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Versions: (draft-boucadair-pcp-nat64-prefix64-option) 00 01 02 03 04 05 06 RFC 7225

PCP Working Group                                           M. Boucadair
Internet-Draft                                            France Telecom
Intended status: Standards Track                            May 22, 2013
Expires: November 23, 2013


                    Learn NAT64 PREFIX64s using PCP
                    draft-ietf-pcp-nat64-prefix64-01

Abstract

   This document defines a new PCP extension to learn the IPv6
   prefix(es) used by a PCP-controlled NAT64 device to build
   IPv4-embedded IPv6 addresses.  This extension is needed for
   successful communications when IPv4 addresses are used in referrals.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 November 23, 2013.

Copyright Notice

   Copyright (c) 2013 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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   2
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   2
     3.1.  Issues  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . .   3
       3.2.1.  AAAA Synthesis by Stub-resolver . . . . . . . . . . .   3
       3.2.2.  Applications Referrals  . . . . . . . . . . . . . . .   3
   4.  PREFIX64 Option . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Format  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Behavior  . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Flow Examples . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  TCP Session Initiated from an IPv6-only Host  . . . . . .   6
     5.2.  SIP Flow Example  . . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   This document defines a new PCP extension [RFC6887] to inform PCP
   clients about the Pref64::/n [RFC6052] used by a PCP-controlled NAT64
   device [RFC6146].  It does so by defining a new PREFIX64 option.

   This extension is required to help establishing communications
   between IPv6-only hosts and remote IPv4-only hosts.

   Some illustration examples are provided in Section 5.  Detailed
   experiment results are available at
   [I-D.boucadair-pcp-nat64-experiments].

   The use of this PCP extension for NAT64 load balancing purposes
   ([I-D.zhang-behave-nat64-load-balancing]) is out of scope.

2.  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].

3.  Problem Statement





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3.1.  Issues

   This document proposes a deterministic solution to solve the
   following issues:

   o  Learn the Pref64::/n used by an upstream NAT64 function.  This is
      needed to help:

      *  distinguishing between IPv4-converted IPv6 addresses and native
         IPv6 addresses.
      *  implementing IPv6 address synthesis for applications not
         relying on DNS.
   o  Avoid stale Pref64::/n.
   o  Discover multiple Pref64::/n when multiple prefixes in a network.
   o  Use DNSSEC in the presence of NAT64.

   Section 3.2 lists some applications which encounter the issues listed
   above.

3.2.  Use Cases

3.2.1.  AAAA Synthesis by Stub-resolver

   The extension defined in this document can be used for hosts with
   DNS64 capability [RFC6147], added to the host's stub-resolver.

   The stub resolver on the host will try to obtain (native) AAAA
   records and if it they are not found, the DNS64 function on the host
   will query for A records and then synthesizes AAAA records.  Using
   the PREFIX64 PCP extension, the host's stub-resolver can learn the
   prefix used for IPv6/IPv4 translator and synthesize AAAA records
   accordingly.

   Learning the Pref64::/n used to construct IPv4-converted IPv6
   addresses [RFC6052] allows to make use of DNSSEC.

3.2.2.  Applications Referrals

   As discussed in [I-D.carpenter-behave-referral-object], a frequently
   occurring situation is that one entity A connected to the Internet
   (or to some private network) needs to inform another entity B how to
   reach either A itself or some third-party entity C.  This is known as
   address referral.

   In the particular context of NAT64 [RFC6146], applications relying on
   address referral will fail because an IPv6-only client won't be able
   to make use of an IPv4 address received in a referral.  A non-
   exhaustive list of applications is provided below:



