermore, for the link verification
   procedure it is assumed that the nodal architecture is designed so



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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-16" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   that messages can be sent and received over any data link.  Note that
   this requirement is trivial for opaque devices since each data link
   is electrically terminated and processed before being forwarded to
   the next opaque device; but that in transparent devices this is an
   additional requirement.

   To interconnect two nodes, a TE link is defined between them, and at
   a minimum, there MUST be at least one active control channel between
   the nodes.  For link verification, a TE link MUST include at least
   one data link.

   Once a control channel has been established between the two nodes,
   data link connectivity can be verified by exchanging Test messages
   over each of the data links specified in the TE link.  It should be
   noted that all LMP messages except the Test message are exchanged
   over the control channels and that Hello messages continue to be
   exchanged over each control channel during the data link verification
   process.  The Test message is sent over the data link that is being
   verified.  Data links are tested in the transmit direction because
   they are unidirectional; therefore, it may be possible for both nodes
   to (independently) exchange the Test messages simultaneously.

   To initiate the link verification procedure, the local node MUST send
   a BeginVerify message over a control channel.  To limit the scope of
   Link Verification to a particular TE Link, the local Link_Id MUST be
   non-zero.  If this field is zero, the data links can span multiple TE
   links and/or they may comprise a TE link that is yet to be
   configured.  For the case where the local Link_Id field is zero, the
   "Verify all Links" flag of the BEGIN_VERIFY object is used to
   distinguish between data links that span multiple TE links and those
   that have not yet been assigned to a TE link.  Specifically,
   verification of data links that span multiple TE links is indicated
   by setting the local Link_Id field to zero and setting the "Verify
   all Links" flag.  Verification of data links that have not yet been
   assigned to a TE link is indicated by setting the local Link_Id field
   to zero and clearing the "Verify all Links" flag.

   The BeginVerify message also contains the number of data links that
   are to be verified; the interval (called VerifyInterval) at which the
   Test messages will be sent; the encoding scheme and transport
   mechanisms that are supported; the data rate for Test messages; and,
   when the data links correspond to fibers, the wavelength identifier
   over which the Test messages will be transmitted.

   If the remote node receives a BeginVerify message and it is ready to
   process Test messages, it MUST send a BeginVerifyAck message back to
   the local node specifying the desired transport mechanism for the
   TEST messages.  The remote node includes a 32-bit, node-unique



<span class="grey">Lang                        Standards Track                    [Page 16]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-17" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   Verify_Id in the BeginVerifyAck message.  The Verify_Id MAY be
   randomly selected; however, it MUST NOT overlap any other Verify_Id
   currently being used by the node selecting it.  The Verify_Id is then
   used in all corresponding verification messages to differentiate them
   from different LMP peers and/or parallel Test procedures.  When the
   local node receives a BeginVerifyAck message from the remote node, it
   may begin testing the data links by transmitting periodic Test
   messages over each data link.  The Test message includes the
   Verify_Id and the local Interface_Id for the associated data link.
   The remote node MUST send either a TestStatusSuccess or a
   TestStatusFailure message in response for each data link.  A
   TestStatusAck message MUST be sent to confirm receipt of the
   TestStatusSuccess and TestStatusFailure messages.  Unacknowledged
   TestStatusSuccess and TestStatusFailure messages SHOULD be
   retransmitted until the message is acknowledged or until a retry
   limit is reached (see also <a href="#section-10">Section 10</a>).

   It is also permissible for the sender to terminate the Test procedure
   anytime after sending the BeginVerify message.  An EndVerify message
   SHOULD be sent for this purpose.

   Message correlation is done using message identifiers and the
   Verify_Id; this enables verification of data links, belonging to
   different link bundles or LMP sessions, in parallel.

   When the Test message is received, the received Interface_Id (used in
   GMPLS as either a Port label or component link identifier, depending
   on the configuration) is recorded and mapped to the local
   Interface_Id for that data link, and a TestStatusSuccess message MUST
   be sent.  The TestStatusSuccess message includes the local
   Interface_Id along with the Interface_Id and Verify_Id received in
   the Test message.  The receipt of a TestStatusSuccess message
   indicates that the Test message was detected at the remote node and
   the physical connectivity of the data link has been verified.  When
   the TestStatusSuccess message is received, the local node SHOULD mark
   the data link as up and send a TestStatusAck message to the remote
   node.  If, however, the Test message is not detected at the remote
   node within an observation period (specified by the
   VerifyDeadInterval), the remote node MUST send a TestStatusFailure
   message over the control channel, which indicates that the
   verification of the physical connectivity of the data link has
   failed.  When the local node receives a TestStatusFailure message, it
   SHOULD mark the data link as FAILED and send a TestStatusAck message
   to the remote node.  When all the data links on the list have been
   tested, the local node SHOULD send an EndVerify message to indicate
   that testing is complete on this link.





<span class="grey">Lang                        Standards Track                    [Page 17]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-18" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   If the local/remote data link mappings are known, then the link
   verification procedure can be optimized by testing the data links in
   a defined order known to both nodes.  The suggested criterion for
   this ordering is by increasing the value of the remote Interface_Id.

   Both the local and remote nodes SHOULD maintain the complete list of
   Interface_Id mappings for correlation purposes.

<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>.  Example of Link Connectivity Verification</span>

   Figure 1 shows an example of the link verification scenario that is
   executed when a link between Node A and Node B is added.  In this
   example, the TE link consists of three free ports (each transmitted
   along a separate fiber) and is associated with a bi-directional
   control channel (indicated by a "c").  The verification process is as
   follows:

   o  A sends a BeginVerify message over the control channel to B,
      indicating it will begin verifying the ports that form the TE
      link.  The LOCAL_LINK_ID object carried in the BeginVerify message
      carries the identifier (IP address or interface index) that A
      assigns to the link.
   o  Upon receipt of the BeginVerify message, B creates a Verify_Id and
      binds it to the TE Link from A.  This binding is used later when B
      receives the Test messages from A, and these messages carry the
      Verify_Id.  B discovers the identifier (IP address or interface
      index) that A assigns to the TE link by examining the
      LOCAL_LINK_ID object carried in the received BeginVerify message.
      (If the data ports are not yet assigned to the TE Link, the
      binding is limited to the Node_Id of A.) In response to the
      BeginVerify message, B sends the BeginVerifyAck message to A.  The
      LOCAL_LINK_ID object carried in the BeginVerifyAck message is used
      to carry the identifier (IP address or interface index) that B
      assigns to the TE link.  The REMOTE_LINK_ID object carried in the
      BeginVerifyAck message is used to bind the Link_Ids assigned by
      both A and B.  The Verify_Id is returned to A in the
      BeginVerifyAck message over the control channel.
   o  When A receives the BeginVerifyAck message, it begins transmitting
      periodic Test messages over the first port (Interface Id=1).  The
      Test message includes the Interface_Id for the port and the
      Verify_Id that was assigned by B.
   o  When B receives the Test messages, it maps the received
      Interface_Id to its own local Interface_Id = 10 and transmits a
      TestStatusSuccess message over the control channel back to Node A.
      The TestStatusSuccess message includes both the local and received
      Interface_Ids for the port as well as the Verify_Id.  The





<span class="grey">Lang                        Standards Track                    [Page 18]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-19" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


      Verify_Id is used to determine the local/remote TE link
      identifiers (IP addresses or interface indices) to which the data
      links belong.
   o  A will send a TestStatusAck message over the control channel back
      to B, indicating it received the TestStatusSuccess message.
   o  The process is repeated until all of the ports are verified.
   o  At this point, A will send an EndVerify message over the control
      channel to B, indicating that testing is complete.
   o  B will respond by sending an EndVerifyAck message over the control
      channel back to A.

      Note that this procedure can be used to "discover" the
      connectivity of the data ports.

   +---------------------+                      +---------------------+
   +                     +                      +                     +
   +      Node A         +&lt;-------- c ---------&gt;+        Node B       +
   +                     +                      +                     +
   +                     +                      +                     +
   +                   1 +---------------------&gt;+ 10                  +
   +                     +                      +                     +
   +                     +                      +                     +
   +                   2 +                /----&gt;+ 11                  +
   +                     +          /----/      +                     +
   +                     +     /---/            +                     +
   +                   3 +----/                 + 12                  +
   +                     +                      +                     +
   +                     +                      +                     +
   +                   4 +---------------------&gt;+ 14                  +
   +                     +                      +                     +
   +---------------------+                      +---------------------+

    Figure 1:  Example of link connectivity between Node A and Node B.

<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>.  Fault Management</span>

   In this section, an optional LMP procedure is described that is used
   to manage failures by rapid notification of the status of one or more
   data channels of a TE Link.  The scope of this procedure is within a
   TE link, and as such, the use of this procedure is negotiated as part
   of the LinkSummary exchange.  The procedure can be used to rapidly
   isolate data link and TE link failures, and is designed to work for
   both unidirectional and bi-directional LSPs.








<span class="grey">Lang                        Standards Track                    [Page 19]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-20" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   An important implication of using transparent devices is that
   traditional methods that are used to monitor the health of allocated
   data links may no longer be appropriate.  Instead of fault detection
   being in layer 2 or layer 3, it is delegated to the physical layer
   (i.e., loss of light or optical monitoring of the data).

   Recall that a TE link connecting two nodes may consist of a number of
   data links.  If one or more data links fail between two nodes, a
   mechanism must be used for rapid failure notification so that
   appropriate protection/restoration mechanisms can be initiated.  If
   the failure is subsequently cleared, then a mechanism must be used to
   notify that the failure is clear and the channel status is OK.

<span class="h3"><a class="selflink" id="section-6.1" href="#section-6.1">6.1</a>.  Fault Detection</span>

   Fault detection should be handled at the layer closest to the
   failure; for optical networks, this is the physical (optical) layer.
   One measure of fault detection at the physical layer is detecting
   loss of light (LOL).  Other techniques for monitoring optical signals
   are still being developed and will not be further considered in this
   document.  However, it should be clear that the mechanism used for
   fault notification in LMP is independent of the mechanism used to
   detect the failure, and simply relies on the fact that a failure is
   detected.

<span class="h3"><a class="selflink" id="section-6.2" href="#section-6.2">6.2</a>.  Fault Localization Procedure</span>

   In some situations, a data link failure between two nodes is
   propagated downstream such that all the downstream nodes detect the
   failure without localizing the failure.  To avoid multiple alarms
   stemming from the same failure, LMP provides failure notification
   through the ChannelStatus message.  This message may be used to
   indicate that a single data channel has failed, multiple data
   channels have failed, or an entire TE link has failed.  Failure
   correlation is done locally at each node upon receipt of the failure
   notification.

   To localize a fault to a particular link between adjacent nodes, a
   downstream node (downstream in terms of data flow) that detects data
   link failures will send a ChannelStatus message to its upstream
   neighbor indicating that a failure has been detected (bundling
   together the notification of all the failed data links).  An upstream
   node that receives the ChannelStatus message MUST send a
   ChannelStatusAck message to the downstream node indicating it has
   received the ChannelStatus message.  The upstream node should
   correlate the failure to see if the failure is also detected locally
   for the corresponding LSP(s).  If, for example, the failure is clear
   on the input of the upstream node or internally, then the upstream



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   node will have localized the failure.  Once the failure is
   correlated, the upstream node SHOULD send a ChannelStatus message to
   the downstream node indicating that the channel is failed or is OK.
   If a ChannelStatus message is not received by the downstream node, it
   SHOULD send a ChannelStatusRequest message for the channel in
   question.  Once the failure has been localized, the signaling
   protocols may be used to initiate span or path protection and
   restoration procedures.

   If all of the data links of a TE link have failed, then the upstream
   node MAY be notified of the TE link failure without specifying each
   data link of the failed TE link.  This is done by sending failure
   notification in a ChannelStatus message identifying the TE Link
   without including the Interface_Ids in the CHANNEL_STATUS object.

<span class="h3"><a class="selflink" id="section-6.3" href="#section-6.3">6.3</a>.  Examples of Fault Localization</span>

   In Figure 2, a sample network is shown where four nodes are connected
   in a linear array configuration.  The control channels are bi-
   directional and are labeled with a "c".  All LSPs are also bi-
   directional.

   In the first example [see Fig. 2(a)], there is a failure on one
   direction of the bi-directional LSP.  Node 4 will detect the failure
   and will send a ChannelStatus message to Node 3 indicating the
   failure (e.g., LOL) to the corresponding upstream node.  When Node 3
   receives the ChannelStatus message from Node 4, it returns a
   ChannelStatusAck message back to Node 4 and correlates the failure
   locally.  When Node 3 correlates the failure and verifies that the
   failure is clear, it has localized the failure to the data link
   between Node 3 and Node 4.  At that time, Node 3 should send a
   ChannelStatus message to Node 4 indicating that the failure has been
   localized.

   In the second example [see Fig. 2(b)], a single failure (e.g., fiber
   cut) affects both directions of the bi-directional LSP.  Node 2 (Node
   3) will detect the failure of the upstream (downstream) direction and
   send a ChannelStatus message to the upstream (in terms of data flow)
   node indicating the failure (e.g., LOL).  Simultaneously (ignoring
   propagation delays), Node 1 (Node 4) will detect the failure on the
   upstream (downstream) direction, and will send a ChannelStatus
   message to the corresponding upstream (in terms of data flow) node
   indicating the failure.  Node 2 and Node 3 will have localized the
   two directions of the failure.







