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rfc:rfc4204

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

                   Link Management Protocol (LMP)

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

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

Lang Standards Track [Page 1] RFC 4204 Link Management Protocol (LMP) October 2005

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

Lang Standards Track [Page 2] RFC 4204 Link Management Protocol (LMP) October 2005

1. Introduction

 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

Lang Standards Track [Page 3] RFC 4204 Link Management Protocol (LMP) October 2005

 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 [RFC4201], 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
 [RFC4201] 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.

Lang Standards Track [Page 4] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

1.1. Terminology

 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 [RFC2119].
 The reader is assumed to be familiar with the terminology in
 [RFC3471], [RFC4202], and [RFC4201].
 Bundled Link:
    As defined in [RFC4201], a bundled link is a TE link such that,
    for the purpose of GMPLS signaling, a combination of <link
    identifier, label> 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 [RFC4201], 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.

Lang Standards Track [Page 5] RFC 4204 Link Management Protocol (LMP) October 2005

 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 [RFC4202], 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.

2. LMP Overview

 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

Lang Standards Track [Page 6] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

Lang Standards Track [Page 7] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

3. Control Channel Management

 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 [RFC3209]), and network topology
 and state distribution information (implemented using traffic
 engineering extensions of protocols such as OSPF [RFC3630] and IS-IS
 [RFC3784]).
 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

Lang Standards Track [Page 8] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

3.1. Parameter Negotiation

 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

Lang Standards Track [Page 9] RFC 4204 Link Management Protocol (LMP) October 2005

 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).

3.2. Hello Protocol

 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

Lang Standards Track [Page 10] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

3.2.1. Hello Parameter Negotiation

 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 Section 3.2.2), 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 Section 11.1 for the complete control
 channel FSM.

Lang Standards Track [Page 11] RFC 4204 Link Management Protocol (LMP) October 2005

3.2.2. Fast Keep-alive

 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 > 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}.

Lang Standards Track [Page 12] RFC 4204 Link Management Protocol (LMP) October 2005

3.2.3. Control Channel Down

 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.

3.2.4. Degraded State

 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.

4. Link Property Correlation

 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.

Lang Standards Track [Page 13] RFC 4204 Link Management Protocol (LMP) October 2005

 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 Section
 5) 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

Lang Standards Track [Page 14] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

5. Verifying Link Connectivity

 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

Lang Standards Track [Page 15] RFC 4204 Link Management Protocol (LMP) October 2005

 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

Lang Standards Track [Page 16] RFC 4204 Link Management Protocol (LMP) October 2005

 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 Section 10).
 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.

Lang Standards Track [Page 17] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

5.1. Example of Link Connectivity Verification

 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

Lang Standards Track [Page 18] RFC 4204 Link Management Protocol (LMP) October 2005

    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         +<-------- c --------->+        Node B       +
 +                     +                      +                     +
 +                     +                      +                     +
 +                   1 +--------------------->+ 10                  +
 +                     +                      +                     +
 +                     +                      +                     +
 +                   2 +                /---->+ 11                  +
 +                     +          /----/      +                     +
 +                     +     /---/            +                     +
 +                   3 +----/                 + 12                  +
 +                     +                      +                     +
 +                     +                      +                     +
 +                   4 +--------------------->+ 14                  +
 +                     +                      +                     +
 +---------------------+                      +---------------------+
  Figure 1:  Example of link connectivity between Node A and Node B.

6. Fault Management

 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.

Lang Standards Track [Page 19] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

6.1. Fault Detection

 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.

6.2. Fault Localization Procedure

 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

Lang Standards Track [Page 20] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

6.3. Examples of Fault Localization

 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.

Lang Standards Track [Page 21] RFC 4204 Link Management Protocol (LMP) October 2005

     +-------+        +-------+        +-------+        +-------+
     + Node1 +        + Node2 +        + Node3 +        + Node4 +
     +       +-- c ---+       +-- c ---+       +-- c ---+       +
 ----+---\   +        +       +        +       +        +       +
 <---+---\\--+--------+-------+---\    +       +        +    /--+--->
     +    \--+--------+-------+---\\---+-------+---##---+---//--+----
     +       +        +       +    \---+-------+--------+---/   +
     +       +        +       +        +       +  (a)   +       +
 ----+-------+--------+---\   +        +       +        +       +
 <---+-------+--------+---\\--+---##---+--\    +        +       +
     +       +        +    \--+---##---+--\\   +        +       +
     +       +        +       +  (b)   +   \\--+--------+-------+--->
     +       +        +       +        +    \--+--------+-------+----
     +       +        +       +        +       +        +       +
     +-------+        +-------+        +-------+        +-------+
       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".