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   o  BitTorrent is a distributed file sharing infrastructure which is
      based on P2P techniques for exchanging files between connected
      users.  In order to download a given file, a BitTorrent client
      needs to obtain the corresponding torrent file.  Then, it connects
      to the tracker to retrieve a list of lechers (clients which are
      currently downloading the file but do not yet detain all the
      portions of the file) and seeders (clients which detain all the
      portions of the file and are uploading them to other requesting
      clients).  The client connects to those machines and downloads the
      available portions of the requested file.  In the presence of an
      address sharing function, some encountered issues are solved if
      PCP is enabled (see [I-D.boucadair-pcp-bittorrent]).
      Nevertheless, an IPv6-only client can not connect to a remote
      IPv4-only machine even if base PCP is enabled.  An extension is
      needed to solve this concern.
   o  In SIP environments [RFC3261], the SDP part of exchanged SIP
      messages includes required information for establishment of RTP
      sessions (particularly IP address and port number).  When a NAT64
      is involved in the path, an IPv6-only SIP UA (User Agent) which
      receives an SDP offer/answer containing an IPv4 address, cannot
      send media streams to the remote endpoint.
   o  An IPv6-only WebRTC (Web Real-Time communication,
      [I-D.ietf-rtcweb-overview]) can not make use of an IPv4 address
      received in referrals to establish a successful session with a
      remote IPv4-only WebRTC agent.

4.  PREFIX64 Option

4.1.  Format

   The format of the PREFIX64 option is depicted in Figure 1.  This
   option follows the guidelines specified in Section 7.3 of [RFC6887].

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Option Code  |  Reserved     |   Option Length               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Prefix64 (Variable)                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 1: Prefix64 PCP Option

   The description of the fields is as follows:

   o  Option Code: To be assigned by IANA.
   o  Option Length: Indicates in octets the length of the Pref64::/n.
      Allowed values are 4, 5, 6, 7, 8, or 12 [RFC6052].



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   o  Prefix64: This field identifies the IPv6 unicast prefix to be used
      for constructing an IPv4-embedded IPv6 address from an IPv4
      address.  The address synthesize MUST follow the guidelines
      documented in [RFC6052].

      Option Name: PREFIX64
      Number: <to be assigned in the optional-to-process range>
      Purpose: Learn the prefix used by the NAT64 to build
       IPv4-embedded IPv6 addresses. This is used by a host
       for local address synthesis (e.g., when IPv4 address is
       present in referrals).
      Valid for Opcodes: MAP, ANNOUNCE
      Length: Variable
      May appear in: request, response.
      Maximum occurrences: 1 for a request. As many as fit within
       maximum PCP message size for a response.


4.2.  Behavior

   The PCP client includes a PREFIX64 option in a MAP or ANNOUNCE
   request to learn the IPv6 prefix used by an upstream PCP-controlled
   NAT64 device.  When enclosed in a PCP request, Prefix64 MUST be set
   to ::/96.  The PREFIX64 option can be inserted in a MAP request used
   to learn the external IP address as detailed in Section 11.6 of
   [RFC6887].

   The PCP server controlling a NAT64 SHOULD be configured to return to
   requesting PCP clients the value of the Pref64::/n used to build
   IPv4-embedded IPv6 addresses.  When enabled, the PREFIX64 option
   conveys the value of Pref64::/n.

   The PCP server controlling a NAT64 MAY be configured to include a
   PREFIX64 option in all MAP responses even if the PREFIX64 option is
   not listed in the associated request.  The PCP server controlling a
   NAT64 MAY be configured to include a PREFIX64 option in its ANNOUNCE
   messages.

   When multiple prefixes are configured in a network, the PCP server
   MAY be configured to return multiple PREFIX64 options in the same
   message to the PCP client.  The PCP server includes in the first
   PREFIX64 option, which appears in the PCP message it sends to the PCP
   client, the prefix to perform local IPv6 address synthesis [RFC6052].
   Remaining PREFIX64 options convey other Pref64::/n configured in the
   network.  Returning these prefixes allows an end host to avoid any
   NAT64 deployed in the network.





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   The host embedding the PCP client uses the prefix included in the
   first PREFIX64 option for local address synthesize.  Remaining
   prefixes are used by the host to avoid any NAT64 deployed in the
   network.  How the content of the PREFIX64 option(s) is passed to the
   OS is implementation-specific.

