





Internet Engineering Task Force (IETF)                        L. Martini
Request for Comments: 7275                                      S. Salam
Category: Standards Track                                     A. Sajassi
ISSN: 2070-1721                                                    Cisco
                                                                M. Bocci
                                                          Alcatel-Lucent
                                                           S. Matsushima
                                                        Softbank Telecom
                                                               T. Nadeau
                                                                 Brocade
                                                               June 2014


                Inter-Chassis Communication Protocol for
 Layer 2 Virtual Private Network (L2VPN) Provider Edge (PE) Redundancy

Abstract

   This document specifies an Inter-Chassis Communication Protocol
   (ICCP) that enables Provider Edge (PE) device redundancy for Virtual
   Private Wire Service (VPWS) and Virtual Private LAN Service (VPLS)
   applications.  The protocol runs within a set of two or more PEs,
   forming a Redundancy Group, for the purpose of synchronizing data
   among the systems.  It accommodates multi-chassis attachment circuit
   redundancy mechanisms as well as pseudowire redundancy mechanisms.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7275.












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Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

























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Table of Contents

   1. Introduction ....................................................5
   2. Specification of Requirements ...................................5
   3. ICCP Overview ...................................................5
      3.1. Redundancy Model and Topology ..............................5
      3.2. ICCP Interconnect Scenarios ................................7
           3.2.1. Co-located Dedicated Interconnect ...................7
           3.2.2. Co-located Shared Interconnect ......................8
           3.2.3. Geo-redundant Dedicated Interconnect ................8
           3.2.4. Geo-redundant Shared Interconnect ...................9
      3.3. ICCP Requirements .........................................10
   4. ICC LDP Protocol Extension Specification .......................11
      4.1. LDP ICCP Capability Advertisement .........................12
      4.2. RG Membership Management ..................................12
           4.2.1. ICCP Connection State Machine ......................13
      4.3. Redundant Object Identification ...........................17
      4.4. Application Connection Management .........................17
           4.4.1. Application Versioning .............................18
           4.4.2. Application Connection State Machine ...............19
      4.5. Application Data Transfer .................................22
      4.6. Dedicated Redundancy Group LDP Session ....................22
   5. ICCP PE Node Failure / Isolation Detection Mechanism ...........22
   6. ICCP Message Formats ...........................................23
      6.1. Encoding ICC into LDP Messages ............................23
           6.1.1. ICC Header .........................................24
           6.1.2. ICC Parameter Encoding .............................26
           6.1.3. Redundant Object Identifier Encoding ...............27
      6.2. RG Connect Message ........................................27
           6.2.1. ICC Sender Name TLV ................................28
      6.3. RG Disconnect Message .....................................29
      6.4. RG Notification Message ...................................31
           6.4.1. Notification Message TLVs ..........................32
      6.5. RG Application Data Message ...............................35
   7. Application TLVs ...............................................35
      7.1. Pseudowire Redundancy (PW-RED) Application TLVs ...........35
           7.1.1. PW-RED Connect TLV .................................36
           7.1.2. PW-RED Disconnect TLV ..............................37
                  7.1.2.1. PW-RED Disconnect Cause TLV ...............38
           7.1.3. PW-RED Config TLV ..................................39
                  7.1.3.1. Service Name TLV ..........................41
                  7.1.3.2. PW ID TLV .................................42
                  7.1.3.3. Generalized PW ID TLV .....................43
           7.1.4. PW-RED State TLV ...................................44
           7.1.5. PW-RED Synchronization Request TLV .................45
           7.1.6. PW-RED Synchronization Data TLV ....................46





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      7.2. Multi-Chassis LACP (mLACP) Application TLVs ...............48
           7.2.1. mLACP Connect TLV ..................................48
           7.2.2. mLACP Disconnect TLV ...............................49
                  7.2.2.1. mLACP Disconnect Cause TLV ................50
           7.2.3. mLACP System Config TLV ............................51
           7.2.4. mLACP Aggregator Config TLV ........................52
           7.2.5. mLACP Port Config TLV ..............................54
           7.2.6. mLACP Port Priority TLV ............................56
           7.2.7. mLACP Port State TLV ...............................58
           7.2.8. mLACP Aggregator State TLV .........................60
           7.2.9. mLACP Synchronization Request TLV ..................61
           7.2.10. mLACP Synchronization Data TLV ....................63
   8. LDP Capability Negotiation .....................................65
   9. Client Applications ............................................66
      9.1. Pseudowire Redundancy Application Procedures ..............66
           9.1.1. Initial Setup ......................................66
           9.1.2. Pseudowire Configuration Synchronization ...........66
           9.1.3. Pseudowire Status Synchronization ..................67
                  9.1.3.1. Independent Mode ..........................69
                  9.1.3.2. Master/Slave Mode .........................69
           9.1.4. PE Node Failure or Isolation .......................70
      9.2. Attachment Circuit Redundancy Application Procedures ......70
           9.2.1. Common AC Procedures ...............................70
                  9.2.1.1. AC Failure ................................70
                  9.2.1.2. Remote PE Node Failure or Isolation .......70
                  9.2.1.3. Local PE Isolation ........................71
                  9.2.1.4. Determining Pseudowire State ..............71
           9.2.2. Multi-Chassis LACP (mLACP) Application Procedures ..72
                  9.2.2.1. Initial Setup .............................72
                  9.2.2.2. mLACP Aggregator and Port Configuration ...74
                  9.2.2.3. mLACP Aggregator and Port Status
                           Synchronization ...........................75
                  9.2.2.4. Failure and Recovery ......................77
   10. Security Considerations .......................................78
   11. Manageability Considerations ..................................79
   12. IANA Considerations ...........................................79
      12.1. Message Type Name Space ..................................79
      12.2. TLV Type Name Space ......................................79
      12.3. ICC RG Parameter Type Space ..............................80
      12.4. Status Code Name Space ...................................81
   13. Acknowledgments ...............................................81
   14. References ....................................................81
      14.1. Normative References .....................................81
      14.2. Informative References ...................................82







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1.  Introduction

   Network availability is a critical metric for service providers, as
   it has a direct bearing on their profitability.  Outages translate
   not only to lost revenue but also to potential penalties mandated by
   contractual agreements with customers running mission-critical
   applications that require tight Service Level Agreements (SLAs).
   This is true for any carrier network, and networks employing Layer 2
   Virtual Private Network (L2VPN) technology are no exception.  A high
   degree of network availability can be achieved by employing intra-
   and inter-chassis redundancy mechanisms.  The focus of this document
   is on the latter.  This document defines an Inter-Chassis
   Communication Protocol (ICCP) that allows synchronization of state
   and configuration data between a set of two or more Provider Edge
   nodes (PEs) forming a Redundancy Group (RG).  The protocol supports
   multi-chassis redundancy mechanisms that can be employed on either
   the attachment circuits or pseudowires (PWs).  A formal definition of
   the term "chassis" can be found in [RFC2922].  For the purpose of
   this document, a chassis is an L2VPN PE node.

   This document assumes that it is normal to run the Label Distribution
   Protocol (LDP) between the PEs in the RG, and that LDP components
   will in any case be present on the PEs to establish and maintain
   pseudowires.  Therefore, ICCP is built as a secondary protocol
   running within LDP and taking advantage of the LDP session mechanisms
   as well as the underlying TCP transport mechanisms and TCP-based
   security mechanisms already necessary for LDP operation.

2.  Specification of Requirements

   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 RFC 2119 [RFC2119].

3.  ICCP Overview

3.1.  Redundancy Model and Topology

   The focus of this document is on PE node redundancy.  It is assumed
   that a set of two or more PE nodes are designated by the operator to
   form an RG.  Members of an RG fall under a single administration
   (e.g., service provider) and employ a common redundancy mechanism
   towards the access (attachment circuits or access pseudowires) and/or
   towards the core (pseudowires) for any given service instance.  It is
   possible, however, for members of an RG to make use of disparate
   redundancy mechanisms for disjoint services.  The PE devices may be
   offering any type of L2VPN service, i.e., Virtual Private Wire
   Service (VPWS) or Virtual Private LAN Service (VPLS).  As a matter of



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   fact, the use of ICCP may even be applicable for Layer 3 service
   redundancy, but this is considered to be outside the scope of this
   document.

   The PEs in an RG offer multi-homed connectivity to either individual
   devices (e.g., Customer Edge (CE), Digital Subscriber Line Access
   Multiplexer (DSLAM)) or entire networks (e.g., access network).
   Figure 1 below depicts the model.

                                    +=================+
                                    |                 |
   Multi-homed         +----+       |  +-----+        |
   Node  ------------> | CE |-------|--| PE1 ||<------|---Pseudowire-->|
                       |    |--+   -|--|     ||<------|---Pseudowire-->|
                       +----+  |  / |  +-----+        |
                               | /  |     ||          |
                               |/   |     || ICCP     |--> Towards Core
              +-------------+  /    |     ||          |
              |             | /|    |  +-----+        |
              |    Access   |/ +----|--| PE2 ||<------|---Pseudowire-->|
              |   Network   |-------|--|     ||<------|---Pseudowire-->|
              |             |       |  +-----+        |
              |             |       |                 |
              +-------------+       |   Redundancy    |
                ^                   |     Group       |
                |                   +=================+
                |
         Multi-homed Network

             Figure 1: Generic Multi-Chassis Redundancy Model

   In the topology shown in Figure 1, the redundancy mechanism employed
   towards the access node/network can be one of a multitude of
   technologies, e.g., it could be IEEE 802.1AX Link Aggregation Groups
   with the Link Aggregation Control Protocol (LACP) or Synchronous
   Optical Network Automatic Protection Switching (SONET APS).  The
   specifics of the mechanism are outside the scope of this document.
   However, it is assumed that the PEs in the RG are required to
   communicate with each other in order for the access redundancy
   mechanism to operate correctly.  As such, it is required that an
   inter-chassis communication protocol among the PEs in the RG be run
   in order to synchronize configuration and/or running state data.

   Furthermore, the presence of the inter-chassis communication channel
   allows simplification of the pseudowire redundancy mechanism.  This
   is primarily because it allows the PEs within an RG to run some
   arbitration algorithm to elect which pseudowire(s) should be in
   active or standby mode for a given service instance.  The PEs can



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   then advertise the outcome of the arbitration to the remote-end
   PE(s), as opposed to having to embed a handshake procedure into the
   pseudowire redundancy status communication mechanism as well as every
   other possible Layer 2 status communication mechanism.

3.2.  ICCP Interconnect Scenarios

   When referring to "interconnect" in this section, we are concerned
   with the links or networks over which Inter-Chassis Communication
   Protocol messages are transported, and not normal data traffic
   between PEs.  The PEs that are members of an RG may be either
   physically co-located or geo-redundant.  Furthermore, the physical
   interconnect between the PEs over which ICCP is to run may comprise
   either dedicated back-to-back links or a shared connection through
   the packet switched network (PSN), e.g., MPLS core network.  This
   gives rise to a matrix of four interconnect scenarios, as described
   in the following subsections.

3.2.1.  Co-located Dedicated Interconnect

   In this scenario, the PEs within an RG are co-located in the same
   physical location, e.g., point of presence (POP) or central office
   (CO).  Furthermore, dedicated links provide the interconnect for ICCP
   among the PEs.

             +=================+     +-----------------+
             |CO               |     |                 |
             |  +-----+        |     |                 |
             |  | PE1 |________|_____|                 |
             |  |     |        |     |                 |
             |  +-----+        |     |                 |
             |     ||          |     |                 |
             |     || ICCP     |     |       Core      |
             |     ||          |     |      Network    |
             |  +-----+        |     |                 |
             |  | PE2 |________|_____|                 |
             |  |     |        |     |                 |
             |  +-----+        |     |                 |
             |                 |     |                 |
             +=================+     +-----------------+

       Figure 2: ICCP Co-located PEs Dedicated Interconnect Scenario

   Given that the PEs are connected back-to-back in this case, it is
   possible to rely on Layer 2 redundancy mechanisms to guarantee the
   robustness of the ICCP interconnect.  For example, if the





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   interconnect comprises IEEE 802.3 Ethernet links, it is possible to
   provide link redundancy by means of IEEE 802.1AX Link Aggregation
   Groups.

3.2.2.  Co-located Shared Interconnect

   In this scenario, the PEs within an RG are co-located in the same
   physical location (POP, CO).  However, unlike the previous scenario,
   there are no dedicated links between the PEs.  The interconnect for
   ICCP is provided through the core network to which the PEs are
   connected.  Figure 3 depicts this model.

              +=================+     +-----------------+
              |CO               |     |                 |
              |  +-----+        |     |                 |
              |  | PE1 |________|_____|                 |
              |  |     |<=================+             |
              |  +-----+   ICCP |     |  ||             |
              |                 |     |  ||             |
              |                 |     |  ||   Core      |
              |                 |     |  ||  Network    |
              |  +-----+        |     |  ||             |
              |  | PE2 |________|_____|  ||             |
              |  |     |<=================+             |
              |  +-----+        |     |                 |
              |                 |     |                 |
              +=================+     +-----------------+

        Figure 3: ICCP Co-located PEs Shared Interconnect Scenario

   Given that the PEs in the RG are connected over the PSN, PSN Layer
   mechanisms can be leveraged to ensure the resiliency of the
   interconnect against connectivity failures.  For example, it is
   possible to employ RSVP Label Switched Paths (LSPs) with Fast Reroute
   (FRR) and/or end-to-end backup LSPs.

3.2.3.  Geo-redundant Dedicated Interconnect

   In this variation, the PEs within an RG are located in different
   physical locations to provide geographic redundancy.  This may be
   desirable, for example, to protect against natural disasters or the
   like.  A dedicated interconnect is provided to link the PEs.  This is
   a costly option, especially when considering the possibility of
   providing multiple such links for interconnect robustness.  The
   resiliency mechanisms for the interconnect are similar to those
   highlighted in the co-located interconnect counterpart.