6.4. Channel Activation Indication

 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 Section 6.2.

Lang Standards Track [Page 22] RFC 4204 Link Management Protocol (LMP) October 2005

6.5. Channel Deactivation Indication

 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.

7. Message_Id Usage

 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 Section 10).
 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 > 0) {
    New value is less than old value;
 }

Lang Standards Track [Page 23] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

8. Graceful Restart

 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.

Lang Standards Track [Page 24] RFC 4204 Link Management Protocol (LMP) October 2005

 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 Section 3.1.  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 Section 4.
 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 Section 4 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.

9. Addressing

 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

Lang Standards Track [Page 25] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

10. Exponential Back-off Procedures

 This section is based on [RFC2961] and provides exponential back-off
 procedures for message retransmission.  Implementations MUST use the
 described procedures or their equivalent.

10.1. Operation

 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.

Lang Standards Track [Page 26] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

10.2. Retransmission Algorithm

 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++ < 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.

Lang Standards Track [Page 27] RFC 4204 Link Management Protocol (LMP) October 2005

11. LMP Finite State Machines

11.1. Control Channel FSM

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

11.1.1. Control Channel States

 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.

Lang Standards Track [Page 28] RFC 4204 Link Management Protocol (LMP) October 2005

11.1.2. Control Channel Events

 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.

Lang Standards Track [Page 29] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

11.1.3. Control Channel FSM Description

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

Lang Standards Track [Page 30] RFC 4204 Link Management Protocol (LMP) October 2005

                             +--------+
          +----------------->|        |<--------------+
          |       +--------->|  Down  |<----------+   |
          |       |+---------|        |<-------+  |   |
          |       ||         +--------+        |  |   |
          |       ||           |    ^       2,9| 2|  2|
          |       ||1b       1a|    |          |  |   |
          |       ||           v    |2,9       |  |   |
          |       ||         +--------+        |  |   |
          |       ||      +->|        |<------+|  |   |
          |       ||  4,7,|  |ConfSnd |       ||  |   |
          |       || 14,15+--|        |<----+ ||  |   |
          |       ||         +--------+     | ||  |   |
          |       ||       3,8a| |          | ||  |   |
          |       || +---------+ |8b  14,12a| ||  |   |
          |       || |           v          | ||  |   |
          |       |+-|------>+--------+     | ||  |   |
          |       |  |    +->|        |-----|-|+  |   |
          |       |  |6,14|  |ConfRcv |     | |   |   |
          |       |  |    +--|        |<--+ | |   |   |
          |       |  |       +--------+   | | |   |   |
          |       |  |          5| ^      | | |   |   |
          |       |  +---------+ | |      | | |   |   |
          |       |            | | |      | | |   |   |
          |       |            v v |6,12b | | |   |   |
          |       |10        +--------+   | | |   |   |
          |       +----------|        |   | | |   |   |
          |       |       +--| Active |---|-+ |   |   |
     10,17|       |   5,16|  |        |-------|---+   |
      +-------+ 9 |   13  +->|        |   |   |       |
      | Going |<--|----------+--------+   |   |       |
      | Down  |   |           11| ^       |   |       |
      +-------+   |             | |5      |   |       |
          ^       |             v |  6,12b|   |       |
          |9      |10        +--------+   |   |12a,14 |
          |       +----------|        |---+   |       |
          |                  |   Up   |-------+       |
          +------------------|        |---------------+
                             +--------+
                               |   ^
                               |   |
                               +---+
                              11,13,16
                     Figure 3: Control Channel FSM

Lang Standards Track [Page 31] RFC 4204 Link Management Protocol (LMP) October 2005

 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).

11.2. TE Link FSM

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

11.2.1. TE Link States

 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.

11.2.2. TE Link Events

 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.