   The PCP client MUST be prepared to receive multiple Pref64::/n (e.g.,
   if several PCP servers are deployed; each of them is configured with
   a distinct Pref64::/n).  The PCP client SHOULD associate each
   received Pref64::/n with the PCP server from which the Pref64::/n
   information was retrieved.  If the PCP client fails to contact a
   given PCP server, the PCP client SHOULD clear the prefix(es) it
   learned from that PCP server.

   If a distinct Pref64::/n is configured to the PCP-controlled NAT64
   device, the PCP server SHOULD issue an unsolicited PCP message to
   inform the PCP client about the new Pref64::/n.  Upon receipt of this
   message, the PCP client replaces the old prefix received from the
   same PCP server with the new Pref64::/n included in the PREFIX64
   option.

5.  Flow Examples

   This section provides a non-normative description of use cases
   relying on the PREFIX64 option.

5.1.  TCP Session Initiated from an IPv6-only Host

   The usage shown in Figure 2 depicts a typical usage of the PREFIX64
   option when a DNS64 capability is embedded in the host.

   In the example shown in Figure 2, once the IPv6-only client
   discovered the IPv4 address of the remote IPv4-only server, it
   retrieves the Pref64::/n (i.e., 2001:db8:122:300::/56) to be used to
   build an IPv4-embedded IPv6 address for that server.  This is
   achieved using the PREFIX64 option (Steps (a) and (b)).  The client
   uses 2001:db8:122:300::/56 to construct an IPv6 address and then
   initiates a TCP connection (Steps (1) to (4)).

         +---------+              +-----+             +---------+
         |IPv6-only|              |NAT64|             |IPv4-only|
         | Client  |              |     |             |  Server |
         +---------+              +-----+             +---------+
             |                       |                     |
             | (a) PCP MAP Request   |                     |
             |      PREFIX64         |                     |
             |======================>|                     |
             | (b) PCP MAP Response  |                     |



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             |      PREFIX64 =       |                     |
             | 2001:db8:122:300::/56 |                     |
             |<======================|                     |
             |    (1) TCP SYN        |    (2) TCP SYN      |
             |======================>|====================>|
             |   (4) TCP SYN/ACK     |   (3) TCP SYN/ACK   |
             |<======================|<====================|
             |    (5) TCP ACK        |    (6) TCP ACK      |
             |======================>|====================>|
             |                       |                     |


     Figure 2: Example of TCP session initiated from an IPv6-only host

5.2.  SIP Flow Example

   Figure 3 shows an example of the use of the option defined in
   Section 4 in a SIP context.  In order for RTP/RTCP flows to be
   exchanged between an IPv6-only SIP UA and an IPv4-only UA without
   requiring any ALG (Application Level Gateway) at the NAT64 nor any
   particular function at the IPv4-only SIP Proxy Server (e.g., Hosted
   NAT traversal), the PORT_SET option [I-D.ietf-pcp-port-set] is used
   in addition to the PREFIX64 option.

   In Steps (a) and (b), the IPv6-only SIP UA retrieves a pair of ports
   to be used for RTP/RTCP sessions, the external IPv4 address and the
   Pref64::/n to build IPv4-embedded IPv6 addresses.  This is achieved
   by issuing a MAP request which includes a PREFIX64 option and a
   PORT_SET option.  A pair of ports (i.e., port_X/port_X+1) and an
   external IPv4 address are then returned by the PCP server to the
   requesting PCP client together with a Pref64::/n (i.e.,
   2001:db8:122::/48).

   The returned external IPv4 address and external port numbers are used
   by the IPv6-only SIP UA to build its SDP offer which contains
   exclusively IPv4 addresses (especially in the "c=" line, the port
   indicated for media port is the external port assigned by the PCP
   server).  The INVITE request including the SDP offer is then
   forwarded by the NAT64 to the Proxy Server which will relay it to the
   called party (i.e., IPv4-only SIP UA) (Steps (1) to (3)).

   The remote IPv4-only SIP UA accepts the offer and sends back its SDP
   answer in a "200 OK" message which is relayed by the SIP Proxy Server
   and NAT64 until being delivered to IPv6-only SIP UA (Steps (4) to
   (6)).






