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INTERNET-DRAFT                                                 Jim Bound
NGTRANS Tools Working Group                         Compaq Computer Corp
Obsoletes draft-ietf-ngtrans-assgn-ipv4-00.txt              January 1999



        Assignment of IPv4 Global Addresses to IPv6 Hosts (AIIH)

              <draft-ietf-ngtrans-assgn-ipv4-addrs-01.txt>


Status of this Memo

        This document is a submission by the Next Generation Transition
        Working Group of the Internet Engineering Task Force (IETF).
        Comments should be submitted to the ngtrans@sunroof.eng.sun.com
        mailing list.

        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 view the entire list of current Internet-Drafts, please check
        the "1id-abstracts.txt" listing contained in the Internet-Drafts
        Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net
        (Europe), munnari.oz.au (Pacific Rim), ftp.ietf.org (US East
        Coast), or ftp.isi.edu (US West Coast).

        Distribution of this memo is unlimited.

Abstract

   The initial deployment of IPv6 will require a tightly coupled use of
   IPv4 addresses to support the interoperation of IPv6 and IPv4.  Nodes
   will be able to be deployed with IPv6 addresses, but will still need
   to communicate with IPv4 nodes that do not have a dual IP layer
   supporting both IPv4 and IPv6.  This specification defines a
   mechanism called Assignment of IPv4 Global Addresses to IPv6 Hosts
   (AIIH), which will assign an IPv6 Host a temporary IPv4 Global
   Address, which can be used to communicate with a Host that supports
   IPv4 or IPv4/IPv6.  An objective of this specification is to avoid
   the use of address translation for the deployment of IPv6 in a
   network.  Another objective is to demonstrate that IPv6 Addresses can
   be deployed now instead of non-Global IPv4 Addresses within an
   Intranet.










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Table of Contents:

1. Introduction.................................................3
2. Terminology..................................................4
2.1 IPv6 AIIH Terminology.......................................4
2.2 Specification Language......................................5
3. AIIH Design Model ...........................................6
3.1 AIIH DHCPv6/DNS Server......................................6
3.2 AIIH Network Configuration Intranet to Internet Taxonomy....6
3.3 Accessing Hosts Services within an IPv6 Intranet............7
3.4 IPv6 Communications over the Internet with IPv4 Tunnels.....8
4. Requesting an IPv4 Global Address............................8
5. IPv4 Query for an IPv6 Host..................................8
5.1 Reaching the Intranet Primary DNS Server....................8
5.2 Getting the A Record Query to the AIIH Server...............9
6. AIIH Server Processing.......................................9
6.1 AIIH DNS Query and DHCPv6 Processing.......................10
6.2 AIIH DHCPv6 Client IPv4 Global Address Requests............11
6.3 Cleaning up the AIIH IPv4 Assigned Address.................11
6.3 Conceptual Model of an AIIH Server Implementation..........11
7. AIIH DHCPv6 Requirements....................................11
7.1 DHCPv6 IPv4 Global Address Extension.......................11
7.2 AIIH Server Processing of an IPv4 Global Address Extension.12
7.3 AIIH Client Processing of an IPv4 Global Address Extension.13
8. Security Considerations.....................................13
9. Year 2000 Considerations....................................14
Appendix A - Open Issues.......................................14
Appendix B - Draft Changes and Rationale History...............15
Acknowledgments................................................17
References.....................................................17
Authors' Address...............................................18





























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1. Introduction

   The initial deployment of IPv6 will require a tightly coupled use of
   IPv4 addresses to support the interoperation of IPv6 and IPv4.  Nodes
   will be able to be deployed with IPv6 addresses, but will still need
   to communicate with IPv4 nodes that do not have a dual IP layer
   supporting both IPv4 and IPv6.  This specification defines a
   mechanism called Assignment of IPv4 Global Addresses to IPv6 Hosts
   (AIIH), which will assign an IPv6 Host a temporary IPv4 Global
   Address, which can be used to communicate with a Host that supports
   IPv4 or IPv4/IPv6.  An objective of this specification is to avoid
   the use of address translation for the deployment of IPv6 in a
   network.  Another objective is to demonstrate that IPv6 Addresses can
   be deployed now instead of non-Global IPv4 Addresses within an
   Intranet.

