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Versions: (draft-huang-behave-bih) 00 01 02 03 04 05 06 07 08 09 RFC 6535

Behave WG                                                       B. Huang
Internet-Draft                                                   H. Deng
Obsoletes: 3338, 2767                                       China Mobile
(if approved)                                              T. Savolainen
Intended status: Standards Track                                   Nokia
Expires: July 27, 2011                                  January 23, 2011


            Dual Stack Hosts Using "Bump-in-the-Host" (BIH)
                     draft-ietf-behave-v4v6-bih-02

Abstract

   Bump-In-the-Host (BIH) is a host based IPv4 to IPv6 protocol
   translation mechanism that allows class of IPv4-only applications
   that work through NATs to communicate with IPv6-only peers.  The host
   applications are running on may be connected to IPv6-only or dual-
   stack access networks.  BIH hides IPv6 and makes the IPv4-only
   applications think they are talking with IPv4 peers by local
   synthetization of A records.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on July 27, 2011.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.



































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Acknowledgement of previous work . . . . . . . . . . . . .  5
   2.  Components of the Bump-in-the-Host . . . . . . . . . . . . . .  6
     2.1.  Function Mapper  . . . . . . . . . . . . . . . . . . . . .  7
     2.2.  Translator . . . . . . . . . . . . . . . . . . . . . . . .  8
     2.3.  Extension Name Resolver  . . . . . . . . . . . . . . . . .  8
       2.3.1.  Special exclusion sets for A and AAAA records  . . . .  9
       2.3.2.  DNSSEC support . . . . . . . . . . . . . . . . . . . .  9
       2.3.3.  Reverse DNS lookup . . . . . . . . . . . . . . . . . .  9
     2.4.  Address Mapper . . . . . . . . . . . . . . . . . . . . . . 10
   3.  Behavior and network Examples  . . . . . . . . . . . . . . . . 11
   4.  Considerations . . . . . . . . . . . . . . . . . . . . . . . . 15
     4.1.  Socket API Conversion  . . . . . . . . . . . . . . . . . . 15
     4.2.  ICMP Message Handling  . . . . . . . . . . . . . . . . . . 15
     4.3.  IPv4 Address Pool and Mapping Table  . . . . . . . . . . . 15
     4.4.  Multi-interface  . . . . . . . . . . . . . . . . . . . . . 16
     4.5.  Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 16
     4.6.  DNS cache  . . . . . . . . . . . . . . . . . . . . . . . . 16
   5.  Considerations due ALG requirements  . . . . . . . . . . . . . 17
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 19
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 20
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 20
   Appendix A.  Implementation option for the ENR . . . . . . . . . . 21
   Appendix B.  API list intercepted by BIH . . . . . . . . . . . . . 22
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24






















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1.  Introduction

   This document describes a Bump-in-the-Host (BIH), successor and
   combination of Bump-in-the-Stack (BIS)[RFC2767] and Bump-in-the-API
   (BIA) [RFC3338] technologies, which enables IPv4-only legacy
   applications to communicate with IPv6-only servers by synthesizing A
   records from AAAA records.

   The supported class of applications includes those that use DNS for
   IP address resolution and that do not embed IP address literals in
   protocol payloads.  This essentially includes legacy client-server
   applications using the DNS that are agnostic to the IP address family
   used by the destination and that are able to do NAT traversal.  The
   synthetic IPv4 addresses shown to applications are taken from RFC1918
   private address pool in order to ensure possible NAT traversal
   techniques will be initiated.

   IETF recommends using dual-stack or tunneling based solutions for
   IPv6 transition and specifically recommends against deployments
   utilizing double protocol translation.  Use of BIH together with a
   network-side IP translation is NOT RECOMMENDED as a competing
   technology for tunneling based transition solutions.

   BIH technique includes two major implementation options: a protocol
   translator between the IPv4 and the IPv6 stacks of a host or API
   translator between the IPv4 socket API module and the TCP/IP module.
   Essentially, IPv4 is translated into IPv6 at the socket API layer or
   at the IP layer.

   When the BIH is implemented at the socket API layer the translator
   intercepts IPv4 socket API function calls and invokes corresponding
   IPv6 socket API function calls to communicate with the IPv6 hosts.

