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Explicit Path Routing for Dynamic Multi-Segment Pseudowires
draft-ietf-pwe3-mspw-er-01

The information below is for an old version of the document.
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This is an older version of an Internet-Draft that was ultimately published as RFC 7392.
Authors Pranjal Dutta , Matthew Bocci , Luca Martini
Last updated 2012-06-18
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draft-ietf-pwe3-mspw-er-01
Network Working Group                                           P. Dutta
Internet-Draft                                                  M. Bocci
Intended status: Standards Track                          Alcatel-Lucent
Expires: December 20, 2012                                    L. Martini
                                                           Cisco Systems
                                                           June 18, 2012

      Explicit Path Routing for Dynamic Multi-Segment Pseudowires
                       draft-ietf-pwe3-mspw-er-01

Abstract

   Dynamic Multi-Segment Pseudowire (MS-PW) setup through an explicit
   path may be required to provide a simple solution for 1:1 protection
   with diverse primary and backup MS-PWs for a service, or to enable
   controlled signaling (strict or loose) for special MS-PWs.  This
   document specifies the extensions and procedures required to enable
   dynamic MS-PWs to be established along explicit paths.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in[RFC2119].

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on December 20, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Explicit Path in MS-PW Signaling . . . . . . . . . . . . . . .  3
     3.1.  S-PE Addressing  . . . . . . . . . . . . . . . . . . . . .  3
     3.2.  Explicit Route TLV (ER-TLV)  . . . . . . . . . . . . . . .  4
     3.3.  Explicit Route Hop TLV (ER-Hop TLV)  . . . . . . . . . . .  4
     3.4.  ER-Hop Semantics . . . . . . . . . . . . . . . . . . . . .  7
       3.4.1.  ER-Hop 1: IPv4 Prefix  . . . . . . . . . . . . . . . .  7
       3.4.2.  ER-Hop 2: IPv6 Prefix  . . . . . . . . . . . . . . . .  8
       3.4.3.  ER-Hop 3: L2 PW Address  . . . . . . . . . . . . . . .  9
   4.  Explicit Route TLV Processing  . . . . . . . . . . . . . . . . 10
     4.1.  Next-Hop Selection . . . . . . . . . . . . . . . . . . . . 10
     4.2.  Adding ER Hops to the Explicit Route TLV . . . . . . . . . 11
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   8.  Normative References . . . . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12

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1.  Introduction

   Procedures for dynamically establishing multi-segment pseudowires
   (MS-PWs), where their paths are automatically determined using a
   dynamic routing protocol, are defined in
   [I-D.ietf-pwe3-dynamic-ms-pw].  For 1:1 protection of MS-PWs with
   primary and backup paths, MS-PWs SHOULD be established through a
   diverse set of S-PEs (Switching Provider-Edge) nodes to avoid any
   single points of failure at PW level.  [I-D.ietf-pwe3-dynamic-ms-pw]
   allows this through BGP based mechanisms.  This draft proposes an
   additional mechanism that allows the ST-PE (Source Terminating PEs)
   to explicitly choose the path that a PW would take through the
   intervening S-PEs.  Explicit path routing of dynamic MS-PWs may also
   be required for controlled set-up of dynamic MS-PWs and network
   resource management.

2.  Terminology

   This document uses the terminology defined in
   [I-D.ietf-pwe3-dynamic-ms-pw], [RFC4447]and [RFC5036].

   The following additional terminology is used:

   Abstract Node:  A group of nodes (S-PEs) representing an explicit hop
      along the path of an MS-PW.  An abstract node is identified by an
      IPv4, IPv6 or S-PE address.

3.  Explicit Path in MS-PW Signaling

   This section describes the LDP (Label Distribution Protocol)
   extensions required for signaling explicit paths in dynamic MS-PW
   set-up messages.

3.1.  S-PE Addressing

   The T-PE MAY elect to select a known explicit path along a set of
   S-PEs for a specific PW.  This requires that each S-PE be uniquely
   addressable in terms of pseudowires.  For this purpose, at least one
   AII (Attachment Individual Indentifier) address of the format similar
   to AII type 2 [RFC5003] composed of the Global ID, and Prefix part,
   only, MUST be assigned to each S-PE.

