PREFIX64 PCP Option for NAT64
draft-boucadair-pcp-nat64-prefix64-option-00

Network Working Group                                       M. Boucadair
Internet-Draft                                            France Telecom
Intended status: Standards Track                       September 6, 2012
Expires: March 10, 2013

                     PREFIX64 PCP Option for NAT64
              draft-boucadair-pcp-nat64-prefix64-option-00

Abstract

   This document defines a new PCP option to learn the Prefix64 used by
   a PCP-controlled NAT64 device to build IPv4-embedded IPv6 addresses.
   This option is needed for successful communications when IPv4
   addresses are used in referrals (e.g., SIP).

Status of this Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . . . 4
   3.  PREFIX64 Option . . . . . . . . . . . . . . . . . . . . . . . . 4
     3.1.  Format  . . . . . . . . . . . . . . . . . . . . . . . . . . 4
     3.2.  Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 8

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1.  Introduction

   This document defines a new PCP option [I-D.ietf-pcp-base] to inform
   PCP Clients about the Prefix64 [RFC6052] used by a PCP-controlled
   NAT64 device [RFC6146].

   This option is required to help establishing communications between
   IPv6-only hosts and remote IPv4-hosts.  An illustration example is
   shown in Figure 1.  In this example, NAT64 is co-located with a PCP
   server while IPv6-only SIP UA interacts with a PCP Client.

   In Figure 1, the PCP Client issues a PCP MAP request with
   PORT_RESERVATION_OPTION to reserve a pair of ports preserving parity
   and contiguity [I-D.boucadair-pcp-rtp-rtcp].  A pair of ports and an
   external IPv4 address are then returned by the PCP server to the
   requesting PCP Client.  This information is 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)).  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)).  At the end of this process, IPv4-only SIP UA can
   send media streams to the IPv4 address/port as indicated in the SDP
   offer while IPv6-only SIP UA can not send media streams as only IPv4
   addresses are present in the SDP answer.

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   +---------+              +-----+       +------------+     +---------+
   |IPv6-only|              |NAT64|       |  IPv4 SIP  |     |IPv4-only|
   | SIP UA  |              |     |       |Proxy Server|     | SIP UA  |
   +---------+              +-----+       +------------+     +---------+
       |  (a) PCP MAP REQ      |                |                 |
       |PORT_RESERVATION_OPTION|                |                 |
       |======================>|                |                 |
       |  (b) PCP MAP REP      |                |                 |
       |PORT_RESERVATION_OPTION|                |                 |
       |<======================|                |                 |
       |                       |                |                 |
       |  (1) SIP INVITE       |                |                 |
       |======================>| (2) SIP INVITE |                 |
       |                       |===============>|  (3) SIP INVITE |
       |                       |                |================>|
       |                       |                |  (4) SIP 200 OK |
       |                       | (5) SIP 200 OK |<================|
       |   (6) SIP 200 OK      |<===============|                 |
       |<======================|                |                 |
       |                       |                |                 |

                                 Figure 1

   This issue is not specific to SIP but it is valid for all
   applications using referrals.

   A solution is proposed in Section 3.

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.  PREFIX64 Option

3.1.  Format

   The format of PREFIX64 PCP Option is depicted in Figure 2.

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

                       Figure 2: 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 Prefix64.
      Allowed values are 32, 40, 48, 56, 64, or 96 [RFC6052].

   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 by IANA.
         Purpose: Learn the prefix used by the NAT64 to build
         IPv4-embedded IPv6 addresses. This is be used by a host
         for local address synthesis (e.g., when IPv4 address is
         present in referrals).
         Valid for Opcodes: MAP
         Length: Variable
         May appear in: request, response.
         Maximum occurrences: 1

3.2.  Behaviour

   A PCP Client MAY include a PREFIX64 PCP Option in a MAP request to
   learn the IPv6 prefix used by an upstream PCP-controlled NAT64
   device.  When enclosed in a MAP request, PREFIX64 MUST be set to
   ::/96.