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              +=================+     +-----------------+
              |CO 1             |     |                 |
              |  +-----+        |     |                 |
              |  | PE1 |________|_____|                 |
              |  |     |        |     |                 |
              |  +-----+        |     |                 |
              +=====||==========+     |                 |
                    || ICCP           |       Core      |
              +=====||==========+     |      Network    |
              |  +-----+        |     |                 |
              |  | PE2 |________|_____|                 |
              |  |     |        |     |                 |
              |  +-----+        |     |                 |
              |CO 2             |     |                 |
              +=================+     +-----------------+

     Figure 4: ICCP Geo-redundant PEs Dedicated Interconnect Scenario

3.2.4.  Geo-redundant Shared Interconnect

   In this scenario, the PEs of an RG are located in different physical
   locations and the interconnect for ICCP is provided over the PSN
   network to which the PEs are connected.  This interconnect option is
   more likely to be the one used for geo-redundancy, as it is more
   economically appealing compared to the geo-redundant dedicated
   interconnect option.  The resiliency mechanisms that can be employed
   to guarantee the robustness of the ICCP transport are PSN Layer
   mechanisms, as described in Section 3.2.2 above.

              +=================+     +-----------------+
              |CO 1             |     |                 |
              |  +-----+        |     |                 |
              |  | PE1 |________|_____|                 |
              |  |     |<=================+             |
              |  +-----+   ICCP |     |  ||             |
              +=================+     |  ||             |
                                      |  ||   Core      |
              +=================+     |  ||  Network    |
              |  +-----+        |     |  ||             |
              |  | PE2 |________|_____|  ||             |
              |  |     |<=================+             |
              |  +-----+        |     |                 |
              |CO 2             |     |                 |
              +=================+     +-----------------+

       Figure 5: ICCP Geo-redundant PEs Shared Interconnect Scenario





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3.3.  ICCP Requirements

   The requirements for the Inter-Chassis Communication Protocol are as
   follows:

      i. ICCP MUST provide a control channel for communication between
         PEs in a Redundancy Group (RG).  PE nodes may be co-located or
         remote (refer to Section 3.2 above).  Client applications that
         make use of ICCP services MUST only use this channel to
         communicate control information and not data traffic.  As such,
         the protocol SHOULD provide relatively low bandwidth, low
         delay, and highly reliable message transfer.

     ii. ICCP MUST accommodate multiple client applications (e.g.,
         multi-chassis LACP, PW redundancy, SONET APS).  This implies
         that the messages SHOULD be extensible (e.g., TLV-based), and
         the protocol SHOULD provide a robust application registration
         and versioning scheme.

    iii. ICCP MUST provide reliable message transport and in-order
         delivery between nodes in an RG with secure authentication
         mechanisms built into the protocol.  The redundancy
         applications that are clients of ICCP expect reliable message
         transfer and as such will assume that the protocol takes care
         of flow control and retransmissions.  Furthermore, given that
         the applications will rely on ICCP to communicate data used to
         synchronize state machines on disparate nodes, it is critical
         that ICCP guarantees in-order message delivery.  Loss of
         messages or out-of-sequence messages would have adverse effects
         on the operation of the client applications.

     iv. ICCP MUST provide a common mechanism to actively monitor the
         health of PEs in an RG.  This mechanism will be used to detect
         PE node failure (or isolation from the MPLS network in the case
         of shared interconnect) and inform the client applications.
         The applications require that the mechanism trigger failover
         according to the procedures of the redundancy protocol employed
         on the attachment circuit (AC) and PW.  The solution SHOULD
         achieve sub-second detection of loss of remote node
         (~50-150 msec) in order to give the client applications
         (redundancy mechanisms) enough reaction time to achieve
         sub-second service restoration times.









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      v. ICCP SHOULD provide asynchronous event-driven state update,
         independent of periodic messages, for immediate notification of
         client applications' state changes.  In other words, the
         transmission of messages carrying application data SHOULD be
         on-demand rather than timer-based to minimize inter-chassis
         state synchronization delay.

     vi. ICCP MUST accommodate multi-link and multi-hop interconnects
         between nodes.  When the devices within an RG are located in
         different physical locations, the physical interconnect between
         them will comprise a network rather than a link.  As such, ICCP
         MUST accommodate the case where the interconnect involves
         multiple hops.  Furthermore, it is possible to have multiple
         (redundant) paths or interconnects between a given pair of
         devices.  This is true for both the co-located and
         geo-redundant scenarios.  ICCP MUST handle this as well.

    vii. ICCP MUST ensure transport security between devices in an RG.
         This is especially important in the scenario where the members
         of an RG are located in different physical locations and
         connected over a shared network (e.g., PSN).  In particular,
         ICCP MUST NOT accept connections arbitrarily from any device;
         otherwise, the state of client applications might be
         compromised.  Furthermore, even if an ICCP connection request
         appears to come from an eligible device, its source address may
         have been spoofed.  Therefore, some means of preventing source
         address spoofing MUST be in place.

   viii. ICCP MUST allow the operator to statically configure members of
         an RG.  Auto-discovery may be considered in the future.

     ix. ICCP SHOULD allow for flexible RG membership.  It is expected
         that only two nodes in an RG will cover most of the redundancy
         applications for common deployments.  ICCP SHOULD NOT preclude
         supporting more than two nodes in an RG by virtue of design.
         Furthermore, ICCP MUST allow a single node to be a member of
         multiple RGs simultaneously.

4.  ICC LDP Protocol Extension Specification

   To address the requirements identified in the previous section, ICCP
   is modeled to comprise three layers:

     i. Application Layer: This provides the interface to the various
        redundancy applications that make use of the services of ICCP.
        ICCP is concerned with defining common connection management
        procedures and the formats of the messages exchanged at this
        layer; however, beyond that, it does not impose any restrictions



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        on the procedures or state machines of the clients, as these are
        deemed application specific and lie outside the scope of ICCP.
        This guarantees implementation interoperability without placing
        any unnecessary constraints on internal design specifics.

    ii. Inter-Chassis Communication (ICC) Layer: This layer implements
        the common set of services that ICCP offers to the client
        applications.  It handles protocol versioning, RG membership,
        Redundant Object identification, PE node identification, and
        ICCP connection management.

   iii. Transport Layer: This layer provides the actual ICCP message
        transport.  It is responsible for addressing, route resolution,
        flow control, reliable and in-order message delivery,
        connectivity resiliency/redundancy, and, finally, PE node
        failure detection.  The Transport layer may differ, depending on
        the Physical Layer of the interconnect.

4.1.  LDP ICCP Capability Advertisement

   When an RG is enabled on a particular PE, an LDP session to every
   remote PE in that RG MUST be created, if one does not already exist.
   The capability of supporting ICCP MUST then be advertised to all of
   those LDP peers in that RG.  This is achieved by using the methods
   described in [RFC5561] and advertising the "ICCP capability TLV".  If
   an LDP peer supports the dynamic capability advertisement, this can
   be done by sending a new capability message with the S-bit set for
   the "ICCP capability TLV" when the first RG is enabled on the PE.  If
   the peer does not support dynamic capability advertisements, then the
   "ICCP TLV" MUST be included in the LDP initialization procedures in
   the capability parameter [RFC5561].

4.2.  RG Membership Management

   ICCP defines a mechanism that enables PE nodes to manage their RG
   membership.  When a PE is configured to be a member of an RG, it will
   first advertise the ICCP capability to its peers.  Subsequently, the
   PE sends an "RG Connect" message to the peers that have also
   advertised ICCP capability.  The PE then waits for the peers to send
   their own "RG Connect" messages, if they haven't done so already.
   For a given RG, the ICCP connection between two devices is considered
   to be operational only when both devices have sent and received ICCP
   "RG Connect" messages for that RG.

   If a PE that has sent a particular "RG Connect" message doesn't
   receive a corresponding RG Connect (or a Notification message
   rejecting the connection) from a destination, it will remain in a
   state of expecting the corresponding "RG Connect" message (or



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   Notification message).  The RG will not become operational until the
   corresponding "RG Connect" message has been received.  If a PE that
   has sent an "RG Connect" message receives a Notification message
   rejecting the connection, with a NAK TLV (Negative Acknowledgement
   TLV) (Section 6.4.1), it will stop attempting to bring up the ICCP
   connection immediately.

   A device MUST reject an incoming "RG Connect" message if at least one
   of the following conditions is satisfied:

    i. the PE is not a member of the RG;

   ii. the maximum number of simultaneous ICCP connections that the PE
       can handle is exceeded.

   Otherwise, the PE MUST bring up the connection by responding to the
   incoming "RG Connect" message with an appropriate RG Connect.

   A PE sends an "RG Disconnect" message to tear down the ICCP
   connection for a given RG.  This is a unilateral operation and
   doesn't require any acknowledgement from the other PEs.  Note that
   the ICCP connection for an RG MUST be operational before any client
   application can make use of ICCP services in that RG.

4.2.1.  ICCP Connection State Machine

   A PE maintains an ICCP Connection state machine instance for every
   ICCP connection with a remote peer in the RG.  This state machine is
   separate from any Application Connection state machine
   (Section 4.4.2).  The ICCP Connection state machine reacts only to
   "RG Connect", "RG Disconnect", and "RG Notification" messages that do
   not contain any "Application TLVs".  Actions and state transitions in
   the Application Connection state machines have no effect on the ICCP
   Connection state machine.

   The ICCP Connection state machine is defined to have six states, as
   follows:

   - NONEXISTENT: This state is the starting point for the state
     machine.  It indicates that no ICCP connection exists and that
     there's no LDP session established between the PEs.

   - INITIALIZED: This state indicates that an LDP session exists
     between the PEs but LDP ICCP capability information has not yet
     been exchanged between them.






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   - CAPSENT: This state indicates that an LDP session exists between
     the PEs and that the local PE has advertised LDP ICCP capability to
     its peer.

   - CAPREC: This state indicates that an LDP session exists between the
     PEs and that the local PE has both received and advertised LDP ICCP
     capability from/to its peer.

   - CONNECTING: This state indicates that the local PE has initiated an
     ICCP connection to its peer and is awaiting its response.

   - OPERATIONAL: This state indicates that the ICCP connection is
     operational.

   The state transition table and state transition diagram follow.




































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                  ICCP Connection State Transition Table

    STATE         EVENT                                     NEW STATE
   --------------------------------------------------------------------
    NONEXISTENT   LDP session established                   INITIALIZED

    INITIALIZED   Transmit LDP ICCP capability              CAPSENT

                  Receive LDP ICCP capability               CAPREC
                     Action: Transmit LDP ICCP capability

                  LDP session torn down                     NONEXISTENT

    CAPSENT       Receive LDP ICCP capability               CAPREC

                  LDP session torn down                     NONEXISTENT

    CAPREC        Transmit RG Connect message               CONNECTING

                  Receive acceptable RG Connect message     OPERATIONAL
                     Action: Transmit RG Connect message

                  Receive any other ICCP message            CAPREC
                     Action: Transmit NAK TLV in RG
                             Notification message

                  LDP session torn down                     NONEXISTENT

    CONNECTING    Receive acceptable RG Connect message     OPERATIONAL

                  Receive any other ICCP message            CAPREC
                     Action: Transmit NAK TLV in RG
                             Notification message

                  LDP session torn down                     NONEXISTENT

    OPERATIONAL   Receive acceptable RG Disconnect message  CAPREC

                  Transmit RG Disconnect message            CAPREC

                  LDP session torn down                     NONEXISTENT










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                 ICCP Connection State Transition Diagram

                              +------------+
                              |            |
          +------------------>|NONEXISTENT |    LDP session torn down
          |                   |            |<--------------------------+
          |                   +------------+                           |
          |         LDP session  |    ^ LDP session                    |
          |         established  |    | torn down                      |
          |                      V    |                                |
          |                  +-----------+                             |
   LDP    |                  |           |  Tx LDP ICCP                |
   session|                  |INITIALIZED|    capability               |
   torn   |              +---|           |---------------+             |
   down   |  Rx other    |   +-----------+               |             |
          |  ICCP msg/   |Rx LDP ICCP                    |             |
          |   Tx NAK TLV |  capability/                  |             |
          |      +---+   |Tx LDP ICCP capability         |             |
          |      |   |   |                               |             |
          |      V   |   V                               V             |
          |   +-----------+   Rx LDP ICCP         +--------+           |
          +---|           |     capability        |        |           |
              |CAPREC     |<----------------------|CAPSENT |---------->+
          +---|           |-------------------+   |        |           |
          |   +-----------+                   |   +--------+           |
          |       ^    ^                      |                        |
   Tx     |       |    |                      |                        |
   RG     |       |    |Rx RG Disconnect msg  |                        |
   Connect|       |    | or                   |Rx RG Connect msg/      |
   msg    |       |    |Tx RG Disconnect msg  | Tx RG Connect msg      |
          |       |    |                      V                        |
          |       |    |                    +------------+             |
          |       |    +--------------------|            |             |
          |       |                         |OPERATIONAL |------------>+
          |       |                         |            |             |
          |       |Rx other ICCP msg/       +------------+             |
          |       | Tx NAK TLV                    ^                    |
          |       |                               |                    |
          |      +----------+  Rx RG Connect msg  |                    |
          |      |          |---------------------+                    |
          +----->|CONNECTING|                                          |
                 |          |----------------------------------------->+
                 +----------+








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4.3.  Redundant Object Identification

   ICCP offers its client applications a uniform mechanism for
   identifying links, ports, forwarding constructs, and, more generally,
   objects (e.g., interfaces, pseudowires, VLANs) that are being
   protected in a redundant setup.  These are referred to as Redundant
   Objects (ROs).  An example of an RO is a multi-chassis link-
   aggregation group that spans two PEs.  ICCP introduces a 64-bit
   opaque identifier to uniquely identify ROs in an RG.  This
   identifier, referred to as the Redundant Object ID (ROID), MUST match
   between RG members for the protected object in question; this allows
   separate systems in an RG to use a common handle to reference the
   protected entity, irrespective of its nature (e.g., physical or
   virtual) and in a manner that is agnostic to implementation
   specifics.  Client applications that need to synchronize state
   pertaining to a particular RO SHOULD embed the corresponding ROID in
   their TLVs.