   AIIH uses the DNS [1,2] mechanisms to resolve a query for an IPv6
   Host name from an IPv4 stack that wants to communicate with the IPv4
   stack of an IPv6 Host that supports both IPv6 and IPv4.  The IPv6
   Host that is the object of such a query will be assigned a temporary
   IPv4 Global Address, thru DHCPv6 [4], and the IPv4 Host performing
   the query will receive the IPv4 address assigned to the IPv6 Host in
   a DNS query response.  Communications between the two Hosts can then
   begin directly without any intermediate nodes performing Network
   Address Translation [14] or Application Level Gateway [7] functions.

   AIIH also permits IPv6 Hosts to request IPv4 Global Addresses thru
   the new DHCPv6 Extension [5] defined in this specification (section
   7).  This new Extension will also provide the Host with the IPv4 or
   IPv6 Tunnel End Point to be used to encapsulate an IPv4 packet [15]
   to reach an IPv4 or IPv4/IPv6 router.

   The reason for this specification is that users deploying IPv6 will
   not want (and most likely will not be able) to assign IPv4 addresses
   to IPv6 nodes as they are deployed into their site, because IPv4
   addresses are a rare commodity.  But, IPv6 Hosts will still need to
   communicate with IPv4 Hosts within an Intranet and across the
   Internet.  The AIIH mechanisms provide a means to avoid address
   translation in a network for IPv6 Hosts that support a dual IPv4/IPv6
   network layer [15].

   The specification will begin by defining the terminology (section 2),
   then discuss the AIIH design model (section 3), then define the
   mechanism for an IPv6 Host to request an IPv4 address (section 4),
   then define the mechanism used for an IPv4 node to query an IPv6 node
   (section 5), then discuss the AIIH Server processing to support this
   mechanism (section 6), and completes the mechanism by defining the
   DHCPv6 Extension needed to assign a temporary IPv4 address to an IPv6
   node (section 7).  The specification then discusses Security (section
   8) and Year 2000 considerations (section 9).  Appendix A will discuss
   Open Issues that need to be discussed in the ngtrans Tools Working
   Group, and maintain the state of Open Issues as STILL OPEN, RESOLVED,
   or PARTIALLY RESOLVED during the draft updates to AIIH.  Appendix B
   will keep a historical account of changes to the draft and rationale
   for those changes as they occur, and maintain consistence with the
   Open Issues in Appendix A.




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2. Terminology



2.1 IPv6 AIIH Terminology

   IPv6 Protocol Terms:    See [3]

   IPv6 Transition Terms:  See [15]

   DHCPv6 Terms:           See [4,5]

   AIIH Server:            A Server that supports DNS [2] and DHCPv6 [4,5]
                           and communications between DNS and DHCPv6, which
                           is implementation defined.  See sections 4, 5
                           and 6.

   IPv4 Global Address:    An IPv4 address that is globally routable on
                           the Internet.









































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2.2 Specification Language

   In this document, several words are used to signify the requirements
   of the specification, in accordance with RFC 2119 [9].  These words
   are often capitalized.

      MUST          This word, or the adjective "required", means that
                    the definition is an absolute requirement of the
                    specification.

      MUST NOT      This phrase means that the definition is an absolute
                    prohibition of the specification.

      SHOULD        This word, or the adjective "recommended", means
                    that there may exist valid reasons in particular
                    circumstances to ignore this item, but the full
                    implications must be understood and carefully
                    weighed before choosing a different course.
                    Unexpected results may result otherwise.

      MAY           This word, or the adjective "optional", means that
                    this item is one of an allowed set of alternatives.
                    An implementation which does not include this option
                    MUST be prepared to interoperate with another
                    implementation which does include the option.

      silently discard
                    The implementation discards the packet without
                    further processing, and without indicating an error
                    to the sender.  The implementation SHOULD provide
                    the capability of logging the error, including the
                    contents of the discarded packet, and SHOULD record
                    the event in a statistics counter.



























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3. AIIH Design Model

   The design model provides two mechanism to assign an IPv6 Host an
   IPv4 address.  The first mechanism is for the Host to request an IPv4
   address that is globally routable, and the second is for an AIIH
   Server to assign an IPv6 Host a globally routable IPv4 address using
   the DHCPv6 Reconfigure Message.  The assumption in this specification
   is that a site has a certain number of IPv4 Global Addresses, which
   can be assigned within their enterprise on a temporary basis for use
   by Hosts in the site.  The design model also assumes the site has an
   IPv4/IPv6 router in the site that is used to send and receive packets
   over the Internet.

   For an IPv6 Host to participate in the AIIH mechanism it MUST have a
   dual IP layer, supporting both an IPv4 and IPv6 stack.  This
   specification makes the assumption that for IPv6 initial deployment
   Host nodes will not ship an IPv6-only stack implementation.  For
   embedded system type nodes that support only an IPv6 stack AIIH
   cannot be a solution.