   A PCP Server controlling a NAT64 SHOULD be configured to return the
   value of the Prefix64 used to build IPv4-embedded IPv6 addresses to
   requesting PCP Clients.  When allowed, PREFIX64 PCP Option conveys
   the value of Prefix64.

   A PCP Server controlling a NAT64 SHOULD inject a PREFIX64 PCP Option
   in MAP responses even if the option is not listed in the associated
   request.

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   Upon receipt of the PREFIX64 PCP Option, the host embedding the PCP
   Client uses Prefix64 for local address synthesize [RFC6052].

4.  Example

   Figure 3 shows an example of the use of the option defined in
   Section 3.

   +---------+              +-----+       +------------+     +---------+
   |IPv6-only|              |NAT64|       |  IPv4 SIP  |     |IPv4-only|
   | SIP UA  |              |     |       |Proxy Server|     | SIP UA  |
   +---------+              +-----+       +------------+     +---------+
       |  (a) PCP MAP REQ      |                |                 |
       |PORT_RESERVATION_OPTION|                |                 |
       |     PREFIX64_OPTION   |                |                 |
       |======================>|                |                 |
       |  (b) PCP MAP REP      |                |                 |
       |PORT_RESERVATION_OPTION|                |                 |
       |     PREFIX64_OPTION   |                |                 |
       |<======================|                |                 |
       |                       |                |                 |
       |  (1) SIP INVITE       |                |                 |
       |======================>| (2) SIP INVITE |                 |
       |                       |===============>|  (3) SIP INVITE |
       |                       |                |================>|
       |                       |                |  (4) SIP 200 OK |
       |                       | (5) SIP 200 OK |<================|
       |   (6) SIP 200 OK      |<===============|                 |
       |<======================|                |                 |
       |                       |                |                 |
       |     (7) SIP ACK       |                |                 |
       |======================>|  (8) SIP ACK   |                 |
       |                       |===============>|    (9) SIP ACK  |
       |                       |                |================>|
       |                       |                                  |
       |<======IPv6 RTP=======>|<============IPv6 RTP============>|
       |<===== IPv6 RTCP======>|<============IPv6 RTCP===========>|
       |                       |                                  |

                                 Figure 3

   In Steps (a) and (b), the IPv6-only SIP UA retrieves a pair of ports
   to be used for RTP/RTCP, the external IPv4 address and the Prefix64
   to be used to build IPv4-embedded IPv6 addresses.

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   The retrieved IPv4 address and port numbers are used to build the SDP
   offer in Step (1) while Prefix64 is used to construct a corresponding
   IPv6 address of the IPv4 address enclosed in the SDP answer made by
   the IPv4-only SIP UA.

   RTP/RTCP flows are exchanged between an IPv6-only SIP UA and an IPv4-
   only UA without requiring any ALG at the NAT64 and no particular
   function to be supported by the IPv4-only SIP Proxy Server to help
   establishing the session (e.g., Hosted NAT traversal).

5.  IANA Considerations

   This document request a new PCP option:

      PREFIX64

6.  Security Considerations

   This document does not introduce any security issue in addition to
   what is taken into account in [I-D.ietf-pcp-base].

7.  Acknowledgements

   TBC.

8.  References

8.1.  Normative References

   [I-D.ietf-pcp-base]
              Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)",
              draft-ietf-pcp-base-26 (work in progress), June 2012.

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

   [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.

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8.2.  Informative References

   [I-D.boucadair-pcp-rtp-rtcp]
              Boucadair, M. and S. Sivakumar, "Reserving N and N+1 Ports
              with PCP", draft-boucadair-pcp-rtp-rtcp-04 (work in
              progress), April 2012.

Author's Address

   Mohamed Boucadair
   France Telecom
   Rennes,   35000
   France

   Email: mohamed.boucadair@orange.com

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