   When the BIH is implemented at the networking layer the IPv4 packets
   are intercepted and converted to IPv6 using the IP conversion
   mechanism defined in SIIT [I-D.ietf-behave-v6v4-xlate].  The protocol
   layer translation has the same benefits and drawbacks as SIIT.

   The BIH can be used whenever an IPv4-only application needs to
   communicate with an IPv6-only server, independently of the address
   families supported by the access network.  Hence the access network
   can be IPv6-only or dual-stack capable.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119] .

   This document uses terms defined in [RFC2460] , [RFC2893] , [RFC2767]



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   and [RFC3338].

1.1.  Acknowledgement of previous work

   This document is direct update to and directly derivative from
   Kazuaki TSHUCHIYA, Hidemitsu HIGUCHI, and Yoshifumi ATARASHI
   [RFC2767] and from Seungyun Lee, Myung-Ki Shin, Yong-Jin Kim, Alain
   Durand, and Erik Nordmark's [RFC3338], which similarly provides a
   dual stack host means to communicate with other IPv6 host using
   existing IPv4 appliations.

   This document combines and updates both [RFC2767] and [RFC3338]

   The changes in this document mainly reflect following components

      1.  Supporting IPv6 only network connections

      2.  IPv4 address pool use private address instead of the
      unassigned IPv4 addresses (0.0.0.1 - 0.0.0.255)

      3.  Extending ENR and address mapper to operate differently

      4.  Adding an alternative way to implement the ENR

      5.  Going for standards track instead of experimental/
      informational

      6.  Supporting reverse (PTR) queries























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2.  Components of the Bump-in-the-Host

   Figure 1 shows the architecture of the host in which BIH is
   implemented as socket API layer translator, i.e. as the original
   "Bump-in-the-API".


                  +----------------------------------------------+
                  | +------------------------------------------+ |
                  | |                                          | |
                  | |            IPv4 applications             | |
                  | |                                          | |
                  | +------------------------------------------+ |
                  | +------------------------------------------+ |
                  | |           Socket API (IPv4, IPv6)        | |
                  | +------------------------------------------+ |
                  | +-[ API translator]------------------------+ |
                  | | +-----------+ +---------+ +------------+ | |
                  | | | Ext. Name | | Address | | Function   | | |
                  | | | Resolver  | | Mapper  | | Mapper     | | |
                  | | +-----------+ +---------+ +------------+ | |
                  | +------------------------------------------+ |
                  | +--------------------+ +-------------------+ |
                  | |                    | |                   | |
                  | |    TCP(UDP)/IPv4   | |   TCP(UDP)/IPv6   | |
                  | |                    | |                   | |
                  | +--------------------+ +-------------------+ |
                  +----------------------------------------------+

     Figure 1: Architecture of the dual stack host using BIH at socket
                                   layer

   Figure 2 shows the architecture of the host in which BIH is
   implemented as network layer translator, i.e. as the original "Bump-
   in-the-Stack".
















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        +-------------------------------------------------------------+
        |  +-------------------------------------------------------+  |
        |  | IPv4 applications                                     |  |
        |  +-------------------------------------------------------+  |
        |  +-------------------------------------------------------+  |
        |  | TCP/IPv4                                              |  |
        |  |   +---------------------------------------------------+  |
        |  |   |  +-----------+    +---------+  +---------------+     |
        |  |   |  | Extension |    | Address |  |  Translator   |     |
        |  |   |  | Name      |    | Mapper  |  +---------------+     |
        |  |   |  | Resolver  |    |         |  +---------------+     |
        |  |   |  |           |    |         |  |     IPv6      |     |
        |  +---+  +-----------+    +---------+  +---------------+     |
        |  +-------------------------------------------------------+  |
        |  |                  Network card drivers                 |  |
        |  +-------------------------------------------------------+  |
        +-------------------------------------------------------------+
        +-------------------------------------------------------------+
        |                        Network cards                        |
        +-------------------------------------------------------------+

    Figure 2: Architecture of the dual-stack host using BIH at network
                                   layer

   Dual stack hosts defined in RFC2893 [RFC2893] need applications,
   TCP/IP modules and addresses for both IPv4 and IPv6.  The proposed
   hosts in this document have an API or network layer translator to
   communicate with IPv6-only peers using existing IPv4 applications.
   The BIH translator consists of an Extension Name Resolver, an Address
   Mapper, and depending on implementation either a Function Mapper or a
   Protocol Translator.

