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Versions: (draft-ietf-mpls-tp-bfd-cc-cv) 00 01 02 03 04 05 06 RFC 6428

MPLS Working Group                                       Dave Allan, Ed.
Internet Draft                                                 Ericsson
Intended status: Standards Track
Expires: April 2011                                   George Swallow Ed.
                                                      Cisco Systems, Inc

                                                          John Drake Ed.

                                                        October 22, 2010

     Proactive Connectivity Verification, Continuity Check and Remote
               Defect indication for MPLS Transport Profile


   Continuity Check (CC), Proactive Connectivity Verification (CV) and
   Remote Defect Indication (RDI) functionalities are required for MPLS-
   TP OAM.

   Continuity Check monitors the integrity of the continuity of the LSP
   for any loss of continuity defect. Connectivity verification monitors
   the integrity of the routing of the LSP between sink and source for
   any connectivity issues. RDI enables an End Point to report, to its
   associated End Point, a fault or defect condition that it detects on
   a PW, LSP or Section.

   This document specifies methods for proactive CV, CC, and RDI for
   MPLS-TP Label Switched Path (LSP), PWs and Sections using
   Bidirectional Forwarding Detection (BFD).

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC2119 [1].

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance
   with the provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet
   Engineering Task Force (IETF), its areas, and its working

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   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

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on November 28, 2010.

Copyright Notice

   Copyright (c) 2010 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
   carefully, as they describe your rights and restrictions with
   respect to this document. Code Components extracted from this
   document must include Simplified BSD License text as described
   in Section 4.e of the Trust Legal Provisions and are provided
   without warranty as described in the Simplified BSD License.

Table of Contents

   1. Introduction...................................................3
   1.1. Authors......................................................4
   2. Conventions used in this document..............................4
   2.1. Terminology..................................................4
   2.2. Issues for discussion........................................5
   3. MPLS CC, proactive CV and RDI Mechanism using BFD..............5
   3.1. ACH code points for CC and proactive CV......................6
   3.2. MPLS BFD CC Message format...................................6
   3.3. MPLS BFD proactive CV Message format.........................7
   3.4. BFD Session in MPLS-TP terminology...........................7
   3.5. BFD Profile for MPLS-TP......................................8
   3.5.1. Session initiation.........................................9
   3.5.2. Defect entry criteria......................................9

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   3.5.3. Defect entry consequent action............................10
   3.5.4. Defect exit criteria......................................11
   3.5.5. State machines............................................11
   3.5.6. Configuration of MPLS-TP BFD sessions.....................14
   3.5.7. Discriminator values......................................14
   4. Acknowledgments...............................................15
   5. IANA Considerations...........................................15
   6. Security Considerations.......................................15
   7. References....................................................15
   7.1. Normative References........................................15
   7.2. Informative References......................................16

1. Introduction

   In traditional transport networks, circuits are provisioned on two or
   more switches. Service Providers (SP) need OAM tools to detect mis-
   connectivity and loss of continuity of transport circuits. Both PWs
   and MPLS-TP LSPs [7] emulating traditional transport circuits need to
   provide the same CC and proactive CV capabilities as required in
   draft-ietf-mpls-tp-oam-requirements[3]. This document describes the
   use of BFD for CC, proactive CV, and RDI of a PW, LSP or SPME between
   two Maintenance Entity Group End Points (MEPs).

   As described in [9], Continuity Check (CC) and Proactive Connectivity
   Verification (CV) functions are used to detect loss of continuity
   (LOC), and unintended connectivity between two MEPs (e.g. mismerging
   or misconnectivity or unexpected MEP).

   The Remote Defect Indication (RDI) is an indicator that is
   transmitted by a MEP to communicate to its peer MEP that a signal
   fail condition exists. RDI is only used for bidirectional LSPs and is
   associated with proactive CC & CV packet generation.

   This document specifies the BFD extension and behavior to satisfy the
   CC, proactive CV monitoring and the RDI functional requirements for
   both co-routed and associated bi-directional LSPs. Supported
   encapsulations include GAL/G-ACh, VCCV and UDP/IP. Procedures for
   uni-directional LSPs are for further study.

   The mechanisms specified in this document are restricted to BFD
   asynchronous mode.

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1.1. Authors

David Allan, John Drake, George Swallow, Annamaria Fulignoli, Sami
Boutros, Siva Sivabalan, David Ward, Martin Vigoureux.

