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INTERNET-DRAFT                                                 Jim Bound
NGTRANS Tools Working Group                                       Compaq
Obsoletes draft-ietf-ngtrans-dstm-01.txt                 Laurent Toutain
Expires January 2001                                        Hossam Afifi
                                                          Francis Dupont
                                                           ENST Bretagne
                                                            Alain Durand
                                                        Sun Microsystems



                 Dual Stack Transition Mechanism (DSTM)

                    <draft-ietf-ngtrans-dstm-02.txt>


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

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   To view the entire list of current Internet-Drafts, please check the
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   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, within
   an IPv6 Network.  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.  The Dual
   Stack Transition Mechanism (DSTM) provides a method to assign
   temporary Global IPv4 Addresses to IPv6 nodes, use of dynamic tunnels
   within an IPv6 Network to carry IPv4 traffic, and a defined set of
   processes and architecture for the supporting infrastructure required
   for this transition mechanism.




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Table of Contents:


1. Introduction.................................................3
2. Terminology..................................................4
2.1 IPv6 AIIH Terminology.......................................4
2.2 Specification Language......................................4
3. DSTM Overview and Assumptions................................5
4. DSTM Deployment Example......................................8
4.1 DSTM Client/Server Example .................................9
5 DTI Architecture..............................................9
5.1 Assignment of the IPv4 address to the DTI..................10
5.2 DTI Encapsulation of IPv4 packets..........................10
5.3 DTI IPv6 destination address...............................11
6. DHCPv6 Requirements.........................................12
6.1 DHCPv6 IPv4 Address Extension..............................12
6.1.1 Client Request of IPv4 Global Address Extension..........12
6.1.2 Server Reply of IPv4 Global Address Extension............13
6.1.3 Client Processing of IPv4 Address Extension..............14
6.2 Server Processing of an IPv4 Address Extension.............14
6.3 Client Processing of an IPv4 Address Extension.............14
7. Applicability Statement.....................................15
8. Security Considerations.....................................16
Changes from draft 01 to draft 02..............................16
Changes from draft 00 to draft 01..............................16
Acknowledgments................................................17
References.....................................................17


























































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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, within an
IPv6 Network.  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.  The Dual Stack Transition
Mechanism (DSTM) provides a method to assign temporary Global IPv4
Addresses to IPv6 nodes, use of dynamic tunnels within an IPv6 Network
to carry IPv4 traffic, and a defined set of processes and architecture
for the supporting infrastructure required for this transition
mechanism.

The DSTM assigns, when needed an IPv4 address to a dual IP layer host.
This will allow either IPv6 hosts to communicate with IPv4-only hosts,
or for IPv4-only applications to run without modification on an IPv6
host. This allocation mechanism is coupled with the ability to perform
dynamic tunneling of an IPv4 packet inside an IPv6 packet, to suppress
the exposure of IPv4 native packets within a DSTM domain of an IPv6
network. This will simplify the network management of IPv6 deployment,
since routers need only IPv6 routing tables to move IPv4 packets across
an IPv6 network.  This means that network managers do not need to
implement a routable IPv4 address plan for DSTM.

DSTM is targeted to help the interoperation of IPv6 newly deployed
networks with existing IPv4 networks. DSTM assumes that a users
objective in deploying an IPv6 network is to reduce the need and
reliability on IPv4 within a portion of their network.  In addition the
IPv4 globally routable address space available to the network is a
scarce resource, and the user does not want to deploy DHCPv4[16] to
assign temporary IPv4 addresses to IPv6 nodes, and would rather require
those nodes to use IPv6 to obtain or be given the IPv4 temporary
addresses from DHCPv6.  Also, to begin to reduce the IPv4 applications a
user has to support to obtain a temporary IPv6 IPv4-Mapped Address (see
Section 6), the client only has to run a DHCPv6 client process with the
DTI mechanisms in this specification.

The DSTM architecture is composed of a DHCPv6 server, that provides for
the assignment of IPv4 Global Addresses to IPv6 Hosts.  The DHCPv6
server will allocate temporary IPv4 Global Addresses to IPv6 hosts. The
DHCPv6 server will also be used to maintain the mapping between the
allocated IPv4 address and the permanent IPv6 address of the host. Each
IPv6 DSTM host will have an IPv4 interface called the Dynamic Tunneling
Interface (DTI) designed to encapsulate IPv4 packets into IPv6 packets.
Also a DSTM daemon exists working with a DHCPv6 client to resolve the
address space mechanics, between IPv4 and IPv6.