2.1.  Function Mapper

   Function mapper translates an IPv4 socket API function into an IPv6
   socket API function, and vice versa.

   When detecting IPv4 socket API function calls from IPv4 applications,
   function mapper intercepts the function calls and invokes IPv6 socket
   API functions which correspond to the IPv4 socket API functions.  The
   IPv6 API functions are used to communicate with the target IPv6
   peers.  When detecting IPv6 socket API function calls triggered by
   the data received from the IPv6 peers, function mapper works
   symmetrically in relation to the previous case.

   See Appendix B for list of functions that may be intercepted by the
   function mapper.




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2.2.  Translator

   Translator translates IPv4 into IPv6 and vice versa using the IP
   conversion mechanism defined in SIIT [I-D.ietf-behave-v6v4-xlate].

   When receiving IPv4 packets from IPv4 applications, translator
   converts IPv4 packet headers into IPv6 packet headers, then, if
   required, fragments the IPv6 packets (because header length of IPv6
   is typically 20 bytes larger than that of IPv4), and sends them to
   IPv6 networks.  When receiving IPv6 packets from the IPv6 networks,
   translator works symmetrically to the previous case, except that
   there is no need to fragment the packets.

   The translator module has to adjust transport protocol checksums when
   translating between IPv4 and IPv6.  In the IPv6 to IPv4 direction the
   translator also has to calculate IPv4 header checksum.

2.3.  Extension Name Resolver

   Extension Name Resolver returns a proper answer in response to the
   IPv4 application's name resolution request.

   In the case of socket API layer implementation option, when an IPv4
   application tries to do forward lookup to resolve names via the
   resolver library (e.g. gethostbyname()), BIH intercept the function
   call and instead calls the IPv6 equivalent functions (e.g.
   getnameinfo()) that will resolve both A and AAAA records.

   In the case of stack layer implementation option the ENR intercepts
   the A query and creates additional AAAA query with essentially the
   same content.  The ENR will then collect replies to both A and AAAA
   queries and depending on results either returns A reply unmodified or
   drops the real A reply and synthesizes a new A reply.

   In either implementation options, if only non-excluded AAAA records
   are available for the queried name, ENR requests the address mapper
   to assign a local IPv4 address corresponding to the IPv6 address(es).
   In the case of API layer implementation option the ENR will simply
   make API (e.g. gethostbyname) to return the synthetic address.  In
   the case of network layer implementation option ENR synthesizes an A
   record for the assigned IPv4 address, and returns the A record to the
   IPv4 application.

   If there is real, non-excluded, A record available, ENR SHOULD NOT
   synthetize IPv4 addresses to be given to the application.  By default
   ENR implementation MUST NOT synthesize IPv4 addresses when real A
   records exist.




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   If the response contains a CNAME or a DNAME record, then the CNAME or
   DNAME chains is followed until the first terminating A or AAAA record
   is reached.

        Application | Network  | ENR behaviour
        query       | response |
        ------------+----------+------------------------
           A        |   A      |  <return real A record>
           A        |   AAAA   |  <synthesize A record>
           A        |  A/AAAA  |  <return real A record>

                   Figure 3: ENR behaviour illustration

2.3.1.  Special exclusion sets for A and AAAA records

   ENR implementation MAY by default exclude certain IPv4 and IPv6
   addresses seen on received A and AAAA records.  The addresses to be
   excluded by default SHOULD include martian addresses such as those
   that should not appear in the DNS or on the wire.  Additional
   addresses MAY be excluded based on possibly configurable local
   policies.

2.3.2.  DNSSEC support

   The A record synthesis done by ENR in the network layer model can
   cause problems for DNSSEC validation possibly done by the host's
   resolver, as the synthetic responses cannot be succesfully validated.
   DNSSEC can be supported by configuring the (stub) resolver on a host
   to trust validations done by the local ENR or alternatively the
   validating resolver can implement ENR on itself and only SIIT takes
   place at network layer.