Lang Standards Track [Page 32] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

11.2.3. TE Link FSM Description

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

Lang Standards Track [Page 33] RFC 4204 Link Management Protocol (LMP) October 2005

                                3,7,8
                                 +--+
                                 |  |
                                 |  v
                              +--------+
                              |        |
                +------------>|  Down  |<---------+
                |             |        |          |
                |             +--------+          |
                |                |  ^             |
                |               1|  |9            |
                |                v  |             |
                |             +--------+          |
                |             |        |<-+       |
                |             |  Init  |  |3,5,6  |9
                |             |        |--+ 7,8   |
               9|             +--------+          |
                |                  |              |
                |               2,4|              |
                |                  v              |
             +--------+   7   +--------+          |
             |        |------>|        |----------+
             |  Deg   |       |   Up   |
             |        |<------|        |
             +--------+   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.

11.3. Data Link FSM

 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.

Lang Standards Track [Page 34] RFC 4204 Link Management Protocol (LMP) October 2005

11.3.1. Data Link States

 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.

11.3.2. Data Link Events

 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 Section 5) was successful
                            for this data link and a TestStatusSuccess
                            message was received over the control
                            channel.

Lang Standards Track [Page 35] RFC 4204 Link Management Protocol (LMP) October 2005

                       (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.

Lang Standards Track [Page 36] RFC 4204 Link Management Protocol (LMP) October 2005

11.3.3. Active Data Link FSM Description

 Figure 5 illustrates operation of the LMP active data link FSM in a
 form of FSM state transition diagram.
                           +------+
                           |      |<-------+
                +--------->| Down |        |
                |     +----|      |<-----+ |
                |     |    +------+      | |
                |     |5b   3|  ^        | |
                |     |      |  |7       | |
                |     |      v  |        | |
                |     |    +------+      | |
                |     |    |      |<-+   | |
                |     |    | Test |  |11 | |
                |     |    |      |--+   | |
                |     |    +------+      | |
                |     |     5a| 3^       | |
                |     |       |  |       | |
                |     |       v  |       | |
                |12   |   +---------+    | |
                |     +-->|         |14  | |
                |         | Up/Free |----+ |
                +---------|         |      |
                          +---------+      |
                             9| ^          |
                              | |          |
                              v |10        |
                          +---------+      |
                          |         |13    |
                          |Up/Alloc |------+
                          |         |
                          +---------+
                  Figure 5: Active LMP Data Link FSM

Lang Standards Track [Page 37] RFC 4204 Link Management Protocol (LMP) October 2005

11.3.4. Passive Data Link FSM Description

 Figure 6 illustrates operation of the LMP passive data link FSM in a
 form of FSM state transition diagram.
                           +------+
                           |      |<------+
               +---------->| Down |       |
               |     +-----|      |<----+ |
               |     |     +------+     | |
               |     |5b    4|  ^       | |
               |     |       |  |8      | |
               |     |       v  |       | |
               |     |    +----------+  | |
               |     |    | PasvTest |  | |
               |     |    +----------+  | |
               |     |       6|  4^     | |
               |     |        |   |     | |
               |     |        v   |     | |
               |12   |    +---------+   | |
               |     +--->| Up/Free |14 | |
               |          |         |---+ |
               +----------|         |     |
                          +---------+     |
                              9| ^        |
                               | |        |
                               v |10      |
                          +---------+     |
                          |         |13   |
                          |Up/Alloc |-----+
                          |         |
                          +---------+
                  Figure 6: Passive LMP Data Link FSM

12. LMP Message Formats

 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).

Lang Standards Track [Page 38] RFC 4204 Link Management Protocol (LMP) October 2005

12.1. Common Header

 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

Lang Standards Track [Page 39] RFC 4204 Link Management Protocol (LMP) October 2005

    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.

Lang Standards Track [Page 40] RFC 4204 Link Management Protocol (LMP) October 2005

12.2. LMP Object Format

 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
    Section 13.
 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.

Lang Standards Track [Page 41] RFC 4204 Link Management Protocol (LMP) October 2005

12.3. Parameter Negotiation Messages

12.3.1. Config Message (Msg Type = 1)

 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:
 <Config Message> ::= <Common Header> <LOCAL_CCID> <MESSAGE_ID>
                      <LOCAL_NODE_ID> <CONFIG>
 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.