3.1 AIIH DHCPv6/DNS Server

   The AIIH Server supports a co-located DHCPv6 and DNS Server and other
   implementation defined software functions.  The AIIH server
   configuration files and database is not defined in this
   specification.  There can be one or many AIIH Servers on an Intranet
   and how they maintain consistency and Tunnel End Point configurations
   for IPv6 links is implementation defined.



3.2 AIIH Network Configuration Intranet to Internet Taxonomy

   The design model supports the following network configuration abstraction:

      Host X ----------------------- Router Y ------------------- Host Z
      (Intranet)                 (Intranet & Internet)        (Intranet)

      Host X represents an IPv4/IPv6 implementation, that has an
      IPv6 address.  The IPv6 addresses is denoted as X6.

      Router Y represents an IPv4/IPv6 implementation that has both
      an IPv4 Global and IPv6 Address.  The IPv4 address is denoted as
      Y4 and the IPv6 address is denoted as Y6.

      Host Z represents an IPv4 or IPv4/IPv6 implementation that has
      an IPv4 Global Address, and MAY have an IPv6 Address.  The IPv4
      address is denoted as Z4 and if an IPv6 address exists it is
      denoted as Z6.

      For Host X to communicate with Host Z4 it must perform several
      operations:

      1.  Obtain an IPv4 Global Address denoted by X4, from an AIIH
          Server.
      2.  Send the packet to Y4 or Y6 so it can be routed to Z4. This can


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          be accomplished in several manners from the information
          provided by the new DHCPv6 IPv4 Global Address Extension
          (section 7) sent to X6:

          2.1   If the Tunnel End Point is an IPv4-Compatible [20]
                address then encapsulate IPv4 packets to Z4 within
                IPv4 to reach Y4 [14].

          2.2   If the Tunnel End Point is an IPv6 Address then
                encapsulate IPv4 packets to Z4 within IPv6 to reach
                Y6 [13], this means an IPv4/IPv6 interim router exists
                between X4 and Y6.

          2.3   If the Tunnel End Point is zero (not present) then
                it is assumed that the router on X4's LAN can route
                IPv4 Global Addresses to Y4 within the site.  This
                means the site has an IPv4 Global Address backbone
                at least for routability to Y4.

          For Y4 to communicate with X4, upon receiving packets from
          Z4 for X4 several options exist:

          1.   When Y4 received an IPv4 or encapsulated packet from
                2.1 above then it MUST maintain that route to X4
               from that IPv4 address and either encapsulate the
               IPv4 packet to X4 or send it directly to the interim
               router that can reach X4.

          2.   When Y4 received an IPv6 packet from X4 in 2.2 above
               it MUST maintain a tunnel route to the IPv6 address
               from which it received the X4 packet.

          3.   When Y4's site has an IPv4 Global Address backbone
               routable network in place, Y4 uses normal routing
               mechanisms to forward the packet to X4.



3.3 Accessing Hosts Services within an IPv6 Intranet

   When Z4 wants to communicate with an application service on X4, the
   mechanisms defined in section 5 will accomplish this task.  For this
   type of service Y4 and X4 MUST be able to communicate by way of an
   IPv4 Global Address backbone network within the Site to X4.  Section
   5 also discusses Hosts within the Intranet accessing X4, when an IPv4
   Global Address is used for that communications.

   If the site is using non-Global IPv4 Addresses as a network topology
   [17] for Intranet communications, Host X can obtain that address from
   an IPv4 DHCPv4 Server [16] using X's IPv4 implementation and such
   addresses are denoted as X4P (for IPv4 private address) and are only
   used for site Intranet communications.








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3.4 IPv6 Communications over the Internet with IPv4 Tunnels

   AIIH could be used to communicate with IPv6 Hosts across the Internet
   by X6 tunneling IPv6 packets in IPv4 to Y4, which would be delivered
   to the network domain at Z.  At Z's network the IPv4 packet would be
   decapsulated and the IPv6 packet would be delivered to Z6.  This
   would add significant mechanisms to this specification and a possible
   extension for future work around AIIH.  But it is noted here now for
   consistency, and as a possible future work item.




4. Requesting an IPv4 Global Address

   An IPv4/IPv6 Host can request an IPv4 Global Address by using the
   IPv4 Global Address Extension defined in section 7.  The IPv4/IPv6
   Host MUST support DHCPv6 [4] and the DHCPv6 Extensions [5].  The
   Requests/Response Model of DHCPv6 will process this new extension as
   any other extension.  There is no need to define a new message type
   for DHCPv6 for this processing or add to the DHCPv6 protocol.