2. Conventions used in this document

2.1. Terminology

ACH: Associated Channel Header

BFD: Bidirectional Forwarding Detection

CV: Connectivity Verification

GAL: Generalized Alert Label

LDI: Link Down Indication

LKI: Lock Instruct

LKR: Lock Report

LSR: Label Switching Router

MEG: Maintenance Entity Group

MEP: Maintenance Entity Group End Point

MIP: Maintenance Entity Group Intermediate Point

MPLS-OAM: MPLS Operations, Administration and Maintenance

MPLS-TP: MPLS Transport Profile

MPLS-TP LSP: Uni-directional or Bidirectional Label Switch Path
representing a circuit

MS-PW: Multi-Segment PseudoWire

NMS: Network Management System

PW: Pseudo Wire

RDI: Remote Defect Indication.

SPME: Sub-Path Maintenance Entity

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TTL: Time To Live

TLV: Type Length Value

VCCV: Virtual Circuit Connectivity Verification

2.2. Issues for discussion

   1) Requirement for additional BFD diagnostic codes?

              1. When periodicity of CV cannot be supported

3. MPLS CC, proactive CV and RDI Mechanism using BFD

   This document proposes distinct encapsulations and code points for
   ACh encapsulated BFD depending on whether the mode of operation is CC
   or CV:

  o  CC mode: defines a new code point in the Associated Channel Header
     (ACH) described in [2].In this mode Continuity Check and RDI
     functionalities are supported.

  o  CV mode: defines a new code point in the Associated Channel Header
     (ACH) described in [2]. The ACH with "MPLS Proactive CV" code
     point indicates that the message is an MPLS BFD proactive CV and
     CC message and CC, CV and RDI functionalities are supported.

   RDI: is communicated via the BFD diagnostic field in BFD CC and CV
   messages. It is not a distinct PDU. A sink MEP will encode a
   diagnostic code of "1- Control detection time expired" when the
   interval times detect multipler have been exceeded, and with "3 -
   neighbor signaled session down" as a consequence of the sink MEP
   receiving AIS with LDI set. A sink MEP that has started sending diag
   code 3 will NOT change it to 1 when the detection timer expires.

   In accordance with RFC 5586, when these packets are encapsulated in
   an IP header the fields in the IP header are set as defined in RFC
   5884. It should also be noted that existing ACh code points and
   mechanisms for negotiating the control channel and connectivity
   verification (i.e. OAM functions) between PEs are specified for

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3.1. ACH code points for CC and proactive CV

    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|Version|     Flags     |0xHH   BFD CC/CV Code Point    |

       Figure 1: ACH Indication of MPLS-TP Connectivity Verification

   The first nibble (0001b) indicates the ACH.

   The version and the flags are set to 0 as specified in [2].

   The code point is either

   - BFD CC code point = 0xHH. [HH to be assigned by IANA from the PW
   Associated Channel Type registry.] or,

   - BFD proactive CV code point = 0xHH. [HH to be assigned by IANA from
   the PW Associated Channel Type registry.]

   Both CC and CV modes apply to PWs, MPLS LSPs (including tandem
   connection monitoring), and Sections.

   CC and CV operation can be simultaneously employed on an ME within a
   single BFD session. The expected usage is that normal operation is to
   send CC BFD PDUs with every nth BFD PDU augmented with a source MEP
   ID and identified as requiring additional processing by the different
   ACh channel type.

3.2. MPLS BFD CC Message format

   The format of an MPLS CC Message 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
   |0 0 0 1|Version|     Flags     |    0xHH BFD CC Code point     |
   |                                                               |
   ~                  BFD Control Packet                           ~
   |                                                               |
                     Figure 2: MPLS CC Message

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3.3. MPLS BFD proactive CV Message format

   The format of an MPLS CV Message 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
   |0 0 0 1|Version|     Flags     |    0xHH  BFD CV Code Point    |
   |                                                               |
   ~                  BFD Control Packet                           ~
   |                                                               |
   |                                                               |
   ~          Unique MEP-ID of source of the BFD packet            ~
   |                                                               |

                     Figure 3: MPLS CV Message

   As shown in Figure 3, BFD Control packet as defined in [4] is
   transmitted as MPLS labeled packets along with the ACH. Appended to
   the BFD control packet is a MEP Source ID TLV. The length in the BFD
   control packet is as per [4]. There are 4 possible Source MEP TLVs
   (corresponding to the MEP IDs defined in [8] [type fields to be
   assigned by IANA]. The type fields are:

      X1 - ICC encoded MEP ID

      X2 - LSP-MEP_ID

      X3 - PW MEP ID

      X4 - PW Segment endpoint ID

   When GAL label is used, the TTL field of the GAL MUST be set to at
   least 1, and the GAL will be the end of stack label (S=1).