12.3.2. ConfigAck Message (Msg Type = 2)

 The ConfigAck message is used to acknowledge receipt of the Config
 message and indicate agreement on all parameters.
 <ConfigAck Message> ::= <Common Header> <LOCAL_CCID> <LOCAL_NODE_ID>
                         <REMOTE_CCID> <MESSAGE_ID_ACK>
                         <REMOTE_NODE_ID>
 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.

12.3.3. ConfigNack Message (Msg Type = 3)

 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:
 <ConfigNack Message> ::= <Common Header> <LOCAL_CCID>
                          <LOCAL_NODE_ID>  <REMOTE_CCID>
                          <MESSAGE_ID_ACK> <REMOTE_NODE_ID> <CONFIG>

Lang Standards Track [Page 42] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

12.4. Hello Message (Msg Type = 4)

 The format of the Hello message is as follows:
 <Hello Message> ::= <Common Header> <LOCAL_CCID> <HELLO>
 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.

12.5. Link Verification Messages

12.5.1. BeginVerify Message (Msg Type = 5)

 The BeginVerify message is sent over the control channel and is used
 to initiate the link verification process.  The format is as follows:
 <BeginVerify Message> ::= <Common Header> <LOCAL_LINK_ID>
                           <MESSAGE_ID> [<REMOTE_LINK_ID>]
                           <BEGIN_VERIFY>

Lang Standards Track [Page 43] RFC 4204 Link Management Protocol (LMP) October 2005

 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 Section 5).
 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.

12.5.2. BeginVerifyAck Message (Msg Type = 6)

 When a BeginVerify message is received and Test messages are ready to
 be processed, a BeginVerifyAck message MUST be transmitted.
 <BeginVerifyAck Message> ::= <Common Header> [<LOCAL_LINK_ID>]
                              <MESSAGE_ID_ACK> <BEGIN_VERIFY_ACK>
                              <VERIFY_ID>
 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.

Lang Standards Track [Page 44] RFC 4204 Link Management Protocol (LMP) October 2005

12.5.3. BeginVerifyNack Message (Msg Type = 7)

 If a BeginVerify message is received and a node is unwilling or
 unable to begin the Verification procedure, a BeginVerifyNack message
 MUST be transmitted.
 <BeginVerifyNack Message> ::= <Common Header> [<LOCAL_LINK_ID>]
                               <MESSAGE_ID_ACK> <ERROR_CODE>
 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".

12.5.4. EndVerify Message (Msg Type = 8)

 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:
 <EndVerify Message> ::=<Common Header> <MESSAGE_ID> <VERIFY_ID>
 The above transmission order SHOULD be followed.

Lang Standards Track [Page 45] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

12.5.5. EndVerifyAck Message (Msg Type =9)

 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:
 <EndVerifyAck Message> ::= <Common Header> <MESSAGE_ID_ACK>
                            <VERIFY_ID>
 The above transmission order SHOULD be followed.
 The contents of the MESSAGE_ID_ACK object MUST be obtained from the
 EndVerify message being acknowledged.

12.5.6. Test Message (Msg Type = 10)

 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:
 <Test Message> ::= <Common Header> <LOCAL_INTERFACE_ID> <VERIFY_ID>
 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 13.8 and 13.9).
 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.

Lang Standards Track [Page 46] RFC 4204 Link Management Protocol (LMP) October 2005

12.5.7. TestStatusSuccess Message (Msg Type = 11)

 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.
 <TestStatusSuccess Message> ::= <Common Header> <LOCAL_LINK_ID>
                                 <MESSAGE_ID> <LOCAL_INTERFACE_ID>
                                 <REMOTE_INTERFACE_ID> <VERIFY_ID>
 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.

12.5.8. TestStatusFailure Message (Msg Type = 12)

 The TestStatusFailure message is transmitted over the control channel
 and is used to indicate that the Test message was not received.
 <TestStatusFailure Message> ::= <Common Header> <MESSAGE_ID>
                                 <VERIFY_ID>
 The above transmission order SHOULD be followed.

12.5.9. TestStatusAck Message (Msg Type = 13)

 The TestStatusAck message is used to acknowledge receipt of the
 TestStatusSuccess or TestStatusFailure messages.
 <TestStatusAck Message> ::= <Common Header> <MESSAGE_ID_ACK>
                             <VERIFY_ID>
 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.