   When ENR is implemented at the socket API level there is no problems
   with DNSSEC, as the ENR itself uses socket APIs.

2.3.3.  Reverse DNS lookup

   When an application initiates a reverse DNS query for a PTR record
   (in-addr.arpa), to find a name for an IP address, the ENR MUST check
   whether the queried IP address can be found in the Address Mapper's
   mapping table and is a local IP address.  If an entry is found and
   the queried address is locally generated, the ENR must initiate
   corresponding reverse DNS query for the real IPv6 address (ip6.arpa).
   In the case application requested reverse lookup for an address not
   part of the local IPv4 address pool, e.g. a global address, the
   request shall be forwarded unmodified to the network.

   For example, when an application initiates reverse DNS query for a



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   synthesized locally valid IPv4 address, the ENR needs to intercept
   that query.  The ENR will ask the address mapper for the IPv6 address
   that corresponds to the IPv4 address.  The ENR shall perform reverse
   lookup procedure for the destination's IPv6 address and return the
   name received as a response to the application that initiated the
   IPv4 query.

2.4.  Address Mapper

   Address mapper maintains a local IPv4 address pool.  The pool
   consists of private IPv4 addresses as per section 4.3.  Also, the
   address mapper maintains a table consisting of pairs of locally
   selected IPv4 addresses and destinations' IPv6 addresses.

   When the extension name resolver, translator, or the function mapper
   requests the address mapper to assign an IPv4 address corresponding
   to an IPv6 address, the address mapper selects and returns an IPv4
   address out of the local pool, and registers a new entry into the
   table.  The registration occurs in the following 3 cases:

   (1) When the extension name resolver gets only an AAAA record for the
   target host name in the dual stack or IPv6 only network and there is
   no existing mapping entry for the IPv6 address.  A local IPv4 address
   will be returned to application and mapping for local IPv4 address to
   real IPv6 address is created.

   (2) When the extension name resolver gets both an A record and an
   AAAA record, but the A record contains only excluded IPv4 addresses.
   Behavior will follow the case (1).

   (3) When the function mapper gets a socket API function call
   triggered by received IPv6 packet and there is no existing mapping
   entry for the IPv6 source address (Editor's note: can this ever
   happen in case of client-server nature of BIH?).

   Other possible combinations are outside of BIH and BIH is not
   involved in those.

   NOTE: There is one exception.  When initializing the table the mapper
   registers a pair of its own IPv4 address and IPv6 address into the
   table.










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3.  Behavior and network Examples

   Figure 4 illustrates the very basic network scenario.  An IPv4-only
   application is running on a host attached to IPv6-only Internet and
   is talking to IPv6-only server.  A communication is made possible by
   Bump-In-the-Host.

     +----+                                   +-------------+
     | H1 |----------- IPv6 Internet -------- | IPv6 server |
     +----+                                   +-------------+
     v4 only
     application

                       Figure 4: Network Scenario #1

   Figure 5 illustrates a possible network scenario where an IPv4-only
   application is running on a host attached to a dual-stack network,
   but the destination server is running on a private site that is
   numbered with public IPv6 addresses and private IPv4 addresses
   without port forwarding setup on NAT44.  The only means to contact to
   server is to use IPv6.

     +----------------------+  +------------------------------+
     | Dual Stack Internet  |  | IPv4 Private site (Net 10)   |
     |                      |  |                              |
     |                      |  |                 +----------+ |
     |                      |  |                 |          | |
     |  +----+           +---------+             |          | |
     |  | H1 |--------   |  NAT44  |-------------|  Server  | |
     |  +----+           +---------+             |          | |
     | v4 only              |  |                 +----------+ |
     | application          |  |                  Dual Stack  |
     |                      |  |                etc. 10.1.1.1 |
     |                      |  |                 AAAA:2009::1 |
     |                      |  |                              |
     +----------------------+  +------------------------------+

                       Figure 5: Network Scenario #2

   Illustrations of host behavior in both implementation options are
   given here.  Figure 6 illustrates the setup where BIH is implemented
   as a bump in the API, and figure 7 illustrates the setup where BIH is
   implemented as a bump in the stack.

