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Versions: (draft-nadeau-pwe3-vccv) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 5085

Network Working Group                            Thomas D. Nadeau
Internet Draft                                   Cisco Systems, Inc.
Expires: April 2004                       =20
                                                 Rahul Aggarwal
                                                 Juniper Networks
                                                 Editors

                                   =20
                                                       October 2003




    Pseudo Wire (PW) Virtual Circuit Connection Verification
                              (VCCV)
                   draft-ietf-pwe3-vccv-01.txt


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC 2026.  Internet-Drafts are
   working documents of the Internet Engineering Task Force (IETF), its
   areas, and its working groups.  Note that other groups may also
   distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress".

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   Distribution of this document is unlimited.  Please send comments to
   the Multiprotocol Label Switching (mpls) Working Group, mpls@uu.net.

Abstract

   This document describes Virtual Circuit Connection Verification=20
   (VCCV) procedures for use with pseudowire connections. VCCV=20
   supports connection verification applications for pseudowire=20
   VCs regardless of the underlying MPLS or IP tunnel technology. =20
   VCCV makes use of IP based protocols such as Ping and MPLS
   LSP Ping to perform operations and maintenance functions.  This=20
   is accomplished by providing an IP control channel associated
   with each pseudowire. A network operator may use the VCCV=20
   procedures to test the network's forwarding plane liveliness.





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Contents

=20
Abstract...............................................................1
1.
Contributors...........................................................1
2.
Introduction...........................................................2
3. Overview of VCCV Modes of
Operation....................................3
4. MPLS as
PSN............................................................3
5. IP Probe
Traffic.......................................................5
6. OAM Capability
Indication..............................................6
7. L2TPv3/IP as
PSN.......................................................8
8.
Acknowledgments.......................................................11
9.
References............................................................11
9.2 Normative
References.................................................11
9.2 Informative
References...............................................11
10. Security
Considerations..............................................12
11. Intellectual Property Rights
Notices.................................12=20
12. Full Copyright
Statement.............................................13


1. Contributors

  Thomas D. Nadeau                             Rahul Aggarwal
  Cisco Systems, Inc.                          Juniper Networks
  250 Apollo Drive                             1194 North Mathilda Ave.
  Chelmsford, MA 01824                         Sunnyvale, CA 94089
  Email: tnadeau@cisco.com                     Email: rahul@juniper.net

  George Swallow                               Monique Morrow
  Cisco Systems, Inc.                          Cisco Systems, Inc.
  250 Apollo Drive                             Glatt-com
  Chelmsford, MA 01824                         CH-8301 Glattzentrum
  Email: swallow@cisco.com                     Switzerland
                                               Email: mmorrow@cisco.com
 =20
  Yuichi Ikejiri                               Kenji Kumaki

  NTT Communications Corporation               KDDI Corporation

  1-1-6, Uchisaiwai-cho, Chiyoda-ku            KDDI Bldg. 2-3-2,

  Tokyo 100-8019                               Nishishinjuku,
Shinjuku-ku,=20
  JAPAN                                        Tokyo 163-8003,

  Email: y.ikejiri@ntt.com                     JAPAN

                                               E-mail :
ke-kumaki@kddi.com=20

  Peter B. Busschbach
  Lucent Technologies
  67 Whippany Road
  Whippany, NJ, 07981
  E-mail: busschbach@lucent.com


2. Introduction



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   As network operators deploy pseudowire services, fault
   detection and diagnostic mechanisms particularly for the PSN
   portion of the network are pivotal. Specifically, the ability
   to provide end-to-end fault detection and diagnostics for an
   emulated pseudowire service is critical for the network
   operator. Operators have indicated in [MPLSOAMREQS] that such
   a tool is required for pseudowire deployments. This document
   describes procedures for PSN-agnostic fault detection and
   diagnostics called virtual circuit connection verification
   (VCCV).


                 |<------- pseudowire ------>|
                 |    |<-- PSN Tunnel -->|    |
          PW     V    V                  V    V     PW
     End Service +----+                  +----+ End Service
+-----+     |    | =
PE1|=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D| PE2|       | =
   +-----+
|     |----------|............PW1.............|------------|     |
| CE1 |     |    |    |                  |    |       |    | CE2 |
|     |----------|............PW2.............|------------|     |
+-----+     |    |    =
|=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D|    |       |    =
+-----+
Customer    |    +----+                  +----+       |    Customer
 Edge 1     |  Provider Edge 1        Provider Edge 2 |     Edge 2
            |<----------- Emulated Service ---------->|
                 |<---------- VCCV ---------->|