   If an S-PE is capable of Dynamic MS-PW signaling, but is not assigned
   with an S-PE address, then on receiving a Dynamic MS-PW label mapping
   message the S-PE MUST return a label release with the "Resources
   Unavailable" ( 0x38)" status code.

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3.2.  Explicit Route TLV (ER-TLV)

   The ER-TLV is an object that specifies the path to be taken by the
   MS-PW being established.  Each hop along the path is represented by
   an abstract node, which is a group of one or more S-PEs, identified
   by an IPv4, and IPv6 or an S-PE address.

   The ER-TLV contains one or more Explicit Route Hop TLVs (ER-Hop TLVs)
   defined in Section 3.3.

   The ER-TLV format 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 = 0x0800     |      Length                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          ER-Hop TLV 1                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          ER-Hop TLV 2                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                          ............                         ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          ER-Hop TLV n                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    U/F
          These bits MUST be set to zero and the procedures of [RFC5036]
          followed when the TLV is not known to the receiving node.

    Type
          A fourteen-bit field carrying the value of the ER-TLV
          Type = 0x0800.

    Length
          Specifies the length of the value field in bytes.

    ER-Hop TLVs
          One or more ER-Hop TLVs defined in Section 3.2.

                            Explicit Route TLV

3.3.  Explicit Route Hop TLV (ER-Hop TLV)

   The contents of an ER-TLV are a series of variable length ER-Hop
   TLVs.  Each hop contains the identification of an "Abstract Node"
   that represents the hop to be traversed.

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   Each ER-Hop TLV has the form:

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     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                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |L|                                  Content //                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    U/F
          These bits MUST be set to zero and the procedures of [RFC5036]
          followed when the TLV is not known to the receiving node.

    ER-Hop Type

          A fourteen-bit field carrying the type of the ER-Hop contents.
          Currently defined values are:

          Value  Type
          ------ ------------------------
          0x0801 IPv4 prefix
          0x0802 IPv6 prefix
          0x0805 L2 PW address of PW Switching Point

    Length
          Specifies the length of the value field in bytes.

    L bit
          The L bit in the ER-Hop is a one-bit attribute.  If the L bit
          is set, then the value of the attribute is "loose." Otherwise,
          the value of the attribute is "strict."  For brevity, we say
          that if the value of the ER-Hop attribute is loose then it is
          a "loose ER-Hop."  Otherwise, it's a "strict ER-Hop." Further,
          we say that the abstract node of a strict or loose ER-Hop is a
          strict or a loose node, respectively.  Loose and strict nodes
          are always interpreted relative to their prior abstract nodes.
          The path between a strict node and its prior node MUST include
          only network nodes from the strict node and its prior abstract
          node.

          The path between a loose node and its prior node MAY include
          other network nodes, which are not part of the strict node or
          its prior abstract node.

    Contents
          A variable length field containing a node or abstract node
          which is one of the consecutive nodes that make up the
          explicitly routed PW.

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                                ER-Hop TLV

   Details of ER Hop semantics are defined in section 2.4.

3.4.  ER-Hop Semantics

   This section describes the various sementics associated with ER-HOP
   TLV.

3.4.1.  ER-Hop 1: IPv4 Prefix

   The abstract node represented by this ER-Hop is the set of nodes,
   which have an IPv4 address, which lies within this prefix.  Note that
   a prefix length of 32 indicates a single IPv4 node.

     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 = 0x0801     |      Length = 8               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |L|      Reserved                               |    PreLen     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    IPv4 Address (4 bytes)                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    U/F
          These bits MUST be set to zero and the procedures of [RFC5036]
          followed when the TLV is not known to the receiving node.

    Type
          A fourteen-bit field carrying the value of the ER-Hop 1, IPv4
          Address, Type = 0x0801

    Length
          Specifies the length of the value field in bytes = 8.