 "dual stack"                                                "host6"
 IPv4    Socket |     [ API Translator ]    | TCP(UDP)/IP          Name
 appli-  API    | ENR      Address  Function| (v6/v4)             Server
 cation         |          Mapper   Mapper  |



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  |        |        |        |        |         |              |       |
 <<Resolve an IPv4 address for "host6".>>       |              |       |
  |        |        |        |        |         |              |       |
  |--------|------->|  Query of 'A' records for host6.         |       |
  |        |        |        |        |         |              |       |
  |        |        |--------|--------|---------|--------------|------>|
  |        |        |  Query of 'A' records and 'AAAA' for host6       |
  |        |        |        |        |         |              |       |
  |        |        |<-------|--------|---------|--------------|-------|
  |        |        |  Reply with the 'AAAA' record.           |       |
  |        |        |        |        |         |              |
  |        |        |<<The 'AAAA' record is resolved.>>        |
  |        |        |        |        |         |              |
  |        |        |+++++++>|  Request one IPv4 address       |
  |        |        |        |  corresponding to the IPv6 address.
  |        |        |        |        |         |              |
  |        |        |        |<<Assign one IPv4 address.>>     |
  |        |        |        |        |         |              |
  |        |        |<+++++++|  Reply with the IPv4 address.   |
  |        |        |        |        |         |              |
  |        |        |<<Create 'A' record for the IPv4 address.>>
  |        |        |        |        |         |              |
  |<-------|--------| Reply with the 'A' record.|              |
  |        |        |        |        |         |              |
  |        |        |        |        |         |              |
 <<Call IPv4 Socket API function >>   |         |              |
  |        |        |        |        |         |              |
  |========|========|========|=======>|An IPv4 Socket API function Call
  |        |        |        |        |         |              |
  |        |        |        |<+++++++|  Request IPv6 addresses|
  |        |        |        |        |  corresponding to the  |
  |        |        |        |        |  IPv4 addresses.       |
  |        |        |        |        |         |              |
  |        |        |        |+++++++>| Reply with the IPv6 addresses.
  |        |        |        |        |         |              |
  |        |        |        |        |<<Translate IPv4 into IPv6.>>
  |        |        |        |        |         |              |
  |  An IPv6 Socket API function call.|=========|=============>|
  |        |        |        |        |         |              |
  |        |        |        |        |<<Reply an IPv6 data    |
  |        |        |        |        |  to dual stack.>>      |
  |        |        |        |        |         |              |
  |  An IPv6 Socket API function call.|<========|==============|
  |        |        |        |        |         |              |
  |        |        |        |        |<<Translate IPv6 into IPv4.>>
  |        |        |        |        |         |              |
  |        |        |        |<+++++++|  Request IPv4 addresses|
  |        |        |        |        |  corresponding to the  |



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  |        |        |        |        |  IPv6 addresses.       |
  |        |        |        |        |         |              |
  |        |        |        |+++++++>| Reply with the IPv4 addresses.
  |        |        |        |        |         |              |
  |<=======|========|========|========|  An IPv4 Socket function call.
  |        |        |        |        |         |              |