            Figure 1: PWE3 VCCV Operation Reference Model

   Figure 1 depicts the basic functionality of VCCV. VCCV provides=20
   several means of creating a control channel between PEs that=20
   attaches the VC under test.=20

                              =20

   +-------------+                                +-------------+
   |  Layer2     |                                |  Layer2     |
   |  Emulated   |                                |  Emulated   |
   |  Services   |         Emulated Service       |  Services   |
   |             =
|<=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D>|             |
   +-------------+        VCCV/pseudowire         +-------------+
   =
|Demultiplexer|<=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D>|Demultiplexor|
   +-------------+                                +-------------+
   |    PSN      |            PSN Tunnel          |    PSN      |
   |   MPLS      =
|<=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D>|   MPLS      |
   +-------------+                                +-------------+
   |  Physical   |                                |  Physical   |
   +-----+-------+                                +-----+-------+
         |                                              |
         |             ____     ___       ____          |



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         |           _/    \___/   \    _/    \__       |
         |          /               \__/         \_     |
         |         /                               \    |
         +=3D=3D=3D=3D=3D=3D=3D=3D/      MPLS or IP Network         =
|=3D=3D=3D+
                  \                                /
                   \   ___      ___     __      _/
                    \_/   \____/   \___/  \____/

      Figure 2: PWE3 Protocol Stack Reference Model=20
                including the VCCV control channel.

   Figure 2 depicts how the VCCV IP control channel is associated=20
   with the pseudowire. Ping and other IP messages are encapsulated=20
   using the PWE3 encapsulation as described below in sections 5 and=20
   6. These messages, referred to as VCCV messages, are exchanged=20
   only after the desire to exchange such traffic has been=20
   negotiated between the PEs (see section 8).

3. Overview of VCCV Modes of Operation

   VCCV defines a set of messages that are exchanged between PEs to=20
   verify connectivity of the pseudowire. To make sure that pseudowire
   packets follow the same path as the data flow, they are encapsulated=20
   with the same labels. Operators can use VCCV in two ways:

   1) as a diagnostic tool
   2) as a fault detection tool

   In the diagnostic mode, the operator triggers LSP-Ping, L2TPV3,
   or ICMP Ping modes depending on the underlying PSN. Since a=20
   pseudowire is bi-directional, it makes sense to require that the=20
   reply is send over the PSN tunnel that makes up the other half=20
   of the PW under test. For example, if the PSN is an MPLS LSP,
   the reply should be sent on the LSP representing the reverse
   path. If this fails, the operator can use other reply modes to=20
   determine what is wrong.

   The fault detection mode is provides a way to emulate fault=20
   detection mechanisms in other technologies, such as ATM for=20
   example. In the fault detection mode, the upstream PE sends=20
   BFD control messages periodically. When the downstream PE=20
   doesn't receive these message for a defined period of time, it=20
   declares that direction of the PW down and it notifies the=20
   upstream PE. Based on the emulated service, the PEs may send=20
   FDI and RDI indications over the related attachment circuits
   to notify the end points of the fault condition.


3.1 LSP Ping




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   When the PSN is MPLS, the LSP Ping header is used as described=20
   in [LSP-PING] for verifying the connectivity status of pseudo
   wires.=20

3.2 L2TPV3

   When L2TPv3 is used as the underlying PSN, a VCCV mechanism is
   needed for the L2TPv3 session. The L2TPv3 control connection does
   employ a keepalive mechanism; however, this mechanism isn't=20
   sufficent for fault detection and diagnostic of the L2TPv3 session
   i.e. data plane. In L2TPv3, a session is analogous to a PW. A L2TPv3=20
   VCCV mechanism is needed in particular for verifying the session=20
   forwarding state at the egress router.=20

3.3 ICMP Ping

   When IP is used as the PSN, ICMP ECHO packets can be used=20
   as the means by which connectivity verificaiton is achived
   using VCCV.=20

3.4 Bidirectional Forwarding Detection

   When heart-beat indication is necessary for one or more
   pseudowires, the Bidirectional Forwarding Detection (BFD)
   [BFD] provides a light-weight means of continuous
   monitoring and propagation of forward and reverse defect
   indications.  BFD can be used regardless of the underlying
   PSN technology.


4. MPLS as PSN

   In order to apply IP monitoring tools to PWE3 circuits, VCCV
   creates a control channel between PWE3 PEs[PWEARCH].  Packets=20
   sent across this channel are IP packets, allowing maximum
   flexibility.