   Once the Host has obtained an IPv4 Global Address it SHOULD NOT
   update DNS to reflect an A type or PTR type record for this address.
   The reason is that the intent is to provide a Host with this
   temporary address to use for communications with an IPv4 node.  Once
   the reason for obtaining an IPv4 Global Address has been satisfied
   the Host MUST Release this IPv4 Global Address from the AIIH DHCPv6
   Server implementation.

   When an IPv4/IPv6 Host receives an IPv4 Global Address either from a
   Request as a Client DHCPv6 Host or from an AIIH Server Reconfigure
   Message as defined in section 6, the Host MUST create any necessary
   configured tunnels using the Tunnel End Point address provided by the
   AIIH DHCPv6 Server in an implementation defined manner.  See section
   7 for additional requirements for processing the DHCPv6 IPv4 Global
   Address Extension.




5. IPv4 Query for an IPv6 Host

   AIIH supports IPv4 DNS queries from the Internet or within an
   Intranet to establish communications with an IPv6 Host.  An IPv4 Host
   will not necessarily know that it is trying to establish
   communications with an IPv6 Host.  The IPv4 Host will communicate
   with the IPv6 Host by first obtaining an IPv4 Global Address for the
   IPv6 node as it does for any other node (e.g. gethostbyname API).



5.1 Reaching the Intranet Primary DNS Server

   The IPv4 DNS query will reach the Primary DNS Name Server for the
   IPv6 Host.  It is implementation defined how the DNS query passes
   thru a domains Firewall [7] to reach the IPv6 nodes Primary DNS
   Server. This is a per user policy that is beyond the scope of this


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   specification.



5.2 Getting the A Record Query to the AIIH Server

   When the Primary DNS Server for the IPv6 node receives the IPv4 Hosts
   query, it will do a DNS search for that IPv6 Host and find that there
   is an Authoritative DNS Server for that specific DNS A record, which
   represents an IPv6 Host.  That DNS Server will be one part of the
   AIIH Server software.  After the AIIH DHCPv6 Server assigns the IPv6
   node a temporary IPv4 Global Address, the AIIH DNS Server will
   respond to the original IPv4 DNS query authoritatively with an IPv4
   Global Address for the IPv6 Host or return Host Not Found.

   For Example:

     IPv4 node "v4host.abc.com" queries for "v6host1.xyz.com"

     Query reaches Primary DNS Server for "v6host1.xyz.com".

-----------
     xyz.com.  IN SOA primary.xyz.com.  etc etc.
     .
     .
     xyz.com          IN  NS  primary.xyz.com
     aiih.xyz.com     IN  NS  v6trans.aiih.xyz.com
     .
     .
     primary.xyz.com          IN   A    202.13.12.6
     v6trans.aiih.xyz.com     IN   A    202.13.12.8
      .
      .
      .
     v6host1.xyz.com        IN   CNAME   v6host1.aiih.xyz.com
     v6host2.xyz.com        IN   CNAME   v6host2.aiih.xyz.com
     v6host3.xyz.com        IN   CNAME   v6host3.aiih.xyz.com

   DNS query will end up going to the authoritative server
   v6trans.aiih.xyz.com looking for v6host1.aiih.xyz.com.  This permits
   the AIIH Server to now process a request for an IPv4 Global Address
   for an IPv6 Host that had no IPv6 DNS AAAA Record [18].



6. AIIH Server Processing

   The AIIH Server is an implementation where DNS, DHCPv6, and
   communications between those two applications exists.  These
   applications MAY be co-located on the same Host, but that is not a
   requirement of this specification.  How DNS and DHCPv6 communicate is
   implementation defined.  The AIIH Server SHOULD support the following
   operations:

     1.  Act as the Authoritative DNS Name Server for a set of IPv6
         Hosts that can be queried for IPv4 Global Addresses.

     2.  Communications between the AIIH DNS server and the AIIH DHCPv6


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         Server.

     3.  An AIIH DHCPv6 Server that can maintain a pool of IPv4 Global
         Addresses in an implementation defined manner.

     4.  An AIIH DHCPv6 Server that can maintain Tunnel End Points for
         IPv6 Links in an implementation defined manner.

     5.  An AIIH DHCPv6 Server to process DNS AIIH IPv6 Host DNS queries,
         and Reconfiguring IPv6 Hosts to assign IPv4 Global Addresses to
         their interfaces.