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       +-------+        +-------+        +-------+        +-------+
       + Node1 +        + Node2 +        + Node3 +        + Node4 +
       +       +-- c ---+       +-- c ---+       +-- c ---+       +
   ----+---\   +        +       +        +       +        +       +
   &lt;---+---\\--+--------+-------+---\    +       +        +    /--+---&gt;
       +    \--+--------+-------+---\\---+-------+---##---+---//--+----
       +       +        +       +    \---+-------+--------+---/   +
       +       +        +       +        +       +  (a)   +       +
   ----+-------+--------+---\   +        +       +        +       +
   &lt;---+-------+--------+---\\--+---##---+--\    +        +       +
       +       +        +    \--+---##---+--\\   +        +       +
       +       +        +       +  (b)   +   \\--+--------+-------+---&gt;
       +       +        +       +        +    \--+--------+-------+----
       +       +        +       +        +       +        +       +
       +-------+        +-------+        +-------+        +-------+

         Figure 2: Two types of data link failures are shown (indicated
         by ## in the figure):
         (A) a data link corresponding to the downstream direction of a
             bi-directional LSP fails,
         (B) two data links corresponding to both directions of a bi-
             directional LSP fail.  The control channel connecting two
             nodes is indicated with a "c".

<span class="h3"><a class="selflink" id="section-6.4" href="#section-6.4">6.4</a>. Channel Activation Indication</span>

   The ChannelStatus message may also be used to notify an LMP neighbor
   that the data link should be actively monitored.  This is called
   Channel Activation Indication.  This is particularly useful in
   networks with transparent nodes where the status of data links may
   need to be triggered using control channel messages.  For example, if
   a data link is pre-provisioned and the physical link fails after
   verification and before inserting user traffic, a mechanism is needed
   to indicate the data link should be active, otherwise the failure may
   not be detectable.

   The ChannelStatus message is used to indicate that a channel or group
   of channels are now active.  The ChannelStatusAck message MUST be
   transmitted upon receipt of a ChannelStatus message.  When a
   ChannelStatus message is received, the corresponding data link(s)
   MUST be put into the Active state.  If upon putting them into the
   Active state, a failure is detected, the ChannelStatus message SHOULD
   be transmitted as described in <a href="#section-6.2">Section 6.2</a>.








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<span class="h3"><a class="selflink" id="section-6.5" href="#section-6.5">6.5</a>.  Channel Deactivation Indication</span>

   The ChannelStatus message may also be used to notify an LMP neighbor
   that the data link no longer needs to be actively monitored.  This is
   the counterpart to the Channel Active Indication.

   When a ChannelStatus message is received with Channel Deactive
   Indication, the corresponding data link(s) MUST be taken out of the
   Active state.

<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>. Message_Id Usage</span>

   The MESSAGE_ID and MESSAGE_ID_ACK objects are included in LMP
   messages to support reliable message delivery.  This section
   describes the usage of these objects.  The MESSAGE_ID and
   MESSAGE_ID_ACK objects contain a Message_Id field.

   Only one MESSAGE_ID/MESSAGE_ID_ACK object may be included in any LMP
   message.

   For control-channel-specific messages, the Message_Id field is within
   the scope of the CC_Id.  For TE link specific messages, the
   Message_Id field is within the scope of the LMP adjacency.

   The Message_Id field of the MESSAGE_ID object contains a generator-
   selected value.  This value MUST be monotonically increasing.  A
   value is considered to be previously used when it has been sent in an
   LMP message with the same CC_Id (for control channel specific
   messages) or LMP adjacency (for TE Link specific messages).  The
   Message_Id field of the MESSAGE_ID_ACK object contains the Message_Id
   field of the message being acknowledged.

   Unacknowledged messages sent with the MESSAGE_ID object SHOULD be
   retransmitted until the message is acknowledged or until a retry
   limit is reached (see also <a href="#section-10">Section 10</a>).

   Note that the 32-bit Message_Id value may wrap.  The following
   expression may be used to test if a newly received Message_Id value
   is less than a previously received value:

   If ((int) old_id - (int) new_id &gt; 0) {
      New value is less than old value;
   }








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   Nodes processing incoming messages SHOULD check to see if a newly
   received message is out of order and can be ignored.  Out-of-order
   messages can be identified by examining the value in the Message_Id
   field.  If a message is determined to be out-of-order, that message
   should be silently dropped.

   If the message is a Config message, and the Message_Id value is less
   than the largest Message_Id value previously received from the sender
   for the CC_Id, then the message SHOULD be treated as being out-of-
   order.

   If the message is a LinkSummary message and the Message_Id value is
   less than the largest Message_Id value previously received from the
   sender for the TE Link, then the message SHOULD be treated as being
   out-of-order.

   If the message is a ChannelStatus message and the Message_Id value is
   less than the largest Message_Id value previously received from the
   sender for the specified TE link, then the receiver SHOULD check the
   Message_Id value previously received for the state of each data
   channel included in the ChannelStatus message.  If the Message_Id
   value is greater than the most recently received Message_Id value
   associated with at least one of the data channels included in the
   message, the message MUST NOT be treated as out of order; otherwise,
   the message SHOULD be treated as being out of order.  However, the
   state of any data channel MUST NOT be updated if the Message_Id value
   is less than the most recently received Message_Id value associated
   with the data channel.

   All other messages MUST NOT be treated as out-of-order.

<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>. Graceful Restart</span>

   This section describes the mechanism to resynchronize the LMP state
   after a control plane restart.  A control plane restart may occur
   when bringing up the first control channel after a control
   communications failure.  A control communications failure may be the
   result of an LMP adjacency failure or a nodal failure wherein the LMP
   control state is lost, but the data plane is unaffected.  The latter
   is detected by setting the "LMP Restart" bit in the Common Header of
   the LMP messages.  When the control plane fails due to the loss of
   the control channel, the LMP link information should be retained.  It
   is possible that a node may be capable of retaining the LMP link
   information across a nodal failure.  However, in both cases the
   status of the data channels MUST be synchronized.






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   It is assumed the Node_Id and Local Interface_Ids remain stable
   across a control plane restart.

   After the control plane of a node restarts, the control channel(s)
   must be re-established using the procedures of <a href="#section-3.1">Section 3.1</a>.  When
   re-establishing control channels, the Config message SHOULD be sent
   using the unicast IP source and destination addresses.

   If the control plane failure was the result of a nodal failure where
   the LMP control state is lost, then the "LMP Restart" flag MUST be
   set in LMP messages until a Hello message is received with the
   RcvSeqNum equal to the local TxSeqNum.  This indicates that the
   control channel is up and the LMP neighbor has detected the restart.

   The following assumes that the LMP component restart only occurred on
   one end of the TE Link.  If the LMP component restart occurred on
   both ends of the TE Link, the normal procedures for LinkSummary
   should be used, as described in <a href="#section-4">Section 4</a>.

   Once a control channel is up, the LMP neighbor MUST send a
   LinkSummary message for each TE Link across the adjacency.  All the
   objects of the LinkSummary message MUST have the N-bit set to 0,
   indicating that the parameters are non-negotiable.  This provides the
   local/remote Link_Id and Interface_Id mappings, the associated data
   link parameters, and indication of which data links are currently
   allocated to user traffic.  When a node receives the LinkSummary
   message, it checks its local configuration.  If the node is capable
   of retaining the LMP link information across a restart, it must
   process the LinkSummary message as described in <a href="#section-4">Section 4</a> with the
   exception that the allocated/de-allocated flag of the DATA_LINK
   object received in the LinkSummary message MUST take precedence over
   any local value.  If, however, the node was not capable of retaining
   the LMP link information across a restart, the node MUST accept the
   data link parameters of the received LinkSummary message and respond
   with a LinkSummaryAck message.

   Upon completion of the LinkSummary exchange, the node that has
   restarted the control plane SHOULD send a ChannelStatusRequest
   message for that TE link.  The node SHOULD also verify the
   connectivity of all unallocated data channels.

<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>. Addressing</span>

   All LMP messages are run over UDP with an LMP port number (except, in
   some cases, the Test messages, which may be limited by the transport
   mechanism for in-band messaging).  The destination address of the IP
   packet MAY be either the address learned in the Configuration
   procedure (i.e., the Source IP address found in the IP header of the



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   received Config message), an IP address configured on the remote
   node, or the Node_Id.  The Config message is an exception as
   described below.

   The manner in which a Config message is addressed may depend on the
   signaling transport mechanism.  When the transport mechanism is a
   point-to-point link, Config messages SHOULD be sent to the Multicast
   address (224.0.0.1 or ff02::1).  Otherwise, Config messages MUST be
   sent to an IP address on the neighboring node.  This may be
   configured at both ends of the control channel or may be
   automatically discovered.

<span class="h2"><a class="selflink" id="section-10" href="#section-10">10</a>.  Exponential Back-off Procedures</span>

   This section is based on [<a href="./rfc2961" title="&quot;RSVP Refresh Overhead Reduction Extensions&quot;">RFC2961</a>] and provides exponential back-off
   procedures for message retransmission.  Implementations MUST use the
   described procedures or their equivalent.

<span class="h3"><a class="selflink" id="section-10.1" href="#section-10.1">10.1</a>. Operation</span>

   The following operation is one possible mechanism for exponential
   back-off retransmission of unacknowledged LMP messages.  The sending
   node retransmits the message until an acknowledgement message is
   received or until a retry limit is reached.  When the sending node
   receives the acknowledgement, retransmission of the message is
   stopped.  The interval between message retransmission is governed by
   a rapid retransmission timer.  The rapid retransmission timer starts
   at a small interval and increases exponentially until it reaches a
   threshold.

   The following time parameters are useful to characterize the
   procedures:

   Rapid retransmission interval Ri:

      Ri is the initial retransmission interval for unacknowledged
      messages.  After sending the message for the first time, the
      sending node will schedule a retransmission after Ri milliseconds.

   Rapid retry limit Rl:

      Rl is the maximum number of times a message will be transmitted
      without being acknowledged.








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   Increment value Delta:

      Delta governs the speed with which the sender increases the
      retransmission interval.  The ratio of two successive
      retransmission intervals is (1 + Delta).

   Suggested default values for an initial retransmission interval (Ri)
   of 500 ms are a power of 2 exponential back-off (Delta = 1) and a
   retry limit of 3.

<span class="h3"><a class="selflink" id="section-10.2" href="#section-10.2">10.2</a>. Retransmission Algorithm</span>

   After a node transmits a message requiring acknowledgement, it should
   immediately schedule a retransmission after Ri seconds.  If a
   corresponding acknowledgement message is received before Ri seconds,
   then message retransmission SHOULD be canceled.  Otherwise, it will
   retransmit the message after (1+Delta)*Ri seconds.  The
   retransmission will continue until either an appropriate
   acknowledgement message is received or the rapid retry limit, Rl, has
   been reached.

   A sending node can use the following algorithm when transmitting a
   message that requires acknowledgement:

      Prior to initial transmission, initialize Rk = Ri and Rn = 0.

      while (Rn++ &lt; Rl) {
        transmit the message;
        wake up after Rk milliseconds;
        Rk = Rk * (1 + Delta);
      }
      /* acknowledged message or no reply from receiver and Rl
      reached*/
      do any needed clean up;
      exit;

   Asynchronously, when a sending node receives a corresponding
   acknowledgment message, it will change the retry count, Rn, to Rl.

   Note that the transmitting node does not advertise or negotiate the
   use of the described exponential back-off procedures in the Config or
   LinkSummary messages.









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<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h2"><a class="selflink" id="section-11" href="#section-11">11</a>.  LMP Finite State Machines</span>

<span class="h3"><a class="selflink" id="section-11.1" href="#section-11.1">11.1</a>.  Control Channel FSM</span>

   The control channel FSM defines the states and logics of operation of
   an LMP control channel.

<span class="h4"><a class="selflink" id="section-11.1.1" href="#section-11.1.1">11.1.1</a>.  Control Channel States</span>

   A control channel can be in one of the states described below.  Every
   state corresponds to a certain condition of the control channel and
   is usually associated with a specific type of LMP message that is
   periodically transmitted to the far end.

   Down:       This is the initial control channel state.  In this
               state, no attempt is being made to bring the control
               channel up and no LMP messages are sent.  The control
               channel parameters should be set to the initial values.

   ConfSnd:    The control channel is in the parameter negotiation
               state.  In this state the node periodically sends a
               Config message, and is expecting the other side to reply
               with either a ConfigAck or ConfigNack message.  The FSM
               does not transition into the Active state until the
               remote side positively acknowledges the parameters.

   ConfRcv:    The control channel is in the parameter negotiation
               state.  In this state, the node is waiting for acceptable
               configuration parameters from the remote side.  Once such
               parameters are received and acknowledged, the FSM can
               transition to the Active state.

   Active:     In this state the node periodically sends a Hello message
               and is waiting to receive a valid Hello message.  Once a
               valid Hello message is received, it can transition to the
               up state.

   Up:         The CC is in an operational state.  The node receives
               valid Hello messages and sends Hello messages.

   GoingDown:  A CC may go into this state because of administrative
               action.  While a CC is in this state, the node sets the
               ControlChannelDown bit in all the messages it sends.








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<span class="h4"><a class="selflink" id="section-11.1.2" href="#section-11.1.2">11.1.2</a>.  Control Channel Events</span>

   Operation of the LMP control channel is described in terms of FSM
   states and events.  Control channel events are generated by the
   underlying protocols and software modules, as well as by the packet
   processing routines and FSMs of associated TE links.  Every event has
   its number and a symbolic name.  Description of possible control
   channel events is given below.

   1 : evBringUp:    This is an externally triggered event indicating
                     that the control channel negotiation should begin.
                     This event, for example, may be triggered by an
                     operator command, by the successful completion of a
                     control channel bootstrap procedure, or by
                     configuration.  Depending on the configuration,
                     this will trigger either
                         1a)  the sending of a Config message,
                         1b)  a period of waiting to receive a Config
                              message from the remote node.

   2 : evCCDn:       This event is generated when there is indication
                     that the control channel is no longer available.

   3 : evConfDone:   This event indicates a ConfigAck message has been
                     received, acknowledging the Config parameters.

   4 : evConfErr:    This event indicates a ConfigNack message has been
                     received, rejecting the Config parameters.

   5 : evNewConfOK:  New Config message was received from neighbor and
                     positively acknowledged.