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   Pref64::/n (2001:db8:122::/48) is used by the IPv6-only SIP UA to
   construct a corresponding IPv6 address of the IPv4 address enclosed
   in the SDP answer made by the IPv4-only SIP UA (Step 6).

   IPv6-only SIP UA and IPv4-only SIP UA are then able to exchange RTP/
   RTCP flows without requiring any ALG at the NAT64 nor any particular
   function at the IPv4-only SIP Proxy Server.

   +---------+              +-----+       +------------+     +---------+
   |IPv6-only|              |NAT64|       |  IPv4 SIP  |     |IPv4-only|
   | SIP UA  |              |     |       |Proxy Server|     | SIP UA  |
   +---------+              +-----+       +------------+     +---------+
       | (a) PCP MAP Request   |                |                 |
       |        PORT_SET       |                |                 |
       |        PREFIX64       |                |                 |
       |======================>|                |                 |
       | (b) PCP MAP Response  |                |                 |
       |        PORT_SET       |                |                 |
       |        PREFIX64:      |                |                 |
       |     2001:db8:122::/48 |                |                 |
       |<======================|                |                 |
       |  (1) SIP INVITE       | (2) SIP INVITE |  (3) SIP INVITE |
       |======================>|===============>|================>|
       |   (6) SIP 200 OK      | (5) SIP 200 OK |  (4) SIP 200 OK |
       |<======================|<===============|<================|
       |     (7) SIP ACK       |  (8) SIP ACK   |    (9) SIP ACK  |
       |======================>|===============>|================>|
       |                       |                |                 |
       |src port:     dst port:|src port:                dst port:|
       |port_A           port_B|port_X                      port_B|
       |<======IPv6 RTP=======>|<============IPv4 RTP============>|
       |<===== IPv6 RTCP======>|<============IPv4 RTCP===========>|
       |src port:     dst port:|src port:                dst port:|
       |port_A+1       port_B+1|port_X+1                  port_B+1|
       |                       |                                  |

          Figure 3: Example of IPv6 to IPv4 SIP initiated Session

   When the session is initiated from the IPv4-only SIP UA (see Figure
   4), the IPv6-only SIP UA retrieves a pair of ports to be used for RTP
   /RTCP session, the external IPv4 address and the Pref64::/n to build
   IPv4-embedded IPv6 addresses (Steps (a) and (b)).  These two steps
   can be delayed until receiving the INVITE message (Step 3).

   The retrieved IPv4 address and port numbers are used to build the SDP
   answer in Step (4) while Pref64::/n is used to construct a
   corresponding IPv6 address of the IPv4 address enclosed in the SDP
   offer made by the IPv4-only SIP UA (Step 3).  RTP/RTCP flows are



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   exchanged between an IPv6-only SIP UA and an IPv4-only UA without
   requiring any ALG at the NAT64 nor any function at the IPv4-only SIP
   Proxy Server.

   +---------+              +-----+       +------------+     +---------+
   |IPv6-only|              |NAT64|       |  IPv4 SIP  |     |IPv4-only|
   | SIP UA  |              |     |       |Proxy Server|     | SIP UA  |
   +---------+              +-----+       +------------+     +---------+
       | (a) PCP MAP Request   |                |                 |
       |        PORT_SET       |                |                 |
       |        PREFIX64       |                |                 |
       |======================>|                |                 |
       | (b) PCP MAP Response  |                |                 |
       |        PORT_SET       |                |                 |
       |        PREFIX64:      |                |                 |
       |     2001:db8:122::/48 |                |                 |
       |<======================|                |                 |
       |  (3) SIP INVITE       | (2) SIP INVITE |  (1) SIP INVITE |
       |<======================|<===============|<================|
       |   (4) SIP 200 OK      | (5) SIP 200 OK |  (6) SIP 200 OK |
       |======================>|===============>|================>|
       |     (9) SIP ACK       |  (8) SIP ACK   |    (7) SIP ACK  |
       |<======================|<===============|<================|
       |                       |                |                 |
       |src port:     dst port:|src port:                dst port:|
       |port_a           port_b|port_Y                      port_b|
       |<======IPv6 RTP=======>|<============IPv4 RTP============>|
       |<===== IPv6 RTCP======>|<============IPv4 RTCP===========>|
       |src port:     dst port:|src port:                dst port:|
       |port_a+1       port_b+1|port_Y+1                  port_b+1|
       |                       |                                  |