12.6. Link Summary Messages

12.6.1. LinkSummary Message (Msg Type = 14)

 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:
 <LinkSummary Message> ::= <Common Header> <MESSAGE_ID> <TE_LINK>
                           <DATA_LINK> [<DATA_LINK>...]

Lang Standards Track [Page 47] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

12.6.2. LinkSummaryAck Message (Msg Type = 15)

 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.
 <LinkSummaryAck Message> ::=  <Common Header> <MESSAGE_ID_ACK>
 The above transmission order SHOULD be followed.

12.6.3. LinkSummaryNack Message (Msg Type = 16)

 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.
 <LinkSummaryNack Message> ::= <Common Header> <MESSAGE_ID_ACK>
                               <ERROR_CODE> [<DATA_LINK>...]
 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."

Lang Standards Track [Page 48] RFC 4204 Link Management Protocol (LMP) October 2005

 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."

12.7. Fault Management Messages

12.7.1. ChannelStatus Message (Msg Type = 17)

 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:
 <ChannelStatus Message> ::= <Common Header> <LOCAL_LINK_ID>
                             <MESSAGE_ID> <CHANNEL_STATUS>
 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.

12.7.2. ChannelStatusAck Message (Msg Type = 18)

 The ChannelStatusAck message is used to acknowledge receipt of the
 ChannelStatus Message.  The format is as follows:
 <ChannelStatusAck Message> ::= <Common Header> <MESSAGE_ID_ACK>
 The above transmission order SHOULD be followed.
 The contents of the MESSAGE_ID_ACK object MUST be obtained from the
 ChannelStatus message being acknowledged.

Lang Standards Track [Page 49] RFC 4204 Link Management Protocol (LMP) October 2005

12.7.3. ChannelStatusRequest Message (Msg Type = 19)

 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:
 <ChannelStatusRequest Message> ::= <Common Header> <LOCAL_LINK_ID>
                                    <MESSAGE_ID>
                                    [<CHANNEL_STATUS_REQUEST>]
 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.

12.7.4. ChannelStatusResponse Message (Msg Type = 20)

 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:
 <ChannelStatusResponse Message> ::= <Common Header> <MESSAGE_ID_ACK>
                                     <CHANNEL_STATUS>
 The above transmission order SHOULD be followed.
 The contents of the MESSAGE_ID_ACK objects MUST be obtained from the
 ChannelStatusRequest message being acknowledged.

13. LMP Object Definitions

13.1. CCID (Control Channel ID) Class

 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                              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Lang Standards Track [Page 50] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

13.2. NODE_ID Class

 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)                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Lang Standards Track [Page 51] RFC 4204 Link Management Protocol (LMP) October 2005

 Node_Id:
    This identities the remote node.
 This object is non-negotiable.

13.3. LINK_ID Class

 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)                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Lang Standards Track [Page 52] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

13.4. INTERFACE_ID Class

 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

Lang Standards Track [Page 53] RFC 4204 Link Management Protocol (LMP) October 2005

  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.

13.5. MESSAGE_ID Class

 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                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Lang Standards Track [Page 54] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

13.6. CONFIG Class

 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.

Lang Standards Track [Page 55] RFC 4204 Link Management Protocol (LMP) October 2005

13.7. HELLO Class

 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.

13.8. BEGIN_VERIFY Class

 Class = 8
 o    C-Type = 1

Lang Standards Track [Page 56] RFC 4204 Link Management Protocol (LMP) October 2005

  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
    [RFC3471].

Lang Standards Track [Page 57] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

13.9. BEGIN_VERIFY_ACK Class

 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   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Lang Standards Track [Page 58] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

13.10. VERIFY_ID Class

 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.

13.11. TE_LINK Class

 Class = 11
 o    C-Type = 1, IPv4 TE_LINK

Lang Standards Track [Page 59] RFC 4204 Link Management Protocol (LMP) October 2005

  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.

Lang Standards Track [Page 60] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

13.12. DATA_LINK Class

 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)                         //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Lang Standards Track [Page 61] RFC 4204 Link Management Protocol (LMP) October 2005

 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)                         //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Lang Standards Track [Page 62] RFC 4204 Link Management Protocol (LMP) October 2005

 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 Section 13.12.1 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.