   6 : evNewConfErr: New Config message was received from neighbor and
                     rejected with a ConfigNack message.

   7 : evContenWin:  New Config message was received from neighbor at
                     the same time a Config message was sent to the
                     neighbor.  The local node wins the contention.  As
                     a result, the received Config message is ignored.

   8 : evContenLost: New Config message was received from neighbor at
                     the same time a Config message was sent to the
                     neighbor.  The local node loses the contention.
                         8a)  The Config message is positively
                              acknowledged.
                         8b)  The Config message is negatively
                              acknowledged.




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   9 : evAdminDown:  The administrator has requested that the control
                     channel is brought down administratively.

   10: evNbrGoesDn:  A packet with ControlChannelDown flag is received
                     from the neighbor.

   11: evHelloRcvd:  A Hello packet with expected SeqNum has been
                     received.

   12: evHoldTimer:  The HelloDeadInterval timer has expired indicating
                     that no Hello packet has been received.  This moves
                     the control channel back into the Negotiation
                     state, and depending on the local configuration,
                     this will trigger either
                         12a) the sending of periodic Config messages,
                         12b) a period of waiting to receive Config
                              messages from the remote node.

   13: evSeqNumErr:  A Hello with unexpected SeqNum received and
                     discarded.

   14: evReconfig:   Control channel parameters have been reconfigured
                     and require renegotiation.

   15: evConfRet:    A retransmission timer has expired and a Config
                     message is resent.

   16: evHelloRet:   The HelloInterval timer has expired and a Hello
                     packet is sent.

   17: evDownTimer:  A timer has expired and no messages have been
                     received with the ControlChannelDown flag set.

<span class="h4"><a class="selflink" id="section-11.1.3" href="#section-11.1.3">11.1.3</a>.  Control Channel FSM Description</span>

   Figure 3 illustrates operation of the control channel FSM in a form
   of FSM state transition diagram.














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<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


                               +--------+
            +-----------------&gt;|        |&lt;--------------+
            |       +---------&gt;|  Down  |&lt;----------+   |
            |       |+---------|        |&lt;-------+  |   |
            |       ||         +--------+        |  |   |
            |       ||           |    ^       2,9| 2|  2|
            |       ||1b       1a|    |          |  |   |
            |       ||           v    |2,9       |  |   |
            |       ||         +--------+        |  |   |
            |       ||      +-&gt;|        |&lt;------+|  |   |
            |       ||  4,7,|  |ConfSnd |       ||  |   |
            |       || 14,15+--|        |&lt;----+ ||  |   |
            |       ||         +--------+     | ||  |   |
            |       ||       3,8a| |          | ||  |   |
            |       || +---------+ |8b  14,12a| ||  |   |
            |       || |           v          | ||  |   |
            |       |+-|------&gt;+--------+     | ||  |   |
            |       |  |    +-&gt;|        |-----|-|+  |   |
            |       |  |6,14|  |ConfRcv |     | |   |   |
            |       |  |    +--|        |&lt;--+ | |   |   |
            |       |  |       +--------+   | | |   |   |
            |       |  |          5| ^      | | |   |   |
            |       |  +---------+ | |      | | |   |   |
            |       |            | | |      | | |   |   |
            |       |            v v |6,12b | | |   |   |
            |       |10        +--------+   | | |   |   |
            |       +----------|        |   | | |   |   |
            |       |       +--| Active |---|-+ |   |   |
       10,17|       |   5,16|  |        |-------|---+   |
        +-------+ 9 |   13  +-&gt;|        |   |   |       |
        | Going |&lt;--|----------+--------+   |   |       |
        | Down  |   |           11| ^       |   |       |
        +-------+   |             | |5      |   |       |
            ^       |             v |  6,12b|   |       |
            |9      |10        +--------+   |   |12a,14 |
            |       +----------|        |---+   |       |
            |                  |   Up   |-------+       |
            +------------------|        |---------------+
                               +--------+
                                 |   ^
                                 |   |
                                 +---+
                                11,13,16

                       Figure 3: Control Channel FSM






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<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   Event evCCDn always forces the FSM to the down state.  Events
   evHoldTimer and evReconfig always force the FSM to the Negotiation
   state (either ConfSnd or ConfRcv).

<span class="h3"><a class="selflink" id="section-11.2" href="#section-11.2">11.2</a>. TE Link FSM</span>

   The TE Link FSM defines the states and logics of operation of the LMP
   TE Link.

<span class="h4"><a class="selflink" id="section-11.2.1" href="#section-11.2.1">11.2.1</a>. TE Link States</span>

   An LMP TE link can be in one of the states described below.  Every
   state corresponds to a certain condition of the TE link and is
   usually associated with a specific type of LMP message that is
   periodically transmitted to the far end via the associated control
   channel or in-band via the data links.

   Down:       There are no data links allocated to the TE link.

   Init:       Data links have been allocated to the TE link, but the
               configuration has not yet been synchronized with the LMP
               neighbor.  The LinkSummary message is periodically
               transmitted to the LMP neighbor.

   Up:         This is the normal operational state of the TE link.  At
               least one LMP control channel is required to be
               operational between the nodes sharing the TE link.  As
               part of normal operation, the LinkSummary message may be
               periodically transmitted to the LMP neighbor or generated
               by an external request.

   Degraded:   In this state, all LMP control channels are down, but the
               TE link still includes some data links that are allocated
               to user traffic.

<span class="h4"><a class="selflink" id="section-11.2.2" href="#section-11.2.2">11.2.2</a>.  TE Link Events</span>

   Operation of the LMP TE link is described in terms of FSM states and
   events.  TE Link events are generated by the packet processing
   routines and by the FSMs of the associated control channel(s) and the
   data links.  Every event has its number and a symbolic name.
   Descriptions of possible events are given below.

   1 : evDCUp:       One or more data channels have been enabled and
                     assigned to the TE Link.

   2 : evSumAck:     LinkSummary message received and positively
                     acknowledged.



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<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   3 : evSumNack:    LinkSummary message received and negatively
                     acknowledged.

   4 : evRcvAck:     LinkSummaryAck message received acknowledging the
                     TE Link Configuration.

   5 : evRcvNack:    LinkSummaryNack message received.

   6 : evSumRet:     Retransmission timer has expired and LinkSummary
                     message is resent.

   7 : evCCUp:       First active control channel goes up.

   8 : evCCDown:     Last active control channel goes down.

   9 : evDCDown:     Last data channel of TE Link has been removed.

<span class="h4"><a class="selflink" id="section-11.2.3" href="#section-11.2.3">11.2.3</a>.  TE Link FSM Description</span>

   Figure 4 illustrates operation of the LMP TE Link FSM in a form of
   FSM state transition diagram.






























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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-34" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


                                  3,7,8
                                   +--+
                                   |  |
                                   |  v
                                +--------+
                                |        |
                  +------------&gt;|  Down  |&lt;---------+
                  |             |        |          |
                  |             +--------+          |
                  |                |  ^             |
                  |               1|  |9            |
                  |                v  |             |
                  |             +--------+          |
                  |             |        |&lt;-+       |
                  |             |  Init  |  |3,5,6  |9
                  |             |        |--+ 7,8   |
                 9|             +--------+          |
                  |                  |              |
                  |               2,4|              |
                  |                  v              |
               +--------+   7   +--------+          |
               |        |------&gt;|        |----------+
               |  Deg   |       |   Up   |
               |        |&lt;------|        |
               +--------+   8   +--------+
                                   |  ^
                                   |  |
                                   +--+
                                 2,3,4,5,6

                       Figure 4: LMP TE Link FSM

   In the above FSM, the sub-states that may be implemented when the
   link verification procedure is used have been omitted.

<span class="h3"><a class="selflink" id="section-11.3" href="#section-11.3">11.3</a>.  Data Link FSM</span>

   The data link FSM defines the states and logics of operation of a
   data link within an LMP TE link.  Operation of a data link is
   described in terms of FSM states and events.  Data links can either
   be in the active (transmitting) mode, where Test messages are
   transmitted from them, or the passive (receiving) mode, where Test
   messages are received through them.  For clarity, separate FSMs are
   defined for the active/passive data links; however, a single set of
   data link states and events are defined.






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<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h4"><a class="selflink" id="section-11.3.1" href="#section-11.3.1">11.3.1</a>.  Data Link States</span>

   Any data link can be in one of the states described below.  Every
   state corresponds to a certain condition of the data link.

   Down:          The data link has not been put in the resource pool
                  (i.e., the link is not 'in service')

   Test:          The data link is being tested.  An LMP Test message is
                  periodically sent through the link.

   PasvTest:      The data link is being checked for incoming test
                  messages.

   Up/Free:       The link has been successfully tested and is now put
                  in the pool of resources (in-service).  The link has
                  not yet been allocated to data traffic.

   Up/Alloc:      The link is up and has been allocated for data
                  traffic.

<span class="h4"><a class="selflink" id="section-11.3.2" href="#section-11.3.2">11.3.2</a>.  Data Link Events</span>

   Data link events are generated by the packet processing routines and
   by the FSMs of the associated control channel and the TE link.

   Every event has its number and a symbolic name.  Description of
   possible data link events is given below:

   1 :evCCUp:         First active control channel goes up.

   2 :evCCDown:       LMP neighbor connectivity is lost.  This indicates
                      the last LMP control channel has failed between
                      neighboring nodes.

   3 :evStartTst:     This is an external event that triggers the
                      sending of Test messages over the data link.

   4 :evStartPsv:     This is an external event that triggers the
                      listening for Test messages over the data link.

   5 :evTestOK:       Link verification was successful and the link can
                      be used for path establishment.
                         (a)  This event indicates the Link Verification
                              procedure (see <a href="#section-5">Section 5</a>) was successful
                              for this data link and a TestStatusSuccess
                              message was received over the control
                              channel.



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<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


                         (b)  This event indicates the link is ready for
                              path establishment, but the Link
                              Verification procedure was not used.  For
                              in-band signaling of the control channel,
                              the control channel establishment may be
                              sufficient to verify the link.

   6 :evTestRcv:      Test message was received over the data port and a
                      TestStatusSuccess message is transmitted over the
                      control channel.

   7 :evTestFail:     Link verification returned negative results.  This
                      could be because (a) a TestStatusFailure message
                      was received, or (b) the Verification procedure
                      has ended without receiving a TestStatusSuccess or
                      TestStatusFailure message for the data link.

   8 :evPsvTestFail:  Link verification returned negative results.  This
                      indicates that a Test message was not detected and
                      either (a) the VerifyDeadInterval has expired or
                      (b) the Verification procedure has ended and the
                      VerifyDeadInterval has not yet expired.

   9 :evLnkAlloc:     The data link has been allocated.

   10:evLnkDealloc:   The data link has been de-allocated.

   11:evTestRet:      A retransmission timer has expired and the Test
                      message is resent.

   12:evSummaryFail:  The LinkSummary did not match for this data port.

   13:evLocalizeFail: A Failure has been localized to this data link.

   14:evdcDown:      The data channel is no longer available.
















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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-37" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h4"><a class="selflink" id="section-11.3.3" href="#section-11.3.3">11.3.3</a>.  Active Data Link FSM Description</span>

   Figure 5 illustrates operation of the LMP active data link FSM in a
   form of FSM state transition diagram.

                             +------+
                             |      |&lt;-------+
                  +---------&gt;| Down |        |
                  |     +----|      |&lt;-----+ |
                  |     |    +------+      | |
                  |     |5b   3|  ^        | |
                  |     |      |  |7       | |
                  |     |      v  |        | |
                  |     |    +------+      | |
                  |     |    |      |&lt;-+   | |
                  |     |    | Test |  |11 | |
                  |     |    |      |--+   | |
                  |     |    +------+      | |
                  |     |     5a| 3^       | |
                  |     |       |  |       | |
                  |     |       v  |       | |
                  |12   |   +---------+    | |
                  |     +--&gt;|         |14  | |
                  |         | Up/Free |----+ |
                  +---------|         |      |
                            +---------+      |
                               9| ^          |
                                | |          |
                                v |10        |
                            +---------+      |
                            |         |13    |
                            |Up/Alloc |------+
                            |         |
                            +---------+

                    Figure 5: Active LMP Data Link FSM















<span class="grey">Lang                        Standards Track                    [Page 37]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-38" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h4"><a class="selflink" id="section-11.3.4" href="#section-11.3.4">11.3.4</a>.  Passive Data Link FSM Description</span>

   Figure 6 illustrates operation of the LMP passive data link FSM in a
   form of FSM state transition diagram.

                             +------+
                             |      |&lt;------+
                 +----------&gt;| Down |       |
                 |     +-----|      |&lt;----+ |
                 |     |     +------+     | |
                 |     |5b    4|  ^       | |
                 |     |       |  |8      | |
                 |     |       v  |       | |
                 |     |    +----------+  | |
                 |     |    | PasvTest |  | |
                 |     |    +----------+  | |
                 |     |       6|  4^     | |
                 |     |        |   |     | |
                 |     |        v   |     | |
                 |12   |    +---------+   | |
                 |     +---&gt;| Up/Free |14 | |
                 |          |         |---+ |
                 +----------|         |     |
                            +---------+     |
                                9| ^        |
                                 | |        |
                                 v |10      |
                            +---------+     |
                            |         |13   |
                            |Up/Alloc |-----+
                            |         |
                            +---------+

                    Figure 6: Passive LMP Data Link FSM

<span class="h2"><a class="selflink" id="section-12" href="#section-12">12</a>.  LMP Message Formats</span>

   All LMP messages (except, in some cases, the Test messages, which are
   limited by the transport mechanism for in-band messaging) are run
   over UDP with an LMP port number (701).