4.4.  Application Connection Management

   ICCP provides a common set of procedures by which applications on one
   PE can connect to their counterparts on another PE, for the purpose
   of inter-chassis communication in the context of a given RG.  The
   prerequisite for establishing an Application Connection is to have an
   operational ICCP RG connection between the two endpoints.  It is
   assumed that the association of applications with RGs is known
   a priori, e.g., by means of device configuration.  ICCP then sends an
   "Application Connect TLV" (carried in an "RG Connect" message), on
   behalf of each client application, to each remote PE within the RG.
   The client may piggyback application-specific information in that
   "Connect TLV", which, for example, can be used to negotiate
   parameters or attributes prior to bringing up the actual Application
   Connection.  The procedures for bringing up the Application
   Connection are similar to those of the ICCP connection: an
   Application Connection between two nodes is up only when both nodes
   have sent and received "RG Connect" messages with the proper
   "Application Connect TLVs".  A PE MUST send a Notification message to
   reject an Application Connection request if one of the following
   conditions is encountered:

    i. the application doesn't exist or is not configured for that RG;

   ii. the Application Connection count exceeds the PE's capabilities.








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   When a PE receives such a rejection notification, it MUST stop
   attempting to bring up the Application Connection until it receives a
   new Application Connection request from the remote PE.  This is done
   by responding to the incoming "RG Connect" message (carrying an
   "Application Connect TLV") with an appropriate "RG Connect" message
   (carrying a corresponding "Application Connect TLV").

   When an application is stopped on a device or it is no longer
   associated with an RG, it MUST signal ICCP to trigger sending an
   "Application Disconnect TLV" (in the "RG Disconnect" message).  This
   is a unilateral notification to the other PEs within an RG and as
   such doesn't trigger any response.

4.4.1.  Application Versioning

   During Application Connection setup, a given application on one PE
   can negotiate with its counterpart on a peer PE the proper
   application version to use for communication.  If no common version
   is agreed upon, then the Application Connection is not brought up.
   This is achieved through the following set of rules:

   - If an application receives an "Application Connect TLV" with a
     version number that is higher than its own, it MUST send a
     Notification message with a "NAK TLV" indicating status code
     "Incompatible Protocol Version" and supplying the version that is
     locally supported by the PE.

   - If an application receives an "Application Connect TLV" with a
     version number that is lower than its own, it MAY respond with an
     RG Connect that has an "Application Connect TLV" using the same
     version that was received.  Alternatively, the application MAY
     respond with a Notification message to reject the request using the
     "Incompatible Protocol Version" code and supply the version that is
     supported.  This allows an application to operate in either
     backwards-compatible or incompatible mode.

   - If an application receives an "Application Connect TLV" with a
     version that is equal to its own, then the application MUST honor
     or reject the request based on whether the application is
     configured for the RG in question, and whether or not the
     Application Connection count has been exceeded.










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4.4.2.  Application Connection State Machine

   A PE maintains one Application Connection state machine instance per
   ICCP application for every ICCP connection with a remote PE in the
   RG.  Each application's state machine reacts only to the "RG
   Connect", "RG Disconnect", and "RG Notification" messages that
   contain an "Application TLV" specifying that particular application.

   The Application Connection state machine has six states, as follows:

   - NONEXISTENT: This state indicates that the Application Connection
     does not exist, since there is no ICCP connection between the PEs.

   - RESET: This state indicates that an ICCP connection is operational
     between the PEs but that the Application Connection has not been
     initialized yet or has been resent.

   - CONNSENT: This state indicates that the local PE has requested
     initiation of an Application Connection with its peer but has not
     received a response yet.

   - CONNREC: This state indicates that the local PE has received a
     request to initiate an Application Connection from its peer but has
     not responded yet.

   - CONNECTING: This state indicates that the local PE has transmitted
     to its peer an "Application Connection" message with the A-bit set
     to 1 and is awaiting the peer's response.

   - OPERATIONAL: This state indicates that the Application Connection
     is operational.

   The state transition table and state transition diagram follow.

            ICCP Application Connection State Transition Table

     STATE          EVENT                                  NEW STATE
   -------------------------------------------------------------------
     NONEXISTENT    ICCP connection established            RESET

     RESET          ICCP connection torn down              NONEXISTENT

                    Transmit Application Connect TLV       CONNSENT

                    Receive Application Connect TLV        CONNREC

                    Receive any other Application TLV      RESET
                      Action: Transmit NAK TLV



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     CONNSENT       Receive NAK TLV                        RESET

                    Receive Application Connect TLV        OPERATIONAL
                    with A-bit=1
                      Action: Transmit Application Connect
                      TLV with A-bit=1

                    Receive any other Application TLV      RESET
                      Action: Transmit NAK TLV

                    ICCP connection torn down              NONEXISTENT

     CONNREC        Transmit NAK TLV                       RESET

                    Transmit Application Connect TLV       CONNECTING
                    with A-bit=1

                    Receive Application Connect TLV        CONNREC

                    Receive any Application TLV except     RESET
                    Connect
                      Action: Transmit NAK TLV

                    ICCP connection torn down              NONEXISTENT

     CONNECTING     Receive Application Connect TLV        OPERATIONAL
                    with A-bit=1

                    Receive any other Application TLV      RESET
                      Action: Transmit NAK TLV

                    ICCP connection torn down              NONEXISTENT

     OPERATIONAL    Receive Application Disconnect TLV     RESET

                    Transmit Application Disconnect TLV    RESET

                    ICCP connection torn down              NONEXISTENT













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           ICCP Application Connection State Transition Diagram

                              +------------+
                              |            |
            +---------------->|NONEXISTENT |  ICCP connection torn down
            |                 |            |<--------------------------+
            |                 +------------+                           |
            |     ICCP connection|    ^ ICCP connection                |
            |       established  |    | torn down                      |
            |                    |    |                                |
            |                    V    |          Rx other App TLV/     |
            |                +-----------+<-----+  Tx NAK TLV          |
     ICCP   |    Rx App      |           |      |                      |
     connect|    Connect TLV |   RESET   |------+                      |
     torn   |  +-------------|           |---------------+             |
     down   |  |             +-----------+    Tx App     |             |
            |  |              ^  ^   ^  ^     Connect TLV|             |
            |  |      Tx NAK  |  |   |  |                |             |
            |  |      or      |  |   |  |                |             |
            |  |      Rx non- |  |   |  |                |             |
            |  |      Connect |  |   |  |                |             |
            |  V      TLV/Tx NAK |   |  |Rx NAK TLV      V             |
            | +-----------+   |  |   |  |or       +--------+           |
            +-|           |---+  |   |  +---------|        |           |
              |CONNREC    |      |   |   Rx other |CONNSENT|---------->+
            +-|           |-+    |   |   App TLV/ |        |           |
            | +-----------+ |    |   |     Tx NAK +--------+           |
            |           ^---+    |   |                 |Rx App Connect |
            |        Rx App      |   |                 |TLV (A=1)/     |
            |    Connect TLV     |   |Rx App Disconn   | Tx App        |
            |                    |   |or               | Connect TLV   |
            | Tx App Connect     |   |Tx App Disconn   V (A=1)         |
            | TLV (A=1)          |   |      +------------+             |
            |                    |   +------|            |             |
            |       Rx other App |          |OPERATIONAL |------------>+
            |       TLV/Tx NAK   |          |            |             |
            |             +------+          +------------+             |
            |             |                       ^ Rx App Connect     |
            |    +----------+                     | TLV (A=1)          |
            |    |          |---------------------+                    |
            +--->|CONNECTING|                                          |
                 |          |----------------------------------------->+
                 +----------+








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4.5.  Application Data Transfer

   When an application has information to transfer over ICCP, it
   triggers the transmission of an "Application Data" message.  ICCP
   guarantees in-order and lossless delivery of data.  An application
   may reject a message or a set of one or more TLVs within a message by
   using the Notification message with a "NAK TLV".  Furthermore, an
   application may implement its own ACK mechanism, if deemed required,
   by defining an application-specific TLV to be transported in an
   "Application Data" message.  Note that this document does not define
   a common ACK mechanism for applications.

   It is left up to the application to define the procedures to handle
   the situation where a PE receives a "NAK TLV" in response to a
   transmitted "Application Data" message.  Depending on the specifics
   of the application, it may be favorable to have the PE that sent the
   NAK explicitly request retransmission of data.  On the other hand,
   for certain applications it may be more suitable to have the original
   sender of the "Application Data" message handle retransmissions in
   response to a NAK.  ICCP supports both models.

4.6.  Dedicated Redundancy Group LDP Session

   For certain ICCP applications, it is required that a fairly large
   amount of RG information be exchanged in a very short period of time.
   In order to better distribute the load in a multiple-processor
   system, and to avoid head-of-line blocking to other LDP applications,
   initiating a separate TCP/IP session between the two LDP speakers may
   be required.

   This procedure is OPTIONAL and does not change the operation of LDP
   or ICCP.

   A PE that requires a separate LDP session will advertise a separate
   LDP adjacency with a non-zero label space identifier.  This will
   cause the remote peer to open a separate LDP session for this label
   space.  No labels need to be advertised in this label space, as it is
   only used for one or a set of ICCP RGs.  All relevant LDP and ICCP
   procedures still apply as described in [RFC5036] and this document.

5.  ICCP PE Node Failure / Isolation Detection Mechanism

   ICCP provides its client applications a notification when a remote PE
   that is a member of the RG is no longer reachable.  In the case of a
   dedicated interconnect, this indicates that the remote PE node has
   failed, whereas in the case of a shared interconnect this indicates
   that the remote PE node has either failed or become isolated from the
   MPLS network.  This information is used by the client applications to



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   trigger failover according to the procedures of the redundancy
   protocol employed on the AC and PW.  To that end, ICCP does not
   define its own Keep-Alive mechanism for the purpose of monitoring the
   health of remote PE nodes but rather reuses existing fault detection
   mechanisms.  The following mechanisms may be used by ICCP to detect
   PE node failure:

   - Bidirectional Forwarding Detection (BFD)

     Run a BFD session [RFC5880] between the PEs that are members of a
     given RG, and use that to detect PE node failure.  This assumes
     that resiliency mechanisms are in place to protect connectivity to
     the remote PE nodes, and hence loss of BFD periodic messages from a
     given PE node can only mean that the node itself has failed.

   - IP Reachability Monitoring

     It is possible for a PE to monitor IP-layer connectivity to other
     members of an RG that are participating in IGP/BGP.  When
     connectivity to a given PE is lost, the local PE interprets that to
     mean loss of the remote PE node.  This technique assumes that
     resiliency mechanisms are in place to protect the route to the
     remote PE nodes, and hence loss of IP reachability to a given node
     can only mean that the node itself has failed.

   It is worth noting here that loss of the LDP session with a PE in an
   RG is not a reliable indicator that the remote PE itself is down.  It
   is possible, for example, that the remote PE could encounter a local
   event that would lead to resetting the LDP session, while the PE node
   would remain operational for traffic forwarding purposes.

6.  ICCP Message Formats

   This section defines the messages exchanged at the Application and
   ICC layers.

6.1.  Encoding ICC into LDP Messages

   ICCP requires reliable, in-order, stateful message delivery, as well
   as capability negotiation between PEs.  LDP offers all of these
   features and is already in wide use in the applications that would
   also require the ICCP protocol extensions.  For these reasons, ICCP
   takes advantage of the already-defined LDP protocol infrastructure.

   [RFC5036], Section 3.5 defines a generic LDP message structure.  A
   new set of LDP message types is defined to communicate the ICCP
   information.  LDP message types in the range 0x0700 to 0x070F will be
   used for ICCP.



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   Message types have been allocated by IANA; see Section 12 below for
   details.

6.1.1.  ICC Header

   Every ICCP message comprises an ICC-specific LDP Header followed by
   message data.  The format of the ICC Header 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|   Message Type              |      Message Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Message ID                                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Type = 0x0005 (ICC RG ID)   |           Length=4            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          ICC RG ID                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                                                               +
     |                   Mandatory ICC Parameters                    |
     ~                                                               ~
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                                                               +
     |                   Optional ICC Parameters                     |
     ~                                                               ~
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit

     Unknown message bit.  Upon receipt of an unknown message, if U is
     clear (=0), a notification is returned to the message originator;
     if U is set (=1), the unknown message is silently ignored.
     Subsequent sections that define messages specify a value for the
     U-bit.

   - Message Type

     Identifies the type of the ICCP message.  Must be in the range
     0x0700 to 0x070F.





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   - Message Length

     2-octet integer specifying the total length of this message in
     octets, excluding the "U-bit", "Message Type", and "Length" fields.

   - Message ID

     4-octet value used to identify this message.  Used by the sending
     PE to facilitate identifying "RG Notification" messages that may
     apply to this message.  A PE sending an "RG Notification" message
     in response to this message SHOULD include this Message ID in the
     "NAK TLV" of the "RG Notification" message; see Section 6.4.

   - ICC RG ID TLV

     A TLV of type 0x0005, length 4, containing a 4-octet unsigned
     integer designating the Redundancy Group of which the sending
     device is a member.  RG ID value 0x00000000 is reserved by the
     protocol.

   - Mandatory ICC Parameters

     Variable-length set of required message parameters.  Some messages
     have no required parameters.

     For messages that have required parameters, the required parameters
     MUST appear in the order specified by the individual message
     specifications in the sections that follow.

   - Optional ICC Parameters

     Variable-length set of optional message parameters.  Many messages
     have no optional parameters.

     For messages that have optional parameters, the optional parameters
     may appear in any order.















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6.1.2.  ICC Parameter Encoding

   The generic format of an ICC parameter 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|       Type                |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   TLV(s)                                                      |
     ~                                                               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit

     Unknown TLV bit.  Upon receipt of an unknown TLV, if U is clear
     (=0), a notification MUST be returned to the message originator and
     the entire message MUST be ignored; if U is set (=1), the unknown
     TLV MUST be silently ignored and the rest of the message processed
     as if the unknown TLV did not exist.  Subsequent sections that
     define TLVs specify a value for the U-bit.