          Figure 4: Example of IPv4 to IPv6 SIP initiated Session

6.  IANA Considerations

   The following PCP Option Code is to be allocated in the optional-to-
   process range (the registry is maintained in http://www.iana.org/
   assignments/pcp-parameters/pcp-parameters.xml#option-rules):

      PREFIX64

7.  Security Considerations

   PCP-related security considerations are discussed in [RFC6887].

   As discussed in [RFC6147], an attacker can manage to change the
   Pref64::/n used by the DNS64, the traffic generated by the host that



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   receives the synthetic reply will be delivered to the altered Pref64.
   This can result in either a denial- of-service (DoS) attack, a
   flooding attack, or an eavesdropping attack.  This attack can be
   achieved by altering PCP messages issued by a legitimate PCP server
   or a fake PCP server is used.

   Means to defend against attackers who can modify between the PCP
   server and the PCP client, or who can inject spoofed packets that
   appear to come from a legitimate PCP server SHOULD be enabled.  For
   example, access control lists (ACLs) can be installed on the PCP
   client, PCP server, and the network between them, so those ACLs allow
   only communications from a trusted PCP server to the PCP client.

   PCP server discovery is out of scope of this document.  It is the
   responsibility of PCP server discovery document(s) to elaborate on
   the security considerations to discover a legitimate PCP server.

8.  Acknowledgements

   Many thanks to S.  Perreault , R.  Tirumaleswar, T.  Tsou, D.  Wing,
   J.  Zhao, R.  Penno and I.  Van Beijnum for the comments and
   suggestions.

9.  References

9.1.  Normative References

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

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              October 2010.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.

   [RFC6147]  Bagnulo, M., Sullivan, A., Matthews, P., and I. van
              Beijnum, "DNS64: DNS Extensions for Network Address
              Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
              April 2011.




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   [RFC6887]  Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)", RFC 6887, April
              2013.

9.2.  Informative References

   [I-D.boucadair-pcp-bittorrent]
              Boucadair, M., Zheng, T., Deng, X., and J. Queiroz,
              "Behavior of BitTorrent service in PCP-enabled networks
              with Address Sharing", draft-boucadair-pcp-bittorrent-00
              (work in progress), May 2012.

   [I-D.boucadair-pcp-nat64-experiments]
              Abdesselam, M., Boucadair, M., Hasnaoui, A., and J.
              Queiroz, "PCP NAT64 Experiments", draft-boucadair-pcp-
              nat64-experiments-00 (work in progress), September 2012.

   [I-D.carpenter-behave-referral-object]
              Carpenter, B., Boucadair, M., Halpern, J., Jiang, S., and
              K. Moore, "A Generic Referral Object for Internet
              Entities", draft-carpenter-behave-referral-object-01 (work
              in progress), October 2009.

   [I-D.ietf-pcp-port-set]
              Sun, Q., Boucadair, M., Sivakumar, S., Zhou, C., Tsou, T.,
              and S. Perreault, "Port Control Protocol (PCP) Extension
              for Port Set Allocation", draft-ietf-pcp-port-set-01 (work
              in progress), May 2013.

   [I-D.ietf-rtcweb-overview]
              Alvestrand, H., "Overview: Real Time Protocols for Brower-
              based Applications", draft-ietf-rtcweb-overview-06 (work
              in progress), February 2013.

   [I-D.zhang-behave-nat64-load-balancing]
              Zhang, D., Xu, X., and M. Boucadair, "Considerations on
              NAT64 Load-Balancing", draft-zhang-behave-nat64-load-
              balancing-03 (work in progress), July 2011.

Author's Address

   Mohamed Boucadair
   France Telecom
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com



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