<span class="grey">Lang                        Standards Track                    [Page 38]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-39" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h3"><a class="selflink" id="section-12.1" href="#section-12.1">12.1</a>.  Common Header</span>

   In addition to the UDP header and standard IP header, all LMP
   messages (except, in some cases, the Test messages which may be
   limited by the transport mechanism for in-band messaging) have the
   following common header:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Vers  |      (Reserved)       |    Flags      |    Msg Type   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          LMP Length           |          (Reserved)           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Reserved field should be sent as zero and ignored on receipt.

   All values are defined in network byte order (i.e., big-endian byte
   order).

   Vers: 4 bits

      Protocol version number.  This is version 1.

   Flags: 8 bits

      The following bit-values are defined.  All other bits are reserved
      and should be sent as zero and ignored on receipt.

      0x01: ControlChannelDown

      0x02: LMP Restart

         This bit is set to indicate that a nodal failure has occurred
         and the LMP control state has been lost.  This flag may be
         reset to 0 when a Hello message is received with RcvSeqNum
         equal to the local TxSeqNum.

   Msg Type: 8 bits

      The following values are defined.  All other values are reserved

      1  = Config

      2  = ConfigAck

      3  = ConfigNack




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<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


      4  = Hello

      5  = BeginVerify

      6  = BeginVerifyAck

      7  = BeginVerifyNack

      8  = EndVerify

      9  = EndVerifyAck

      10 = Test

      11 = TestStatusSuccess

      12 = TestStatusFailure

      13 = TestStatusAck

      14 = LinkSummary

      15 = LinkSummaryAck

      16 = LinkSummaryNack

      17 = ChannelStatus

      18 = ChannelStatusAck

      19 = ChannelStatusRequest

      20 = ChannelStatusResponse

      All of the messages are sent over the control channel EXCEPT the
      Test message, which is sent over the data link that is being
      tested.

   LMP Length: 16 bits

      The total length of this LMP message in bytes, including the
      common header and any variable-length objects that follow.









<span class="grey">Lang                        Standards Track                    [Page 40]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-41" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h3"><a class="selflink" id="section-12.2" href="#section-12.2">12.2</a>.  LMP Object Format</span>

   LMP messages are built using objects.  Each object is identified by
   its Object Class and Class-type.  Each object has a name, which is
   always capitalized in this document.  LMP objects can be either
   negotiable or non-negotiable (identified by the N bit in the object
   header).  Negotiable objects can be used to let the devices agree on
   certain values.  Non-negotiable objects are used for announcement of
   specific values that do not need or do not allow negotiation.

   All values are defined in network byte order (i.e., big-endian byte
   order).

   The format of the LMP object is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |N|   C-Type    |     Class     |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                       (object contents)                     //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   N: 1 bit

      The N flag indicates if the object is negotiable (N=1) or non-
      negotiable (N=0).

   C-Type: 7 bits

      Class-type, unique within an Object Class.  Values are defined in
      <a href="#section-13">Section 13</a>.

   Class: 8 bits

      The Class indicates the object type.  Each object has a name,
      which is always capitalized in this document.

   Length: 16 bits

      The Length field indicates the length of the object in bytes,
      including the N, C-Type, Class, and Length fields.







<span class="grey">Lang                        Standards Track                    [Page 41]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-42" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h3"><a class="selflink" id="section-12.3" href="#section-12.3">12.3</a>.  Parameter Negotiation Messages</span>

<span class="h4"><a class="selflink" id="section-12.3.1" href="#section-12.3.1">12.3.1</a>.  Config Message (Msg Type = 1)</span>

   The Config message is used in the control channel negotiation phase
   of LMP.  The contents of the Config message are built using LMP
   objects.  The format of the Config message is as follows:

   &lt;Config Message&gt; ::= &lt;Common Header&gt; &lt;LOCAL_CCID&gt; &lt;MESSAGE_ID&gt;
                        &lt;LOCAL_NODE_ID&gt; &lt;CONFIG&gt;

   The above transmission order SHOULD be followed.

   The MESSAGE_ID object is within the scope of the LOCAL_CCID object.

   The Config message MUST be periodically transmitted until (1) it
   receives a ConfigAck or ConfigNack message, (2) a retry limit has
   been reached and no ConfigAck or ConfigNack message has been
   received, or (3) it receives a Config message from the remote node
   and has lost the contention (e.g., the Node_Id of the remote node is
   higher than the Node_Id of the local node).  Both the retransmission
   interval and the retry limit are local configuration parameters.

<span class="h4"><a class="selflink" id="section-12.3.2" href="#section-12.3.2">12.3.2</a>.  ConfigAck Message (Msg Type = 2)</span>

   The ConfigAck message is used to acknowledge receipt of the Config
   message and indicate agreement on all parameters.

   &lt;ConfigAck Message&gt; ::= &lt;Common Header&gt; &lt;LOCAL_CCID&gt; &lt;LOCAL_NODE_ID&gt;
                           &lt;REMOTE_CCID&gt; &lt;MESSAGE_ID_ACK&gt;
                           &lt;REMOTE_NODE_ID&gt;

   The above transmission order SHOULD be followed.

   The contents of the REMOTE_CCID, MESSAGE_ID_ACK, and REMOTE_NODE_ID
   objects MUST be obtained from the Config message being acknowledged.

<span class="h4"><a class="selflink" id="section-12.3.3" href="#section-12.3.3">12.3.3</a>.  ConfigNack Message (Msg Type = 3)</span>

   The ConfigNack message is used to acknowledge receipt of the Config
   message and indicate disagreement on non-negotiable parameters or
   propose other values for negotiable parameters.  Parameters where
   agreement was reached MUST NOT be included in the ConfigNack Message.
   The format of the ConfigNack message is as follows:

   &lt;ConfigNack Message&gt; ::= &lt;Common Header&gt; &lt;LOCAL_CCID&gt;
                            &lt;LOCAL_NODE_ID&gt;  &lt;REMOTE_CCID&gt;
                            &lt;MESSAGE_ID_ACK&gt; &lt;REMOTE_NODE_ID&gt; &lt;CONFIG&gt;



<span class="grey">Lang                        Standards Track                    [Page 42]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-43" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   The above transmission order SHOULD be followed.

   The contents of the REMOTE_CCID, MESSAGE_ID_ACK, and REMOTE_NODE_ID
   objects MUST be obtained from the Config message being negatively
   acknowledged.

   It is possible that multiple parameters may be invalid in the Config
   message.

   If a negotiable CONFIG object is included in the ConfigNack message,
   it MUST include acceptable values for the parameters.

   If the ConfigNack message includes CONFIG objects for non-negotiable
   parameters, they MUST be copied from the CONFIG objects received in
   the Config message.

   If the ConfigNack message is received and only includes CONFIG
   objects that are negotiable, then a new Config message SHOULD be
   sent.  The values in the CONFIG object of the new Config message
   SHOULD take into account the acceptable values included in the
   ConfigNack message.

   If a node receives a Config message and recognizes the CONFIG object,
   but does not recognize the C-Type, a ConfigNack message including the
   unknown CONFIG object MUST be sent.

<span class="h3"><a class="selflink" id="section-12.4" href="#section-12.4">12.4</a>.  Hello Message (Msg Type = 4)</span>

   The format of the Hello message is as follows:

   &lt;Hello Message&gt; ::= &lt;Common Header&gt; &lt;LOCAL_CCID&gt; &lt;HELLO&gt;

   The above transmission order SHOULD be followed.

   The Hello message MUST be periodically transmitted at least once
   every HelloInterval msec.  If no Hello message is received within the
   HelloDeadInterval, the control channel is assumed to have failed.

<span class="h3"><a class="selflink" id="section-12.5" href="#section-12.5">12.5</a>.  Link Verification Messages</span>

<span class="h4"><a class="selflink" id="section-12.5.1" href="#section-12.5.1">12.5.1</a>.  BeginVerify Message (Msg Type = 5)</span>

   The BeginVerify message is sent over the control channel and is used
   to initiate the link verification process.  The format is as follows:

   &lt;BeginVerify Message&gt; ::= &lt;Common Header&gt; &lt;LOCAL_LINK_ID&gt;
                             &lt;MESSAGE_ID&gt; [&lt;REMOTE_LINK_ID&gt;]
                             &lt;BEGIN_VERIFY&gt;



<span class="grey">Lang                        Standards Track                    [Page 43]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-44" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   The above transmission order SHOULD be followed.

   To limit the scope of Link Verification to a particular TE Link, the
   Link_Id field of the LOCAL_LINK_ID object MUST be non-zero.  If this
   field is zero, the data links can span multiple TE links and/or they
   may comprise a TE link that is yet to be configured.  In the special
   case where the local Link_Id field is zero, the "Verify all Links"
   flag of the BEGIN_VERIFY object is used to distinguish between data
   links that span multiple TE links and those that have not yet been
   assigned to a TE link (see <a href="#section-5">Section 5</a>).

   The REMOTE_LINK_ID object may be included if the local/remote Link_Id
   mapping is known.

   The Link_Id field of the REMOTE_LINK_ID object MUST be non-zero if
   included.

   The BeginVerify message MUST be periodically transmitted until (1)
   the node receives either a BeginVerifyAck or BeginVerifyNack message
   to accept or reject the verify process or (2) a retry limit has been
   reached and no BeginVerifyAck or BeginVerifyNack message has been
   received.  Both the retransmission interval and the retry limit are
   local configuration parameters.

<span class="h4"><a class="selflink" id="section-12.5.2" href="#section-12.5.2">12.5.2</a>.  BeginVerifyAck Message (Msg Type = 6)</span>

   When a BeginVerify message is received and Test messages are ready to
   be processed, a BeginVerifyAck message MUST be transmitted.

   &lt;BeginVerifyAck Message&gt; ::= &lt;Common Header&gt; [&lt;LOCAL_LINK_ID&gt;]
                                &lt;MESSAGE_ID_ACK&gt; &lt;BEGIN_VERIFY_ACK&gt;
                                &lt;VERIFY_ID&gt;

   The above transmission order SHOULD be followed.

   The LOCAL_LINK_ID object may be included if the local/remote Link_Id
   mapping is known or learned through the BeginVerify message.

   The Link_Id field of the LOCAL_LINK_ID MUST be non-zero if included.

   The contents of the MESSAGE_ID_ACK object MUST be obtained from the
   BeginVerify message being acknowledged.

   The VERIFY_ID object contains a node-unique value that is assigned by
   the generator of the BeginVerifyAck message.  This value is used to
   uniquely identify the Verification process from multiple LMP
   neighbors and/or parallel Test procedures between the same LMP
   neighbors.



<span class="grey">Lang                        Standards Track                    [Page 44]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-45" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h4"><a class="selflink" id="section-12.5.3" href="#section-12.5.3">12.5.3</a>.  BeginVerifyNack Message (Msg Type = 7)</span>

   If a BeginVerify message is received and a node is unwilling or
   unable to begin the Verification procedure, a BeginVerifyNack message
   MUST be transmitted.

   &lt;BeginVerifyNack Message&gt; ::= &lt;Common Header&gt; [&lt;LOCAL_LINK_ID&gt;]
                                 &lt;MESSAGE_ID_ACK&gt; &lt;ERROR_CODE&gt;

   The above transmission order SHOULD be followed.

   The contents of the MESSAGE_ID_ACK object MUST be obtained from the
   BeginVerify message being negatively acknowledged.

   If the Verification process is not supported, the ERROR_CODE MUST
   indicate "Link Verification Procedure not supported".

   If Verification is supported, but the node is unable to begin the
   procedure, the ERROR_CODE MUST indicate "Unwilling to verify".  If a
   BeginVerifyNack message is received with such an ERROR_CODE, the node
   that originated the BeginVerify SHOULD schedule a BeginVerify
   retransmission after Rf seconds, where Rf is a locally defined
   parameter.

   If the Verification Transport mechanism is not supported, the
   ERROR_CODE MUST indicate "Unsupported verification transport
   mechanism".

   If remote configuration of the Link_Id is not supported and the
   content of the REMOTE_LINK_ID object (included in the BeginVerify
   message) does not match any configured values, the ERROR_CODE MUST
   indicate "Link_Id configuration error".

   If a node receives a BeginVerify message and recognizes the
   BEGIN_VERIFY object but does not recognize the C-Type, the ERROR_CODE
   MUST indicate "Unknown object C-Type".

<span class="h4"><a class="selflink" id="section-12.5.4" href="#section-12.5.4">12.5.4</a>.  EndVerify Message (Msg Type = 8)</span>

   The EndVerify message is sent over the control channel and is used to
   terminate the link verification process.  The EndVerify message may
   be sent any time the initiating node desires to end the Verify
   procedure.  The format is as follows:

   &lt;EndVerify Message&gt; ::=&lt;Common Header&gt; &lt;MESSAGE_ID&gt; &lt;VERIFY_ID&gt;

   The above transmission order SHOULD be followed.




<span class="grey">Lang                        Standards Track                    [Page 45]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-46" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   The EndVerify message will be periodically transmitted until (1) an
   EndVerifyAck message has been received or (2) a retry limit has been
   reached and no EndVerifyAck message has been received.  Both the
   retransmission interval and the retry limit are local configuration
   parameters.

<span class="h4"><a class="selflink" id="section-12.5.5" href="#section-12.5.5">12.5.5</a>.  EndVerifyAck Message (Msg Type =9)</span>

   The EndVerifyAck message is sent over the control channel and is used
   to acknowledge the termination of the link verification process.  The
   format is as follows:

   &lt;EndVerifyAck Message&gt; ::= &lt;Common Header&gt; &lt;MESSAGE_ID_ACK&gt;
                              &lt;VERIFY_ID&gt;

   The above transmission order SHOULD be followed.

   The contents of the MESSAGE_ID_ACK object MUST be obtained from the
   EndVerify message being acknowledged.