   - F-bit

     Forward unknown TLV bit.  This bit applies only when the U-bit is
     set and the LDP message containing the unknown TLV is to be
     forwarded.  If F is clear (=0), the unknown TLV is not forwarded
     with the LDP message; if F is set (=1), the unknown TLV is
     forwarded with the LDP message.  Subsequent sections that define
     TLVs specify a value for the F-bit.  By setting both the U- and
     F-bits, a TLV can be propagated as opaque data through nodes that
     do not recognize the TLV.

   - Type

     14 bits indicating the ICC Parameter type.

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - TLV(s):  A set of 0 or more TLVs.  Contents will vary according to
     the message type.







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6.1.3.  Redundant Object Identifier Encoding

   The Redundant Object Identifier (ROID) is a generic opaque handle
   that uniquely identifies a Redundant Object (e.g., link, bundle,
   VLAN) that is being protected in an RG.  It is encoded 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ROID                             |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where the ROID is an 8-octet field encoded as an unsigned integer.
   The ROID value of 0 is reserved.

   The ROID is carried within application-specific TLVs.

6.2.  RG Connect Message

   The "RG Connect" message is used to establish the ICCP RG connection
   in addition to individual Application Connections between PEs in an
   RG.  An "RG Connect" message with no "Application Connect TLV"
   signals establishment of the ICCP RG connection, whereas an "RG
   Connect" message with a valid "Application Connect TLV" signals the
   establishment of an Application Connection in addition to the ICCP RG
   connection if the latter is not already established.

   An implementation MAY send a dedicated "RG Connect" message to set up
   the ICCP RG connection and a separate "RG Connect" message for each
   client application.  However, all implementations MUST support the
   receipt of an "RG Connect" message that triggers the setup of the
   ICCP RG connection as well as a single Application Connection
   simultaneously.

   A PE sends an "RG Connect" message to declare its membership in a
   Redundancy Group.  One such message should be sent to each PE that is
   a member of the same RG.  The set of PEs to which "RG Connect"
   messages should be transmitted is known via configuration or an auto-
   discovery mechanism that is outside the scope of this specification.
   If a device is a member of multiple RGs, it MUST send separate "RG
   Connect" messages for each RG even if the receiving device(s) happens
   to be the same.







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   The format of the "RG Connect" message is as follows:

     i. ICC Header with Message type = "RG Connect Message" (0x0700)

    ii. ICC Sender Name TLV

   iii. Zero or one "Application Connect TLV"

   The currently defined "Application Connect TLVs" are as follows:

   - PW-RED Connect TLV (Section 7.1.1)

   - mLACP Connect TLV (Section 7.2.1)

   The details of these TLVs are discussed in Section 7.

   The "RG Connect" message can contain zero or one "Application Connect
   TLV".

6.2.1.  ICC Sender Name TLV

   The "ICC Sender Name TLV" carries the hostname of the sender, encoded
   in UTF-8 [RFC3629] format.  This is used primarily for the purpose of
   management of the RG and easing network operations.  The specific
   format is shown below:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|       Type = 0x0001       |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Sender Name                                                  |
     +                                             +-+-+-+-+-+-+-+-+-+
     ~                                             ~
     |      ...                                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U=F=0

   - Type

     Set to 0x0001 (from the ICC parameter name space).

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.




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   - Sender Name

     An administratively assigned name of the sending device, encoded in
     UTF-8 format and limited to a maximum of 80 octets.  This field
     does not include a terminating null character.

6.3.  RG Disconnect Message

   The "RG Disconnect" message serves a dual purpose: to signal that a
   particular Application Connection is being closed within an RG or
   that the ICCP RG connection itself is being disconnected because the
   PE wishes to leave the RG.  The format of this message 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|   Message Type = 0x0701     |      Message Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Message ID                                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Type = 0x0005 (ICC RG ID)   |           Length=4            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     ICC RG ID                                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Disconnect Code TLV                        |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Optional Application Disconnect TLV              |
     ~                                                               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Optional Parameter TLVs                     |
     +                                                               +
     |                                                               |
     ~                                                               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit

     U=0

   - Message Type

     The message type for the "RG Disconnect" message is set to 0x0701.







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   - Length

     Length of the TLV in octets, excluding the "U-bit", "Message Type",
     and "Message Length" fields.

   - Message ID

     Defined in Section 6.1.1 above.

   - ICC RG ID

     Defined in Section 6.1.1 above.

   - Disconnect Code TLV

     The format of this TLV 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |U|F|         Type = 0x0004     |    Length                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      ICCP Status Code                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     - U-bit and F-bit

       Both are set to 0.

     - Type

       Set to "Disconnect Code TLV" (0x0004).

     - Length

       Length of the TLV in octets, excluding the "U-bit", "F-bit",
       "Type", and "Length" fields.

     - ICCP Status Code

       A status code that reflects the reason for the disconnect
       message.  Allowed values are "ICCP RG Removed" and "ICCP
       Application Removed from RG".








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   - Optional Application Disconnect TLV

     Zero or one "Application Disconnect TLV" (defined in Sections 7.1.2
     and 7.2.2).  If the "RG Disconnect" message has a status code of
     "RG Removed", then it MUST NOT contain any "Application Disconnect
     TLVs", as the sending PE is signaling that it has left the RG and
     thus is disconnecting the ICCP RG connection with all associated
     client Application Connections.  If the message has a status code
     of "Application Removed from RG", then it MUST contain exactly one
     "Application Disconnect TLV", as the sending PE is only tearing
     down the connection for the specified application.  Other
     applications, and the ICCP RG connection, are not to be affected.

   - Optional Parameter TLVs

     None are defined for this message in this document.  This is
     specified to allow for future extensions.

6.4.  RG Notification Message

   A PE sends an "RG Notification" message to indicate one of the
   following: to reject an ICCP connection, to reject an Application
   Connection, to reject an entire message, or to reject one or more
   TLVs within a message.  The Notification message MUST only be sent to
   a PE that is already part of an RG.

   The "RG Notification" message MUST only be used to reject messages or
   TLVs corresponding to a single ICCP application.  In other words,
   there is a limit of at most a single ICCP application per "RG
   Notification" message.

   The format of the "RG Notification" message is as follows:

    i. ICC Header with Message type = "RG Notification Message" (0x0702)

   ii. Notification Message TLVs

   The currently defined Notification message TLVs are as follows:

    i. ICC Sender Name TLV

   ii. Negative Acknowledgement (NAK) TLV









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6.4.1.  Notification Message TLVs

   The "ICC Sender Name TLV" uses the same format as the format used in
   the "RG Connect" message and was described above.

   The "NAK TLV" is defined 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|       Type = 0x0002       |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      ICCP Status Code                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Rejected Message ID                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  Optional TLV(s)                              |
     +                                                               +
     |                                                               |
     ~                                                               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to "NAK TLV" (0x0002).

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - ICCP Status Code

     A status code that reflects the reason for the "NAK TLV".  Allowed
     values are as follows:

       i. Unknown ICCP RG (0x00010001)

          This code is used to reject a new incoming ICCP connection for
          an RG that is not configured on the local PE.  When this code
          is used, the "Rejected Message ID" field MUST contain the
          message ID of the rejected "RG Connect" message.





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      ii. ICCP Connection Count Exceeded (0x00010002)

          This is used to reject a new incoming ICCP connection that
          would cause the local PE's ICCP connection count to exceed its
          capabilities.  When this code is used, the "Rejected Message
          ID" field MUST contain the message ID of the rejected "RG
          Connect" message.

     iii. ICCP Application Connection Count Exceeded (0x00010003)

          This is used to reject a new incoming Application Connection
          that would cause the local PE's ICCP connection count to
          exceed its capabilities.  When this code is used, the
          "Rejected Message ID" field MUST contain the message ID of the
          rejected "RG Connect" message and the corresponding
          "Application Connect TLV" MUST be included in the "Optional
          TLV".

      iv. ICCP Application not in RG (0x00010004)

          This is used to reject a new incoming Application Connection
          when the local PE doesn't support the application or the
          application is not configured in the RG.  When this code is
          used, the "Rejected Message ID" field MUST contain the message
          ID of the rejected "RG Connect" message and the corresponding
          "Application Connect TLV" MUST be included in the "Optional
          TLV".

       v. Incompatible ICCP Protocol Version (0x00010005)

          This is used to reject a new incoming Application Connection
          when the local PE has an incompatible version of the
          application.  When this code is used, the "Rejected Message
          ID" field MUST contain the message ID of the rejected "RG
          Connect" message and the corresponding "Application Connect
          TLV" MUST be included in the "Optional TLV".

      vi. ICCP Rejected Message (0x00010006)

          This is used to reject an "RG Application Data" message, or
          one or more TLVs within the message.  When this code is used,
          the "Rejected Message ID" field MUST contain the message ID of
          the rejected "RG Application Data" message.








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     vii. ICCP Administratively Disabled (0x00010007)

          This is used to reject any ICCP messages from a peer from
          which the PE is not allowed to exchange ICCP messages due to
          local administrative policy.

   - Rejected Message ID

     If non-zero, a 4-octet value that identifies the peer message to
     which the "NAK TLV" refers.  If zero, no specific peer message is
     being identified.

   - Optional TLV(s)

     A set of one or more optional TLVs.  If the status code is
     "Rejected Message", then this field contains the TLV or TLVs that
     were rejected.  If the entire message is rejected, all of its TLVs
     MUST be present in this field; otherwise, the subset of TLVs that
     were rejected MUST be echoed in this field.

     If the status code is "Incompatible Protocol Version", then this
     field contains the original "Application Connect TLV" sent by the
     peer, in addition to the "Requested Protocol Version TLV" defined
     below:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |U|F|     Type = 0x0003         |    Length                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Connection Reference        |   Requested Version           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     - U-bit and F-bit

       Both are set to 0.

     - Type

       Set to 0x0003 for "Requested Protocol Version TLV".

     - Length

       Length of the TLV in octets, excluding the "U-bit", "F-bit",
       "Type", and "Length" fields.






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     - Connection Reference

       Set to the "Type" field of the "Application Connect TLV" that was
       rejected because of incompatible version.

     - Requested Version

       The version of the application supported by the transmitting
       device.  For this version of the protocol, it is set to 0x0001.

6.5.  RG Application Data Message

   The "RG Application Data" message is used to transport application
   data between PEs within an RG.  A single message can be used to carry
   data from only one application.  Multiple Application TLVs are
   allowed in a single message, as long as all of these TLVs belong to
   the same application.  The format of the "Application Data" message
   is as follows:

    i. ICC Header with Message type = "RG Application Data Message"
       (0x0703)

   ii. Application-specific TLVs

   The details of these TLVs are discussed in Section 7.  All
   application-specific TLVs in one "RG Application Data" message MUST
   belong to a single application but MAY reference different ROs.

7.  Application TLVs

7.1.  Pseudowire Redundancy (PW-RED) Application TLVs

   This section discusses the "ICCP TLVs" for the Pseudowire Redundancy
   application.

















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7.1.1.  PW-RED Connect TLV

   This TLV is included in the "RG Connect" message to signal the
   establishment of a PW-RED Application Connection.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x0010         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Protocol Version         |A|         Reserved            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Optional Sub-TLVs                        |
     ~                                                               ~
     |                                                               |
     +                                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             ...                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0010 for "PW-RED Connect TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - Protocol Version

     The version of this particular protocol for the purposes of ICCP.
     This is set to 0x0001.

   - A-bit

     Acknowledgement bit.  Set to 1 if the sender has received a "PW-RED
     Connect TLV" from the recipient.  Otherwise, set to 0.

   - Reserved

     Reserved for future use.






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   - Optional Sub-TLVs

     There are no optional sub-TLVs defined for this version of the
     protocol.  This document does not impose any restrictions on the
     length of the sub-TLVs.

7.1.2.  PW-RED Disconnect TLV

   This TLV is used in an "RG Disconnect" message to indicate that the
   connection for the PW-RED application is to be terminated.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x0011         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Optional Sub-TLVs                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0011 for "PW-RED Disconnect TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - Optional Sub-TLVs

     The only optional sub-TLV defined for this version of the protocol
     is the "PW-RED Disconnect Cause TLV" defined in Section 7.1.2.1.















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7.1.2.1.  PW-RED Disconnect Cause TLV

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x0019         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Disconnect Cause String                  |
     ~                                                               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0019 for "PW-RED Disconnect Cause TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - Disconnect Cause String

     Variable-length string specifying the reason for the disconnect,
     encoded in UTF-8 format.  The string does not include a terminating
     null character.  Used for network management.






















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7.1.3.  PW-RED Config TLV

   The "PW-RED Config TLV" is used in the "RG Application Data" message
   and has the following format:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|   Type = 0x0012           |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ROID                             |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      PW Priority              |            Flags              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  Service Name TLV                             |
     ~                                                               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            PW ID TLV or Generalized PW ID TLV                 |
     ~                                                               ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0012 for "PW-RED Config TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - ROID

     As defined in Section 6.1.3.

   - PW Priority

     2 octets.  Pseudowire Priority.  Used to indicate which PW has
     better priority to go into active state.  Numerically lower numbers
     are better priority.  In case of a tie, the PE with the numerically
     lower identifier (i.e., IP Address) has better priority.




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   - Flags

     Valid values are as follows:

       i. Synchronized (0x01)

          Indicates that the sender has concluded transmitting all
          pseudowire configuration for a given service.

      ii. Purge Configuration (0x02)

          Indicates that the pseudowire is no longer configured for
          PW-RED operation.

     iii. Independent Mode (0x04)

          Indicates that the pseudowire is configured for redundancy
          using the Independent Mode of operation, per Section 5.1 of
          [RFC6870].

      iv. Independent Mode with Request Switchover (0x08)

          Indicates that the pseudowire is configured for redundancy
          using the Independent Mode of operation with the use of the
          "Request Switchover" bit, per Section 6.3 of [RFC6870].

       v. Master Mode (0x10)

          Indicates that the pseudowire is configured for redundancy
          using the Master/Slave Mode of operation, with the advertising
          PE acting as Master, per Section 5.2 of [RFC6870].

      vi. Slave Mode (0x20)

          Indicates that the pseudowire is configured for redundancy
          using the Master/Slave Mode of operation, with the advertising
          PE acting as Slave, per Section 5.2 of [RFC6870].