     6.  Support DHCPv6 Client's requesting IPv4 Global Addresses.

     7.  Dynamically Updating DNS with an IPv4 Global Address for
         an IPv6 Host that supports IPv4/IPv6.

   An AIIH Server MUST support a dual IPv4/IPv6 network layer and
   implementation of IPv4/IPv6.



6.1 AIIH DNS Query and DHCPv6 Processing

   Once the AIIH DNS finds the IPv6 Host (v6host1.xyz.com) being queried
   the AIIH DNS requests from its corresponding AIIH DHCPv6 Server to
   assign an IPv4 Global Address to the IPv6 Host being queried.

   The AIIH DHCPv6 Server will look within its pool of IPv4 Global
   Addresses for an address and if a Tunnel End Point address is
   required for the IPv6 Host to reach the router (Y4) to route packets
   onto the Internet.  If an address is available the DHCPv6 Server will
   send a DHCPv6 Reconfigure Message to the IPv6 node to temporarily
   assign the node an IPv4 Global Address (see section 7).

   Once the AIIH DHCPv6 server is certain that the IPv6 Host has
   assigned the address to an interface, the AIIH DHCPv6 Server responds
   back to the corresponding AIIH DNS Server with the IPv4 Global
   Address assigned to the IPv6 Host being queried (v6host1.xyz.com), or
   that an address could not be assigned to this IPv6 Host.

   The AIIH DNS Server will now respond to the IPv4 DNS Query (Z4) as
   the Authoritative DNS Name Server with an address or Host not found.

   The AIIH DHCPv6 Server MAY send a dynamic update to DNS [6] to add an
   A type record to the Primary DNS Server, where the query came from to
   the AIIH DNS Server.  The Time-To-Live (TTL) field in the update MUST
   NOT be set to be greater than the valid lifetime for the IPv4-
   Compatible address in the DHCPv6 Extension provided to the DHCPv6
   Client.  It is highly recommended that the DNS not be updated with an
   A record for the IPv6 Host, unless that IPv6 Host provides a
   permanent IPv4 Application service needed by IPv4 Hosts.








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6.2 AIIH DHCPv6 Client IPv4 Global Address Requests

   An AIIH DHCPv6 Server will receive DHCPv6 Requests for IPv4 Global
   Addresses from IPv6 Host's.  The AIIH DHCPv6 Server will determine if
   an address is available and assign the address to the DHCPv6 Client
   as specified in section 7 of this specification.

   A DHCPv6 Client MUST NOT dynamically update DNS with an A record for
   an IPv4 Global Address it has been assigned.  All updates to DNS MUST
   be done by the AIIH DHCPv6 Server.  A DHCPv6 Client MAY request an
   that an address it has been assigned be added to the DNS, but as
   stated in section 6.1 this behavior is discouraged unless the Client
   perceives that an application it is providing will be of a permanent
   nature for IPv4 Hosts, as opposed to a transient need for an IPv4
   Global Address from the AIIH DHCPv6 Server.



6.3 Cleaning up the AIIH IPv4 Assigned Address

   Once the IPv4 address expires the DHCPv6 Server will permit the IPv4
   address to be reused.  But before the address can be reused the
   DHCPv6 Server MUST delete the IPv4 address from the Primary DNS
   Server, thru the Dynamic Updates to DNS mechanism, if an A record was
   added to the relative Primary DNS Server.



6.3 Conceptual Model of an AIIH Server Implementation

   A conceptual model (not part of this specification) for the AIIH DNS
   Server and DHCPv6 Server to communicate could be a number of
   mechanisms that support interprocess communications between two
   processes (e.g.  Threads, Local Domain Sockets, Shared Memory).  The
   IPv4 pool of addresses maintained by the DHCPv6 server is
   implementation defined how that is obtained and configured as is
   specified for IPv6 addresses in DHCPv6.  Once the IPv4 address is
   assigned it can be kept as part of the IPv6 nodes binding entry on
   the DHCPv6 Server as other configuration data is specified in DHCPv6.



7. AIIH DHCPv6 Requirements

   The AIIH DHCPv6 processes will use the DHCPv6 protocol and extensions
   to communicate between the AIIH DHCPv6 Server and the DHCPv6 Client.
   A new extension is required for DHCPv6 (section 7.1) to support AIIH.
   But there are some additional requirements placed on the AIIH
   processes that are not specific to the DHCPv6 protocol, but as
   transition and interoperation mechanisms for the IPv6 Hosts.