   Ideally such a control channel would be completely in band.
   When a control word is present on virtual circuit, it is
   possible to indicate the control channel by setting a bit in
   the control header.  This method is described in section 7.1
   and is referred to as PWE3 inband VCCV.

   However in order to address the case when the control header
   is not in use as well as to deal with a number of existent
   hardware devices, use of the MPLS Router Alert Label to indicate=20
   the IP control channel is also proposed.  This is described in
   section 7.2.

   The actual channel type is agreed through signaling as



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   described in section 8.

4.1.  PWE3 Inband VCCV

   The PW set-up protocol determines whether a PW uses a control word.
   When a control word is used, it SHOULD have the following preferred
   form:

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 0| Flags |FRG|  Length   | Sequence Number               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   for the purpose of indicating VCCV control channel messages.=20

   Note that for data, one uses the control word defined just
   above the MPLS payload [PWEARCH].

   The PWE3 payload type identifier 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 1|  reserved             | PPP DLL Protocol Number       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           As defined by PPP DLL protocol definition           |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The first nibble 0000 indicates data.  When the first nibble is=20
   0001, the protocol of the frame is indicated by the Protocol
   Number.  IP OAM flows are identified by either an IPv4 or IPv6
   codepoint.=20

4.2.  Router Alert Label Approach

   When the control word is not used, or the receiving hardware
   cannot divert control traffic based on information in the control
   word (i.e.: older hardware), an IP control channel can be
   created by including the MPLS router alert label immediately
   above the VC label.  If the control word is in use on this VC
   it is also included in the IP control flow.


5. IP Probe Traffic

   For connectivity verification, both ICMP Ping and LSP-Ping
   packets may be used on the control channel.  The type of



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   packets used is indicated during signaling as described in=20
   section 6.

5.1.  ICMP Ping

   When ICMP packets are used, the source address should be set
   to the source address of the LDP session and the destination
   address to the destination of the LDP session.  The Identifier
   and Sequence Number fields of the ICMP Echo Request/Echo
   Reply messages are used to track what VCs are being tested.

   These fields are only interpreted by the sending PE.  Specific
   use of these fields is an implementation matter.


5.2.  MPLS Ping Packet

   The LSP Ping header must be used as described [LSP-PING] and
   must also contain the sub-TLV of 8 for PW circuits.  This
   sub-TLV must be sent containing the circuit to be verified as
   the "VC ID" field:

5.3   Bidirectional Forwarding Detection

   When heart-beat indication is necessary for one or more
   pseudowires, the Bidirectional Forwarding Detection (BFD)
   [BFD] provides a light-weight means of continuous
   monitoring and propagation of forward and reverse defect
   indications. =20

   In order to use BFD, both ends of the pseudowire connection must
   have signaled the existence of a control channel and the ability to
   run BFD.  Once a node has both signaled and received signaling from
   its peer of these capabilities, it MUST begin sending BFD control
   packets.  The packets MUST be sent on the control channel.  The use
   of the control channel provides the context required to bind the=20
   BFD session to a particular pseudowire (FEC).  Thus normal BFD=20
   initialization procedures are followed.  BFD MUST be run in=20
   asynchronous mode.

   When one of the PEs (PE2) doesn't receive control messages=20
   from PE1 during the specified amount of time, or if it=20
   determines in another way that communication is lost , it=20
   declares that the PW in the direction from PE1 to PE2 is down.=20
   It stores the cause (e.g. control detection time expired) and=20
   sends a message to PE1 with H=3D0 (i.e. "I don't hear you"). In=20
   turn, PE1 declares the PW in the direction from PE1 to PE2=20
   down and stores as cause: neighbor signaled session down.=20
   Depending on the emulated services, PE2 may send a FDI=20
   indication on its attachment circuits and PE1 may send an RDI=20



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   indication on its attachment circuits.

   BFD defines the following diagnostics:

       0 -- No Diagnostic
       1 -- Control Detection Time Expired
       2 -- Echo Function Failed
       3 -- Neighbor Signaled Session Down
       4 -- Forwarding Plane Reset (Local equipment failure)
       5 -- Path Down (Alarm Suppression)
       6 -- Concatenated Path Down (Propagating access link alarm)
       7 -- Administratively Down

    Of these, 0 is used when the PW is up and 2 is not applicable=20
    to asynchronous mode.