   - Sub-TLVs

     The "PW-RED Config TLV" includes the following two sub-TLVs:

       i. Service Name TLV

      ii. One of the following: PW ID TLV or Generalized PW ID TLV

     The format of the sub-TLVs is defined in Sections 7.1.3.1 through
     7.1.3.3.



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7.1.3.1.  Service Name TLV

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|    Type = 0x0013          |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Service Name                           |
     ~                                                               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0013 for "Service Name TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - Service Name

     The name of the L2VPN service instance, encoded in UTF-8 format and
     up to 80 octets in length.  The string does not include a
     terminating null character.






















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7.1.3.2.  PW ID TLV

   This TLV is used to communicate the configuration of PWs for VPWS.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|    Type = 0x0014          |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Peer ID                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Group ID                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         PW ID                                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0014 for "PW ID TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - Peer ID

     4-octet LDP Router ID of the peer at the far end of the PW.

   - Group ID

     Same as Group ID in [RFC4447], Section 5.2.

   - PW ID

     Same as PW ID in [RFC4447], Section 5.2.











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7.1.3.3.  Generalized PW ID TLV

   This TLV is used to communicate the configuration of PWs for VPLS.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|   Type = 0x0015           |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   AGI Type    |    Length     |      Value                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                    AGI  Value (continued)                     ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   AII Type    |    Length     |      Value                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                   SAII  Value (continued)                     ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   AII Type    |    Length     |      Value                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                   TAII Value (continued)                      ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0015 for "Generalized PW ID TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - AGI, AII, SAII, and TAII

     Defined in [RFC4447], Section 5.3.2.










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7.1.4.  PW-RED State TLV

   The "PW-RED State TLV" is used in the "RG Application Data" message.
   This TLV is used by a device to report its PW status to other members
   in the RG.

   The format of this TLV 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x0016         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ROID                             |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Local PW State                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Remote PW State                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0016 for "PW-RED State TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - ROID

     As defined in Section 6.1.3.

   - Local PW State

     The status of the PW as determined by the sending PE, encoded in
     the same format as the "Status Code" field of the "PW Status TLV"
     defined in [RFC4447] and extended in [RFC6870].







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   - Remote PW State

     The status of the PW as determined by the remote peer of the
     sending PE.  Encoded in the same format as the "Status Code" field
     of the "PW Status TLV" defined in [RFC4447] and extended in
     [RFC6870].

7.1.5.  PW-RED Synchronization Request TLV

   The "PW-RED Synchronization Request TLV" is used in the "RG
   Application Data" message.  This TLV is used by a device to request
   that its peer retransmit configuration or operational state.  The
   following information can be requested:

   - configuration and/or state for one or more pseudowires

   - configuration and/or state for all pseudowires

   - configuration and/or state for all pseudowires in a given service

   The format of the TLV 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x0017         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Request Number           |C|S|    Request Type           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Optional Sub-TLVs                          |
     ~                                                               ~
     |                                                               |
     +                                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             ...                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0017 for "PW-RED Synchronization Request TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.



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   - Request Number

     2 octets.  Unsigned integer uniquely identifying the request.  Used
     to match the request with a response.  The value of 0 is reserved
     for unsolicited synchronization and MUST NOT be used in the "PW-RED
     Synchronization Request TLV".  Given the use of TCP, there are no
     issues associated with the wrap-around of the Request Number.

   - C-bit

     Set to 1 if the request is for configuration data.  Otherwise,
     set to 0.

   - S-bit

     Set to 1 if the request is for running state data.  Otherwise,
     set to 0.

   - Request Type

     14 bits specifying the request type, encoded as follows:

       0x00    Request Data for specified pseudowire(s)
       0x01    Request Data for all pseudowires in specified service(s)
       0x3FFF  Request All Data

   - Optional Sub-TLVs

     A set of zero or more TLVs, as follows:

     If the "Request Type" field is set to 0x00, then this field
     contains one or more "PW ID TLVs" or "Generalized PW ID TLVs".  If
     the "Request Type" field is set to 0x01, then this field contains
     one or more "Service Name TLVs".  If the "Request Type" field is
     set to 0x3FFF, then this field MUST be empty.  This document does
     not impose any restrictions on the length of the sub-TLVs.

7.1.6.  PW-RED Synchronization Data TLV

   The "PW-RED Synchronization Data TLV" is used in the "RG Application
   Data" message.  A pair of these TLVs is used by a device to delimit a
   set of TLVs that are sent in response to a "PW-RED Synchronization
   Request TLV".  The delimiting TLVs signal the start and end of the
   synchronization data and associate the response with its
   corresponding request via the "Request Number" field.






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   The "PW-RED Synchronization Data TLVs" are also used for unsolicited
   advertisements of complete PW-RED configuration and operational state
   data.  In this case, the "Request Number" field MUST be set to 0.

   This TLV has the following format:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|    Type = 0x0018          |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Request Number            |     Flags                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0018 for "PW-RED Synchronization Data TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - Request Number

     2 octets.  Unsigned integer identifying the Request Number from the
     "PW-RED Synchronization Request TLV" that solicited this
     synchronization data response.

   - Flags

     2 octets.  Response flags encoded as follows:

       0x00  Synchronization Data Start
       0x01  Synchronization Data End












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7.2.  Multi-Chassis LACP (mLACP) Application TLVs

   This section discusses the "ICCP TLVs" for Ethernet attachment
   circuit redundancy using the multi-chassis LACP (mLACP) application.

7.2.1.  mLACP Connect TLV

   This TLV is included in the "RG Connect" message to signal the
   establishment of an mLACP Application Connection.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x0030         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Protocol Version         |A|         Reserved            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Optional Sub-TLVs                          |
     ~                                                               ~
     |                                                               |
     +                                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             ...                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0030 for "mLACP Connect TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - Protocol Version

     The version of this particular protocol for the purposes of ICCP.
     This is set to 0x0001.

   - A-bit

     Acknowledgement bit.  Set to 1 if the sender has received an "mLACP
     Connect TLV" from the recipient.  Otherwise, set to 0.





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   - Reserved

     Reserved for future use.

   - Optional Sub-TLVs

     There are no optional sub-TLVs defined for this version of the
     protocol.

7.2.2.  mLACP Disconnect TLV

   This TLV is used in an "RG Disconnect" message to indicate that the
   connection for the mLACP application is to be terminated.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x0031         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Optional Sub-TLVs                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0031 for "mLACP Disconnect TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - Optional Sub-TLVs

     The only optional sub-TLV defined for this version of the protocol
     is the "mLACP Disconnect Cause TLV" defined in Section 7.2.2.1.












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7.2.2.1.  mLACP Disconnect Cause TLV

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x003A         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Disconnect Cause String                  |
     ~                                                               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x003A for "mLACP Disconnect Cause TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - Disconnect Cause String

     Variable-length string specifying the reason for the disconnect.
     Used for network management.























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7.2.3.  mLACP System Config TLV

   The "mLACP System Config TLV" is sent in the "RG Application Data"
   message.  This TLV announces the local node's LACP system parameters
   to the RG peers.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x0032         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         System ID                             |
     +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                               |         System Priority       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Node ID    |
     +-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0032 for "mLACP System Config TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - System ID

     6-octet field encoding the System ID used by LACP, as specified in
     [IEEE-802.1AX], Section 5.3.2.

   - System Priority

     2 octets encoding the LACP System Priority, as defined in
     [IEEE-802.1AX], Section 5.3.2.











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   - Node ID

     1 octet.  LACP Node ID.  Used to ensure that the LACP Port Numbers
     are unique across all devices in an RG.  Valid values are in the
     range 0-7.  Uniqueness of the LACP Port Numbers across RG members
     is ensured by encoding the Port Numbers as follows:

     - Most significant bit always set to 1

     - The next 3 most significant bits set to Node ID

     - Remaining 12 bits freely assigned by the system

7.2.4.  mLACP Aggregator Config TLV

   The "mLACP Aggregator Config TLV" is sent in the "RG Application
   Data" message.  This TLV is used to notify RG peers about the local
   configuration state of an Aggregator.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x0036         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ROID                             |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       Aggregator ID           |    MAC Address                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       Actor Key               |    Member Ports Priority      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Flags     | Agg Name Len  |    Aggregator Name            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
     ~                                                               ~
     |                                        ...                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0036 for "mLACP Aggregator Config TLV".




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   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - ROID

     Defined in Section 6.1.3 above.

   - Aggregator ID

     2 octets.  LACP Aggregator Identifier, as specified in
     [IEEE-802.1AX], Section 5.4.6.

   - MAC Address

     6 octets encoding the Aggregator Media Access Control (MAC)
     address.

   - Actor Key

     2 octets.  LACP Actor Key for the corresponding Aggregator, as
     specified in [IEEE-802.1AX], Section 5.3.5.

   - Member Ports Priority

     2 octets.  LACP administrative port priority associated with all
     interfaces bound to the Aggregator.  This field is valid only when
     the "Flags" field has "Priority Set" asserted.

   - Flags

     Valid values are as follows:

       i. Synchronized (0x01)

          Indicates that the sender has concluded transmitting all
          Aggregator configuration information.

      ii. Purge Configuration (0x02)

          Indicates that the Aggregator is no longer configured for
          mLACP operation.

     iii. Priority Set (0x04)

          Indicates that the "Member Ports Priority" field is valid.




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   - Agg Name Len

     1 octet.  Length of the "Aggregator Name" field in octets.

   - Aggregator Name

     Aggregator name, encoded in UTF-8 format, up to a maximum of
     20 octets.  Used for ease of management.  The string does not
     include a terminating null character.

7.2.5.  mLACP Port Config TLV

   The "mLACP Port Config TLV" is sent in the "RG Application Data"
   message.  This TLV is used to notify RG peers about the local
   configuration state of a port.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x0033         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       Port Number             |    MAC Address                |
     +-------------------------------+                               +
     |                                                               |
     +---------------------------------------------------------------+
     |       Actor Key               |     Port Priority             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Port Speed                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Flags     | Port Name Len |         Port Name             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
     ~                                                               ~
     |                                        ...                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0033 for "mLACP Port Config TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.




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   - Port Number

     2 octets.  LACP Port Number for the corresponding interface, as
     specified in [IEEE-802.1AX], Section 5.3.4.  The Port Number MUST
     be encoded with the Node ID, as discussed above.

   - MAC Address

     6 octets encoding the port MAC address.

   - Actor Key

     2 octets.  LACP Actor Key for the corresponding interface, as
     specified in [IEEE-802.1AX], Section 5.3.5.

   - Port Priority

     2 octets.  LACP administrative port priority for the corresponding
     interface, as specified in [IEEE-802.1AX], Section 5.3.4.  This
     field is valid only when the "Flags" field has "Priority Set"
     asserted.

   - Port Speed

     4-octet integer encoding the port's current bandwidth in units of
     1,000,000 bits per second.  This field corresponds to the
     ifHighSpeed object of the IF-MIB [RFC2863].

   - Flags

     Valid values are as follows:

       i. Synchronized (0x01)

          Indicates that the sender has concluded transmitting all
          member link port configurations for a given Aggregator.

      ii. Purge Configuration (0x02)

          Indicates that the port is no longer configured for mLACP
          operation.

     iii. Priority Set (0x04)

          Indicates that the "Port Priority" field is valid.






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   - Port Name Len

     1 octet.  Length of the "Port Name" field in octets.

   - Port Name

     Corresponds to the ifName object of the IF-MIB [RFC2863].  Encoded
     in UTF-8 format and truncated to 20 octets.  Port Name does not
     include a terminating null character.

7.2.6.  mLACP Port Priority TLV

   The "mLACP Port Priority TLV" is sent in the "RG Application Data"
   message.  This TLV is used by a device to either advertise its
   operational Port Priority to other members in the RG or
   authoritatively request that a particular member of an RG change its
   port priority.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x0034         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          OpCode               |          Port Number          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Aggregator ID         |    Last Port Priority         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Current Port Priority      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0034 for "mLACP Port Priority TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.









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   - OpCode

     2 octets identifying the operational code point for the TLV,
     encoded as follows:

       0x00  Local Priority Change Notification
       0x01  Remote Request for Priority Change

   - Port Number

     2-octet field representing the LACP Port Number, as specified in
     [IEEE-802.1AX], Section 5.3.4.  When the value of this field is 0,
     it denotes all ports bound to the Aggregator specified in the
     "Aggregator ID" field.  When non-zero, the Port Number MUST be
     encoded with the Node ID, as discussed above.

   - Aggregator ID

     2 octets.  LACP Aggregator Identifier, as specified in
     [IEEE-802.1AX], Section 5.4.6.

   - Last Port Priority

     2 octets.  LACP port priority for the corresponding interface, as
     specified in [IEEE-802.1AX], Section 5.3.4.  For local ports, this
     field encodes the previous operational value of port priority.  For
     remote ports, this field encodes the operational port priority last
     known to the PE via notifications received from its peers in the
     RG.

   - Current Port Priority

     2 octets.  LACP port priority for the corresponding interface, as
     specified in [IEEE-802.1AX], Section 5.3.4.  For local ports, this
     field encodes the new operational value of port priority being
     advertised by the PE.  For remote ports, this field specifies the
     new port priority being requested by the PE.














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7.2.7.  mLACP Port State TLV

   The "mLACP Port State TLV" is used in the "RG Application Data"
   message.  This TLV is used by a device to report its LACP port status
   to other members in the RG.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x0035         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Partner System ID                        |
     +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                               |     Partner System Priority   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Partner Port Number       |     Partner Port Priority     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       Partner Key             | Partner State |  Actor State  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Actor Port Number        |           Actor Key           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Selected     |  Port State   |        Aggregator ID          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0035 for "mLACP Port State TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - Partner System ID

     6 octets.  The LACP Partner System ID for the corresponding
     interface, encoded as a MAC address as specified in [IEEE-802.1AX],
     Section 5.4.2.2, item r.

