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Expires in six month                                K. Watanabe, Hitachi
                                                    Y. Atarashi, Hitachi
                                                    T. Miyamoto, Hitachi
                                                      K. Yamamoto, NAIST
                                               J. Murai, Keio University


            A Communication Mechanism between IPv4 and IPv6

              <draft-tsuchiya-ipv4-ipv6-translator-00.txt>

Status of this Memo

    This document is an Internet-Draft. 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.''

    To learn the current status of any Internet-Draft, please check the
    ``1id-abstracts.txt'' listing contained in the Internet-Drafts
    Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net
    (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific
    Rim).

Abstract

    In the late stage of the transition from IPv4 to IPv6, IPv4 lands
    are interconnected by IPv6 ocean and it is necessary for an IPv4
    node and an IPv6 to communicate directly. This memo proposes a
    mechanism to enable such direct communication with extension name
    servers, an address mapper, and translators for each IPv4 land.

1. Introduction

    RFC1933 [TRANS-MECH] proposed mechanisms to transit IPv4 [IPv4] to
    IPv6 [IPv6], including dual stack and tunneling, for the early
    stage. IPv6 nodes are assumed to have IPv4 stack and IPv4 addresses.
    In the late stage of the transition, however, the space of IPv4



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    address will be exhausted. So, an IPv4 address cannot be assigned to
    dual-stack hosts. Moreover, IPv6-only hosts will appear for cost
    reasons. It is expected that IPv4 hosts will retain for a long time,
    even after appearance of IPv6-only hosts. Therefore, it is highly
    desired to develop a mechanism to enable a communication between an
    IPv4 host and an IPv6 host directly.

    Though a header conversion mechanism is defined in [HDRCNV],
    interaction for an IPv4 host, an IPv6 host, a header conversion
    router, and name servers is not mentioned. This memo describes an
    entire scheme of direct communications between IPv4 hosts and IPv6
    hosts. The scheme is applicable to environments where there are
    multiple name servers and multiple site boundary routes thanks to
    one "address mapper".  It is not necessary to modify IPv4 hosts and
    IPv6 hosts.

    This document uses the words defined in [IPV4], [IPV6], and
    [TRANS-MECH].

2. Components

    In the late stage of the transition, IPv4 "land"s are interconnected
    by IPv6 "ocean". A set of IPv4-only nodes in an organization is an
    example of IPv6 island.

    The proposed system consists of extension name servers, one address
    mapper, and translators. To implement communication between IPv4
    nodes and IPv6 nodes, each IPv4 island needs to install such
    components.

    Extension name servers have both IPv4 stack and IPv6 stack and
    provides name service to IPv4 nodes and IPv6 nodes. Translators also
    have dual-stack functionality and translates "language" of IPv4
    nodes and that of IPv6 nodes. The address mapper is communicates
    only with the extension name servers and the translators.














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    Figure 1 illustrates an IPv4 land which installed the proposed
    system.

      +---------+                                +-------- //
      |IPv4 node|                                |
      +----+----+                                |
           |                                     |
    +------+------+                              |
    |             |                              |
    |An IPv4 land |                              | IPv6 ocean
    |             |                              |
    |             |  +------------------------+  |         +---------+
    |             +--+ extension name servers +--+         |IPv6 node|
    |             |  +------------+-----------+  |         +---------+
    |             |               |              |
    |             |  +------------+-----------+  |         +---------+
    |             |  |   one address mapper   |  |         |IPv6 node|
    |             |  +------------+-----------+  |         +---------+
    |             |               |              |
    |             |  +------------+-----------+  |         +---------+
    |             +--+       translators      +--+         |IPv6 node|
    |             |  +------------------------+  |         +---------+
    |             |                              |
    +------+------+                              |
           |                                     |
      +----+----+                                |
      |IPv4 node|                                +-------- //
      +---------+

                                Figure 1


2.1 Translator between IPv4 and IPv6

    The followings are examples of Translator between IPv4 and IPv6.

    (1) Proxy gateway

        An proxy gateway locates between an IPv4 host and an IPv6 host
        and establishes both an IPv4 connection to the IPv4 host and an
        IPv6 connection to the IPv6 host. The proxy gateway relays data
        from the IPv4 host to the IPv6 host and vice versa.