  =20
6. OAM Capability Indication

   To permit negotiation of the use and type of OAM for
   Connectivity Verification, a VCCV parameter is defined below.
   When a PE signals a PWE3 VC and desires OAM for that VC, it
   MUST indicate this during VC establishment using the messages
   defined below.  Specifically for LDP it MUST include the VCCV=20
   parameter in the VC setup message.

   As the overall method of PWE3 signaling is
   downstream, unsolicited, the decision of the type
   of IP control channel is left completely to the receiving control
   entity.  OAM capability MUST be signaled BEFORE a PE may send
   OAM messages. If a PE receives OAM messages prior to sending
   a VCCV parameter, it MUST discard these messages and not reply
   to them. In this case, the LSR SHOULD increment an error counter=20
   and optionally issues a system and/or SNMP notification to indicate=20
   to the system administrator that a mis-configuration exists.

   The requesting PE indicates its desire for the remote PE to
   support OAM capability by including the VCCV parameter with
   appropriate options set to indicate which methods of OAM are
   acceptable.  The requesting PE MAY indicate multiple IP control
   IP control channel options.  The absence of the VCCV FEC TLV=20
   indicates that no OAM functions are supported or desired by
   the requesting PE.  This last method MUST be supported by all
   PEs in order to handle backward-compatibility with older PEs.
   The receiving PE agrees to accept any of the indicated=20
   OAM types and options by virtue of establishing the VC. If
   it does not or cannot support at least one of the options
   specified, it MUST not establish the VC. If the requesting
   PE wishes to continue, it may choose different options and
   try to signal the PE again.



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6.1.  Optional VCCV Parameter

   [PWE3CONTROL] defines a VC FEC TLV for LDP.  Parameters can be
   carried within that TLV to signal different capabilities for
   specific PWs. We propose an optional parameter to be used to
   indicate the desire to use a control channel for VCCV as
   follows.

   The TLV field structure is defined in [PWE3CONTROL] 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Parameter ID |    Length     |    Variable Length Value      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Variable Length Value                 |
   |                             "                                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The VCCV parameter ID is defined as follows in [PWE3IANA]:

     Parameter ID   Length     Description
       0x0a           4           VCCV


   The format of the VCCV parameter 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      0x0a     |       0x04    |   CC Type     |   CV Types    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The CC type field defines the type of IP control channel.
   The defined values are:

    0x1  OAM Flag set in PWE header
    0x2  MPLS Router Alert Label

   The CV Types field defines the types of IP control packets
   that may be sent on the control channel.  The defined values=20
   are:

    0x01  ICMP Ping
    0x02  LSP Ping=20
    0x03  BFD




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7.  L2TPV3 as PSN

   When L2TPv3 is used as the underlying PSN, a VCCV mechanism is
   needed for the L2TPv3 session. The L2TPv3 control connection does
   employ a keepalive mechanism. However this mechanism is not
   sufficent for fault detection and diagnostic of the L2TPv3 session
   i.e. data plane. In L2TPv3 a session is analogous to a PW. A L2TPv3=20
   VCCV mechanism is needed in particular for verifying the session=20
   forwarding state at the egress router.=20

   When a PE verifies the connection status of a L2TPv3 session it must
   transmit a L2TPv3 VCCV message encoded in the L2TPv3 session packet.

   The presence of a VCCV message in a L2TPv3 session packet can be
   indicated by reserving a bit in the default L2-specific sublayer=20
   format.=20

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |P|S|V|x|x|x|x|x|              Sequence Number                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Default L2-Specific Sublayer Format with V bit.

   The 'V' bit indicates that this is a VCCV session packet. If the PW=20
   has not been signaled to include a L2-specific sublayer format, other

   mechanisms are needed to indicate the VCCV message. Such mechanisms
are
   for further study.

7.1. L2TPv3 VCCV Message

   The VCCV message MUST contain a VCCV AVP. It does not contain a
message
   header. A new AVP, called the VCCV AVP is defined. The usage of the=20
   L2TPv3 AVP format leaves room for adding further AVPs to this message

   in the future as needed.=20

7.1.1. L2TPv3 VCCV AVP

   This AVP encodes the LSP Ping header as defined in [LSP-PING]. M and
H=20
   bits must not be set. The attribute type is TBD. The LSP Ping header
is=20
   not encapsulated in UDP. The modifications to the semantics of the=20
   fields of this header are specified here. Unless otherwise specified=20
   the semantics of the fields as explained in [LSP-PING] are to be=20
   followed. For reference the format of the LSP Ping header is shown=20
   below.