    L Bit
          Set to indicate Loose hop.
          Cleared to indicate a strict hop.

    Reserved
          Zero on transmission.  Ignored on receipt.

    PreLen
          Prefix Length 1-32

    IP Address
          A four-byte field indicating the IP Address.

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                          ER-Hop with IPv4 Prefix

3.4.2.  ER-Hop 2: IPv6 Prefix

   The abstract node represented by this ER-Hop is the set of nodes,
   which have an IPv6 address, which lies within this prefix.  Note that
   a prefix length of 128 indicates a single IPv6 node.
     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|          0x0802           |      Length = 20              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |L|             Reserved                        |    PreLen     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  IPV6 address                                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  IPV6 address (continued)                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  IPV6 address (continued)                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  IPV6 address (continued)                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    U/F
          These bits MUST be set to zero and the procedures of [RFC5036]
          followed when the TLV is not known to the receiving node.

    Type
          A fourteen-bit field carrying the value of the ER-Hop 2, IPv6
          Address, Type = 0x0802

    Length
          Specifies the length of the value field in bytes = 20.

    L Bit
          Set to indicate Loose hop.
          Cleared to indicate a strict hop.

    Reserved
          Zero on transmission.  Ignored on receipt.

    PreLen
          Prefix Length 1-128

    IPv6 address
          A 128-bit unicast host addresses.

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3.4.3.  ER-Hop 3: L2 PW Address

   The L2 PW Address follows attachment circuit addressing which is
   derived from [RFC5003] AII type 2, as shown here:

     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|          0x0802           |      Length = 18              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |L|             Reserved                        |    PreLen     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  AII Type=02  |    Length     |        Global ID              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       Global ID (contd.)      |        Prefix                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       Prefix (contd.)         |        AC ID                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      AC ID                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    U/F
          These bits MUST be set to zero and the procedures of [RFC5036]
          followed when the TLV is not known to the receiving node.

     Type
          A fourteen-bit field carrying the value of the ER-Hop 3, L2 PW
          Address, Type = 0x0805

    Length
          Specifies the length of the value field in bytes = 18.

    L Bit
          Set to indicate Loose hop.
          Cleared to indicate a strict hop.

    Reserved
          Zero on transmission.  Ignored on receipt.

    PreLen
          Prefix Length 1-96

    L2 PW Address
          An AII Address as defined in [RFC5003].

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4.  Explicit Route TLV Processing

4.1.  Next-Hop Selection

   A PW Label Mapping Message containing an explicit route TLV MUST
   specify the next hop for a given MS-PW path.  Selection of this next
   hop MAY involve a selection from a set of possible alternatives.  The
   mechanism for making a selection from this set is implementation
   specific and is outside of the scope of this document.  The mechanism
   used to select a particular path is also outside of the scope of this
   document, but each node MUST attempt to determine a loop-free path.
   Note that such mechanisms MAY be overridden by local policy.

   To determine the next hop for the MS-PW path, a node performs the
   following steps.  Note that these procedures assume that a valid S-PE
   address has been assigned to the node, as per Section 3.1, above.

   1.  The node receiving the Label Mapping Message must evaluate the
       first ER-Hop.  If the L bit is not set in the first ER-Hop and if
       the node is not part of the abstract node described by the first
       ER-Hop, it has received the message in error, and MUST reply with
       a Label Release Message with a "Bad Initial ER-Hop Error"
       (0x04000004) status code.  If the L bit is set and the local node
       is not part of the abstract node described by the first ER-Hop,
       the node selects a next hop that is along the path to the
       abstract node described by the first ER-Hop.  If there is no
       first ER-Hop, the message is also in error and the node should
       return a "Bad Explicit Routing TLV Error" (0x04000001) status
       code in a Label Release Message sent to upstream node.

   2.  If there are no further ER-Hop TLVs following the first ER-Hop
       TLV, this indicates the end of the explicit route.  The explicit
       route TLV MUST be removed from the Label Mapping Message.  This
       node may or may not be the end of the PW.  Processing continues
       as per Section 4.2, where a new explicit route TLV MAY be added
       to the Label Mapping Message.