Lang Standards Track [Page 63] RFC 4204 Link Management Protocol (LMP) October 2005

13.12.1. Data Link Subobjects

 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.

13.12.1.1. Subobject Type 1: Interface Switching Type

  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 [RFC3471].
 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
    [RFC3471].

Lang Standards Track [Page 64] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

13.12.1.2. Subobject Type 2: Wavelength

  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.

13.13. CHANNEL_STATUS Class

 Class = 13

Lang Standards Track [Page 65] RFC 4204 Link Management Protocol (LMP) October 2005

 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                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Lang Standards Track [Page 66] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

Lang Standards Track [Page 67] RFC 4204 Link Management Protocol (LMP) October 2005

 This object is non-negotiable.

13.14. CHANNEL_STATUS_REQUEST Class

 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.

Lang Standards Track [Page 68] RFC 4204 Link Management Protocol (LMP) October 2005

 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)                   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Lang Standards Track [Page 69] RFC 4204 Link Management Protocol (LMP) October 2005

 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.

13.15. ERROR_CODE Class

 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                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Lang Standards Track [Page 70] RFC 4204 Link Management Protocol (LMP) October 2005

    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.

14. References

14.1. Normative References

 [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC4201]   Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling
             in MPLS Traffic Engineering (TE)", RFC 4201, October
             2005.
 [RFC4202]   Kompella, K., Ed. and Y. Rekhter, Ed., "Routing
             Extensions in Support of Generalized Multi-Protocol Label
             Switching (GMPLS)", RFC 4202, October 2005.
 [RFC2961]   Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F.,
             and S. Molendini, "RSVP Refresh Overhead Reduction
             Extensions", RFC 2961, April 2001.
 [RFC2402]   Kent, S. and R. Atkinson, "IP Authentication Header", RFC
             2402, November 1998.
 [RFC2406]   Kent, S. and R. Atkinson, "IP Encapsulating Security
             Payload (ESP)", RFC 2406, November 1998.
 [RFC2407]   Piper, D., "The Internet IP Security Domain of
             Interpretation for ISAKMP", RFC 2407, November 1998.
 [RFC2409]   Harkins, D. and D. Carrel, "The Internet Key Exchange
             (IKE)", RFC 2409, November 1998.

Lang Standards Track [Page 71] RFC 4204 Link Management Protocol (LMP) October 2005

 [RFC3471]   Berger, L., Ed.,  "Generalized MPLS - Signaling
             Functional Description", RFC 3471, January 2003.

14.2. Informative References

 [RFC3630]   Katz, D., Kompella, K., and D. Yeung, "Traffic
             Engineering (TE) Extensions to OSPF Version 2", RFC 3630,
             September 2003.
 [RFC3784]   Smit, H. and T. Li, "Intermediate System to Intermediate
             System (IS-IS) Extensions for Traffic Engineering (TE)",
             RFC 3784, June 2004.
 [RFC2401]   Kent, S. and R. Atkinson, "Security Architecture for the
             Internet Protocol", RFC 2401, November 1998.
 [RFC2434]   Narten, T. and H. Alvestrand, "Guidelines for Writing an
             IANA Considerations Section in RFCs", BCP 26, RFC 2434,
             October 1998.
 [RFC3209]   Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
             and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
             Tunnels", RFC 3209, December 2001.

Lang Standards Track [Page 72] RFC 4204 Link Management Protocol (LMP) October 2005

15. Security Considerations

 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.

15.1. Security Requirements

 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.

Lang Standards Track [Page 73] RFC 4204 Link Management Protocol (LMP) October 2005

15.2. Security Mechanisms

 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 [RFC2401], IKE [RFC2409], IPsec AH
 [RFC2402], and IPsec ESP [RFC2406].  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 Section 15.1, 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 [RFC2409] MUST be used as the key exchange protocol if keys
    are dynamically negotiated between peers.
 4. Implementation MUST use the IPsec DOI [RFC2407].
 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.

Lang Standards Track [Page 74] RFC 4204 Link Management Protocol (LMP) October 2005

    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.

Lang Standards Track [Page 75] RFC 4204 Link Management Protocol (LMP) October 2005

    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.

16. IANA Considerations

 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 [RFC2434].
 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.