The specification will begin by defining the terminology (section 2),
then section 3 provides a technical overview of the DSTM methodology as
a transition mechanism.  Then in section 4 we provide a DSTM example.
Section 5 describes the DTI Architecture and Section 6 discusses
discusses the DHCPv6 extension requirements.  Section 7 provides the
DSTM Applicability Statement.







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2. Terminology



2.1 IPv6 AIIH Terminology


   DSTM Domain             The network areas on an Intranet where a
                           DHCPv6 Server has access to IPv6 nodes participating
                           in DSTM for that network.

   DSTM Border Router      A border router within a DSTM domain and
                           an IPv4-ONLY domain.

   IPv6 Protocol Terms:    See [3]

   IPv6 Transition Terms:  See [15]

   DHCPv6 Terms:           See [4,5]

   DTI:                    Dynamic Tunneling Interface. An interface
                           encapsulating IPv4 packets into IPv6 packets.

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

   Tunnel End Point (TEP)  Destination of the IPv6 packet containing an
                           IPv4 packet.  In most cases this will be
                           a dual stack border router.



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.


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      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.



3. DSTM Overview and Assumptions

DSTM as discussed in the introduction is a method which uses existing
protocols.  DSTM does not specify a protocol. However, DSTM defines a
new DHCPv6 Extension for transition.

The motivation for DSTM is to provide IPv6 nodes a means to acquire an
IPv4 Global Address, for communications with IPv4-only nodes or IPv4
applications.

The core assumption within this mechanism is that it is totally
transparent to applications, which can continue to work with IPv4
addresses. It is also transparent to the network which carry only IPv6
packets.  It is the authors viewpoint that the user in this case, has
deployed IPv6 to support end to end computing, without translation.
This aspect is fundamental during a transition process to guarantee that
every existing application will continue to work (e.g. IPsec, H.323),
which embed IPv4 addresses in the payload of a packet.

The DSTM model and assumptions are as follows:

  - The DSTM domain is within an Intranet not on the Internet.

  - IPv6 nodes do not maintain IPv4 addresses except on a temporary basis,
    to communicate with IPv4-only and IPv4 Applications.

  - Standard DHCPv6 is used to support the extension to provide
    and accept from DHCPv6 Servers Global IPv4 Addresses.

  - The DSTM domain for the IPv6 nodes will keep IPv4 routing
    tables to a minimum and use IPv6 routing, hence, reducing
    the network management required for IPv4 during transition.

  - Once IPv6 nodes have obtained IPv4 addresses Dynamic Tunneling is
    used to encapsulate the IPv4 packet within IPv6 and then forward
    that packet to an IPv6 TEP, where the packet will be decapulated and
    forwarded using IPv4.  DHCPv6 is used to provide TEPs to IPv6 nodes
    supporting DTI, as part of the new DHCPv6 Extension.

  - Existing IPv4 Applications or nodes do not have to be modified to
    communicate with DSTM.

  - Implementation defined software will have to exist to support DSTM:

    o  Ability within a DHCPv6 Server implementation to maintain
       configuration information about TEPs for encapsulating IPv4
       packets between IPv6 nodes that can forward IPv4 packets to an
       IPv4 routing realm, and to maintain a pool of Global IPv4


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       Addresses.

    o  Software within an IPv6 node to support the dynamic tunneling
       mechanisms in this specification to encapsulate IPv4 packets
       within IPv6 to send IPv4 packets on an IPv6 node.  In addition
       a daemon must exist to access a DHCPv6 client for Global IPv4
       Mapped Addresses and TEPs. How this daemon communicates with
       a DHCPv6 Client implementation is implementation defined, and
       left as an exercise for implementors of this transition
       mechanism.

    o  Software in DSTM Border Routers to recall or be able to cache
       the association of IPv6 and IPv4 addresses of nodes during
       decapsulation and encapsulation.














































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A simplistic overview of DSTM is as follows:

-----------------------------------------------
                                              |    IPv4 Internet or Intranet
        DSTM Domain Intranet                  |      IPv4 Applications
                                              |         Domain
                _____________________         |
               |                     |        |
               | DHCPv6 Server       |        |
               |_____________________|        |
                             ^                |
                             |                |
   __________________        |               _|_______
  |                  |       |              |        |
  | IPv6/IPv4 Node   |       |              |  DSTM  |
  |------------------|       |              | Border |
  |  DSTM Daemon     |       |              | Router |
  |  DHCPv6 client   |<-------              |  IPv6  |
  |------------------|                      |    &   |
  |    DTI/Route     |<-------------------->|  IPv4  |
   -------------------                       ---------
                                             |
----------------------------------------------

For an IPv6 host to participate in DSTM it MUST have a dual IP layer,
supporting both an IPv4 and an IPv6 stack.  DSTM is not a solution for
IPv6 ONLY nodes.

































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4. DSTM Deployment Example

In the example below, the following notation will be used:


   X    will designate an IPv6 host with a dual stack, X6 will be the IPv6
        address of this host and X4 the IPv4 address
   Y    will designate a DSTM border router at the boundary between an
        IPv6 DSTM domain and an IPv4-only domain.
   Z    will designate an IPv4-only host and Z4 its address.
   ==>  means an IPv6 packet
   -->  means an IPv4 packet
   ++>  means a tunneled IPv4 packet is encapsulated in an IPv6 packet
   ..>  means a DNS query or response. The path taken by this
        packet does not matter in the examples
   "a"  means the DNS name of a host












































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4.1 DSTM Client/Server Example

This example describes the case where an application (either compiled
for the IPv6 or IPv4 API) running on an IPv6 host (X6) wants to
establish a session with an IPv4 application on an IPv4-only host (Z4).

The IPv6 host is configured with the IPv6 address of a TEP, where an
IPv4 encapsulated packet will be sent.

The IPv4 routing table of node X is configured to send IPv4 packets to
the DTI interface.

        DHCPv6
        DNS
   X6          Y6/Y4          Z4
    |            |            |
    |. . . . . . . .>    Z    |    - X6 asks the DNS for an AAAA for "Z"
    |<. . . . . . . .   error |    - the DNS answers with an error
    |. . . . . . . .>    Z    |    - X6 asks for the A RR for "Z"
    |<. . . . . . . .    Z4   |    - the answer is Z4
    |            |            |
    |            |            |    - The application sends its first IPv4
    |            |            |      packet which arrives to the DTI interface
    |            |            |      (If the application is compiled for IPv6
    |            |            |      this can be done through an IPv4-mapped
    |            |            |      address).
    |            |            |
    |            |            |    - X6 needs an IPv4 address (first use)
    |====>       |            |    - X6 queries the DHCPv6 server for an
    |            |            |      IPv4 address using DHCPv6
    |<====       |            |    - The DHCPv6 server locates the client
    |            |            |      and provides a temporary IPv4
    |            |            |      global address.
    |+++++++++++>|            |    - The DTI sends the IPv6 packet to the
    |            |            |      TEP.
    |            |----------->|    - Y sends the packet to the destination Z4
    |            |            |    - Y caches the association between
    |            |            |      the IPv4 and IPv6 address of X.

When Z responds the packet returns back through Y.  Y having cached the
association between the IPv4 and the IPv6 address of X, is able to send
the packet encapsulating the IPv4 packet within IPv6 back to X.



5 DTI Architecture

The DTI interface is responsible for encapslating IPv4 packets within
IPv6 ones. IPv4 trafic can be directed to use this interface by an entry
in the host IPv4 routing table. This entry MUST be configured prior to
any use of the DSTM mechanism.

A conceptual model (not required) is the DTI interface is placed between
the IPv4 API and the IPv6 layer, as shown in the following figure, the
architectural example assumes a BSD UNIX type platform.


          +------------||------------+------------||------------+--||--+


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          |         IPv6 API         |          IPv4 API        | PF_  |
          |                          |                          | ROUTE|
          |                          +--------------------------+      |

          |                                                     |      |
          +-----------------------------------------------------+------+


On a DSTM IPv6 node a DHCPv6 client is running to manage the allocation
of the IPv4 Mapped Address.