   3.  If a second ER-Hop TV does exist, and the node is also a part of
       the abstract node described by the second ER-Hop, then the node
       deletes the first ER-Hop and continues processing with step 2,
       above.  Note that this makes the second ER-Hop into the first ER-
       Hop for the iteration for the next PW segment.

   4.  The node determines if it is topologically adjacent to the
       abstract node described by the second ER-Hop.  That is, it is
       directly connected to the next node by a PW control plane
       adjacency.  If so, the node selects a particular next hop which
       is a member of the abstract node.  The node then deletes the

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       first ER-Hop and continues processing as per Section 4.2, below.

   5.  Next, the node selects a next hop within the abstract node of the
       first ER-Hop that is along the path to the abstract node of the
       second ER-Hop.  If no such path exists then there are two cases:

       A.  If the second ER-Hop is a strict ER-Hop, then there is an
           error and the node MUST return a Label Release Message to
           upstream node with "Bad Strict Node Error" (0x04000002)
           status code.

       B.  Otherwise, if the second ER-Hop is a loose ER-Hop, then the
           node selects any next hop that is along the path to the next
           abstract node.  If no path exists within the MPLS domain,
           then there is an error, and the node MUST return a Label
           Release Message to upstream node with "Bad Loose Node Error"
           (0x04000002) status code.

   6.  Finally, the node replaces the first ER-Hop with any ER-Hop that
       denotes an abstract node containing the next hop.  This is
       necessary so that when the explicit route is received by the next
       hop, it will be accepted.

   7.  Progress the Label Mapping Message to the next hop.

4.2.  Adding ER Hops to the Explicit Route TLV

   After selecting a next hop, the node may alter the explicit route in
   the following ways.

   If, as part of executing the algorithm in Section 4.1, the explicit
   route TLV is removed, the node may add a new explicit route TLV.

   Otherwise, if the node is a member of the abstract node for the first
   ER-Hop, then a series of ER-Hops may be inserted before the First ER-
   Hop or may replace the first ER-Hop.  Each ER-Hop in this series must
   denote an abstract node that is a subset of the current abstract
   node.

   Alternately, if the first ER-Hop is a loose ER-Hop, an arbitrary
   series of ER-Hops may be inserted prior to the first ER-Hop.

5.  IANA Considerations

   RFC5036 [RFC5036] defines the LDP TLV name space which is maintained
   by IANA as "LDP TLV Registry".  TLV types for the Explicit Route TLV,
   IPv4 Prefix ER-Hop TLV, and the IPv6 Prefix ER-Hop TLV are already

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   defined in the LDP TLV Registry.

   This draft proposes one new TLV type:

   TLV Type                               Suggested Value
   ------------------------------------   ---------------
   L2 PW Address of Switching point        0x0805

6.  Security Considerations

   This document introduces no new security considerations over
   [RFC5036], [RFC4447] and [I-D.ietf-pwe3-dynamic-ms-pw].

7.  Acknowledgements

   The authors gratefully acknowledge the input of Lizhong Jin.

8.  Normative References

   [I-D.ietf-pwe3-dynamic-ms-pw]
              Martini, L., Bocci, M., and F. Balus, "Dynamic Placement
              of Multi Segment Pseudowires",
              draft-ietf-pwe3-dynamic-ms-pw-14 (work in progress),
              July 2011.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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

   [RFC5003]  Metz, C., Martini, L., Balus, F., and J. Sugimoto,
              "Attachment Individual Identifier (AII) Types for
              Aggregation", RFC 5003, September 2007.

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

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Authors' Addresses

   Pranjal Kumar Dutta
   Alcatel-Lucent
   701 E Middlefield Road
   Mountain View, California  94043
   USA

   Email: pranjal.dutta@alcatel-lucent.com

   Matthew Bocci
   Alcatel-Lucent

   Email: matthew.bocci@alcatel-lucent.com

   Luca Martini
   Cisco Systems

   Email: lmartini@cisco.com

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