       0                   1                   2                   3



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       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Version Number        |         Must Be Zero          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Message Type |   Reply mode  |  Return Code  | Return Subcode|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Sender's Handle                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Sequence Number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    TimeStamp Sent (seconds)                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  TimeStamp Sent (microseconds)                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  TimeStamp Received (seconds)                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                TimeStamp Received (microseconds)              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            TLVs ...                           |
      .                                                               .
      .                                                               .
      .                                                               .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The version number is currently 1. The message type is one of the=20
   following:

   1 - L2TPv3 VCCV Echo Request
   2 - L2TPv3 VCCV Echo Reply

   The Reply Mode is:

   1 - Do not reply
   2 - Reply using the L2TPv3 session

   As explained in [LSP-PING] a reply mode of "do not reply" can be used

   for one way connectivity tests. The VCCV message will normally
contain=20
   a reply mode of "reply using the L2TPv3 session".=20

   The return code can be set to the following by the receiver:

   1 - Malformed echo request received
   2 - One or more of the TLVs was not understood
   3 - Replying router has a session mapping for the verified pseudo
wire
   4 - Replying router does not have a mapping for the verified pseudo=20
       wire

   The LSP Ping header must contain the L2 Circuit ID TLV as defined in=20



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   section 8.2. This TLV identifies the pseudo wire associated with the
   session, that is being verified. For L2TPv3 the remote PE address is=20
   the address of the session's remote end. A new PWID type is defined
   for L2TPv3, in addition to the ones defined in section 8.2:

   3. L2TPv3 Remote End Identifier AVP

7.2. L2TPv3 VCCV Capability Negotiation

   A LCCE or a LAC should be able to indicate whether the session is
   capable of processing VCCV packets. This is done by including the
   optional VCCV capability AVP in an ICRQ, ICRP, OCRQ or OCRP.

7.2.1. L2TPv3 VCCV Capability AVP

   This AVP specifies the VCCV capability. Its attribute type
   is TBD. The value field has the following format:

       0                   1         =20
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
      | Reserved                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-=20

7.3. L2TPv3 VCCV Operation

   A PE sends VCCV echo requests on a L2TPv3 signaled pseudo wire for=20
   fault detection and diagnostic of the L2TPv3 session. The destination

   IP address in the echo request is set to the remote PE's IP address,=20
   while the source IP address is set to the local PE's IP address. The=20
   egress of the L2TPv3 session verifies the signaling and forwarding
state
   of the pseudo wire, on reception of the VCCV message. Any faults=20
   detected can be signaled in the VCCV echo response. Its to be noted=20
   that the VCCV mechanism for L2TPv3 is primarily targeted at verifying

   the pseudo wire forwarding and signaling state at the egress PE. It=20
   also helps when L2TPv3 control and session paths are not identical.=20

   A PE must send VCCV packets on a L2TPv3 session only if it has
signaled
   VCCV capability to the remote end and received VCCV capability from
the=20
   remote end. If a PE receives VCCV packets and its not VCCV capable or

   it has not received VCCV capability indication from the remote end,
it=20
   must discard these messages. In addition if a PE receives VCCV
messages
   and it has not received VCCV capability from the remote end, it
should=20
   increment an error counter. In this case the PE can optionally issue
a
   system and/or SNMP notification.





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8.   Acknowledgments

   The authors would like to thank Hari Rakotoranto, Michel
   Khouderchah, Bertrand Duvivier, Vanson Lim, Chris Metz, W.
   Mark Townsley, Eric Rosen, Dan Tappan, and
   Danny McPherson for their valuable comments and suggestions.


9.   References

9.1 Normative References

[BFD]      Katz, D., Ward, D., Bidirectional Forwarding
           Indication, draft-katz-ward-bfd-00.txt, December
           2003, work in progress.

[PWREQ]    Xiao, X., McPherson, D., Pate, P., Gill, V.,
           Kompella, K., Nadeau, T., White, C., "Requirements=20
           for Pseudo Wire Emulation Edge-to-Edge (PWE3)",=20
           <draft-ietf-pwe3-requirements-02.txt>, November 2001.

[PWE3FW]   Prayson Pate, et al., Internet draft, Framework for
           Pseudo Wire Emulation Edge-to-Edge (PWE3), draft-
           ietf-pwe3-framework-01.txt, work in progress.=20

[PWEARCH]  Bryant, S., Pate, P., Johnson, T., Kompella, K.,
           Malis, A., McPherson, D., Nadeau, T., So, T., Townsley,=20
           W., Systems, White., C., Wood, L., Xiao, X., Internet=20
           draft, Framework for Pseudo Wire Emulation Edge-to-Edge=20
           (PWE3), draft-ietf-pwe3-framework-01.txt, work in=20
           progress.