Lang Standards Track [Page 76] RFC 4204 Link Management Protocol (LMP) October 2005

 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 [RFC2434].
 LMP defines the following name spaces that require management:
  1. LMP Message Type.
  2. LMP Object Class.
  3. LMP Object Class type (C-Type). These are unique within the

Object Class.

  1. 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 [RFC2434], 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 [RFC2434], 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.

Lang Standards Track [Page 77] RFC 4204 Link Management Protocol (LMP) October 2005

 The following name spaces have been assigned by IANA:
  1. —————————————————————–

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)
  1. —————————————————————–

Lang Standards Track [Page 78] RFC 4204 Link Management Protocol (LMP) October 2005

 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 [RFC2434], 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.
  1. LOCAL_CCID (C-Type = 1)
  2. 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 [RFC2434], 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.
  1. LOCAL_NODE_ID (C-Type = 1)
  2. 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 [RFC2434], 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.
  1. IPv4 LOCAL_LINK_ID (C-Type = 1)
  2. IPv4 REMOTE_LINK_ID (C-Type = 2)
  3. IPv6 LOCAL_LINK_ID (C-Type = 3)
  4. IPv6 REMOTE_LINK_ID (C-Type = 4)
  5. Unnumbered LOCAL_LINK_ID (C-Type = 5)
  6. 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 [RFC2434], 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.

Lang Standards Track [Page 79] RFC 4204 Link Management Protocol (LMP) October 2005

  1. IPv4 LOCAL_INTERFACE_ID (C-Type = 1)
  2. IPv4 REMOTE_INTERFACE_ID (C-Type = 2)
  3. IPv6 LOCAL_INTERFACE_ID (C-Type = 3)
  4. IPv6 REMOTE_INTERFACE_ID (C-Type = 4)
  5. Unnumbered LOCAL_INTERFACE_ID (C-Type = 5)
  6. 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 [RFC2434], 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.
  1. MESSAGE_ID (C-Type = 1)
  2. 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 [RFC2434], 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.
  1. 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 [RFC2434], 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.
  1. 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 [RFC2434], 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.
  1. Type 1 (C-Type = 1)

Lang Standards Track [Page 80] RFC 4204 Link Management Protocol (LMP) October 2005

 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 [RFC2434], 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.
  1. 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 [RFC2434], 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.
  1. 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 [RFC2434], 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.
  1. IPv4 TE_LINK (C-Type = 1)
  2. IPv6 TE_LINK (C-Type = 2)
  3. 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 [RFC2434], 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.
  1. IPv4 DATA_LINK (C-Type = 1)
  2. IPv6 DATA_LINK (C-Type = 2)
  3. Unnumbered DATA_LINK (C-Type = 3)

Lang Standards Track [Page 81] RFC 4204 Link Management Protocol (LMP) October 2005

 The DATA_LINK Sub-object Class name space should be allocated as
 follows: pursuant to the policies outlined in [RFC2434], 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.
  1. Interface Switching Type (sub-object Type = 1)
  2. 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 [RFC2434], 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.
  1. IPv4 INTERFACE_ID (C-Type = 1)
  2. IPv6 INTERFACE_ID (C-Type = 2)
  3. 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 [RFC2434],
 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.
  1. IPv4 INTERFACE_ID (C-Type = 1)
  2. IPv6 INTERFACE_ID (C-Type = 2)
  3. 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 [RFC2434], 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.
  1. BEGIN_VERIFY_ERROR (C-Type = 1)
  2. LINK_SUMMARY_ERROR (C-Type = 2)

Lang Standards Track [Page 82] RFC 4204 Link Management Protocol (LMP) October 2005

17. Acknowledgements

 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.

18. Contributors

 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

Lang Standards Track [Page 83] RFC 4204 Link Management Protocol (LMP) October 2005

 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

Lang Standards Track [Page 84] RFC 4204 Link Management Protocol (LMP) October 2005

Contact Address

 Jonathan P. Lang
 Sonos, Inc.
 829 De La Vina, Suite 220
 Santa Barbara, CA 93101
 EMail: jplang@ieee.org

Lang Standards Track [Page 85] RFC 4204 Link Management Protocol (LMP) October 2005

Full Copyright Statement

 Copyright (C) The Internet Society (2005).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
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 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
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 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
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 The IETF invites any interested party to bring to its attention any
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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Lang Standards Track [Page 86]

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