<span class="h4"><a class="selflink" id="section-12.5.6" href="#section-12.5.6">12.5.6</a>.  Test Message (Msg Type = 10)</span>

   The Test message is transmitted over the data link and is used to
   verify its physical connectivity.  Unless explicitly stated, these
   messages MUST be transmitted over UDP like all other LMP messages.
   The format of the Test messages is as follows:

   &lt;Test Message&gt; ::= &lt;Common Header&gt; &lt;LOCAL_INTERFACE_ID&gt; &lt;VERIFY_ID&gt;

   The above transmission order SHOULD be followed.

   Note that this message is sent over a data link and NOT over the
   control channel.  The transport mechanism for the Test message is
   negotiated using the Verify Transport Mechanism field of the
   BEGIN_VERIFY object and the Verify Transport Response field of the
   BEGIN_VERIFY_ACK object (see Sections <a href="#section-13.8">13.8</a> and <a href="#section-13.9">13.9</a>).

   The local (transmitting) node sends a given Test message periodically
   (at least once every VerifyInterval ms) on the corresponding data
   link until (1) it receives a correlating TestStatusSuccess or
   TestStatusFailure message on the control channel from the remote
   (receiving) node or (2) all active control channels between the two
   nodes have failed.  The remote node will send a given TestStatus
   message periodically over the control channel until it receives
   either a correlating TestStatusAck message or an EndVerify message.






<span class="grey">Lang                        Standards Track                    [Page 46]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-47" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h4"><a class="selflink" id="section-12.5.7" href="#section-12.5.7">12.5.7</a>.  TestStatusSuccess Message (Msg Type = 11)</span>

   The TestStatusSuccess message is transmitted over the control channel
   and is used to transmit the mapping between the local Interface_Id
   and the Interface_Id that was received in the Test message.

   &lt;TestStatusSuccess Message&gt; ::= &lt;Common Header&gt; &lt;LOCAL_LINK_ID&gt;
                                   &lt;MESSAGE_ID&gt; &lt;LOCAL_INTERFACE_ID&gt;
                                   &lt;REMOTE_INTERFACE_ID&gt; &lt;VERIFY_ID&gt;

   The above transmission order SHOULD be followed.

   The contents of the REMOTE_INTERFACE_ID object MUST be obtained from
   the corresponding Test message being positively acknowledged.

<span class="h4"><a class="selflink" id="section-12.5.8" href="#section-12.5.8">12.5.8</a>.  TestStatusFailure Message (Msg Type = 12)</span>

   The TestStatusFailure message is transmitted over the control channel
   and is used to indicate that the Test message was not received.

   &lt;TestStatusFailure Message&gt; ::= &lt;Common Header&gt; &lt;MESSAGE_ID&gt;
                                   &lt;VERIFY_ID&gt;

   The above transmission order SHOULD be followed.

<span class="h4"><a class="selflink" id="section-12.5.9" href="#section-12.5.9">12.5.9</a>.  TestStatusAck Message (Msg Type = 13)</span>

   The TestStatusAck message is used to acknowledge receipt of the
   TestStatusSuccess or TestStatusFailure messages.

   &lt;TestStatusAck Message&gt; ::= &lt;Common Header&gt; &lt;MESSAGE_ID_ACK&gt;
                               &lt;VERIFY_ID&gt;

   The above transmission order SHOULD be followed.

   The contents of the MESSAGE_ID_ACK object MUST be obtained from the
   TestStatusSuccess or TestStatusFailure message being acknowledged.

<span class="h3"><a class="selflink" id="section-12.6" href="#section-12.6">12.6</a>.  Link Summary Messages</span>

<span class="h4"><a class="selflink" id="section-12.6.1" href="#section-12.6.1">12.6.1</a>.  LinkSummary Message (Msg Type = 14)</span>

   The LinkSummary message is used to synchronize the Interface_Ids and
   correlate the properties of the TE link.  The format of the
   LinkSummary message is as follows:

   &lt;LinkSummary Message&gt; ::= &lt;Common Header&gt; &lt;MESSAGE_ID&gt; &lt;TE_LINK&gt;
                             &lt;DATA_LINK&gt; [&lt;DATA_LINK&gt;...]



<span class="grey">Lang                        Standards Track                    [Page 47]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-48" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   The above transmission order SHOULD be followed.

   The LinkSummary message can be exchanged any time a link is not in
   the Verification process.  The LinkSummary message MUST be
   periodically transmitted until (1) the node receives a LinkSummaryAck
   or LinkSummaryNack message or (2) a retry limit has been reached and
   no LinkSummaryAck or LinkSummaryNack message has been received.  Both
   the retransmission interval and the retry limit are local
   configuration parameters.

<span class="h4"><a class="selflink" id="section-12.6.2" href="#section-12.6.2">12.6.2</a>.  LinkSummaryAck Message (Msg Type = 15)</span>

   The LinkSummaryAck message is used to indicate agreement on the
   Interface_Id synchronization and acceptance/agreement on all the link
   parameters.  It is on the reception of this message that the local
   node makes the Link_Id associations.

   &lt;LinkSummaryAck Message&gt; ::=  &lt;Common Header&gt; &lt;MESSAGE_ID_ACK&gt;

   The above transmission order SHOULD be followed.

<span class="h4"><a class="selflink" id="section-12.6.3" href="#section-12.6.3">12.6.3</a>.  LinkSummaryNack Message (Msg Type = 16)</span>

   The LinkSummaryNack message is used to indicate disagreement on non-
   negotiated parameters or propose other values for negotiable
   parameters.  Parameters on which agreement was reached MUST NOT be
   included in the LinkSummaryNack message.

   &lt;LinkSummaryNack Message&gt; ::= &lt;Common Header&gt; &lt;MESSAGE_ID_ACK&gt;
                                 &lt;ERROR_CODE&gt; [&lt;DATA_LINK&gt;...]

   The above transmission order SHOULD be followed.

   The DATA_LINK objects MUST include acceptable values for all
   negotiable parameters.  If the LinkSummaryNack includes DATA_LINK
   objects for non-negotiable parameters, they MUST be copied from the
   DATA_LINK objects received in the LinkSummary message.

   If the LinkSummaryNack message is received and only includes
   negotiable parameters, then a new LinkSummary message SHOULD be sent.
   The values received in the new LinkSummary message SHOULD take into
   account the acceptable parameters included in the LinkSummaryNack
   message.

   If the LinkSummary message is received with unacceptable, non-
   negotiable parameters, the ERROR_CODE MUST indicate "Unacceptable
   non-negotiable LINK_SUMMARY parameters."




<span class="grey">Lang                        Standards Track                    [Page 48]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-49" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   If the LinkSummary message is received with unacceptable negotiable
   parameters, the ERROR_CODE MUST indicate "Renegotiate LINK_SUMMARY
   parameters."

   If the LinkSummary message is received with an invalid TE_LINK
   object, the ERROR_CODE MUST indicate "Invalid TE_LINK object."

   If the LinkSummary message is received with an invalid DATA_LINK
   object, the ERROR_CODE MUST indicate "Invalid DATA_LINK object."

   If the LinkSummary message is received with a TE_LINK object but the
   C-Type is unknown, the ERROR_CODE MUST indicate, "Unknown TE_LINK
   object C-Type."

   If the LinkSummary message is received with a DATA_LINK object but
   the C-Type is unknown, the ERROR_CODE MUST indicate, "Unknown
   DATA_LINK object C-Type."

<span class="h3"><a class="selflink" id="section-12.7" href="#section-12.7">12.7</a>.  Fault Management Messages</span>

<span class="h4"><a class="selflink" id="section-12.7.1" href="#section-12.7.1">12.7.1</a>.  ChannelStatus Message (Msg Type = 17)</span>

   The ChannelStatus message is sent over the control channel and is
   used to notify an LMP neighbor of the status of a data link.  A node
   that receives a ChannelStatus message MUST respond with a
   ChannelStatusAck message.  The format is as follows:

   &lt;ChannelStatus Message&gt; ::= &lt;Common Header&gt; &lt;LOCAL_LINK_ID&gt;
                               &lt;MESSAGE_ID&gt; &lt;CHANNEL_STATUS&gt;

   The above transmission order SHOULD be followed.

   If the CHANNEL_STATUS object does not include any Interface_Ids, then
   this indicates the entire TE Link has failed.

<span class="h4"><a class="selflink" id="section-12.7.2" href="#section-12.7.2">12.7.2</a>.  ChannelStatusAck Message (Msg Type = 18)</span>

   The ChannelStatusAck message is used to acknowledge receipt of the
   ChannelStatus Message.  The format is as follows:

   &lt;ChannelStatusAck Message&gt; ::= &lt;Common Header&gt; &lt;MESSAGE_ID_ACK&gt;

   The above transmission order SHOULD be followed.

   The contents of the MESSAGE_ID_ACK object MUST be obtained from the
   ChannelStatus message being acknowledged.





<span class="grey">Lang                        Standards Track                    [Page 49]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-50" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h4"><a class="selflink" id="section-12.7.3" href="#section-12.7.3">12.7.3</a>.  ChannelStatusRequest Message (Msg Type = 19)</span>

   The ChannelStatusRequest message is sent over the control channel and
   is used to request the status of one or more data link(s).  A node
   that receives a ChannelStatusRequest message MUST respond with a
   ChannelStatusResponse message.  The format is as follows:

   &lt;ChannelStatusRequest Message&gt; ::= &lt;Common Header&gt; &lt;LOCAL_LINK_ID&gt;
                                      &lt;MESSAGE_ID&gt;
                                      [&lt;CHANNEL_STATUS_REQUEST&gt;]

   The above transmission order SHOULD be followed.

   If the CHANNEL_STATUS_REQUEST object is not included, then the
   ChannelStatusRequest is being used to request the status of ALL of
   the data link(s) of the TE Link.

<span class="h4"><a class="selflink" id="section-12.7.4" href="#section-12.7.4">12.7.4</a>.  ChannelStatusResponse Message (Msg Type = 20)</span>

   The ChannelStatusResponse message is used to acknowledge receipt of
   the ChannelStatusRequest Message and notify the LMP neighbor of the
   status of the data channel(s).  The format is as follows:

   &lt;ChannelStatusResponse Message&gt; ::= &lt;Common Header&gt; &lt;MESSAGE_ID_ACK&gt;
                                       &lt;CHANNEL_STATUS&gt;

   The above transmission order SHOULD be followed.

   The contents of the MESSAGE_ID_ACK objects MUST be obtained from the
   ChannelStatusRequest message being acknowledged.

<span class="h2"><a class="selflink" id="section-13" href="#section-13">13</a>.  LMP Object Definitions</span>

<span class="h3"><a class="selflink" id="section-13.1" href="#section-13.1">13.1</a>.  CCID (Control Channel ID) Class</span>

   Class = 1

   o    C-Type = 1, LOCAL_CCID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            CC_Id                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+







<span class="grey">Lang                        Standards Track                    [Page 50]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-51" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   CC_Id:  32 bits

      This MUST be node-wide unique and non-zero.  The CC_Id identifies
      the control channel of the sender associated with the message.

   This object is non-negotiable.

   o    C-Type = 2, REMOTE_CCID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             CC_Id                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   CC_Id:  32 bits

      This identifies the remote node's CC_Id and MUST be non-zero.

   This object is non-negotiable.

<span class="h3"><a class="selflink" id="section-13.2" href="#section-13.2">13.2</a>.  NODE_ID Class</span>

   Class = 2

   o    C-Type = 1, LOCAL_NODE_ID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Node_Id (4 bytes)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Node_Id:

      This identities the node that originated the LMP packet.

   This object is non-negotiable.

   o    C-Type = 2, REMOTE_NODE_ID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Node_Id (4 bytes)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





<span class="grey">Lang                        Standards Track                    [Page 51]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-52" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   Node_Id:

      This identities the remote node.

   This object is non-negotiable.

<span class="h3"><a class="selflink" id="section-13.3" href="#section-13.3">13.3</a>.  LINK_ID Class</span>

   Class = 3

   o    C-Type = 1, IPv4 LOCAL_LINK_ID

   o    C-Type = 2, IPv4 REMOTE_LINK_ID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Link_Id (4 bytes)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o    C-Type = 3, IPv6 LOCAL_LINK_ID

   o    C-Type = 4, IPv6 REMOTE_LINK_ID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                        Link_Id (16 bytes)                     +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o    C-Type = 5, Unnumbered LOCAL_LINK_ID

   o    C-Type = 6, Unnumbered REMOTE_LINK_ID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Link_Id (4 bytes)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






<span class="grey">Lang                        Standards Track                    [Page 52]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-53" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   Link_Id:

      For LOCAL_LINK_ID, this identifies the sender's Link associated
      with the message.  This value MUST be non-zero.

      For REMOTE_LINK_ID, this identifies the remote node's Link_Id and
      MUST be non-zero.

   This object is non-negotiable.

<span class="h3"><a class="selflink" id="section-13.4" href="#section-13.4">13.4</a>.  INTERFACE_ID Class</span>

   Class = 4

   o    C-Type = 1, IPv4 LOCAL_INTERFACE_ID

   o    C-Type = 2, IPv4 REMOTE_INTERFACE_ID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Interface_Id (4 bytes)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o    C-Type = 3, IPv6 LOCAL_INTERFACE_ID

   o    C-Type = 4, IPv6 REMOTE_INTERFACE_ID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                       Interface_Id (16 bytes)                 +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o    C-Type = 5, Unnumbered LOCAL_INTERFACE_ID

   o    C-Type = 6, Unnumbered REMOTE_INTERFACE_ID








<span class="grey">Lang                        Standards Track                    [Page 53]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-54" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Interface_Id (4 bytes)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Interface_Id:

      For the LOCAL_INTERFACE_ID, this identifies the data link.  This
      value MUST be node-wide unique and non-zero.

      For the REMOTE_INTERFACE_ID, this identifies the remote node's
      data link.  The Interface_Id MUST be non-zero.

   This object is non-negotiable.

<span class="h3"><a class="selflink" id="section-13.5" href="#section-13.5">13.5</a>.  MESSAGE_ID Class</span>

   Class = 5

   o    C-Type=1, MessageId

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Message_Id                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Message_Id:

      The Message_Id field is used to identify a message.  This value is
      incremented and only decreases when the value wraps.  This is used
      for message acknowledgment.