The following example gives the configuration of an IPv4 routing table
with DTI.

All IPv4 packets except those to the 192.44.77/24 prefix are sent
through the dti0 interface. They will be encapsulated into IPv6 packets.
Packet to the 192.44.77/24 prefix will be sent natively on the link.

Routing tables

Internet:
Destination    Gateway          Flags    Refs     Use   Mtu  Netif Expire
default        link#1           UGSc       3        0  1460   dti0
192.44.77.0/24 192.44.77.3      UC         0        0  1500    le0   -
192.44.77.3    8:0:2b:1c:af:15  UHLW       4        0  1500    le0    649
127.0.0.1      127.0.0.1        UHl        1      102 16384    lo0



5.1 Assignment of the IPv4 address to the DTI

When the DTI interface is activated, an IPv4 address is not given to
that interface. If the interface is active, but has no IPv4 address.
When it has to send the first IPv4 packet, a request is sent to the
DHCPv6 client. The DHCPv6 client will send a DHCPv6 request to the
DHCPv6 server to get the temporary IPv4 Mapped Address and a TEP.

An IPv6 node can know it needs an IPv4 address if the DNS resolver on
the node knows that the destination address will be an IPv4 address.
Once the resolver knows this then a query to the interface index of the
node will inform the IPv6 node if it has an IPv4 interface configured.
This is just one example of how an implementation can determine if the
DSTM daemon must be called.




5.2 DTI Encapsulation of IPv4 packets

The protocol value for IPv4 encapsulation is 4 (as for IPv4 tunneling
over IPv4). When a tunneled packet arrives to the IPv6 destination, the
IPv6 header is removed and the packet is processed by the IPv4 layer.
The DSTM Border Router SHOULD cache the association between the IPv4 and
IPv6 source address.  The IPv4 packet will then be forwarded by the DSTM
border router using the IPv4 infrastructure.

The IPv6 source address of an encapsulated packet will be the IPv6
address of the interface on which the IPv6 packet will be sent.


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5.3 DTI IPv6 destination address

When a DTI has to encapsulate an IPv4 packet into an IPv6 packet. The
DTI has to determine the TEP IPv6 address for the destination. The TEP
can be the host destination or, if the destination host is IPv4-only,
the IPv6 address of an IPv4/IPv6 DSTM Border Router.

The TEP can be either statically configured or dynamically acquired when
the IPv6 node acquires an IPv4 Compatible Address from a DHCPv6 Server.

The TEP SHOULD be provided by the DHCPv6 server when the DSTM node
receives an IPv6 Mapped Address (section 6).  But, a DSTM node MAY
manually configure the TEP during early deployment of IPv6, but this
will not scale and is not recommended as a long term transition
solution.













































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6. DHCPv6 Requirements

The DSTM processes will use the DHCPv6 protocol and extensions to
communicate between the DHCPv6 Server and the DHCPv6 Client. A new
extension is required for DHCPv6 to support DSTM. But there are some
additional requirements placed on the DSTM processes that are not
specific to the DHCPv6 protocol as a transition and interoperation set
of mechanisms for the IPv6 hosts.



6.1 DHCPv6 IPv4 Address Extension

The DHCPv6 IPv4 Address Extension informs a DHCPv6 Server or Client that
the IPv6 Address Extension [5] following this extension will contain an
IPv4 Mapped Address [20], or is a Request for an IPv4 Mapped Address
from a client.  The extension can also provide an IPv6 address to be
used as the TEP to encapsulate an IPv4 packet within IPv6.

This extension can be used with the DHCPv6 Request, Reply, Release, and
Reconfigure-Init Messages for cases where a DHCPv6 wants to assign
clients IPv4 Mapped Addresses.

    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.




6.1.1 Client Request of IPv4 Global Address Extension

When the client requests an IPv4 address from the DHCPv6 Server the TEP
field MUST not be present, in the IPv4 Address Extension.