7.1 DHCPv6 IPv4 Global Address Extension

   The DHCPv6 IPv4 Global Address Extension informs a DHCPv6
   Server or Client that the IPv6 Address Extension [5] following this
   extension will contain an IPv4-Compatible Address [20], or is a Request


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   for an IPv4 Global Address from a Client, or a Reply assigning a Global
   IPv4 Address to a Client from a Server.  The extension can also
   provide an IPv4-Compatible or IPv6 address to be used as the Tunnel
   End Point to encapsulate an IPv6 packet within IPv4, or an IPv4
   packet within IPv6.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Tunnel End Point                     |
   |                           (If Present)                        |
   |                            (16 octets)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:                   TBD
   Length:                 0 or 16
   Tunnel End Point:       IPv6 Address if Present

   An IPv4 Global Address Extension MUST only apply to the extension
   following and not to any additional extensions in the DHCPv6
   protocol.



7.2 AIIH Server Processing of an IPv4 Global Address Extension

   When a DHCPv6 Server receives an IPv4 Global Address Extension it
   MUST assume that the next extension in a DHCPv6 Request or Release
   Message; the Client is either Requesting an IPv4 Global Address or
   Releasing an IPv4 Global Address.  If an address is present in either
   of these messages it will be in the form of an IPv4-Compatible
   Address.

   When a DHCPv6 Server sends a Client a Reconfigure Message to assign
   an IPv4 Global Address to an interface the Server MUST NOT set the
   "N" bit in the Reconfigure Message, so the Client performs the
   necessary Request/Reply DHCPv6 processing to obtain the address from
   the Server.  The Server MUST NOT assume that the Client has assigned
   the address to an interface until it has sent the corresponding Reply
   to the Client.

   The Server will no a priori the IPv6 routable address, when sending a
   Reconfiguration Message, of a Client within the Intranet, and should
   use that address with its own IPv6 address as the transaction binding
   cache until the DHCPv6 Client/Server protocol processing has
   completed.

   The Server will look in its implementation defined IPv4 Global
   Address configuration to determine if a Tunnel End Point is required
   for a specific IPv6 Address Prefix.  If that is the case the Server
   will put the address for the Tunnel End Point in the IPv4 Global
   Address Extension.  If the Tunnel End Point address is an IPv4
   address the Server will put that address in the extension as an
   IPv4-Compatible address.




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7.3 AIIH Client Processing of an IPv4 Global Address Extension

   When a DHCPv6 Client receives an IPv4 Global Address Extension it
   MUST assume that the next extension in a DHCPv6 Reconfigure or Reply
   Message; the Server is either assigning an IPv4 Global Address or
   supplying an IPv4 Global Address.  The address present in either of
   these messages will be in the form of an IPv4-Compatible Address.

   When the Client supplies an IPv4 Global Address as a Request or
   Release it MUST represent that address as an IPv4-Compatible Address.

   The Client MUST not assume it can use the IPv4 Global Address until
   it has received a corresponding Reply to the Client Request, which is
   required for a Reconfigure Message too as specified in section 7.2.

   Once the Client is assured it can use the IPv4 Global Address it can
   perform the following operations:


   1.  In an implementation defined manner the Client MUST assign the
       address to an interface, supporting the Client's IPv4 stack
       implementation.

   2.  In an implementation defined manner the Client MUST create an entry
       as an IPv4-Compatible Address supporting the processing required
       for an IPv6 address regarding the valid and preferred lifetimes
       as specified in IPv6 Addrconf [19].  Once the IPv4-Compatible
       address valid lifetime expires the IPv4 address MUST be deleted
       from the respective interface and a DHCPv6 Release Message
       MUST be sent to the AIIH DHCPv6 Server to delete the IPv4 Global
       Address from the Servers bindings.

   3.  If a Tunnel End Point address is provided in the IPv4 Global
       Address Extension, the Client MUST create a configured tunnel
       to the Tunnel End Point address, in an implementation defined
       manner.  If the Tunnel End Point address is an IPv4-Compatible
       address then the encapsulation is IPv4 within IPv4, if the
       Tunnel End Point is an IPv6 address then the encapsulation
       is IPv6 in IPv4.  These encapsulation mechanisms are defined
       in other IPv6 specifications [13, 15].




8. Security Considerations

   The AIIH mechanism can use all the defined security specifications
   for each functional part of the operation.  For DNS the DNS Security
   Extensions/Update can be used [10, 11], for DHCPv6 the DHCPv6
   Authentication Message can be used [5], and for communications
   between the IPv6 node, once it has an IPv4 address, and the remote
   IPv4 node, IPSEC [8] can be used as AIIH does not break secure end-
   to-end communications at any point in the mechanism.