   This object is non-negotiable.

   o    C-Type = 2, MessageIdAck

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Message_Id                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+








<span class="grey">Lang                        Standards Track                    [Page 54]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-55" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   Message_Id:

      The Message_Id field is used to identify the message being
      acknowledged.  This value is copied from the MESSAGE_ID object of
      the message being acknowledged.

   This object is non-negotiable.

<span class="h3"><a class="selflink" id="section-13.6" href="#section-13.6">13.6</a>.  CONFIG Class</span>

   Class = 6.

   o    C-Type = 1, HelloConfig

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         HelloInterval         |      HelloDeadInterval        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   HelloInterval:  16 bits.

      Indicates how frequently the Hello packets will be sent and is
      measured in milliseconds (ms).

   HelloDeadInterval:  16 bits.

      If no Hello packets are received within the HelloDeadInterval, the
      control channel is assumed to have failed.  The HelloDeadInterval
      is measured in milliseconds (ms).  The HelloDeadInterval MUST be
      greater than the HelloInterval, and SHOULD be at least 3 times the
      value of HelloInterval.

   If the fast keep-alive mechanism of LMP is not used, the
   HelloInterval and HelloDeadInterval MUST be set to zero.
















<span class="grey">Lang                        Standards Track                    [Page 55]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-56" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h3"><a class="selflink" id="section-13.7" href="#section-13.7">13.7</a>.  HELLO Class</span>

   Class = 7

   o    C-Type = 1, Hello

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           TxSeqNum                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           RcvSeqNum                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   TxSeqNum:  32 bits

      This is the current sequence number for this Hello message.  This
      sequence number will be incremented when the sequence number is
      reflected in the RcvSeqNum of a Hello packet that is received over
      the control channel.

      TxSeqNum=0 is not allowed.  TxSeqNum=1 is used to indicate that
      this is the first Hello message sent over the control channel.

   RcvSeqNum:  32 bits

      This is the sequence number of the last Hello message received
      over the control channel.  RcvSeqNum=0 is used to indicate that a
      Hello message has not yet been received.

   This object is non-negotiable.

<span class="h3"><a class="selflink" id="section-13.8" href="#section-13.8">13.8</a>.  BEGIN_VERIFY Class</span>

   Class = 8

   o    C-Type = 1














<span class="grey">Lang                        Standards Track                    [Page 56]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-57" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Flags                      |         VerifyInterval        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Number of Data Links                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    EncType    |  (Reserved)   |  Verify Transport Mechanism   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       TransmissionRate                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Wavelength                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Reserved field should be sent as zero and ignored on receipt.

   Flags:  16 bits

      The following flags are defined:

      0x0001 Verify all Links

            If this bit is set, the verification process checks all
            unallocated links; else it only verifies new ports or
            component links that are to be added to this TE link.

         0x0002 Data Link Type

            If set, the data links to be verified are ports, otherwise
            they are component links

   VerifyInterval:  16 bits

      This is the interval between successive Test messages and is
      measured in milliseconds (ms).

   Number of Data Links:  32 bits

      This is the number of data links that will be verified.

   EncType:  8 bits

      This is the encoding type of the data link.  The defined EncType
      values are consistent with the LSP Encoding Type values of
      [<a href="./rfc3471" title="&quot;Generalized MPLS - Signaling Functional Description&quot;">RFC3471</a>].






<span class="grey">Lang                        Standards Track                    [Page 57]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-58" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   Verify Transport Mechanism:  16 bits

      This defines the transport mechanism for the Test Messages.  The
      scope of this bit mask is restricted to each encoding type.  The
      local node will set the bits corresponding to the various
      mechanisms it can support for transmitting LMP test messages.  The
      receiver chooses the appropriate mechanism in the BeginVerifyAck
      message.

      The following flag is defined across all Encoding Types.  All
      other flags are dependent on the Encoding Type.

      0x8000 Payload:Test Message transmitted in the payload

               Capable of transmitting Test messages in the payload.
               The Test message is sent as an IP packet as defined
               above.

   TransmissionRate:  32 bits

      This is the transmission rate of the data link over which the Test
      messages will be transmitted.  This is expressed in bytes per
      second and represented in IEEE floating-point format.

   Wavelength:  32 bits

      When a data link is assigned to a port or component link that is
      capable of transmitting multiple wavelengths (e.g., a fiber or
      waveband-capable port), it is essential to know which wavelength
      the test messages will be transmitted over.  This value
      corresponds to the wavelength at which the Test messages will be
      transmitted over and has local significance.  If there is no
      ambiguity as to the wavelength over which the message will be
      sent, then this value SHOULD be set to 0.

<span class="h3"><a class="selflink" id="section-13.9" href="#section-13.9">13.9</a>.  BEGIN_VERIFY_ACK Class</span>

   Class = 9

   o    C-Type = 1

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      VerifyDeadInterval       |   Verify_Transport_Response   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





<span class="grey">Lang                        Standards Track                    [Page 58]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-59" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   VerifyDeadInterval:  16 bits

      If a Test message is not detected within the
      VerifyDeadInterval, then a node will send the TestStatusFailure
      message for that data link.

   Verify_Transport_Response:  16 bits

      The recipient of the BeginVerify message (and the future
      recipient of the TEST messages) chooses the transport mechanism
      from the various types that are offered by the transmitter of
      the Test messages.  One and only one bit MUST be set in the
      verification transport response.

   This object is non-negotiable.

<span class="h3"><a class="selflink" id="section-13.10" href="#section-13.10">13.10</a>.  VERIFY_ID Class</span>

   Class = 10

   o    C-Type = 1

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Verify_Id                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Verify_Id:  32 bits

      This is used to differentiate Test messages from different TE
      links and/or LMP peers.  This is a node-unique value that is
      assigned by the recipient of the BeginVerify message.

   This object is non-negotiable.

<span class="h3"><a class="selflink" id="section-13.11" href="#section-13.11">13.11</a>.  TE_LINK Class</span>

   Class = 11

   o    C-Type = 1, IPv4 TE_LINK










<span class="grey">Lang                        Standards Track                    [Page 59]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-60" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Flags     |                   (Reserved)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Local_Link_Id (4 bytes)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Remote_Link_Id (4 bytes)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o    C-Type = 2, IPv6 TE_LINK

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Flags     |                   (Reserved)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                      Local_Link_Id (16 bytes)                 +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                      Remote_Link_Id (16 bytes)                +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o    C-Type = 3, Unnumbered TE_LINK

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Flags     |                   (Reserved)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Local_Link_Id (4 bytes)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Remote_Link_Id (4 bytes)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Reserved field should be sent as zero and ignored on receipt.




<span class="grey">Lang                        Standards Track                    [Page 60]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-61" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   Flags: 8 bits

      The following flags are defined.  All other bit-values are
      reserved and should be sent as zero and ignored on receipt.

      0x01 Fault Management Supported.

      0x02 Link Verification Supported.

   Local_Link_Id:

      This identifies the node's local Link_Id and MUST be non-zero.

   Remote_Link_Id:

      This identifies the remote node's Link_Id and MUST be non-zero.

<span class="h3"><a class="selflink" id="section-13.12" href="#section-13.12">13.12</a>.  DATA_LINK Class</span>

   Class = 12

   o    C-Type = 1, IPv4 DATA_LINK

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Flags     |                   (Reserved)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Local_Interface_Id (4 bytes)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Remote_Interface_Id (4 bytes)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                        (Subobjects)                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+















<span class="grey">Lang                        Standards Track                    [Page 61]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-62" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   o    C-Type = 2, IPv6 DATA_LINK

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Flags     |                   (Reserved)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                   Local_Interface_Id (16 bytes)               +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                   Remote_Interface_Id (16 bytes)              +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                        (Subobjects)                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o    C-Type = 3, Unnumbered DATA_LINK

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Flags     |                   (Reserved)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Local_Interface_Id (4 bytes)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Remote_Interface_Id (4 bytes)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                        (Subobjects)                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+








<span class="grey">Lang                        Standards Track                    [Page 62]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-63" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   The Reserved field should be sent as zero and ignored on receipt.

   Flags: 8 bits

      The following flags are defined.  All other bit-values are
      reserved and should be sent as zero and ignored on receipt.

      0x01 Interface Type: If set, the data link is a port, otherwise it
                           is a component link.

      0x02 Allocated Link: If set, the data link is currently allocated
                           for user traffic.  If a single Interface_Id
                           is used for both the transmit and receive
                           data links, then this bit only applies to the
                           transmit interface.

      0x04 Failed Link:    If set, the data link is failed and not
                           suitable for user traffic.

   Local_Interface_Id:

      This is the local identifier of the data link.  This MUST be
      node-wide unique and non-zero.

   Remote_Interface_Id:

      This is the remote identifier of the data link.  This MUST be
      non-zero.

   Subobjects

      The contents of the DATA_LINK object consist of a series of
      variable-length data items called subobjects.  The subobjects are
      defined in <a href="#section-13.12.1">Section 13.12.1</a> below.

   A DATA_LINK object may contain more than one subobject.  More than
   one subobject of the same Type may appear if multiple capabilities
   are supported over the data link.













<span class="grey">Lang                        Standards Track                    [Page 63]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-64" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h4"><a class="selflink" id="section-13.12.1" href="#section-13.12.1">13.12.1</a>.  Data Link Subobjects</span>

   The contents of the DATA_LINK object include a series of variable-
   length data items called subobjects.  Each subobject has the form:

    0                   1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------//--------------+
   |    Type       |    Length     |      (Subobject contents)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--------------//---------------+

   Type: 8 bits

      The Type indicates the type of contents of the subobject.
      Currently defined values are:

      Type = 1, Interface Switching Type

      Type = 2, Wavelength

   Length: 8 bits

      The Length contains the total length of the subobject in bytes,
      including the Type and Length fields.  The Length MUST be at
      least 4, and MUST be a multiple of 4.

<span class="h5"><a class="selflink" id="section-13.12.1.1" href="#section-13.12.1.1">13.12.1.1</a>.  Subobject Type 1: Interface Switching Type</span>

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Type       |    Length     | Switching Type|   EncType     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Minimum Reservable Bandwidth                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Maximum Reservable Bandwidth                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Switching Type: 8 bits

      This is used to identify the local Interface Switching Type of the
      TE link as defined in [<a href="./rfc3471" title="&quot;Generalized MPLS - Signaling Functional Description&quot;">RFC3471</a>].

   EncType: 8 bits

      This is the encoding type of the data link.  The defined EncType
      values are consistent with the LSP Encoding Type values of
      [<a href="./rfc3471" title="&quot;Generalized MPLS - Signaling Functional Description&quot;">RFC3471</a>].



<span class="grey">Lang                        Standards Track                    [Page 64]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-65" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   Minimum Reservable Bandwidth: 32 bits

      This is measured in bytes per second and represented in IEEE
      floating point format.

   Maximum Reservable Bandwidth: 32 bits

      This is measured in bytes per second and represented in IEEE
      floating point format.

   If the interface only supports a fixed rate, the minimum and maximum
   bandwidth fields are set to the same value.

<span class="h5"><a class="selflink" id="section-13.12.1.2" href="#section-13.12.1.2">13.12.1.2</a>.  Subobject Type 2: Wavelength</span>

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Type       |    Length     |         (Reserved)            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Wavelength                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Reserved field should be sent as zero and ignored on receipt.

   Wavelength: 32 bits

      This value indicates the wavelength carried over the port.  Values
      used in this field only have significance between two neighbors.

<span class="h3"><a class="selflink" id="section-13.13" href="#section-13.13">13.13</a>.   CHANNEL_STATUS Class</span>

   Class = 13


















<span class="grey">Lang                        Standards Track                    [Page 65]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-66" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   o    C-Type = 1, IPv4 INTERFACE_ID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Interface_Id (4 bytes)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |A|D|                     Channel Status                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              :                                |
   //                             :                               //
   |                              :                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Interface_Id (4 bytes)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |A|D|                     Channel Status                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o    C-Type = 2, IPv6 INTERFACE_ID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                       Interface_Id (16 bytes)                 +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |A|D|                     Channel Status                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              :                                |
   //                             :                               //
   |                              :                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                       Interface_Id (16 bytes)                 +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |A|D|                     Channel Status                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




<span class="grey">Lang                        Standards Track                    [Page 66]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-67" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   o    C-Type = 3, Unnumbered INTERFACE_ID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Interface_Id (4 bytes)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |A|D|                     Channel Status                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              :                                |
   //                             :                               //
   |                              :                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Interface_Id (4 bytes)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |A|D|                     Channel_Status                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Active bit: 1 bit

      This indicates that the Channel is allocated to user traffic and
      the data link should be actively monitored.

   Direction bit: 1 bit

      This indicates the direction (transmit/receive) of the data
      channel referred to in the CHANNEL_STATUS object.  If set, this
      indicates the data channel is in the transmit direction.

   Channel_Status: 30 bits

      This indicates the status condition of a data channel.  The
      following values are defined.  All other values are reserved.

      1   Signal Okay (OK):    Channel is operational
      2   Signal Degrade (SD): A soft failure caused by a BER exceeding
                               a preselected threshold.  The specific
                               BER used to define the threshold is
                               configured.
      3   Signal Fail (SF):    A hard signal failure including (but not
                               limited to) loss of signal (LOS), loss of
                               frame (LOF), or Line AIS.

   This object contains one or more Interface_Ids followed by a
   Channel_Status field.

   To indicate the status of the entire TE Link, there MUST be only one
   Interface_Id, and it MUST be zero.



<span class="grey">Lang                        Standards Track                    [Page 67]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-68" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   This object is non-negotiable.