The IPv6 Address Extension fields as specified in [5] and depicted below
for reference MUST be filled in as follows:


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Type = 1            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


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   |    status     |C|I|L|Q|A|P|   reserved    |scope| prefix-len  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         (if present)                          |
   |                    IP address (16 octets)                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          (if present) preferred lifetime (4 octets)           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            (if present) valid lifetime (4 octets)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         (if present) DNS name (variable length)  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type      1


      Length    (unsigned integer, variable) The length of the Extension
                in Octets.

      status    zero

      bits C-P  not set

      scope     zero

      prefix-len zero

      All other fields are not present.




6.1.2 Server Reply of IPv4 Global Address Extension

The server will reply to the client with an IPv4 Address Extension, that
can contain an IPv6 Address Tunnel End Point.

The server will fill in the IPv6 Address Extension depicted in 6.1.1 as
follows:

      Type      1


      Length    (unsigned integer, variable) The length of the Extension
               in Octets.

      status    zero unless the server could not provide the address
                then the status will be set as defined in [5].

      bits C    set
           I    not set
           L    set
           Q-P  not set

      scope     zero

      prefix-len zero

      IP Address  IPv4 Mapped Address


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      Preferred Lifetime  Present

      Valid Lifetime      Present

      DNS Name            Not Present



6.1.3 Client Processing of IPv4 Address Extension

The processing of the IPv4 Address Extension on the client is
implementation defined but here are some guidelines for developers.

When processing the IPv6 Address Extension following the IPv4 Address
Extension, the IP Address provided will be an IPv4 Mapped Address.  A
conceptual implementation model would be to add this address to the IPv6
mechanisms that maintain timing procedures for IPv6  addresses on the
IPv6 stack, and then configure the IPv4 interface for DTI, as a
procedure called from the DHCPv6 client.



6.2 Server Processing of an IPv4 Address Extension

When a DHCPv6 Server receives an IPv4 Address Extension it MUST assume
that the next extension is 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 Mapped Address.

A DHCPv6 Server MAY send a Client a Reconfigure-Init message using the
IPv4 Address Extension to ask the Client to request an IPv4 Compatible
Address.  The Client will recognize this by processing the IPv4 Address
Extension, as an Extension Request Extension in the Reconfigure-Init
message.

The Server will know a priori the IPv6 routable address, when sending a
Reconfiguration-Init message, of a Client within the Intranet, and may
use that address with its own IPv6 address as the transaction binding
cache until the DHCPv6 Client/Server protocol processing has completed,
if the server supports this optimization.

The Server will look in its implementation defined IPv4 Address
configuration to determine if a TEP is available for a specific IPv6
Address Prefix. If that is the case the Server will put the address for
the TEP in the IPv4 Address Extension.



6.3 Client Processing of an IPv4 Address Extension

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

The Client MUST not assume it can use the IPv4 Address until it has
received a corresponding Reply to the Client Request.

The Client MUST not update the DNS with this new address.


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Once the Client is assured it can use the IPv4 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 Mapped Address supporting the processing required
       for an IPv6 address regarding the valid and preferred lifetimes
       as specified in IPv6 Addrconf [19].  Once the IPv4 Mapped
       address valid lifetime expires the IPv4 address MUST be deleted
       from the respective interface and a DHCPv6 Release Message
       MUST be sent to the DHCPv6 Server to delete the IPv4
       Address from the Servers bindings.

   3.  If a TEP address is provided in the IPv4
       Address Extension, the Client MUST create a configured tunnel
       to the TEP address, in an implementation defined
       manner. These encapsulation mechanisms are defined
       in other IPv6 specifications [13, 15].




7. Applicability Statement

DSTM is applicable for use from within the DSTM Domain to IPv4 nodes or
applications on a users Intranet or to access services over the
Internet.

DSTM's motivation is to support dual IP layer DSTM hosts to communicate
using global IPv4 addresses across an Intranet or Internet, where global
addresses are required.  But, DSTM has been defined to also permit the
use of Private IPv4 address space to permit the Intranet use of DSTM
where users require temporary access to IPv4 services within their
Intranet.

DSTM requires the use of DHCPv6 to obtain IPv4 addresses and TEPs for a
DSTM host.  Communications between the DSTM Daemon and the DHCPv6 client
is implementation defined.  The DTI mechanism is also implementation
defined.  DSTM does permit optionally for DSTM hosts to manually
configure TEPs for DTI for early deployment of DSTM but highly
recommends not doing this and configuring DHCPv6 servers with this
information is really the way to execute DSTM on an IPv6 Network.