[PWE3IANA] Martini, L., Townsley, M., "IANA Allocations for=20
           pseudo Wire Edge to Edge Emulation (PWE3)",
           draft-ietf-pwe3-iana-allocation-01.txt, June
           2003,  work in progress.

[L2SIG]    Rosen, E., LDP-based Signaling for L2VPNs,
           Internet Draft <draft-rosen-ppvpn-l2-signaling-02.txt>,=20
           September 2002.

[LSPPING]  Kompella, K., Pan, P., Sheth, N., Cooper, D.,
           Swallow, G., Wadhwa, S., Bonica, R., " Detecting=20
           Data Plane Liveliness in MPLS", Internet Draft=20
           <draft-ietf-mpls-lsp-ping-01.txt>, April 2003.=20

[MARTINISIG] "Transport of Layer 2 Frames Over MPLS", Martini et.
             al., draft-martini-l2circuit-trans-mpls-10.txt,=20
             August 2002




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[GTTP]     Bonica, R., Kompella, K., Meyer, D., "Generic
           Tunnel Tracing Protocol (GTTP) Specification", Internet=20
           Draft <draft-bonica-tunproto-01.txt>, April, 2003=20

[FRF 8.1]  Frame Relay Forum, Frame Relay / ATM PVC Service
           Interworking Implementation Agreement, February 2000

[ITU-T]    "Draft Recommendation Y.17fw" (MPLS Management
           Framework), July 2002.

[ITU-T]    "Frame Relay Bearer Service Interworking," I.555,
           September 2997.

[ITU-T],   "Frame Relay Operations Principles and Functions",=20
           I.620, October, 1996.

[ITU-T]    Q.933, ISDN Digital Subscriber Signalling System
           No. 1 (DSS 1) - Signalling specification for frame=20
           mode basic call control, November 1995.


9.2 Informative References

[ICMP]     Postel, J. "Internet Control Message Protocol, "
           RFC 792
[PWEATM]   Martini, L., et al., "Encapsulation Methods for
           Transport of ATM Cells/Frame Over IP and MPLS=20
           Networks", Internet Draft <draft-ietf-pwe3-atm-
           encap-00.txt>, October 2002
[MPLSOAMREQS] Nadeau, T., et al,"OAM Requirements for MPLS
              Networks, Internet Draft <draft-ietf-oam-
              requirements-01.txt>, June 2003.
[OAMMsgMap] Nadeau, T., et al, " Pseudo Wire (PW) OAM Message
            Mapping, Internet Draft < draft-nadeau-pwe3-OAMMap.txt>,
            December, 2002.
[PWE3CONTROL] L.Martini et al., "Transport of Layer 2 Frames
              over MPLS, Internet Draft, <draft-ietf-pwe3-control-
              protocol-01.txt>, May 2003
[PPVPNFW]     Callon, R., Suzuki, M., Gleeson, B., Malis, A.,
              Muthukrishnan, K., Rosen, E., Sargor, C., and J. Yu,=20
              "A Framework for Provider Provisioned Virtual=20
              Private Networks", Internet Draft <draft-ietf-
              ppvpn-framework-01.txt>, July 2001.
[RFC3031]  Rosen, E., Viswanathan, A., and R. Callon,
           "Multiprotocol Label Switching Architecture", RFC=20
           3031, January 2001.

10.   Security Considerations

      TBD.



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11.   Intellectual Property Rights Notices

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on=20
   the IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication and any assurances
   of licenses to be made available, or the result of an attempt made
   to obtain a general license or permission for the use of such
   proprietary rights by implementers or users of this specification=20
   can be obtained from the IETF Secretariat.
   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF=20
   Executive Director.


11.   Full Copyright Statement

   Copyright (C) The Internet Society (2003). All Rights
   Reserved.
   This document and translations of it may be copied and
   furnished to others, and derivative works that comment on
   or otherwise explain it or assist in its implementation may
   be prepared, copied, published and distributed, in whole or
   in part, without restriction of any kind, provided that the
   above copyright notice and this paragraph are included on
   all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by
   removing the copyright notice or references to the Internet
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   case the procedures for copyrights defined in the Internet
   Standards process must be followed, or as required to
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   The limited permissions granted above are perpetual and
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   INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE
   DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
   NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION



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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
   PURPOSE.


















































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