    (2) Header conversion router

        A header conversion router locates between an IPv4 host and an



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        IPv6 host. When the router receives an IPv4 packet, the router
        converts its IPv4 header to an IPv6 header then forwards it.
        When the router receives an IPv6 packet, the router converts its
        IPv6 header to an IPv4 header then fragments the packet if
        necessary and forwards it.

2.2 Extension Name Server

    Extension name servers returns a "proper" answer in a response to
    IPv4 node's request or IPv6 node's request.

    An IPv4 node typically requests one of extension name servers to
    resolve 'A' record correspond to a host name. If 'A' record is
    resolved, the server returns it. If only 'AAAA' record is available,
    the server requests an address mapper to assign one IPv4 address
    correspond to its IPv6 address. Then the server returns the assigned
    IPv4 address to the IPv4 node.

    An IPv6 node typically requests one of extension name servers to
    resolve 'AAAA' record correspond to a host name. If 'AAAA' record is
    resolved, the server returns it. If only 'A' record is available,
    the server requests the address mapper to assign one IPv6 address
    correspond to its IPv4 address. Then the server returns the assigned
    IPv6 address to IPv6 node.

2.3 Address Mapper

    An address mapper maintains an IPv4 address spool and an IPv6
    address spool. An example of the IPv4 address spool is private
    addresses(e.g number 10). An example of the IPv6 address spool is a
    part of IPv6 space assigned to the organization where the IPv4 land
    locates inside.

    When an extension name server or a translator requests one IPv6
    address for an IPv4 address, the address mapper selects one IPv6
    address from the IPv6 address spool and returns it.

    When an extension name server or a translator requests one IPv4
    address for an IPv6 address, the address mapper selects one IPv4
    address from the IPv4 address spool and returns it.

3. Interaction Examples

    The following subsection explains communication from an IPv4 node to
    an IPv6 node and communication from an IPv6 node to an IPv4 node,
    respectively.



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3.1 Communication from an IPv4 node to an IPv6 node

    This subsection describes communication between an IPv4 node called
    "host4" and an IPv6 node called "host6". The communication is
    triggered by "host4".

    "host4" sends a query to an extension name server to resolves 'A'
    record for "host6".

    The extension name server tries resolving both 'A' record and 'AAAA'
    record for "host6" but only 'AAAA' record is resolved. Then the
    server requests an address mapper to assign one IPv4 address
    correspond to the IPv6 address.

    The address mapper selects one IPv4 address out of its IPv4 address
    spool and returns it to the server.

    The server creates 'A' record for the assigned IPv4 address and
    returns it to "host4".

    "host4" sends IPv4 data to "host6".

    The IPv4 data reaches a translator. The translator tries translating
    the IPv4 data to IPv6 data but does not know how to translate. (For
    example, a proxy gateway cannot create an IPv6 connection to "host6"
    since the IPv6 address of "host6" is not available.)  So, the
    translator requests the mapper to tell mapping entries for the IPv4
    source address and the IPv4 destination address.

    The mapper looks up its mapping table with the IPv4 destination
    address and finds one IPv6 address for it. Then the mapper looks up
    its mapping table with the IPv4 source address. In this case, there
    is not a mapping entry so the mapper selects one IPv6 address for
    the IPv4 source address. Finally, the mapper returns a pair of the
    IPv6 source address and the IPv6 destination address to the
    translator.

    The translator translates the IPv4 data to IPv6 data. (For example,
    the proxy gateway creates one IPv6 connection to "host6" and relay
    the IPv4 data.)

    The IPv6 data reaches "host6". "host6" sends new IPv6 data to
    "host4".

    The IPv6 data reaches the translator. This time the translator has
    mapping entries for the IPv6 source address and the IPv6 destination



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    address. The translator translates the IPv6 data to IPv4 data. (For
    example, the proxy gateway just relays the data.)

    The IPv4 data reaches "host4".

    The following diagram illustrates the interaction above:


        IPv4    extension      address    translator    IPv6
        node    name server    mapper                   node
        "host4"                                         "host6"

        Resolve an IPv4 address for host6

            ---> Query of 'A' record for "host6".

                only 'AAAA' record is resolved.

                           ---> Request one IPv4 address correspond to
                                the IPv6 address.

                               Assign on IPv4 address.

                           <--- Reply with the IPv4 address.

                Create 'A' record for the IPv4 address.