DSTM also assumes that all packets returning from an IPv4 node to a DSTM
dual IP layer node return through the orginating DSTM Border Router, who
has cached the association of the DSTM's IPv4+IPv6 address.  At this
time it is beyond the scope of DSTM to permit IPv4 packets destined for
DSTM hosts to return packets through a non-orginating DSTM border
router.

DSTM also through the new DHCPv6 extension permits Network Operators to
inform DSTM Hosts they will need IPv4 addresses for communications using
the DHCPv6 Reconfigure-Init message.

DSTM in the future can be extended to support multiple border routers


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for returning IPv4 packets, and for the discovery of DSTM hosts using
IPv4 DNS queries as future work for DSTM.

NOTE - Authors will expand this section if required after the IETF 48
meeting at the NGTRANS meeting.



8. Security Considerations

The DSTM 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 DSTM does not break secure end- to-end
communications at any point in the mechanism.



Changes from draft 01 to draft 02


   1.  Added futher clarifications to DSTM components.

   2.  Added client/server details for DHCPv6 ngtrans extension.

   3.  Removed optional scenarios to simplify this mechanism.

   4.  Removed AIIH concepts and changed to be DSTM components.

   5.  Add Applicability Statement

   6.  Added acknowledgment section and new coauthors Francis Dupont
       and Alain Durand.




Changes from draft 00 to draft 01


   1.  Added text explaining why the draft does not use DHCPv4 to assign
       IPv4 compatible addresses to the "Introduction".

   2.  Defined what is mandatory and what is optional and added relative
       text in various places to clarify this change.  And added RFC
       2119 adjectives to the spec where appropriate.

   3.  Scenario 1 where IPv6 node wants to communicate with IPv4
       node is mandatory.

   4.  Scenarios 2 and 3 are now optional where an IPv6 node is
       assigned an IPv4 compatible address because an external
       IPv4 node is attempting communications with the IPv6 node.

   5.  For scenario 1 DHCPv6 is only needed for DSTM and not the
       tightly coupled paradigm of a co-existent DHCPv6 and


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       DNS server.  Also added mandatory and optional to the
       DSTM AIIH/NODE/ROUTER Diagram.

   6.  Made Static Tunnel Endpoints mandatory and Dyanmic Tunnel
       End Points optional.

   7.  Fixed DHCPv6 Reconfigure statements to take into account
       changes to the Reconfigure message in the DHCPv6 working
       group, to support AIIH processing.




Acknowledgments

The authors would like to acknowledge the implementation contributions
by Stephane Atheo at ENST Bretagne who has implemented a DSTM prototype
on FreeBsd and their input to this specification.  We would also like to
thank the NGTRANS Working Group for their input.



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, M. Carney, and C. Perkins.  Dynamic host Configuration
        Protocol for IPv6.  draft-ietf-dhc-dhcpv6-15.txt May 2000 (work
        in progress).

   [5]  J. Bound, M. Carney, and C Perkins.  Extensions for the Dynamic
        host Configuration Protocol for IPv6.
        draft-ietf-dhc-dhcpv6ext-12.txt May 2000. (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.



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   [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.

   [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/W20
    Nashua, NH 03062
    Phone: (603) 884-0400
    Email: bound@zk3.dec.com

    Laurent Toutain
    ENST Bretagne
    BP 78
    35 512 Cesson Sëvignë Cedex
    Phone : +33 2 99 12 70 26
    Email : Laurent.Toutain@enst-bretagne.fr

    Hossam Afifi
    ENST Bretagne
    BP 78
    35 512 Cesson Sëvignë Cedex
    Phone : +33 2 99 12 70 36
    Email : Hossam.Afifi@enst-bretagne.fr

    Francis Dupont
    ENST Bretagne
    BP 78


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    35 512 Cesson Sëvignë Cedex
    Phone : +33 2 99 12 70 36
    Email : Francis.Duponti@enst-bretagne.fr

    Alain Durand
    Sun Microsystems
    901 San Antonio Road
    UMPK 17-202
    Palo Alto, CA 94303-4900
    Tel: +1 650 786 7503
    Fax: +1 650 786 5896
    Email: Alain.Durand@sun.com
















































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