   - Partner System Priority

     2-octet field specifying the LACP Partner System Priority, as
     specified in [IEEE-802.1AX], Section 5.4.2.2, item q.




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   - Partner Port Number

     2 octets encoding the LACP Partner Port Number, as specified in
     [IEEE-802.1AX], Section 5.4.2.2, item u.  The Port Number MUST be
     encoded with the Node ID, as discussed above.

   - Partner Port Priority

     2-octet field encoding the LACP Partner Port Priority, as specified
     in [IEEE-802.1AX], Section 5.4.2.2, item t.

   - Partner Key

     2-octet field representing the LACP Partner Key, as defined in
     [IEEE-802.1AX], Section 5.4.2.2, item s.

   - Partner State

     1-octet field encoding the LACP Partner State Variable, as defined
     in [IEEE-802.1AX], Section 5.4.2.2, item v.

   - Actor State

     1 octet encoding the LACP Actor State Variable for the port, as
     specified in [IEEE-802.1AX], Section 5.4.2.2, item m.

   - Actor Port Number

     2-octet field representing the LACP Actor Port Number, as specified
     in [IEEE-802.1AX], Section 5.3.4.  The Port Number MUST be encoded
     with the Node ID, as discussed above.

   - Actor Key

     2-octet field encoding the LACP Actor Operational Key, as specified
     in [IEEE-802.1AX], Section 5.3.5.

   - Selected

     1 octet encoding the LACP "Selected" variable, defined in
     [IEEE-802.1AX], Section 5.4.8 as follows:

       0x00  SELECTED
       0x01  UNSELECTED
       0x02  STANDBY






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   - Port State

     1 octet encoding the operational state of the port as follows:

       0x00  Up
       0x01  Down
       0x02  Administratively Down
       0x03  Test (e.g., IEEE 802.3ah OAM Intrusive Loopback mode)

   - Aggregator ID

     2 octets.  LACP Aggregator Identifier to which this port is bound
     based on the outcome of the LACP selection logic.

7.2.8.  mLACP Aggregator State TLV

   The "mLACP Aggregator State TLV" is used in the "RG Application Data"
   message.  This TLV is used by a device to report its Aggregator
   status to other members in the RG.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x0037         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Partner System ID                        |
     +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                               |     Partner System Priority   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Partner Key              |         Aggregator ID         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Actor Key                |   Agg State   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0037 for "mLACP Aggregator State TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.





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   - Partner System ID

     6 octets.  The LACP Partner System ID for the corresponding
     interface, encoded as a MAC address as specified in [IEEE-802.1AX],
     Section 5.4.2.2, item r.

   - Partner System Priority

     2-octet field specifying the LACP Partner System Priority, as
     specified in [IEEE-802.1AX], Section 5.4.2.2, item q.

   - Partner Key

     2-octet field representing the LACP Partner Key, as defined in
     [IEEE-802.1AX], Section 5.4.2.2, item s.

   - Aggregator ID

     2 octets.  LACP Aggregator Identifier, as specified in
     [IEEE-802.1AX], Section 5.4.6.

   - Actor Key

     2-octet field encoding the LACP Actor Operational Key, as specified
     in [IEEE-802.1AX], Section 5.3.5.

   - Agg State

     1 octet encoding the operational state of the Aggregator as
     follows:

       0x00  Up
       0x01  Down
       0x02  Administratively Down
       0x03  Test (e.g., IEEE 802.3ah OAM Intrusive Loopback mode)

7.2.9.  mLACP Synchronization Request TLV

   The "mLACP Synchronization Request TLV" is used in the "RG
   Application Data" message.  This TLV is used by a device to request
   that its peer retransmit configuration or operational state.  The
   following information can be requested:

   - system configuration and/or state

   - configuration and/or state for a specific port

   - configuration and/or state for all ports with a specific LACP Key



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   - configuration and/or state for all mLACP ports

   - configuration and/or state for a specific Aggregator

   - configuration and/or state for all Aggregators with a specific LACP
     Key

   - configuration and/or state for all mLACP Aggregators

   The format of the TLV 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x0038         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Request Number           |C|S|    Request Type           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Port Number / Aggregator ID  |             Actor Key         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0038 for "mLACP Synchronization Request TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - Request Number

     2 octets.  Unsigned integer uniquely identifying the request.  Used
     to match the request with a response.  The value of 0 is reserved
     for unsolicited synchronization and MUST NOT be used in the "mLACP
     Synchronization Request TLV".

   - C-bit

     Set to 1 if the request is for configuration data.  Otherwise,
     set to 0.






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   - S-bit

     Set to 1 if the request is for running state data.  Otherwise,
     set to 0.

   - Request Type

     14 bits specifying the request type, encoded as follows:

       0x00    Request System Data
       0x01    Request Aggregator Data
       0x02    Request Port Data
       0x3FFF  Request All Data

   - Port Number / Aggregator ID

     2 octets.  When the "Request Type" field is set to "Request Port
     Data", this field encodes the LACP Port Number for the requested
     port.  When the "Request Type" field is set to "Request Aggregator
     Data", this field encodes the Aggregator ID of the requested
     Aggregator.  When the value of this field is 0, it denotes that
     information for all ports (or Aggregators) whose LACP Key is
     specified in the "Actor Key" field is being requested.

   - Actor Key

     2 octets.  LACP Actor Key for the corresponding port or Aggregator.
     When the value of this field is 0 (and the
     Port Number / Aggregator ID field is 0 as well), it denotes that
     information for all ports or Aggregators in the system is being
     requested.

7.2.10.  mLACP Synchronization Data TLV

   The "mLACP Synchronization Data TLV" is used in the "RG Application
   Data" message.  A pair of these TLVs is used by a device to delimit a
   set of TLVs that are being transmitted in response to an "mLACP
   Synchronization Request TLV".  The delimiting TLVs signal the start
   and end of the synchronization data and associate the response with
   its corresponding request via the "Request Number" field.

   The "mLACP Synchronization Data TLVs" are also used for unsolicited
   advertisements of complete mLACP configuration and operational state
   data.  The "Request Number" field MUST be set to 0 in this case.  For
   such unsolicited synchronization, the PE MUST advertise all system,
   Aggregator, and port information, as done during the initialization
   sequence.




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   This TLV has the following format:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|     Type = 0x0039         |    Length                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Request Number            |     Flags                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit and F-bit

     Both are set to 0.

   - Type

     Set to 0x0039 for "mLACP Synchronization Data TLV".

   - Length

     Length of the TLV in octets, excluding the "U-bit", "F-bit",
     "Type", and "Length" fields.

   - Request Number

     2 octets.  Unsigned integer identifying the Request Number from the
     "mLACP Synchronization Request TLV" that solicited this
     synchronization data response.

   - Flags

     2 octets.  Response flags, encoded as follows:

       0x00  Synchronization Data Start
       0x01  Synchronization Data End
















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8.  LDP Capability Negotiation

   As required in [RFC5561], the following TLV is defined to indicate
   the ICCP capability:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F| TLV Code Point = 0x0700   |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |S| Reserved    |    Reserved   |  Ver/Maj      |  Ver/Min      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   - U-bit

     SHOULD be 1 (ignore if not understood).

   - F-bit

     SHOULD be 0 (don't forward if not understood).

   - TLV Code Point

     The TLV type, which identifies a specific capability.  The ICCP
     code point is listed in Section 12 below.

   - S-bit

     State bit.  Indicates whether the sender is advertising or
     withdrawing the ICCP capability.  The State bit is used as follows:

     1 - The TLV is advertising the capability specified by the TLV Code
         Point.

     0 - The TLV is withdrawing the capability specified by the TLV Code
         Point.

   - Ver/Maj

     The major version revision of ICCP.  This document specifies 1.0,
     and so this field is set to 1.

   - Ver/Min

     The minor version revision of ICCP.  This document specifies 1.0,
     and so this field is set to 0.





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   ICCP capability is advertised to an LDP peer if there is at least one
   RG enabled on the local PE.

9.  Client Applications

9.1.  Pseudowire Redundancy Application Procedures

   This section defines the procedures for the Pseudowire Redundancy
   (PW-RED) application.

   It should be noted that the PW-RED application SHOULD NOT be enabled
   together with an AC redundancy application for the same service
   instance.  This simplifies the operation of the multi-chassis
   redundancy solution (Figure 1) and eliminates the possibility of
   deadlock conditions between the AC and PW redundancy mechanisms.

9.1.1.  Initial Setup

   When an RG is configured on a system and multi-chassis pseudowire
   redundancy is enabled in that RG, the PW-RED application MUST send an
   "RG Connect" message with a "PW-RED Connect TLV" to each PE that is a
   member of the same RG.  The sending PE MUST set the A-bit to 1 if it
   has already received a "PW-RED Connect TLV" from its peer; otherwise,
   the PE MUST set the A-bit to 0.  If a PE that has sent the TLV with
   the A-bit set to 0 receives a "PW-RED Connect TLV" from a peer, it
   MUST repeat its advertisement with the A-bit set to 1.  The PW-RED
   Application Connection is considered to be operational when both PEs
   have sent and received "PW-RED Connect TLVs" with the A-bit set to 1.
   Once the Application Connection becomes operational, the two devices
   can start exchanging "RG Application Data" messages for the PW-RED
   application.

   If a system receives an "RG Connect" message with a "PW-RED Connect
   TLV" that has a different Protocol Version, it must follow the
   procedures outlined in Section 4.4.1 above.

   When the PW-RED application is disabled on the device or is
   unconfigured for the RG in question, the system MUST send an "RG
   Disconnect" message with a "PW-RED Disconnect TLV".

9.1.2.  Pseudowire Configuration Synchronization

   A system MUST advertise its local PW configuration to other PEs that
   are members of the same RG.  This allows the PEs to build a view of
   the redundant nodes and pseudowires that are protecting the same
   service instances.  The advertisement MUST be initiated when the
   PW-RED Application Connection first comes up.  To that end, the
   system sends "RG Application Data" messages with "PW-RED Config TLVs"



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   as part of an unsolicited synchronization.  A PE MUST use a pair of
   "PW-RED Synchronization Data TLVs" to delimit the set of TLVs that
   are being sent as part of this unsolicited advertisement.

   In the case of a configuration change, a PE MUST re-advertise the
   most up-to-date information for the affected pseudowires.

   As part of the configuration synchronization, a PE advertises the
   ROID associated with the pseudowire.  This is used to correlate the
   pseudowires that are protecting each other on different PEs.  A PE
   also advertises the configured PW redundancy mode.  This can be one
   of the following four options: Master Mode, Slave Mode, Independent
   Mode, or Independent Mode with Request Switchover.  If the received
   redundancy mode does not match the locally configured mode for the
   same ROID, then the PE MUST respond with an "RG Notification" message
   to reject the "PW-RED Config TLV".  The PE MUST disable the
   associated local pseudowire until a satisfactory "PW-RED Config TLV"
   is received from the peer.  This guarantees that device
   misconfiguration does not lead to network-wide problems (e.g., by
   creating forwarding loops).  The PE SHOULD also raise an alarm to
   alert the operator.  If a PE receives a "NAK TLV" for an advertised
   "PW-RED Config TLV", it MUST disable the associated pseudowire and
   SHOULD raise an alarm to alert the operator.

   Furthermore, a PE advertises in its "PW-RED Config TLVs" a priority
   value that is used to determine the precedence of a given pseudowire
   to assume the active role in a redundant setup.  A PE also advertises
   a Service Name that is global in the context of an RG and is used to
   identify which pseudowires belong to the same service.  Finally, a PE
   also advertises the pseudowire identifier as part of this
   synchronization.

9.1.3.  Pseudowire Status Synchronization

   PEs that are members of an RG synchronize pseudowire status for the
   purpose of identifying, on a per-ROID basis, which pseudowire will be
   actively used for forwarding and which pseudowire(s) will be placed
   in standby state.

   Synchronization of pseudowire status is done by sending the "PW-RED
   State TLV" whenever the pseudowire state changes on a PE.  This
   includes changes to the local end as well as the remote end of the
   pseudowire.








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   A PE may request that its peer retransmit previously advertised
   PW-RED state.  This is useful, for instance, when the PE is
   recovering from a soft failure.  To request such a retransmission, a
   PE MUST send a set of one or more "PW-RED Synchronization Request
   TLVs".

   A PE MUST respond to a "PW-RED Synchronization Request TLV" by
   sending the requested data in a set of one or more "PW-RED TLVs"
   delimited by a pair of "PW-RED Synchronization Data TLVs".  The TLVs
   comprising the response MUST be ordered such that the
   "Synchronization Response TLV" with the "Synchronization Data Start"
   flag precedes the various other "PW-RED TLVs" encoding the requested
   data.  These, in turn, MUST precede the "Synchronization Data TLV"
   with the "Synchronization Data End" flag.  It is worth noting that
   the response may span multiple "RG Application Data" messages;
   however, the above TLV ordering MUST be retained across messages, and
   only a single pair of "Synchronization Data TLVs" must be used to
   delimit the response across all "Application Data" messages.

   A PE MAY re-advertise its PW-RED state in an unsolicited manner.
   This is done by sending the appropriate Config and State TLVs
   delimited by a pair of "PW-RED Synchronization Data TLVs" and using a
   "Request Number" of 0.

   While a PE has a pending synchronization request for a pseudowire or
   a service, it SHOULD silently ignore all TLVs for said pseudowire or
   service that are received prior to the synchronization response and
   that carry the same type of information being requested.  This saves
   the system from the burden of updating state that will ultimately be
   overwritten by the synchronization response.  Note that TLVs
   pertaining to other pseudowires or services are to continue to be
   processed per normal procedures in the interim.