                 Figure 6: Example of BIH as API addition


      "dual stack"                                            "host6"
      IPv4    TCP/    ENR     address  translator  IPv6
      appli-  IPv4            mapper
      cation
        |      |       |         |       |           |         |
      <<Resolve an IPv4 address for "host6".>>       |         |
        |      |       |         |       |           |         |
        |------|------>|  Query of 'A' records for "host6".    | Name
        |      |       |         |       |           |         | Server
        |      |       |---------|-------|-----------|---------|--->|
        |      |       |  Query of 'A' records and 'AAAA' for "host6"
        |      |       |         |       |           |         |    |
        |      |       |<--------|-------|-----------|---------|----|
        |      |       |  Reply only with 'AAAA' record.       |
        |      |       |         |       |           |         |
        |      |       |<<Only 'AAAA' record is resolved.>>    |
        |      |       |         |       |           |         |
        |      |       |-------->|  Request one IPv4 address   |
        |      |       |         |  corresponding to the IPv6 address.
        |      |       |         |       |           |         |
        |      |       |         |<<Assign one IPv4 address.>> |
        |      |       |         |       |           |         |
        |      |       |<--------|  Reply with the IPv4 address.
        |      |       |         |       |           |         |
        |      |       |<<Create 'A' record for the IPv4 address.>>
        |      |       |         |       |           |         |
        |<-----|-------|  Reply with the 'A' record. |         |
        |      |       |         |       |           |         |
        |      |       |         |       |           |         |
      <<Send an IPv4 packet to "host6".>>|           |         |
        |      |       |         |       |           |         |
        |======|=======|=========|======>|  An IPv4 packet.    |
        |      |       |         |       |           |         |
        |      |       |         |<------|  Request IPv6 addresses
        |      |       |         |       |  corresponding to the IPv4
        |      |       |         |       |  addresses.         |
        |      |       |         |       |           |         |
        |      |       |         |------>|  Reply with the IPv6|



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        |      |       |         |       |  addresses.         |
        |      |       |         |       |           |         |
        |      |       |         |       |<<Translate IPv4 into IPv6.>>
        |      |       |         |       |           |         |
        |      |       |An IPv6 packet.  |===========|========>|
        |      |       |         |       |           |         |
        |      |       |         |     <<Reply an IPv6 packet to
        |      |       |         |       "dual stack".>>       |
        |      |       |         |       |           |         |
        |      |       |An IPv6 packet.  |<==========|=========|
        |      |       |         |       |           |         |
        |      |       |         |       |<<Translate IPv6 into IPv4.>>
        |      |       |         |       |           |         |
        |<=====|=======|=========|=======|  An IPv4 packet.    |
        |      |       |         |       |           |         |

                 Figure 7: Example of BIH at network layer


































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4.  Considerations

4.1.  Socket API Conversion

   IPv4 socket API functions are translated into semantically as same
   IPv6 socket API functions as possible and vice versa.  See Appendix B
   for the API list intercepted by BIH.  However, IPv4 socket API
   functions are not fully compatible with IPv6 since the IPv6 has new
   advanced features, but IPv4-only application are unlikely to need
   them.

4.2.  ICMP Message Handling

   When an application needs ICMP messages values (e.g., Type, Code,
   etc.) sent from a network layer, ICMPv4 message values MAY be
   translated into ICMPv6 message values based on SIIT
   [I-D.ietf-behave-v6v4-xlate], and vice versa.

4.3.  IPv4 Address Pool and Mapping Table

   The address pool consists of the private IPv4 addresses as per
   [RFC1918].  This pool can be implemented at different granularity in
   the node e.g., a single pool per node, or at some finer granularity
   such as per user or per process.  In he case of large number of IPv4
   applications would communicate with large number of IPv6 servers, the
   available address spaces may be exhausted.  This should be quite rare
   event and changes will decrease as IPv6 support increases.  The
   possible problem can also mitigated with smart management techniques
   of the address pool.  For example, entries with longest inactivity
   time can be cleared and IPv4 addresess reused for creating new
   entries.

   The RFC1918 address space was chosen because generally legacy
   applications understand that as a private address space.  A new
   dedicated address space would run a risk of not being understood by
   applications as private. 127/8 or 169.254/16 are rejected due
   possible assumptions applications may make when seeing those.

   The RFC1918 addresses have a risk of conflicting with other
   interfaces.  The conflicts can be mitigated by using least commonly
   used network number of the RFC1918 address space.  Addresses from
   172.16/12 prefix are thought to be less likely to conflict than
   addresses from 10/8 or 192.168/16 spaces, hence the used IPv4
   addresses are following (Editor's comment: this is first proposal,
   educated better quesses are welcome):

   Source addresses: 172.21.112.0/30.  Source address have to be
   allocated because applications use getsockname() calls and as in the



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   BIS mode an IP address of the IPv4 interface has to be shown (e.g. by
   'ifconfig').  More than one address is allocated to allow
   implementation flexibility, e.g. for cases where a host has multiple
   IPv6 interfaces.  The source addresses are from different subnet than
   destination addresses to ensure applications would not do on-link
   assumptions and would enable NAT traversal functions.