<span class="h3"><a class="selflink" id="section-13.14" href="#section-13.14">13.14</a>.  CHANNEL_STATUS_REQUEST Class</span>

   Class = 14

   o    C-Type = 1, IPv4 INTERFACE_ID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Interface_Id (4 bytes)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              :                                |
   //                             :                               //
   |                              :                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Interface_Id (4 bytes)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This object contains one or more Interface_Ids.

   The Length of this object is 4 + 4N in bytes, where N is the number
   of Interface_Ids.



























<span class="grey">Lang                        Standards Track                    [Page 68]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-69" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   o    C-Type = 2, IPv6 INTERFACE_ID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                       Interface_Id (16 bytes)                 +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              :                                |
   //                             :                               //
   |                              :                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                       Interface_Id (16 bytes)                 +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This object contains one or more Interface_Ids.

   The Length of this object is 4 + 16N in bytes, where N is the number
   of Interface_Ids.

   o    C-Type = 3, Unnumbered INTERFACE_ID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Interface_Id (4 bytes)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              :                                |
   //                             :                               //
   |                              :                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Interface_Id (4 bytes)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+







<span class="grey">Lang                        Standards Track                    [Page 69]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-70" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   This object contains one or more Interface_Ids.

   The Length of this object is 4 + 4N in bytes, where N is the number
   of Interface_Ids.

   This object is non-negotiable.

<span class="h3"><a class="selflink" id="section-13.15" href="#section-13.15">13.15</a>.  ERROR_CODE Class</span>

   Class = 20

   o    C-Type = 1, BEGIN_VERIFY_ERROR

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          ERROR CODE                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      The following bit-values are defined in network byte order (i.e.,
      big-endian byte order):

      0x01 = Link Verification Procedure not supported.
      0x02 = Unwilling to verify.
      0x04 = Unsupported verification transport mechanism.
      0x08 = Link_Id configuration error.
      0x10 = Unknown object C-Type.

      All other bit-values are reserved and should be sent as zero and
      ignored on receipt.

      Multiple bits may be set to indicate multiple errors.

      This object is non-negotiable.

   If a BeginVerifyNack message is received with Error Code 2, the node
   that originated the BeginVerify SHOULD schedule a BeginVerify
   retransmission after Rf seconds, where Rf is a locally defined
   parameter.

   o    C-Type = 2, LINK_SUMMARY_ERROR

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          ERROR CODE                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




<span class="grey">Lang                        Standards Track                    [Page 70]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-71" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


      The following bit-values are defined in network byte order (i.e.,
      big-endian byte order):

      0x01 = Unacceptable non-negotiable LINK_SUMMARY parameters.
      0x02 = Renegotiate LINK_SUMMARY parameters.
      0x04 = Invalid TE_LINK Object.
      0x08 = Invalid DATA_LINK Object.
      0x10 = Unknown TE_LINK object C-Type.
      0x20 = Unknown DATA_LINK object C-Type.

      All other bit-values are reserved and should be sent as zero and
      ignored on receipt.

      Multiple bits may be set to indicate multiple errors.

      This object is non-negotiable.

<span class="h2"><a class="selflink" id="section-14" href="#section-14">14</a>.  References</span>

<span class="h3"><a class="selflink" id="section-14.1" href="#section-14.1">14.1</a>.  Normative References</span>

   [<a id="ref-RFC2119">RFC2119</a>]   Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.

   [<a id="ref-RFC4201">RFC4201</a>]   Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling
               in MPLS Traffic Engineering (TE)", <a href="./rfc4201">RFC 4201</a>, October
               2005.

   [<a id="ref-RFC4202">RFC4202</a>]   Kompella, K., Ed. and Y. Rekhter, Ed., "Routing
               Extensions in Support of Generalized Multi-Protocol Label
               Switching (GMPLS)", <a href="./rfc4202">RFC 4202</a>, October 2005.

   [<a id="ref-RFC2961">RFC2961</a>]   Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F.,
               and S. Molendini, "RSVP Refresh Overhead Reduction
               Extensions", <a href="./rfc2961">RFC 2961</a>, April 2001.

   [<a id="ref-RFC2402">RFC2402</a>]   Kent, S. and R. Atkinson, "IP Authentication Header", <a href="./rfc2402">RFC</a>
               <a href="./rfc2402">2402</a>, November 1998.

   [<a id="ref-RFC2406">RFC2406</a>]   Kent, S. and R. Atkinson, "IP Encapsulating Security
               Payload (ESP)", <a href="./rfc2406">RFC 2406</a>, November 1998.

   [<a id="ref-RFC2407">RFC2407</a>]   Piper, D., "The Internet IP Security Domain of
               Interpretation for ISAKMP", <a href="./rfc2407">RFC 2407</a>, November 1998.

   [<a id="ref-RFC2409">RFC2409</a>]   Harkins, D. and D. Carrel, "The Internet Key Exchange
               (IKE)", <a href="./rfc2409">RFC 2409</a>, November 1998.




<span class="grey">Lang                        Standards Track                    [Page 71]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-72" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   [<a id="ref-RFC3471">RFC3471</a>]   Berger, L., Ed.,  "Generalized MPLS - Signaling
               Functional Description", <a href="./rfc3471">RFC 3471</a>, January 2003.

<span class="h3"><a class="selflink" id="section-14.2" href="#section-14.2">14.2</a>.  Informative References</span>

   [<a id="ref-RFC3630">RFC3630</a>]   Katz, D., Kompella, K., and D. Yeung, "Traffic
               Engineering (TE) Extensions to OSPF Version 2", <a href="./rfc3630">RFC 3630</a>,
               September 2003.

   [<a id="ref-RFC3784">RFC3784</a>]   Smit, H. and T. Li, "Intermediate System to Intermediate
               System (IS-IS) Extensions for Traffic Engineering (TE)",
               <a href="./rfc3784">RFC 3784</a>, June 2004.

   [<a id="ref-RFC2401">RFC2401</a>]   Kent, S. and R. Atkinson, "Security Architecture for the
               Internet Protocol", <a href="./rfc2401">RFC 2401</a>, November 1998.

   [<a id="ref-RFC2434">RFC2434</a>]   Narten, T. and H. Alvestrand, "Guidelines for Writing an
               IANA Considerations Section in RFCs", <a href="https://www.rfc-editor.org/bcp/bcp26">BCP 26</a>, <a href="./rfc2434">RFC 2434</a>,
               October 1998.

   [<a id="ref-RFC3209">RFC3209</a>]   Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
               and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
               Tunnels", <a href="./rfc3209">RFC 3209</a>, December 2001.




























<span class="grey">Lang                        Standards Track                    [Page 72]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-73" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h2"><a class="selflink" id="section-15" href="#section-15">15</a>.  Security Considerations</span>

   There are number of attacks that an LMP protocol session can
   potentially experience.  Some examples include:

      o  an adversary may spoof control packets;

      o  an adversary may modify the control packets in transit;

      o  an adversary may replay control packets;

      o  an adversary may study a number of control packets and try to
         break the key using cryptographic tools.  If the
         hash/encryption algorithm used has known weaknesses, then it
         becomes easy for the adversary to discover the key using simple
         tools.

   This section specifies an IPsec-based security mechanism for LMP.

<span class="h3"><a class="selflink" id="section-15.1" href="#section-15.1">15.1</a>.  Security Requirements</span>

   The following requirements are applied to the mechanism described in
   this section.

      o  LMP security MUST be able to provide authentication, integrity,
         and replay protection.

      o  For LMP traffic, confidentiality is not needed.  Only
         authentication is needed to ensure that the control packets
         (packets sent along the LMP Control Channel) are originating
         from the right place and have not been modified in transit.
         LMP Test packets exchanged through the data links do not need
         to be protected.

      o  For LMP traffic, protecting the identity of LMP end-points is
         not commonly required.

      o  The security mechanism should provide for well defined key
         management schemes.  The key management schemes should be well
         analyzed to be cryptographically secure.  The key management
         schemes should be scalable.  In addition, the key management
         system should be automatic.

      o  The algorithms used for authentication MUST be
         cryptographically sound.  Also, the security protocol MUST
         allow for negotiating and using different authentication
         algorithms.




<span class="grey">Lang                        Standards Track                    [Page 73]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-74" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h3"><a class="selflink" id="section-15.2" href="#section-15.2">15.2</a>.  Security Mechanisms</span>

   IPsec is a protocol suite that is used to secure communication at the
   network layer between two peers.  This protocol is comprised of IP
   Security architecture document [<a href="./rfc2401" title="&quot;Security Architecture for the Internet Protocol&quot;">RFC2401</a>], IKE [<a href="./rfc2409" title="&quot;The Internet Key Exchange (IKE)&quot;">RFC2409</a>], IPsec AH
   [<a href="./rfc2402" title="&quot;IP Authentication Header&quot;">RFC2402</a>], and IPsec ESP [<a href="./rfc2406" title="&quot;IP Encapsulating Security Payload (ESP)&quot;">RFC2406</a>].  IKE is the key management
   protocol for IP networks, while AH and ESP are used to protect IP
   traffic.  IKE is defined specific to IP domain of interpretation.

   Considering the requirements described in <a href="#section-15.1">Section 15.1</a>, it is
   recommended that, where security is needed for LMP, implementations
   use IPsec as described below:

   1. Implementations of LMP over IPsec protocol SHOULD support manual
      keying mode.

      Manual keying mode provides an easy way to set up and diagnose
      IPsec functionality.

      However, note that manual keying mode cannot effectively support
      features such as replay protection and automatic re-keying.  An
      implementer using manual keys must be aware of these limits.

      It is recommended that an implementer use manual keying only for
      diagnostic purposes and use dynamic keying protocol to make use of
      features such as replay protection and automatic re-keying.

   2. IPsec ESP with trailer authentication in tunnel mode MUST be
      supported.

   3. Implementations MUST support authenticated key exchange protocols.
      IKE [<a href="./rfc2409" title="&quot;The Internet Key Exchange (IKE)&quot;">RFC2409</a>] MUST be used as the key exchange protocol if keys
      are dynamically negotiated between peers.

   4. Implementation MUST use the IPsec DOI [<a href="./rfc2407" title="&quot;The Internet IP Security Domain of Interpretation for ISAKMP&quot;">RFC2407</a>].

   5. For IKE protocol, the identities of the SAs negotiated in Quick
      Mode represent the traffic that the peers agree to protect and are
      comprised of address space, protocol, and port information.

      For LMP over IPsec, it is recommended that the identity payload
      for Quick mode contain the following information:

      The identities MUST be of type IP addresses and the value of the
      identities SHOULD be the IP addresses of the communicating peers.






<span class="grey">Lang                        Standards Track                    [Page 74]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-75" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


      The protocol field MUST be UDP.  The port field SHOULD be set to
      zero to indicate port fields should be ignored.  This implies all
      UDP traffic between the peers must be sent through the IPsec
      tunnel.  If an implementation supports port-based selectors, it
      can opt for a more finely grained selector by specifying the port
      field to the LMP port.  If, however, the peer does not use port-
      based selectors, the implementation MUST fall back to using a port
      selector value of 0.

   6. Aggressive mode of IKE negotiation MUST be supported.

      When IPsec is configured to be used with a peer, all LMP messages
      are expected to be sent over the IPsec tunnel (crypto channel).
      Similarly, an LMP receiver configured to use Ipsec with a peer
      should reject any LMP traffic that does not come through the
      crypto channel.

      The crypto channel can be pre-setup with the LMP neighbor, or the
      first LMP message sent to the peer can trigger the creation of the
      IPsec tunnel.

      A set of control channels can share the same crypto channel.  When
      LMP Hellos are used to monitor the status of the control channel,
      it is important to keep in mind that the keep-alive failure in a
      control channel may also be due to a failure in the crypto
      channel.  The following method is recommended to ensure that an
      LMP communication path between two peers is working properly.

      o  If LMP Hellos detect a failure on a control channel, switch to
         an alternate control channel and/or try to establish a new
         control channel.

      o  Ensure the health of the control channels using LMP Hellos.  If
         all control channels indicate a failure and it is not possible
         to bring up a new control channel, tear down all existing
         control channels.  Also, tear down the crypto channel (both the
         IKE SA and IPsec SAs).

      o  Reestablish the crypto channel.  Failure to establish a crypto
         channel indicates a fatal failure for LMP communication.

      o  Bring up the control channel.  Failure to bring up the control
         channel indicates a fatal failure for LMP communication.








<span class="grey">Lang                        Standards Track                    [Page 75]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-76" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


      When LMP peers are dynamically discovered (particularly the
      initiator), the following points should be noted:

         When using pre-shared key authentication in identity protection
         mode (main mode), the pre-shared key is required to compute the
         value of SKEYID (used for deriving keys to encrypt messages
         during key exchange).  In main mode of IKE, the pre-shared key
         to be used has to be identified before receiving the peer's
         identity payload.  The pre-shared key is required for
         calculating SKEYID.  The only information available about the
         peer at this point is its IP address from which the negotiation
         came from.  Keying off the IP address of a peer to get the
         pre-shared key is not possible since the addresses are dynamic
         and not known beforehand.

         Aggressive mode key exchange can be used since identification
         payloads are sent in the first message.

         Note, however, that aggressive mode is prone to passive denial
         of service attacks.  Using a shared secret (group shared
         secret) among a number of peers is strongly discouraged because
         this opens up the solution to man-in-the-middle attacks.

         Digital-signature-based authentication is not prone to such
         problems.  It is RECOMMENDED that a digital-signature-based
         authentication mechanism be used where possible.

         If pre-shared-key-based authentication is required, then
         aggressive mode SHOULD be used.  IKE pre-shared authentication
         key values SHOULD be protected in a manner similar to the
         user's account password.

<span class="h2"><a class="selflink" id="section-16" href="#section-16">16</a>.  IANA Considerations</span>

   The IANA has assigned port number 701 to LMP.

   In the following, guidelines are given for IANA assignment for each
   LMP name space.  Ranges are specified for Private Use, to be assigned
   by Expert Review, and to be assigned by Standards Action (as defined
   in [<a href="./rfc2434" title="">RFC2434</a>].