   If a PE receives a synchronization request for a pseudowire or
   service that doesn't exist or is not known to the PE, then it MUST
   trigger an unsolicited synchronization of all pseudowire information
   (i.e., replay the initialization sequence).

   In the subsections that follow, we describe the details of pseudowire
   status synchronization for each of the PW redundancy modes defined in
   [RFC6870].










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9.1.3.1.  Independent Mode

   This section covers the operation in Independent Mode with or without
   Request Switchover capability.

   In this mode, the operator must ensure that for a given RO the PW
   Priority values configured for all associated pseudowires on a given
   PE are collectively higher (or lower) than those configured on other
   PEs in the same RG.  If this condition is not satisfied after the PEs
   have exchanged "PW-RED State TLVs", a PE MUST disable the associated
   pseudowire(s) and SHOULD raise an alarm to alert the operator.  Note
   that the PW Priority MAY be the same as the PW Precedence as defined
   in [RFC6870].

   For a given RO, after all of the PEs in an RG have exchanged their
   "PW-RED State TLVs", the PE with the best PW Priority (i.e., least
   numeric value) advertises active Preferential Forwarding status in
   LDP on all of its associated pseudowires, whereas all other PEs in
   the RG advertise standby Preferential Forwarding status in LDP on
   their associated pseudowires.

   If the service is VPWS, then only a single pseudowire per service
   will be selected for forwarding.  This is the pseudowire that is
   independently advertised with active Preferential Forwarding status
   on both endpoints, as described in [RFC6870].

   If the service is VPLS, then one or multiple pseudowires per service
   will be selected for forwarding.  These are the pseudowires that are
   independently advertised with active Preferential Forwarding status
   on both PW endpoints, as described in [RFC6870].

9.1.3.2.  Master/Slave Mode

   In this mode, the operator must ensure that for a given RO the PW
   Priority values configured for all associated pseudowires on a given
   PE are collectively higher (or lower) than those configured on other
   PEs in the same RG.  If this condition is not satisfied after the PEs
   have exchanged "PW-RED State TLVs", a PE MUST disable the associated
   pseudowire(s) and SHOULD raise an alarm to alert the operator.  Note
   that the PW Priority MAY be the same as the PW Precedence as defined
   in [RFC6870].  In addition, the operator must ensure that for a given
   RO all of the PEs in the RG are consistently configured as Master or
   Slave.

   In the context of a given RO, if the PEs in the RG are acting as
   Master, then the PE with the best PW Priority (i.e., least numeric
   value) advertises active Preferential Forwarding status in LDP on




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   only a single pseudowire, following the procedures in Sections 5.2
   and 6.2 of [RFC6870], whereas all of the other pseudowires on other
   PEs in the RG are advertised with standby Preferential Forwarding
   status in LDP.

9.1.4.  PE Node Failure or Isolation

   When a PE node detects that a remote PE that is a member of the same
   RG is no longer reachable (using the mechanisms described in
   Section 5), the local PE determines if it has redundant PWs for the
   affected services.  If the local PE has the highest priority (after
   the failed PE), then it becomes the active node for the services in
   question and subsequently activates its associated PW(s).

9.2.  Attachment Circuit Redundancy Application Procedures

9.2.1.  Common AC Procedures

   This section describes generic procedures for AC redundancy
   applications, independent of the type of the AC (ATM, FR, or
   Ethernet).

9.2.1.1.  AC Failure

   When the AC redundancy mechanism on the active PE detects a failure
   of the AC, it should send an ICCP "Application Data" message to
   inform the redundant PEs of the need to take over.  The AC failures
   can be categorized into the following scenarios:

   - Failure of CE interface connecting to PE

   - Failure of CE uplink to PE

   - Failure of PE interface connecting to CE

9.2.1.2.  Remote PE Node Failure or Isolation

   When a PE node detects that a remote PE that is a member of the same
   RG is no longer reachable (using the mechanisms described in
   Section 5), the local PE determines if it has redundant ACs for the
   affected services.  If the local PE has the highest priority (after
   the failed PE), then it becomes the active node for the services in
   question and subsequently activates its associated ACs.








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9.2.1.3.  Local PE Isolation

   When a PE node detects that it has been isolated from the core
   network (i.e., all core-facing interfaces/links are not operational),
   then it should ensure that its AC redundancy mechanism will change
   the status of any active ACs to standby.  The AC redundancy
   application SHOULD then send ICCP "Application Data" messages in
   order to trigger failover to a standby PE.  Note that this works only
   in the case of dedicated interconnect (Sections 3.2.1 and 3.2.3),
   since ICCP will still have a path to the peer, even though the PE is
   isolated from the MPLS core network.

9.2.1.4.  Determining Pseudowire State

   If the PEs in an RG are running an AC redundancy application over
   ICCP, then the Independent Mode of PW redundancy, as defined in
   [RFC6870], MUST be used.  On a given PE, the Preferential Forwarding
   status of the PW (active or standby) is derived from the state of the
   associated AC(s).  This simplifies the operation of the multi-chassis
   redundancy solution (Figure 1) and eliminates the possibility of
   deadlock conditions between the AC and PW redundancy mechanisms.  The
   rules by which the PW status is derived from the AC status are as
   follows:

   - VPWS

     For VPWS, there's a single AC per service instance.  If the AC is
     active, then the PW status should be active.  If the AC is standby,
     then the PW status should be standby.

   - VPLS

     For VPLS, there could be multiple ACs per service instance (i.e.,
     Virtual Switch Instance (VSI) [RFC4026]).  If AT LEAST ONE AC is
     active, then the PW status should be active.  If ALL ACs are
     standby, then the PW status should be standby.

   In this case, the PW-RED application is not used to synchronize PW
   status between PEs.  Rather, the AC redundancy application should
   synchronize AC status between PEs, in order to establish which AC
   (and subsequently which PE) is active or standby for a given service.
   When that is determined, each PE will then derive its local PW's
   state according to the rules described above.  The Preferential
   Forwarding status bit, described in [RFC6870], is used to advertise
   PW status to the remote peers.






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9.2.2.  Multi-Chassis LACP (mLACP) Application Procedures

   This section defines the procedures that are specific to the
   multi-chassis LACP (mLACP) application, which is applicable for
   Ethernet ACs.

9.2.2.1.  Initial Setup

   When an RG is configured on a system and mLACP is enabled in that RG,
   the mLACP application MUST send an "RG Connect" message with an
   "mLACP Connect TLV" to each PE that is a member of the same RG.  The
   sending PE MUST set the A-bit to 1 in said TLV if it has received a
   corresponding "mLACP Connect TLV" from its peer PE; otherwise, the
   sending PE MUST set the A-bit to 0.  If a PE receives an "mLACP
   Connect TLV" from its peer after sending said TLV with the A-bit set
   to 0, it MUST resend the TLV with the A-bit set to 1.  A system
   considers the mLACP Application Connection to be operational when it
   has sent and received "mLACP Connect TLVs" with the A-bit set to 1.
   When the mLACP Application Connection between a pair of PEs is
   operational, the two devices can start exchanging "RG Application
   Data" messages for the mLACP application.  This involves having each
   PE advertise its mLACP configuration and operational state in an
   unsolicited manner.  A PE SHOULD use the following sequence when
   advertising its mLACP state upon initial Application Connection
   setup:

   - Advertise system configuration

   - Advertise Aggregator configuration

   - Advertise port configuration

   - Advertise Aggregator state

   - Advertise port state

   A PE MUST use a pair of "mLACP Synchronization Data TLVs" to delimit
   the entire set of TLVs that are being sent as part of this
   unsolicited advertisement.

   If a system receives an "RG Connect" message with an "mLACP Connect
   TLV" that has a different Protocol Version, it MUST follow the
   procedures outlined in Section 4.4.1 above.








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   After the mLACP Application Connection has been established, every PE
   MUST communicate its system-level configuration to its peers via the
   use of the "mLACP System Config TLV".  This allows every PE to
   discover the Node ID and the locally configured System ID and System
   Priority values of its peers.

   If a PE receives an "mLACP System Config TLV" from a remote peer
   advertising the same Node ID value as the local system, then the PE
   MUST respond with an "RG Notification" message to reject the "mLACP
   System Config TLV".  The PE MUST suspend the mLACP application until
   a satisfactory "mLACP System Config TLV" is received from the peer.
   It SHOULD also raise an alarm to alert the operator.  Furthermore, if
   a PE receives a "NAK TLV" for an "mLACP System Config TLV" that it
   has advertised, the PE MUST suspend the mLACP application and SHOULD
   raise an alarm to alert the network operator of potential device
   misconfiguration.

   If a PE receives an "mLACP System Config TLV" from a new peer
   advertising the same Node ID value as another existing peer with
   which the local system has an established mLACP Application
   Connection, then the PE MUST respond to the new peer with an "RG
   Notification" message to reject the "mLACP System Config TLV" and
   MUST ignore the offending TLV.

   If the Node ID of a particular PE changes due to administrative
   configuration action, the PE MUST then inform its peers to purge the
   configuration of all previously advertised ports and/or Aggregators
   and MUST replay the initialization sequence by sending an unsolicited
   synchronization of the system configuration, Aggregator
   configuration, port configuration, Aggregator state, and port state.

   It is necessary for all PEs in an RG to agree upon the System ID and
   System Priority values to be used ubiquitously.  To achieve this,
   every PE MUST use the values for the two parameters that are supplied
   by the PE with the numerically lowest value (among RG members) of
   System Aggregation Priority.  This guarantees that the PEs always
   agree on uniform values that yield the highest System Priority.

   When the mLACP application is disabled on the device or is
   unconfigured for the RG in question, the system MUST send an "RG
   Disconnect" message with an "mLACP Disconnect TLV".










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9.2.2.2.  mLACP Aggregator and Port Configuration

   A system MUST synchronize the configuration of its mLACP-enabled
   Aggregators and ports with other RG members.  This is achieved via
   the use of "mLACP Aggregator Config TLVs" and "mLACP Port Config
   TLVs", respectively.  An implementation MUST advertise the
   configuration of Aggregators prior to advertising the configuration
   of any of their associated member ports.

   The PEs in an RG MUST all agree on the MAC address to be associated
   with a given Aggregator.  It is possible to achieve this via
   consistent configuration on member PEs.  However, in order to protect
   against possible misconfiguration, a system MUST use, for any given
   Aggregator, the MAC address supplied by the PE with the numerically
   lowest System Aggregation Priority in the RG.

   A system that receives an "mLACP Aggregator Config TLV" with an ROID-
   to-Key association that is different from its local association MUST
   reject the corresponding TLV and disable the Aggregator with the same
   ROID.  Furthermore, it SHOULD raise an alarm to alert the operator.
   Similarly, a system that receives a "NAK TLV" in response to a
   transmitted "mLACP Aggregator Config TLV" MUST disable the associated
   Aggregator and SHOULD raise an alarm to alert the network operator.

   A system MAY enforce a restriction that all ports that are to be
   bundled together on a given PE share the same Port Priority value.
   If so, the system MUST advertise this common priority in the "mLACP
   Aggregator Config TLV" and assert the "Priority Set" flag in that
   TLV.  Furthermore, the system in this case MUST NOT advertise
   individual Port Priority values in the associated "mLACP Port Config
   TLVs" (i.e., the "Priority Set" flag in these TLVs should be 0).

   A system MAY support individual Port Priority values to be configured
   on ports that are to be bundled together on a PE.  If so, the system
   MUST advertise the individual Port Priority values in the appropriate
   "mLACP Port Config TLVs" and MUST NOT assert the "Priority Set" flag
   in the corresponding "mLACP Aggregator Config TLV".

   When the configurations of all ports for member links associated with
   a given Aggregator have been sent by a device, it asserts that fact
   by setting the "Synchronized" flag in the last port's "mLACP Port
   Config TLV".  If an Aggregator doesn't have any candidate member
   ports configured, this is indicated by asserting the "Synchronized"
   flag in its "mLACP Aggregator Config TLV".

   Furthermore, for a given port/Aggregator, an implementation MUST
   advertise the port/Aggregator configuration prior to advertising its
   state (via the "mLACP Port State TLV" or "mLACP Aggregator State



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   TLV").  If a PE receives an "mLACP Port State TLV" or "mLACP
   Aggregator State TLV" for a port or Aggregator that it had not
   previously learned via an appropriate "Port Config TLV" or
   "Aggregator Config TLV", then the PE MUST request synchronization of
   the configuration and state of all mLACP ports as well as all mLACP
   Aggregators from its respective peer.  During a synchronization
   (solicited or unsolicited), if a PE receives a "State TLV" for a port
   or Aggregator that it has not learned before, then the PE MUST send a
   "NAK TLV" for the offending TLV.  The PE MUST NOT request
   resynchronization in this case.

   When mLACP is unconfigured on a port/Aggregator, a PE MUST send a
   "Port/Aggregator Config TLV" with the "Purge Configuration" flag
   asserted.  This allows receiving PEs to purge any state maintained
   for the decommissioned port/Aggregator.  If a PE receives a
   "Port/Aggregator Config TLV" with the "Purge Configuration" flag
   asserted and the PE is not maintaining any state for that
   port/Aggregator, then it MUST silently discard the TLV.

9.2.2.3.  mLACP Aggregator and Port Status Synchronization

   PEs within an RG need to synchronize their state machines for proper
   mLACP operation with a multi-homed device.  This is achieved by
   having each system advertise its Aggregators and ports running state
   in "mLACP Aggregator State TLVs" and "mLACP Port State TLVs",
   respectively.  Whenever any LACP parameter for an Aggregator or a
   port -- whether on the Partner (i.e., multi-homed device) side or the
   Actor (i.e., PE) side -- is changed, a system MUST transmit an
   updated TLV for the affected Aggregator and/or port.  Moreover, when
   the administrative or operational state of an Aggregator or port
   changes, the system MUST transmit an updated Aggregator or Port State
   TLV to its peers.