   Primary destination addresses: 172.21.80.0/20.  Address mapper will
   select destination addresses primarily out of this pool.

   Secondary destination addresses: 10.170.160.0/20.  Address mapper
   will select destination addresses out of this pool if the node has
   dual-stack connection conflicting with primary destination addresses.

4.4.  Multi-interface

   In the case of dual-stack destinations BIH must do protocol
   translation from IPv4 to IPv6 only when the host does not have any
   IPv4 interfaces, native or tunneled, available for use.

   It is possible that an IPv4 interface is activated during BIH
   operation, for example if a node moves to a coverage area of IPv4
   enabled network.  In such an event BIH MUST stop initiating protocol
   translation sessions for new connections and BIH MAY disconnect
   active sessions.  The choice of disconnection is left for
   implementatations and it may depend on whether IPv4 address conflict
   situation occurs between addresses used by BIH and addresses used by
   new IPv4 interface.

4.5.  Multicast

   Protocol translation for multicast is not supported.

4.6.  DNS cache

   When BIH module shuts down, e.g. due IPv4 interface becoming
   available, BIH must flush node's DNS cache of possible locally
   generated entries.













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5.  Considerations due ALG requirements

   No ALG functionality is specified herein as ALG design is generally
   not encouraged for host based translation and as BIH is intended for
   applications not including IP addresses in protocol payloads.














































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6.  Security Considerations

   The security consideration of BIH mostly relies on that of
   [I-D.ietf-behave-v6v4-xlate-stateful].

   In the socket layer implementation approach the differences are due
   to the address translation occurring at the API and not in the
   network layer.  That is, since the mechanism uses the API translator
   at the socket API layer, hosts can utilize the security of the
   network layer (e.g., IPSec) when they communicate with IPv6 hosts
   using IPv4 applications via the mechanism.  As well, there is no need
   for DNS ALG as in NAT-PT, so there is no interference with DNSSEC
   either.

   In the network layer implementation approach hosts cannot utilize the
   security above network layer when they communicate with IPv6 hosts
   using IPv4 applications via BIH and encrypt embedded IP addresses, or
   when the protocol data is encrypted using IP addresses as keys.  In
   these cases it is impossible for the mechanism to translate the IPv4
   data into IPv6 and vice versa.  Therefore it is highly desirable to
   upgrade to the applications modified into IPv6 for utilizing the
   security at communication with IPv6 hosts.

   The use of address pooling may open a denial of service attack
   vulnerability.  So BIH should employ the same sort of protection
   techniques as NAT64 [I-D.ietf-behave-v6v4-xlate-stateful] does.

























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7.  Acknowledgments

   The author thanks the discussion from Gang Chen, Dapeng Liu, Bo Zhou,
   Hong Liu, Tao Sun, Zhen Cao, Feng Cao et al. in the development of
   this document.

   The efforts of Suresh Krishnan, Mohamed Boucadair, Yiu L. Lee, James
   Woodyatt, Lorenzo Colitti, Qibo Niu, Pierrick Seite, Dean Cheng,
   Christian Vogt, Jan M. Melen, Ed Jankiewizh, Marnix Goossens, Ala
   Hamarsheh, and Julien Laganier in reviewing this document are
   gratefully acknowledged.

   Advice from Dan Wing, Dave Thaler and Magnus Westerlund are greatly
   appreciated

   The authors of RFC2767 acknowledged WIDE Project, Kazuhiko YAMAMOTO,
   Jun MURAI, Munechika SUMIKAWA, Ken WATANABE, and Takahisa MIYAMOTO.
   The authors of RFC3338 acknowledged implementation contributions by
   Wanjik Lee (wjlee@arang.miryang.ac.kr) and i2soft Corporation
   (www.i2soft.net).

   The authors of Bump-in-the-Wire (draft-ietf-biw-00.txt, October
   2006), P. Moster, L. Chin, and D. Green, are acknowledged.  Few ideas
   and clarifications from BIW have been adapted to this document.



