   Assignments made from LMP number spaces set aside for Private Use
   (i.e., for proprietary extensions) need not be documented.
   Independent LMP implementations using the same Private Use code
   points will in general not interoperate, so care should be exercised
   in using these code points in a multi-vendor network.





<span class="grey">Lang                        Standards Track                    [Page 76]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-77" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   Assignments made from LMP number spaces to be assigned by Expert
   Review are to be reviewed by an Expert designated by the IESG.  The
   intent in this document is that code points from these ranges are
   used for Experimental extensions; as such, assignments MUST be
   accompanied by Experimental RFCs.  If deployment suggests that these
   extensions are useful, then they should be described in Standards
   Track RFCs, and new code points from the Standards Action ranges MUST
   be assigned.

   Assignments from LMP number spaces to be assigned by Standards Action
   MUST be documented by a Standards Track RFC, typically submitted to
   an IETF Working Group, but in any case following the usual IETF
   procedures for Proposed Standards.

   The Reserved bits of the LMP Common Header should be allocated by
   Standards Action, pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>].

   LMP defines the following name spaces that require management:

   -  LMP Message Type.
   -  LMP Object Class.
   -  LMP Object Class type (C-Type).  These are unique within the
      Object Class.
   -  LMP Sub-object Class type (Type).  These are unique within the
      Object Class.

   The LMP Message Type name space should be allocated as follows:
   pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the numbers in the
   range 0-127 are allocated by Standards Action, 128-240 are allocated
   through an Expert Review, and 241-255 are reserved for Private Use.

   The LMP Object Class name space should be allocated as follows:
   pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the numbers in the
   range of 0-127 are allocated by Standards Action, 128-247 are
   allocated through an Expert Review, and 248-255 are reserved for
   Private Use.

   The policy for allocating values out of the LMP Object Class name
   space is part of the definition of the specific Class instance.  When
   a Class is defined, its definition must also include a description of
   the policy under which the Object Class names are allocated.

   The policy for allocating values out of the LMP Sub-object Class name
   space is part of the definition of the specific Class instance.  When
   a Class is defined, its definition must also include a description of
   the policy under which sub-objects are allocated.





<span class="grey">Lang                        Standards Track                    [Page 77]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-78" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   The following name spaces have been assigned by IANA:

   ------------------------------------------------------------------
   LMP Message Type name space

   o Config message                     (Message type = 1)

   o ConfigAck message                  (Message type = 2)

   o ConfigNack message                 (Message type = 3)

   o Hello message                      (Message type = 4)

   o BeginVerify message                (Message type = 5)

   o BeginVerifyAck message             (Message type = 6)

   o BeginVerifyNack message            (Message type = 7)

   o EndVerify message                  (Message type = 8)

   o EndVerifyAck message               (Message type = 9)

   o Test message                       (Message type = 10)

   o TestStatusSuccess message          (Message type = 11)

   o TestStatusFailure message          (Message type = 12)

   o TestStatusAck message              (Message type = 13)

   o LinkSummary message                (Message type = 14)

   o LinkSummaryAck message             (Message type = 15)

   o LinkSummaryNack message            (Message type = 16)

   o ChannelStatus message              (Message type = 17)

   o ChannelStatusAck message           (Message type = 18)

   o ChannelStatusRequest message       (Message type = 19)

   o ChannelStatusResponse message      (Message type = 20)

   ------------------------------------------------------------------





<span class="grey">Lang                        Standards Track                    [Page 78]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-79" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   LMP Object Class name space and Class type (C-Type)

   o CCID                  Class name (1)

   The CCID Object Class type name space should be allocated as follows:
   pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the numbers in the
   range 0-111 are allocated by Standards Action, 112-119 are allocated
   through an Expert Review, and 120-127 are reserved for Private Use.

     - LOCAL_CCID                      (C-Type = 1)
     - REMOTE_CCID                     (C-Type = 2)

   o NODE_ID               Class name (2)

   The NODE ID Object Class type name space should be allocated as
   follows: pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the numbers
   in the range 0-111 are allocated by Standards Action, 112-119 are
   allocated through an Expert Review, and 120-127 are reserved for
   Private Use.

     - LOCAL_NODE_ID                   (C-Type = 1)
     - REMOTE_NODE_ID                  (C-Type = 2)

   o LINK_ID               Class name (3)

   The LINK_ID Object Class type name space should be allocated as
   follows: pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the numbers
   in the range 0-111 are allocated by Standards Action, 112-119 are
   allocated through an Expert Review, and 120-127 are reserved for
   Private Use.

     - IPv4 LOCAL_LINK_ID              (C-Type = 1)
     - IPv4 REMOTE_LINK_ID             (C-Type = 2)
     - IPv6 LOCAL_LINK_ID              (C-Type = 3)
     - IPv6 REMOTE_LINK_ID             (C-Type = 4)
     - Unnumbered LOCAL_LINK_ID        (C-Type = 5)
     - Unnumbered REMOTE_LINK_ID       (C-Type = 6)

   o INTERFACE_ID          Class name (4)

   The INTERFACE_ID Object Class type name space should be allocated as
   follows: pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the numbers
   in the range 0-111 are allocated by Standards Action, 112-119 are
   allocated through an Expert Review, and 120-127 are reserved for
   Private Use.






<span class="grey">Lang                        Standards Track                    [Page 79]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-80" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


     - IPv4 LOCAL_INTERFACE_ID         (C-Type = 1)
     - IPv4 REMOTE_INTERFACE_ID        (C-Type = 2)
     - IPv6 LOCAL_INTERFACE_ID         (C-Type = 3)
     - IPv6 REMOTE_INTERFACE_ID        (C-Type = 4)
     - Unnumbered LOCAL_INTERFACE_ID   (C-Type = 5)
     - Unnumbered REMOTE_INTERFACE_ID  (C-Type = 6)

   o MESSAGE_ID            Class name (5)

   The MESSAGE_ID Object Class type name space should be allocated as
   follows: pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the numbers
   in the range 0-111 are allocated by Standards Action, 112-119 are
   allocated through an Expert Review, and 120-127 are reserved for
   Private Use.

     - MESSAGE_ID                      (C-Type = 1)
     - MESSAGE_ID_ACK                  (C-Type = 2)

   o CONFIG                Class name (6)

   The CONFIG Object Class type name space should be allocated as
   follows: pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the numbers
   in the range 0-111 are allocated by Standards Action, 112-119 are
   allocated through an Expert Review, and 120-127 are reserved for
   Private Use.

     - HELLO_CONFIG                    (C-Type = 1)

   o HELLO                 Class name (7)

   The HELLO Object Class type name space should be allocated as
   follows: pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the numbers
   in the range 0-111 are allocated by Standards Action, 112-119 are
   allocated through an Expert Review, and 120-127 are reserved for
   Private Use.

     - HELLO                           (C-Type = 1)

   o BEGIN_VERIFY          Class name (8)

   The BEGIN_VERIFY Object Class type name space should be allocated as
   follows: pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the numbers
   in the range 0-111 are allocated by Standards Action, 112-119 are
   allocated through an Expert Review, and 120-127 are reserved for
   Private Use.

     - Type 1                          (C-Type = 1)




<span class="grey">Lang                        Standards Track                    [Page 80]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-81" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   o BEGIN_VERIFY_ACK      Class name (9)

   The BEGIN_VERIFY_ACK Object Class type name space should be allocated
   as follows: pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the
   numbers in the range 0-111 are allocated by Standards Action, 112-119
   are allocated through an Expert Review, and 120-127 are reserved for
   Private Use.

     - Type 1                          (C-Type = 1)

   o VERIFY_ID             Class name (10)

   The VERIFY_ID Object Class type name space should be allocated as
   follows: pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the numbers
   in the range 0-111 are allocated by Standards Action, 112-119 are
   allocated through an Expert Review, and 120-127 are reserved for
   Private Use.

     - Type 1                          (C-Type = 1)

   o TE_LINK               Class name (11)

   The TE_LINK Object Class type name space should be allocated as
   follows: pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the numbers
   in the range 0-111 are allocated by Standards Action, 112-119 are
   allocated through an Expert Review, and 120-127 are reserved for
   Private Use.

     - IPv4 TE_LINK                    (C-Type = 1)
     - IPv6 TE_LINK                    (C-Type = 2)
     - Unnumbered TE_LINK              (C-Type = 3)

   o DATA_LINK             Class name (12)

   The DATA_LINK Object Class type name space should be allocated as
   follows: pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the numbers
   in the range 0-111 are allocated by Standards Action, 112-119 are
   allocated through an Expert Review, and 120-127 are reserved for
   private Use.

    - IPv4 DATA_LINK                  (C-Type = 1)
    - IPv6 DATA_LINK                  (C-Type = 2)
    - Unnumbered DATA_LINK            (C-Type = 3)








<span class="grey">Lang                        Standards Track                    [Page 81]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-82" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   The DATA_LINK Sub-object Class name space should be allocated as
   follows: pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the numbers
   in the range of 0-127 are allocated by Standards Action, 128-247 are
   allocated through an Expert Review, and 248-255 are reserved for
   private Use.

    - Interface Switching Type        (sub-object Type = 1)
    - Wavelength                      (sub-object Type = 2)

   o CHANNEL_STATUS        Class name (13)

   The CHANNEL_STATUS Object Class type name space should be allocated
   as follows: pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the
   numbers in the range 0-111 are allocated by Standards Action, 112-119
   are allocated through an Expert Review, and 120-127 are reserved for
   Private Use.

    - IPv4 INTERFACE_ID               (C-Type = 1)
    - IPv6 INTERFACE_ID               (C-Type = 2)
    - Unnumbered INTERFACE_ID         (C-Type = 3)

   o CHANNEL_STATUS_REQUESTClass name (14)

   The CHANNEL_STATUS_REQUEST Object Class type name space should be
   allocated as follows: pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>],
   the numbers in the range 0-111 are allocated by Standards Action,
   112-119 are allocated through an Expert Review, and 120-127 are
   reserved for Private Use.

    - IPv4 INTERFACE_ID               (C-Type = 1)
    - IPv6 INTERFACE_ID               (C-Type = 2)
    - Unnumbered INTERFACE_ID         (C-Type = 3)

   o ERROR_CODE            Class name (20)

   The ERROR_CODE Object Class type name space should be allocated as
   follows: pursuant to the policies outlined in [<a href="./rfc2434" title="">RFC2434</a>], the numbers
   in the range 0-111 are allocated by Standards Action, 112-119 are
   allocated through an Expert Review, and 120-127 are reserved for
   private Use.

    - BEGIN_VERIFY_ERROR              (C-Type = 1)
    - LINK_SUMMARY_ERROR              (C-Type = 2)








<span class="grey">Lang                        Standards Track                    [Page 82]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-83" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


<span class="h2"><a class="selflink" id="section-17" href="#section-17">17</a>.  Acknowledgements</span>

   The authors would like to thank Andre Fredette for his many
   contributions to this document.  We would also like to thank Ayan
   Banerjee, George Swallow, Adrian Farrel, Dimitri Papadimitriou, Vinay
   Ravuri, and David Drysdale for their insightful comments and
   suggestions.  We would also like to thank John Yu, Suresh Katukam,
   and Greg Bernstein for their helpful suggestions for the in-band
   control channel applicability.

<span class="h2"><a class="selflink" id="section-18" href="#section-18">18</a>.  Contributors</span>

   Jonathan P. Lang
   Sonos, Inc.
   223 E. De La Guerra St.
   Santa Barbara, CA 93101

   EMail: jplang@ieee.org


   Krishna Mitra
   Independent Consultant

   EMail: kmitra@earthlink.net


   John Drake
   Calient Networks
   5853 Rue Ferrari
   San Jose, CA 95138

   EMail: jdrake@calient.net


   Kireeti Kompella
   Juniper Networks, Inc.
   1194 North Mathilda Avenue
   Sunnyvale, CA 94089

   EMail: kireeti@juniper.net


   Yakov Rekhter
   Juniper Networks, Inc.
   1194 North Mathilda Avenue
   Sunnyvale, CA 94089

   EMail: yakov@juniper.net



<span class="grey">Lang                        Standards Track                    [Page 83]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-84" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


   Lou Berger
   Movaz Networks

   EMail: lberger@movaz.com


   Debanjan Saha
   IBM Watson Research Center

   EMail: dsaha@us.ibm.com


   Debashis Basak
   Accelight Networks
   70 Abele Road, Suite 1201
   Bridgeville, PA 15017-3470

   EMail: dbasak@accelight.com


   Hal Sandick
   Shepard M.S.
   2401 Dakota Street
   Durham, NC 27705

   EMail: sandick@nc.rr.com


   Alex Zinin
   Alcatel

   EMail: alex.zinin@alcatel.com


   Bala Rajagopalan
   Intel Corp.
   2111 NE 25th Ave
   Hillsboro, OR 97123

   EMail: bala.rajagopalan@intel.com


   Sankar Ramamoorthi
   Juniper Networks, Inc.
   1194 North Mathilda Avenue
   Sunnyvale, CA 94089

   EMail: sankarr@juniper.net



<span class="grey">Lang                        Standards Track                    [Page 84]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-85" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


Contact Address

   Jonathan P. Lang
   Sonos, Inc.
   829 De La Vina, Suite 220
   Santa Barbara, CA 93101

   EMail: jplang@ieee.org











































<span class="grey">Lang                        Standards Track                    [Page 85]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-86" ></span>
<span class="grey"><a href="./rfc4204">RFC 4204</a>             Link Management Protocol (LMP)         October 2005</span>


Full Copyright Statement

   Copyright (C) The Internet Society (2005).

   This document is subject to the rights, licenses and restrictions
   contained in <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a>, and except as set forth therein, the authors
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
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Lang                        Standards Track                    [Page 86]
</pre>