            <--- Reply with the 'A' record.





















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        IPv4    extension      address    translator    IPv6
        node    name server    mapper                   node
        "host4"                                         "host6"

        Send data to host6

            =============================> IPv4 data

                                          Try translating but don't
                                          know how to translate it.

                                      <--- Request IPv6 addresses
                                           corresond to the IPv4 source
                                           address and to the IPv4
                                           destination address.

                                One IPv6 address correspond to the IPv4
                                destination address is already
                                available. Assign one IPv6 address for
                                the IPv4 source address.

                                      ---> Reply with the IPv6 source
                                           address and the IPv6
                                           destination address.

                                          Translate IPv4 to IPv6.

                                                    ===> IPv6 data

                                                        Reply data to
                                                        host4

                                                    <=== IPv6 data

                                          Translate IPv6 to IPv4

           <============================== IPv6 data


3.2 Communication from an IPv6 node to an IPv4 node

    In a case where communication is triggered by "host6", its query to
    resolve 'AAAA' record for "host4" is eventually delivered to one of
    extension name servers. After interaction is symmetric to the case
    described in Sention 3.1.




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4. Security Consideration

    Header conversions of AH [AH] and ESP [ESP] are cryptographically
    impossible. This is a big disadvantage of header conversion router
    approach. On the other hand, it is possible to use AH and ESP in
    proxy gateway approach.


5. References

    [AH] Stephen Kent and Randall Atkinson, "IP Authentication Header",
        Internet-Draft, July 1997.

    [ESP] Stephen Kent and Randall Atkinson, "IP Encapsulating Security
        Payload (ESP)", Internet-Draft, July 1997.

    [HDRCNV] Erik Nordmark, "IPv4/IPv6 Stateless Header Translator",
        Inernet-Draft, July 1997.

    [IPV4] J. Postel, "Internet Protocol", RFC 791, September 1981.

    [IPV6] S. Deering and R. Hinden, "Internet Protocol, Version 6
        (IPv6) Specification", RFC 1883, January 1996.

    [TRANS-MECH] R. Gilligan and E. Nordmark, "Transition Mechanisms for
        IPv6 Hosts and Routers", RFC 1933, April 1996.

10. Author's Addresses

    Kazuaki TSUCHIYA
    Hitachi, Ltd.
    Hitachi Systemplaza Shinkawasaki
    890 Kashimada, Saiwai, Kawasaki, 211 Japan

    Phone: +81-44-549-1714
    Fax:   +81-44-549-1721
    Email: tsuchi@isrd.hitachi.co.jp

    Munechika SUMIKAWA
    Office Systems Division, Hitachi, Ltd.
    810 Shimoimaizumi, Ebina-shi 243-04 JAPAN

    Phone: +81-462-35-2111
    FAX:   +81-462-35-8325
    EMail: sumikawa@ebina.hitachi.co.jp




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    Ken WATANABE
    Hitachi, Ltd.
    Hitachi Systemplaza Shinkawasaki
    890 Kashimada, Saiwai, Kawasaki, 211 Japan

    Phone: +81-44-549-1714
    Fax:   +81-44-549-1721
    Email: nabeken@isrd.hitachi.co.jp

    Yoshifumi ATARASHI
    Office Systems Division, Hitachi, Ltd.
    810 Shimoimaizumi, Ebina-shi 243-04 JAPAN

    Phone: +81-462-35-2111
    FAX:   +81-462-35-8325
    EMail: atarashi@ebina.hitachi.co.jp

    Takahisa MIYAMOTO
    Hitachi, Ltd.
    Hitachi Systemplaza Shinkawasaki
    890 Kashimada, Saiwai, Kawasaki, 211 Japan

    Phone: +81-44-549-1714
    Fax:   +81-44-549-1721
    Email: t-miyamo@isrd.hitachi.co.jp

    Kazu YAMAMOTO
    Nara Institute of Science and Technology
    8916-5 Takayama, Ikoma City 630-01 JAPAN

    Phone: +81-7437-2-5322
    FAX:   +81-7437-2-5329
    EMail: Kazu@Mew.org

    Jun MURAI
    Keio University
    5322 Endo, Fujisawa 252 JAPAN

    Phone: +81-466-47-5111
    Fax:   +81-466-49-1101
    EMail: jun@wide.ad.jp

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