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8.  References

8.1.  Normative References

   [I-D.ietf-behave-v6v4-xlate]
              Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", draft-ietf-behave-v6v4-xlate-23 (work in
              progress), September 2010.

   [I-D.ietf-behave-v6v4-xlate-stateful]
              Bagnulo, M., Matthews, P., and I. Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers",
              draft-ietf-behave-v6v4-xlate-stateful-12 (work in
              progress), July 2010.

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

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

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC2767]  Tsuchiya, K., HIGUCHI, H., and Y. Atarashi, "Dual Stack
              Hosts using the "Bump-In-the-Stack" Technique (BIS)",
              RFC 2767, February 2000.

   [RFC2893]  Gilligan, R. and E. Nordmark, "Transition Mechanisms for
              IPv6 Hosts and Routers", RFC 2893, August 2000.

   [RFC3338]  Lee, S., Shin, M-K., Kim, Y-J., Nordmark, E., and A.
              Durand, "Dual Stack Hosts Using "Bump-in-the-API" (BIA)",
              RFC 3338, October 2002.

8.2.  Informative References

   [RFC2553]  Gilligan, R., Thomson, S., Bound, J., and W. Stevens,
              "Basic Socket Interface Extensions for IPv6", RFC 2553,
              March 1999.









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Appendix A.  Implementation option for the ENR

   It is not necessary to implement the ENR at the kernel level, but it
   can be implemented instead at the user space by setting the host's
   default DNS server to point to 127.0.0.1.  DNS queries would then
   always be sent to the ENR, which furthermore ensures both A and AAAA
   queries are sent to the actual DNS server and A queries are always
   answered and required mappings created.











































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Appendix B.  API list intercepted by BIH

   The following functions are the API list which SHOULD be intercepted
   by BIH module when implemented at socket layer.

   The functions that the application uses to pass addresses into the
   system are:

      bind()

      connect()

      sendmsg()

      sendto()

   The functions that return an address from the system to an
   application are:

      accept()

      recvfrom()

      recvmsg()

      getpeername()

      getsockname()

   The functions that are related to socket options are:

      getsocketopt()

      setsocketopt()

   The functions that are used for conversion of IP addresses embedded
   in application layer protocol (e.g., FTP, DNS, etc.) are:

      recv()

      send()

      read()

      write()

   As well, raw sockets for IPv4 and IPv6 MAY be intercepted.




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   Most of the socket functions require a pointer to the socket address
   structure as an argument.  Each IPv4 argument is mapped into
   corresponding an IPv6 argument, and vice versa.

   According to [RFC2553], the following new IPv6 basic APIs and
   structures are required.

         IPv4                     new IPv6
         ------------------------------------------------
         AF_INET                  AF_INET6
         sockaddr_in              sockaddr_in6
         gethostbyname()          getaddrinfo()
         gethostbyaddr()          getnameinfo()
         inet_ntoa()/inet_addr()  inet_pton()/inet_ntop()
         INADDR_ANY               in6addr_any

                                 Figure 8

   BIH MAY intercept inet_ntoa() and inet_addr() and use the address
   mapper for those.  Doing that enables BIH to support literal IP
   addresses.

   The gethostbyname() call return a list of addresses.  When the name
   resolver function invokes getaddrinfo() and getaddrinfo() returns
   multiple IP addresses, whether IPv4 or IPv6, they SHOULD all be
   represented in the addresses returned by gethostbyname().  Thus if
   getaddrinfo() returns multiple IPv6 addresses, this implies that
   multiple address mappings will be created; one for each IPv6 address.























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Authors' Addresses

   Bill Huang
   China Mobile
   53A,Xibianmennei Ave.,
   Xuanwu District,
   Beijing  100053
   China

   Email: bill.huang@chinamobile.com


   Hui Deng
   China Mobile
   53A,Xibianmennei Ave.,
   Xuanwu District,
   Beijing  100053
   China

   Email: denghui02@gmail.com


   Teemu Savolainen
   Nokia
   Hermiankatu 12 D
   FI-33720 TAMPERE
   Finland

   Email: teemu.savolainen@nokia.com






















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