   If a PE receives an Aggregator or Port State TLV where the Actor Key
   doesn't match what was previously received in a corresponding
   "Aggregator Config TLV" or "Port Config TLV", the PE MUST then
   request synchronization of the configuration and state of the
   affected Aggregator or port.  If such a mismatch occurs between the
   Config and State TLVs as part of a synchronization (solicited or
   unsolicited), then the PE MUST send a "NAK TLV" for the "State TLV".
   Furthermore, if a PE receives a "Port State TLV" with the "Aggregator
   ID" set to a value that doesn't map to some Aggregator that the PE
   had learned via a previous "Aggregator Config TLV", then the PE MUST
   request synchronization of the configuration and state of all
   Aggregators and ports.  If the above anomaly occurs during a
   synchronization, then the PE MUST send a "NAK TLV" for the offending
   "Port State TLV".




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   A PE MAY request that its peer retransmit previously advertised
   state.  This is useful, for example, when the PE is recovering from a
   soft failure and attempting to relearn state.  To request such
   retransmissions, a PE MUST send a set of one or more "mLACP
   Synchronization Request TLVs".

   A PE MUST respond to an "mLACP Synchronization Request TLV" by
   sending the requested data in a set of one or more mLACP TLVs
   delimited by a pair of "mLACP Synchronization Data TLVs".  The TLVs
   comprising the response MUST be ordered in the "RG Application Data"
   message(s) such that the "Synchronization Response TLV" with the
   "Synchronization Data Start" flag precedes the various other mLACP
   TLVs encoding the requested data.  These, in turn, MUST precede the
   "Synchronization Data TLV" with the "Synchronization Data End" flag.
   Note that the response may span multiple "RG Application Data"
   messages -- for example, when MTU limits are exceeded; however, the
   above ordering MUST be retained across messages, and only a single
   pair of "Synchronization Data TLVs" MUST be used to delimit the
   response across all "Application Data" messages.

   A PE device MAY re-advertise its mLACP state in an unsolicited
   manner.  This is done by sending the appropriate Config and State
   TLVs delimited by a pair of "mLACP Synchronization Data TLVs" and
   using a "Request Number" of 0.

   While a PE has a pending synchronization request for a system,
   Aggregator, or port, it SHOULD silently ignore all TLVs for said
   system, Aggregator, or port that are received prior to the
   synchronization response and that carry the same type of information
   being requested.  This saves the system from the burden of updating
   state that will ultimately be overwritten by the synchronization
   response.  Note that TLVs pertaining to other systems, Aggregators,
   or ports are to continue to be processed per normal procedures in
   this case.

   If a PE receives a synchronization request for an Aggregator, port,
   or key that doesn't exist or is not known to the PE, then it MUST
   trigger an unsolicited synchronization of all system, Aggregator, and
   port information (i.e., replay the initialization sequence).

   If a PE learns, as part of a synchronization operation from its peer,
   that the latter is advertising a Node ID value that is different from
   the value previously advertised, then the PE MUST purge all
   Port/Aggregator data previously learned from that peer prior to the
   last synchronization.






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9.2.2.4.  Failure and Recovery

   When a PE that is active for a multi-chassis link aggregation group
   encounters a core isolation fault, it SHOULD attempt to fail over to
   a peer PE that hosts the same RO.  The default failover procedure is
   to have the failed PE bring down the link or links towards the
   multi-homed CE (e.g., by bringing down the line protocol).  This will
   cause the CE to fail over to the other member link or links of the
   bundle that are connected to the other PE(s) in the RG.  Other
   procedures for triggering failover are possible; such procedures are
   outside the scope of this document.

   Upon recovery from a previous fault, a PE MAY reclaim the active role
   for a multi-chassis link aggregation group if configured for
   revertive protection.  Otherwise, the recovering PE may assume the
   standby role when configured for non-revertive protection.  In the
   revertive scenario, a PE SHOULD assume the active role within the RG
   by sending an "mLACP Port Priority TLV" to the currently active PE,
   requesting that the latter change its port priority to a value that
   is lower (i.e., numerically larger) for the Aggregator in question.

   If a system is operating in a mode where different ports of a bundle
   are configured with different Port Priorities, then the system MUST
   NOT advertise or request changes of Port Priority values for
   aggregated ports collectively (i.e., by using a "Port Number" of 0 in
   the "mLACP Port Priority TLV").  This is to avoid ambiguity in the
   interpretation of the "Last Port Priority" field.

   If a PE receives an "mLACP Port Priority TLV" requesting a priority
   change for a port or Aggregator that is not local to the device, then
   the PE MUST re-advertise the local configuration of the system, as
   well as the configuration and state of all of its mLACP ports and
   Aggregators.

   If a PE receives an "mLACP Port Priority TLV" in which the remote
   system is advertising priority change for a port or Aggregator that
   the local PE had not previously learned via an appropriate "Port
   Config TLV" or "Aggregator Config TLV", then the PE MUST request
   synchronization of the configuration and state of all mLACP ports as
   well as all mLACP Aggregators from its respective peer.











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10.  Security Considerations

   ICCP SHOULD only be used in well-managed and highly monitored
   networks.  It ought not be deployed on or over the public Internet.
   ICCP is not intended to be applicable when the Redundancy Group spans
   PEs in different administrative domains.

   The security considerations described in [RFC5036] and [RFC4447] that
   apply to the base LDP specification and to the PW LDP control
   protocol extensions apply to the capability mechanism described in
   this document.  In particular, ICCP implementations MUST provide a
   mechanism to select to which LDP peers the ICCP capability will be
   advertised, and from which LDP peers the ICCP messages will be
   accepted.  Therefore, an incoming ICCP connection request MUST NOT be
   accepted unless its source IP address is known to be the source of an
   "eligible" ICCP peer.  The set of eligible peers could be
   preconfigured (as a list of either IP addresses or address/mask
   combinations), or it could be discovered dynamically via some secure
   discovery protocol.  The TCP Authentication Option (TCP-AO), as
   defined in [RFC5925], SHOULD be used.  This provides integrity and
   authentication for the ICCP messages and eliminates the possibility
   of source address spoofing.  However, for backwards compatibility
   and/or to accommodate the ease of migration, the LDP MD5
   authentication key option, as described in Section 2.9 of [RFC5036],
   MAY be used instead.

   The security framework and considerations for MPLS in general, and
   LDP in particular, as described in [RFC5920] apply to this document.
   Moreover, the recommendations of [RFC6952] and mechanisms of
   [LDP-CRYPTO] aimed at addressing LDP's vulnerabilities are applicable
   as well.

   Furthermore, activity on the attachment circuits may cause security
   threats or be exploited to create denial-of-service attacks.  For
   example, a malicious CE implementation may trigger continuously
   varying LACP messages that lead to excessive ICCP exchanges.  Also,
   excessive link bouncing of the attachment circuits may lead to the
   same effect.  Similar arguments apply to the inter-PE MPLS links.
   Implementations SHOULD provide mechanisms to perform control-plane
   policing and mitigate these types of attacks.











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11.  Manageability Considerations

   Implementations SHOULD generally minimize the number of parameters
   required to configure ICCP in order to help make ICCP easier to use.
   Implementations SHOULD allow the user to control the RGID via
   configuration, as this is required to support flexible grouping of
   PEs in RGs.  Furthermore, implementations SHOULD provide mechanisms
   to troubleshoot the correct operation of ICCP; this includes
   providing mechanisms to diagnose ICCP connections as well as
   Application Connections.  Implementations MUST provide a means for
   the user to indicate the IP addresses of remote PEs that are to be
   members of a given RG.  Automatic discovery of RG membership MAY be
   supported; this topic is outside the scope of this specification.

12.  IANA Considerations

12.1.  Message Type Name Space

   This document uses several new LDP message types.  IANA maintains the
   "Message Type Name Space" registry as defined by [RFC5036].  The
   following values have been assigned:

        Message Type    Description
        -------------   ----------------------------
        0x0700          RG Connect Message
        0x0701          RG Disconnect Message
        0x0702          RG Notification Message
        0x0703          RG Application Data Message
        0x0704-0x070F   Reserved for future ICCP use

12.2.  TLV Type Name Space

   This document uses a new LDP TLV type.  IANA maintains the "TLV Type
   Name Space" registry as defined by [RFC5036].  The following value
   has been assigned:

        TLV Type      Description
        --------      -------------------
        0x0700        ICCP capability TLV












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12.3.  ICC RG Parameter Type Space

   IANA has created a registry called "ICC RG Parameter Types", within
   the "Pseudowire Name Spaces (PWE3)" registry.  ICC RG parameter types
   are 14-bit values.  Parameter Type values 1 through 0x003A are
   specified in this document.  Parameter Type values 0x003B through
   0x1FFF are to be assigned by IANA, using the "Expert Review" policy
   defined in [RFC5226].  Parameter Type values 0x2000 through 0x2FFF,
   0x3FFF, and 0 are to be allocated using the "IETF Review" policy
   defined in [RFC5226].  Parameter Type values 0x3000 through 0x3FFE
   are reserved for vendor proprietary extensions and are to be assigned
   by IANA, using the "First Come First Served" policy defined in
   [RFC5226].

   Initial ICC parameter type space value allocations are specified
   below:

      Parameter Type   Description
      --------------   ----------------------------------
      0x0001           ICC Sender Name
      0x0002           NAK TLV
      0x0003           Requested Protocol Version TLV
      0x0004           Disconnect Code TLV
      0x0005           ICC RG ID TLV
      0x0006-0x000F    Reserved
      0x0010           PW-RED Connect TLV
      0x0011           PW-RED Disconnect TLV
      0x0012           PW-RED Config TLV
      0x0013           Service Name TLV
      0x0014           PW ID TLV
      0x0015           Generalized PW ID TLV
      0x0016           PW-RED State TLV
      0x0017           PW-RED Synchronization Request TLV
      0x0018           PW-RED Synchronization Data TLV
      0x0019           PW-RED Disconnect Cause TLV
      0x001A-0x002F    Reserved
      0x0030           mLACP Connect TLV
      0x0031           mLACP Disconnect TLV
      0x0032           mLACP System Config TLV
      0x0033           mLACP Port Config TLV
      0x0034           mLACP Port Priority TLV
      0x0035           mLACP Port State TLV
      0x0036           mLACP Aggregator Config TLV
      0x0037           mLACP Aggregator State TLV
      0x0038           mLACP Synchronization Request TLV
      0x0039           mLACP Synchronization Data TLV
      0x003A           mLACP Disconnect Cause TLV




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12.4.  Status Code Name Space

   This document uses several new Status codes.  IANA maintains the
   "Status Code Name Space" registry as defined by [RFC5036].  The
   following values have been assigned; the "E" column is the required
   setting of the Status Code E-bit.

     Range/Value     E     Description
     ------------  -----   ------------------------------------------
     0x00010001      0     Unknown ICCP RG
     0x00010002      0     ICCP Connection Count Exceeded
     0x00010003      0     ICCP Application Connection Count Exceeded
     0x00010004      0     ICCP Application not in RG
     0x00010005      0     Incompatible ICCP Protocol Version
     0x00010006      0     ICCP Rejected Message
     0x00010007      0     ICCP Administratively Disabled
     0x00010010      0     ICCP RG Removed
     0x00010011      0     ICCP Application Removed from RG

13.  Acknowledgments

   The authors wish to acknowledge the important contributions of Dennis
   Cai, Neil McGill, Amir Maleki, Dan Biagini, Robert Leger, Sami
   Boutros, Neil Ketley, and Mark Christopher Sains.

   The authors also thank Daniel Cohn, Lizhong Jin, and Ran Chen for
   their valuable input, discussions, and comments.

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.

   [RFC5036]  Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
              "LDP Specification", RFC 5036, October 2007.

   [RFC5561]  Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.
              Le Roux, "LDP Capabilities", RFC 5561, July 2009.

   [RFC4447]  Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and
              G. Heron, "Pseudowire Setup and Maintenance Using the
              Label Distribution Protocol (LDP)", RFC 4447, April 2006.







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   [IEEE-802.1AX]
              IEEE Std. 802.1AX-2008, "IEEE Standard for Local and
              metropolitan area networks--Link Aggregation", IEEE
              Computer Society, November 2008.

   [RFC2863]  McCloghrie, K. and F. Kastenholz, "The Interfaces Group
              MIB", RFC 2863, June 2000.

   [RFC6870]  Muley, P., Ed., and M. Aissaoui, Ed., "Pseudowire
              Preferential Forwarding Status Bit", RFC 6870,
              February 2013.

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

   [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP, and MSDP Issues According to the Keying
              and Authentication for Routing Protocols (KARP) Design
              Guide", RFC 6952, May 2013.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, June 2010.

14.2.  Informative References

   [RFC2922]  Bierman, A. and K. Jones, "Physical Topology MIB",
              RFC 2922, September 2000.

   [RFC4026]  Andersson, L. and T. Madsen, "Provider Provisioned Virtual
              Private Network (VPN) Terminology", RFC 4026, March 2005.

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

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of
              ISO 10646", STD 63, RFC 3629, November 2003.

   [LDP-CRYPTO]
              Zheng, L., Chen, M., and M. Bhatia, "LDP Hello
              Cryptographic Authentication", Work in Progress,
              June 2014.






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Authors' Addresses

   Luca Martini
   Cisco Systems, Inc.
   9155 East Nichols Avenue, Suite 400
   Englewood, CO  80112
   United States
   EMail: lmartini@cisco.com


   Samer Salam
   Cisco Systems, Inc.
   595 Burrard Street, Suite 2123
   Vancouver, BC V7X 1J1
   Canada
   EMail: ssalam@cisco.com


   Ali Sajassi
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA  95134
   United States
   EMail: sajassi@cisco.com


   Matthew Bocci
   Alcatel-Lucent
   Voyager Place
   Shoppenhangers Road
   Maidenhead
   Berks, SL6 2PJ
   UK
   EMail: matthew.bocci@alcatel-lucent.com


   Satoru Matsushima
   Softbank Telecom
   1-9-1, Higashi-Shinbashi, Minato-ku
   Tokyo  105-7304
   Japan
   EMail: satoru.matsushima@g.softbank.co.jp


   Thomas Nadeau
   Brocade
   EMail: tnadeau@brocade.com




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