3.4. BFD Session in MPLS-TP terminology

   A BFD session corresponds to a CC or a proactive CV OAM instance in
   MPLS-TP terminology.

   A BFD session is enabled when the CC or proactive CV functionality is
   enabled on a configured Maintenance Entity (ME)..

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   On a Sink MEP, a BFD session can be in DOWN, INIT or UP state as
   detailed in [4].

   When on a ME the CC or proactive CV functionality is disabled, the
   BFD session transitions to the ADMIN DOWN State and the BFD session

   A new BFD session is initiated when the operator enables or re-
   enables the CC or CV functionality on the same ME.

3.5. BFD Profile for MPLS-TP

   BFD MUST operate in asynchronous mode. In this mode, the BFD Control
   packets are periodically sent at configurable time rate. This rate is
   typically a fixed value for the lifetime of the session. In the rare
   circumstance where an operator has a reason to change session
   parameters, the session must be moved to the ADMIN DOWN state.
   Poll/final discipline can only used for VCCV and UDP/IP encapsulated

   The transport profile is designed to operate independent of the
   control plane; hence the C bit SHOULD be set.

   This document specifies bi-directional BFD for p2p transport LSPs,
   hence the M bit MUST be clear.

   There are two modes of operation for bi-directional LSPs. One in
   which the session state of both directions of the LSP is coordinated
   and one constructed from BFD sessions in such a way that the two
   directions operate independently. A single bi-directional BFD session
   is used for coordinated operation. Two independent BFD sessions are
   used for independent operation.

   Coordinated operation is as described in [4]. Independent operation
   requires clarification of two aspects of [4]. Independent operation
   is characterized by the setting of MinRxInterval to zero by the MEP
   that is typically the session originator (referred to as the source
   MEP), and there will be a session originator at either end of the bi-
   directional LSP. Each source MEP will have a corresponding sink MEP
   that has been configured to a Tx interval of zero.

   The base spec is unclear on aspects of how a MEP with a BFD transmit
   rate set to zero behaves. One interpretation is that no periodic
   messages on the reverse component of the bi-directional LSP originate
   with that MEP, it will only originate messages on a state change.

   The first clarification is that when a state change occurs a MEP set
   to a transmit rate of zero sends BFD control messages with a one

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   second period on the reverse component until such time that the state
   change is confirmed by the session peer. At this point the MEP set to
   a transmit rate of zero can resume quiescent behavior. This adds
   robustness to all state transitions in the RxInterval=0 case.

   The second is that the originating MEP (the one with a non-zero
   TxInterval) will ignore a DOWN state received from a zero interval
   peer. This means that the zero interval peer will continue to send
   DOWN state messages that include the RDI diagnostic code as the state
   change is never confirmed. This adds robustness to the exchange of
   RDI indication on a uni-directional failure (for both session types
   DOWN with a diagnostic of either control detection period expired or
   neighbor signaled session down offering RDI functionality).

   A further extension to the base specification is that there are
   additional OAM protocol exchanges that act as inputs to the BFD state
   machine; these are the Link Down Indication [5] and the Lock
   Instruct/Lock Report transactions; Lock Report interaction being

3.5.1. Session initiation

   In all scenarios a BFD session starts with both ends in the DOWN
   state. DOWN state messages exchanged include the desired Tx and Rx
   rates for the session. If a node cannot support the Min Tx rate
   desired by a peer MEP it does not transition from down to the INIT
   state and sends a diagnostic code (TBD) indicating that the requested
   Tx rate cannot be supported.

   Otherwise once a transition from DOWN to INIT has occurred, the
   session progresses as per [4]. In both the DOWN and INIT states
   messages are transmitted at a rate of one per second and the defect
   detection interval is fixed at 3.5 seconds. On transition to the UP
   state message periodicity changes to the negotiated rate and the
   detect interval switches to detect multiplier times the session
   peer's Tx Rate.

3.5.2. Defect entry criteria

   There are further defect criteria beyond those that are defined in
   [4] to consider given the possibility of mis-connectivity and mis-
   configuration defects. The result is the criteria for a LSP direction
   to transition from the defect free state to a defect state is a
   superset of that in the BFD base specification [4].
   The following conditions cause a MEP to enter the defect state for CC
   or CV:
     1. BFD session times out (Loss of Continuity defect).