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9. Year 2000 Considerations

   There are no Year 2000 issues in this specification.



Appendix A - Open Issues

   -  Need to add Examples for the new A6 Record types and how
      AAAA records can be used initially and references.

      OPEN 1/99

   -  Should use new Basic API terms for APIs.

      OPEN 1/99

   -  Need to add references for IPsec.

      OPEN 1/99

   -  Need to change references for DNS SEC esp solutions
      for Dynamic Updates to DNS.

      OPEN 1/99

   -  Need to look at issues for TCP TIME_WAIT state and other
      issues of addresses timing out.

      OPEN 1/99

   -  Need to add words to the design objective of preserving the
      end-to-end model for IPv6.

      OPEN 1/99

   -  The draft does not speak of PTR records for the IPv6 node
      A record once its created.  But its only useful during the
      lifetime of the assigned IPv4 address.

      STILL OPEN 3/98 Draft.  Closed - New A6 Records

   -  RFC 1183 RT Record is Experimental and there is some concern
      its obsolete.  Though some implementations still support some
      code for the RT record.  Also the Route Through semantics
      specified may need to strongly state the query is passed thru
      to the AIIH server.  This needs to be discussed.

      RESOLVED 3/98 Draft RT record deprecated.

   -  The Primary Server must look for the IPv6 node A record first
      before finding the RT record.  This needs to be verified
      as an implementation issue.

      RESOLVED 3/98 Draft - Use CNAME Records.

   -  When the AIIH Server responds to the query it may not be
      authoritative.  This needs to be verified and checked.


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      RESOLVED 3/98 Draft - Use CNAME Records and AIIH Server will
      be authoritative for the AIIH ZONE.

   -  Use of TTL for DNS Caches can cause problems for existing IPv4
      applications that cache IPv4 addresses.

      PARTIALLY RESOLVED - 3/98 Draft do not update DNS unless
      application will be permanent as opposed to transient.
      But TTL's that are updated still need some thought for
      legacy applications.  This also points to possibly adding
      new fields to the hostent structure which will at least
      help new IPv6 applications and legacy IPv4 applications
      to change to act in a well behaved manner.

   -  Specification needs a design example to get packets from
      the IPv6 node to an egress IPv4 router.

      PARTIALLY RESOLVED - 3/98 Draft added Design Section discussing
      tunneling mechanisms to be used and added Tunnel End Point address
      supplied by the AIIH DHCPv6 Server.  Still needs more discussion.

   -  NNAT name does not state what the specification does.

      RESOLVED - 3/98 Draft changed name to AIIH.




Appendix B - Draft Changes and Rationale History

Prior to January 1999:

  -  Changed the name of the draft from NNAT to AIIH. This also
      was done to prevent any perceived antagonism towards the NAT
      IETF work, which is not an objective of this work.

   -  Changed the Introduction to be more descriptive of the task
      at hand.

   -  Added IPv4 Global Address definition to terminology section.

   -  Added tunnel routability discussion to Design Model and a
      diagram abstraction to be used by the specification as
      a point of reference.

   -  Added to the architecture the ability for an IPv6 node to
      request an IPv4 Global Address from an AIIH DHCPv6 Server.
      This will permit AIIH to not only be useful for incoming
      IPv4 Host communications with IPv6 Hosts but also for outgoing
      IPv4 communications to the Internet from IPv6 Hosts and for
      Intranet enterprise communications between an IPv6 Host and
      IPv4 Host.

   -  Hinted that AIIH could be used in future work to define
      the capability for two IPv6 Hosts separated by an IPv4 cloud to
      to communicate thru tunnels, like thru a production 6bone
      network on the Internet.



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   -  Added new section to define how an IPv6 Host can request
      an IPv4 Global Address.

   -  Defined new mechanism for DNS query processing when an IPv6
      Host is looked for from an IPv4 Host, thru the use of CNAME
      and NS records.  This also permits IPv4 Host Intranet queries
      too now.

   -  New text clarifying that within the Intranet processing AIIH
      must only be used with IPv4 Global Addresses and Private
      IPv4 addresses should be retrieved from DHCPv4, via the IPv6
      Hosts IPv4 stack.

   -  Added new text defining the AIIH Server and the interaction
      with DHCPv6 and DNS applications.  Also further refined the
      requirements of the AIIH Server model.

   -  Expanded the section on the new DHCPv6 Section defining the
      required Server and Client behavior.  Added support to permit
      AIIH to be used for Intranet and Internet communications from
      within the site.