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     2. Receipt of a link down indication.
     3. Receipt of an unexpected M bit (Session Mis-configuration

   And the following will cause the MEP to enter the defect state for CV
     1. BFD control packets are received with an unexpected
        encapsulation (mis-connectivity defect), these include:
          - a PW receiving a packet with a GAL
          - an LSP receiving an IP header instead of a GAL
          (note there are other possibilities that can also alias as an
          OAM packet)
     2. Receipt of an unexpected globally unique Source MEP identifier
        (Mis-connectivity defect).
     3. Receipt of an unexpected session discriminator in the your
        discriminator field (mis-connectivity defect).
     4. Receipt of an expected session discriminator with an unexpected
        label (mis-connectivity defect).

   The effective defect hierarchy (order of checking) is

     1. Receiving nothing.

     2. Receiving link down indication.

     3. Receiving from an incorrect source (determined by whatever

     4. Receiving from a correct source (as near as can be determined),
        but with incorrect session information).

     5. Receiving control packets in all discernable ways correct.

3.5.3. Defect entry consequent action

   Upon defect entry a sink MEP will assert signal fail into any client
   (sub-)layers. It will also communicate session DOWN to its session

   The blocking of traffic as consequent action MUST be driven only by a
   defect's consequent action as specified in draft-ietf-mpls-tp-oam-
   framework [9] section

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   When the defect is mis-branching, the LSP termination will silently
   discard all non-oam traffic received.

3.5.4. Defect exit criteria Exit from a Loss of continuity defect

   For a coordinated session, exit from a loss of connectivity defect is
   as described in figure 4 which updates [4].

   For an independent session, exit from a loss of connectivity defect
   occurs upon receipt of a well formed control packet from the peer MEP
   as described in figures 5 and 6. Exit from a session mis-configuration defect

   [editors: for a future version of the document] Exit from a mis-connectivity defect

   [Editors node: The shift to CC with interleaved CV suggests the CV
   periodicity may not be known by a sink MEP, hence exit criteria from
   a mis-connectivity defect may not be able to be established. We
   suggest two possible resolutions for this:

      1. Exit criteria is manual intervention.

      2. A minimum CV insertion rate (say 1/sec) be specified such that
         the exit criteria be specified as no mis-connected CV PDUs be
         received for a minimum of 3 times the minimum insertion rate]

3.5.5. State machines

   The following state machines update [4]. They have been modified to
   include AIS with LDI set and LKI as inputs to the state machine and
   to clarify the behavior for independent mode. LKR is an optional

   The coordinated session state machine has been augmented to indicate
   AIS with LDI set and optionally LKR as inputs to the state machine.
   For a session that is in the UP state, receipt of AIS with LDI set or
   optionally LKR will transition the session into the DOWN state.

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                             |  | UP, ADMIN DOWN, TIMER, AIS-LDI, LKR
                             |  V
               DOWN        +------+  INIT
              +------------|      |------------+
              |            | DOWN |            |
              |  +-------->|      |<--------+  |
              |  |         +------+         |  |
              |  |                          |  |
              |  |               ADMIN DOWN,|  |
              |  |ADMIN DOWN,          DOWN,|  |
              |  |TIMER               TIMER,|  |
              V  |AIS-LDI,LKR   AIS-LDI,LKR |  V
            +------+                      +------+
       +----|      |                      |      |----+
   DOWN|    | INIT |--------------------->|  UP  |    |INIT, UP
       +--->|      | INIT, UP             |      |<---+
            +------+                      +------+

       Figure 4: State machine for coordinated session operation

   For independent mode, there are two state machines. One for the
   source MEP (who requested MinRxInterval=0) and the sink MEP (who
   agreed to MinRxInterval=0).

   The source MEP will not transition out of the UP state once
   initialized except in the case of a forced ADMIN DOWN. Hence AIS-with
   LDI set and optionally LKR do not enter into the state machine
   transition from the UP state, but do enter into the INIT and DOWN

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                             |  | UP, ADMIN DOWN, TIMER
                             |  V
               DOWN        +------+  INIT
              +------------|      |------------+
              |            | DOWN |            |
              |  +-------->|      |<--------+  |
              |  |         +------+         |  |
              |  |                          |  |
              |  |ADMIN DOWN     ADMIN DOWN |  |
              |  |TIMER,                    |  |
              |  |AIS-LDI,                  |  |
              V  |LKR                       |  V
            +------+                      +------+
       +----|      |                      |      |----+
   DOWN|    | INIT |--------------------->|  UP  |    | INIT, UP, DOWN,
       +--->|      | INIT, UP             |      |<---+ AIS-LDI, LKR
            +------+                      +------+

     Figure 5: State machine for source MEP for independent session

   The sink MEP state machine (for which the transmit interval has been
   set to zero) is modified to:

   1) Permit direct transition from DOWN to UP once the session has been
   initialized. With the exception of via the ADMIN DOWN state, the
   source MEP will never transition from the UP state, hence in normal
   unidirectional fault scenarios will never transition to the INIT

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                             |  | ADMIN DOWN, TIMER, AIS-LDI, LKR
                             |  V
               DOWN        +------+  INIT, UP
              +------------|      |------------+
              |            | DOWN |            |
              |  +-------->|      |<--------+  |
              |  |         +------+         |  |
              |  |                          |  |
              |  |               ADMIN DOWN,|  |
              |  |ADMIN DOWN,    TIMER,     |  |
              |  |TIMER,         DOWN,      |  |
              |  |AIS-LDI,       AIS-LDI,   |  V
             V  |LKR            LKR        |  |
            +------+                      +------+
       +----|      |                      |      |----+
   DOWN|    | INIT |--------------------->|  UP  |    |INIT, UP
       +--->|      | INIT, UP             |      |<---+
            +------+                      +------+

     Figure 6: State machine for the sink MEP for independent session

3.5.6. Configuration of MPLS-TP BFD sessions

   [Editors note, for a future revision of the document]

3.5.7. Discriminator values

   In the BFD control packet the discriminator values have either local
   to the sink MEP or no significance (when not known).

   My Discriminator field MUST be set to a nonzero value (it can be a
   fixed value), the transmitted your discriminator value MUST reflect
   back the received value of My discriminator field or be set to 0 if
   that value is not known.

   Although the BFD base specification permits an implementation to
   change the my discriminator field at arbitrary times, this is not
   permitted for CV mode in order to avoid race conditions in mis-
   connectivity defects.

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4. Acknowledgments

   To be added in a later version of this document

5. IANA Considerations

   To be added in a later version of this document

6. Security Considerations

   The security considerations for the authentication TLV need further

   Base BFD foresees an optional authentication section (see [4]
   section 6.7); that can be extended also to the tool proposed in
   this document.

   Authentication methods that require checksum calculation on the
   outgoing packet must extend the checksum also on the ME
   Identifier Section. This is possible but seems uncorrelated with
   the solution proposed in this document: it could be better to
   use the simple password authentication method.

7. References

7.1. Normative References

  [1]   Bradner, S., "Key words for use in RFCs to Indicate
        Requirement Levels", BCP 14, RFC 2119, March 1997.

  [2]   Bocci, M. et al., " MPLS Generic Associated Channel ", RFC
        5586 , June 2009

  [3]   Vigoureux, M., Betts, M. and D. Ward, "Requirements for
        Operations Administration and Maintenance in MPLS
        Transport Networks", RFC5860, May 2010

  [4]   Katz, D. and D. Ward, "Bidirectional Forwarding
        Detection", RFC 5880, June 2010

  [5]   Swallow, G. et al., "MPLS Fault Management OAM", draft-
        ietf-mpls-tp-fault-02 (work in progress), July 2010

  [6]   Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
        Connectivity Verification (VCCV): A Control Channel for
        Pseudowires", RFC 5085, December 2007

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7.2. Informative References

  [7]   Bocci, M., et al., "A Framework for MPLS in Transport
        Networks", RFC5921, July 2010

  [8]   Bocci, M. and G. Swallow, "MPLS-TP Identifiers", draft-
        swallow-mpls-tp-identifiers-02 (work in progress), July

  [9]   Allan, D., and Busi, I. "MPLS-TP OAM Framework", draft-
        ietf-mpls-tp-oam-framework-09 (work in progress), October

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   Authors' Addresses

   Dave Allan
   Email: david.i.allan@ericsson.com

   John Drake
   Email: jdrake@juniper.net

   George Swallow
   Cisco Systems, Inc.
   Email: swallow@cisco.com

   Annamaria Fulignoli
   Email: annamaria.fulignoli@ericsson.com

   Sami Boutros
   Cisco Systems, Inc.
   Email: sboutros@cisco.com

   Martin Vigoureux
   Email: martin.vigoureux@alcatel-lucent.com

   Siva Sivabalan
   Cisco Systems, Inc.
   Email: msiva@cisco.com

   David Ward
   Email: dward@juniper.net

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