   -  Changed the DHCPv6 Extension for IPv4 Global Addresses to
      make it an extension which defines the next extension to
      be a request for AIIH processing relative to DHCPv6.

   -  Added a Tunnel End Point address to the new extension so
      IPv6 Hosts can configure tunnels to communicate with the
      egress router to transmit or reply with IPv4 on the Internet
      or within the Intranet.

   -  Defined the AIIH side affect requirements for IPv6 Hosts using
      this mechanism with DHCPv6.

   -  Updated and added to the Acknowledgment and References Section.

   -  Updated the Open Issues from December 1997 draft and noted
      the status of each issue as STILL OPEN, RESOLVED, or PARTIALLY
      RESOLVED.

   -  Updated the Changes from this draft.

January 1999:

   -  Updated References.

   -  Fixed Edit Issues

   -  Added new Open Issues.

   -  Removed all terms of NNAT except for History.









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Acknowledgments

   The author would like to thank Erik Nordmark for spending time
   reviewing with him this idea and suggesting the use of the DHCPv6
   Reconfigure Message, Richard Johnson for suggesting the use of the
   DNS CNAME Record, and Robert Watson who suggested that the AIIH
   DHCPv6 and DNS Server be co-located. George Tsirtsis who suggested
   using AIIH to assign IPv4 Global Addresses to IPv6 Hosts in general.
   Richard Draves and Jack McCann who have provided many helpful
   technical suggestions, and the NGTRANS working group for taking the
   time to work on AIIH.



References

   [1]  Mockapetris, P., "Domain Names - Concepts and Facilities", STD
        13, RFC 1034, USC/Information Sciences Institute, November 1987.

   [2]  Mockapetris, P., "Domain Names - Implementation and Specifica-
        tion", STD 13, RFC 1035, USC/Information Sciences Institute,
        November 1987.

   [3]  S. Deering and R. Hinden.  Internet Protocol, Version 6 (IPv6)
        Architecture", RFC 2460, December 1998.

   [4]  J. Bound and C. Perkins.  Dynamic Host Configuration Protocol
        for IPv6.  draft-ietf-dhc-dhcpv6-13.txt March 1998 (work
        in progress).

   [5]  C. Perkins.  Extensions for the Dynamic Host Configuration
        Protocol for IPv6.  draft-ietf-dhc-dhcpv6ext-10.txt March
        1998. (work in progress).

   [6]  P. Vixie, S. Thomson, Y. Rekhter, and J. Bound. Dynamic Updates
        to the Domain Name System (DNS).  RFC 2136, April 1997.

   [7]  William R. Cheswick and Steven Bellovin.  Firewalls and Internet
        Security.  Addison-Wesley, Reading, MA 1994 (ISBN:
        0-201-63357-4).

   [8]  IPSEC - This needs to include the Arch, Auth, and ESP specs.

   [9]  S. Bradner.  Key words for use in RFCs to indicate Requirement
        Levels.  RFC 2119, March 1997.

   [10] D. Eastlake and C. Kaufman. Domain Name System Security
        Extensions.  RFC 2065, January 1997.

   [11] D. Eastlake. Secure Domain Name System Dynamic Update.
        RFC 2137, April 1997.

   [12] R. Callon and D. Haskins. Routing Aspects Of IPv6 Transition
        RFC 2185, September 1997.

   [13] A. Conta and S. Deering.  Generic Packet Tunneling in IPv6.
        RFC 2473, December 1998.



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   [14] E. Nordmark. Stateless IP/ICMP Translator (SIIT)
         draft-ietf-ngtrans-siit-03.txts, November 1998
        (work in progress)

   [15] R. Gilligan and E. Nordmark.  Transition Mechanisms for IPv6
        Hosts and Routers. draft-ietf-ngtrans-trans-mech-01.txt,
        August 1998 (work in progress).

   [16] R. Droms.  Dynamic Host Configuration Protocol.
        RFC 2131, March 1997.

   [17] Rekhter, Moskowitz, Karrenburg, Groot.  Address Allocation
        for Private Networks. RFC 1918.  February 1996.

   [18] This needs to reflect the new DNS work for IPv6.

   [19] Thomson, Narten.  IPv6 Stateless Address Configuration.
        RFC 2462, December 1998.

   [20] Hinden, Deering.  IP Version 6 Addressing Architecture.
        RFC 2373, July 1998.



Authors' Address

    Jim Bound
    Compaq Computer Corporation
    110 Spitbrook Road, ZKO3-3/U14
    Nashua, NH 03062
    Phone: (603) 884-0400
    Email: bound@zk3.dec.com




























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