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Versions: (RFC 3338) 00 01 02

Behave                                                          B. Huang
Internet-Draft                                                   H. Deng
Obsoletes: 3338 (if approved)                               China Mobile
Intended status: Experimental                              T. Savolainen
Expires: August 21, 2010                                           Nokia
                                                       February 17, 2010


             Dual Stack Hosts Using "Bump-in-the-API" (BIA)
                    draft-huang-behave-rfc3338bis-01

Abstract

   This document describes the "Bump-In-the-API" (BIA) host based
   protocol translation mechanism that allows applications supporting
   only one IP address family to communicate with peers that are
   reachable or supporting only the other address family.

   This specification addresses scenarios where a host is provided dual
   stack, IPv6 only or IPv4 only network connectivity.  In the dual
   stack network case, single address family applications in the host
   sometime will communicate directly with other hosts using the
   different address family.  In the case of IPv6 only network or IPv6
   only destination, IPv4- originated communications have to be
   translated into IPv6.  IPv6 communications may have to be translated
   similarly to IPv4.  Technically, the BIA-enabled host resolves both A
   and AAAA addresses of the destination and behaves according to
   received responses.

   Acknowledgement of previous work

   This document is an update to and directly derivative 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.The
   original document was a product of the NGTRANS working group.

   The changes in this document reflect four components

      1.  Supporting IPv6 only network connections

      2.  Supporting IPv4 only network connections

      3.  Removing Applicability and Disclaimer

      4.  Supporting dual stack network connections with translation

   The goal of this mechanism is the same as that of the Bump-in-the-



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   stack mechanism, but this mechanism provides the translation method
   between the IPv4 APIs and IPv6 APIs.  Thus, the goal is simply
   achieved without IP header translation.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 21, 2010.

Copyright Notice

   Copyright (c) 2010 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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   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 BSD License.










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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Dual Stack Host Architecture Using BIA . . . . . . . . . . . .  6
     2.1.  Function Mapper  . . . . . . . . . . . . . . . . . . . . .  6
     2.2.  Extension Name Resolver  . . . . . . . . . . . . . . . . .  7
     2.3.  Address Mapper . . . . . . . . . . . . . . . . . . . . . .  8
   3.  Behavior Examples -- dual stack network and IPv6 only peer . .  9
     3.1.  Originator Behavior  . . . . . . . . . . . . . . . . . . .  9
     3.2.  Recipient Behavior . . . . . . . . . . . . . . . . . . . . 11
   4.  Behavior Examples -- IPv6 only network and dual-stack peer . . 13
     4.1.  Originator Behavior  . . . . . . . . . . . . . . . . . . . 13
     4.2.  Recipient Behavior . . . . . . . . . . . . . . . . . . . . 15
   5.  Behavior Examples -- IPv4 only network and IPv4 only peer  . . 16
     5.1.  Originator Behavior  . . . . . . . . . . . . . . . . . . . 16
     5.2.  Recipient Behavior . . . . . . . . . . . . . . . . . . . . 18
   6.  Considerations . . . . . . . . . . . . . . . . . . . . . . . . 20
     6.1.  Socket API Conversion  . . . . . . . . . . . . . . . . . . 20
     6.2.  ICMP Message Handling  . . . . . . . . . . . . . . . . . . 20
     6.3.  IPv4 or IPv6 Address Pool and Mapping Table  . . . . . . . 20
     6.4.  Internally Assigned IPv4 or IPv6 Addresses . . . . . . . . 20
     6.5.  Implementation Issues  . . . . . . . . . . . . . . . . . . 21
   7.  Limitations  . . . . . . . . . . . . . . . . . . . . . . . . . 22
   8.  ALG related  . . . . . . . . . . . . . . . . . . . . . . . . . 23
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 24
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 25
   11. Normative References . . . . . . . . . . . . . . . . . . . . . 26
   Appendix A.  API list intercepted by BIA . . . . . . . . . . . . . 27
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29






















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1.  Introduction

   RFC3338 [RFC3338] stated that there are few applications for IPv6
   [RFC2460] as compared with IPv4 in which a great number of
   applications are available.  In order to advance the transition
   smoothly, it is highly desirable to make the availability of IPv6
   applications increase to the same level as IPv4.  Unfortunately,
   however, this is expected to take a long time.  Meanwhile, there are
   scenarios where a dual stack host is connected to IPv6-only network
   but it is running IPv4-only applications, or a host is running IPv6-
   only applications while connected to IPv4-only network.

   BIA [RFC3338] proposed a mechanism of dual stack hosts using the
   technique called "Bump-in-the-API" in the IP security area.  The
   technique inserts an API translator between the socket API module and
   the TCP/IP module in the dual stack hosts, so that it translates the
   IPv4 socket API function into IPv6 socket API function and vice
   versa.

   BIS [RFC2767] specifies a host translation mechanism using a
   technique called "Bump-in-the-Stack".  It translates IPv4 into IPv6,
   and vice versa using the IP conversion mechanism defined in SIIT
   [RFC2765].  BIS allows hosts to communicate with other IPv6 hosts
   using existing IPv4 applications.  However, this approach is to use a
   translator which is inserted between the TCP/IP module and network
   card driver, so that it has the same limitations as the SIIT based IP
   header translation methods.  In addition, its implementation is
   dependent upon the network interface driver.

   When IPv4 or IPv6 applications on the dual stack communicate with
   other IPv6 or IPv4 hosts, the API translator detects the socket API
   functions from IPv4 or IPv6 applications and invokes the IPv6 or IPv4
   socket API functions to communicate with the IPv6 or IPv4 hosts, and
   vice versa.  In order to support communication between IPv4 or IPv6
   applications and the target IPv6 or IPv4 hosts, pooled IPv4 or IPv6
   addresses will be assigned through the extension name resolver in the
   API translator.  But the those IPv4 or IPv6 addresses never flow out
   from them.

   The network scenario specified in RFC3338 is a dual stack network.
   where IPv4 communication can be transported independently of IPv6.
   However, if the network provides only IPv6 transport, applications's
   IPv4 packets have to be translated into IPv6.  The opposite happens
   when the network is IPv4-only and application is IPv6-only capable.

   This specification assumes that host knows it is connected with a
   dual stack network, IPv6-only network or IPv4-only network.  The host
   learns that from layer 2 or from results of layer 3 IP address



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   configuration mechanisms.

   If the network which host is connecting with is IPv4 only network,
   then host's IPv4 application will behave regularly, and it's IPv6
   application's packets have to be translated into IPv4 packets.

   If the network which host is connecting with is IPv6 only network,
   then host's IPv6 application will behave reguarly, and it's IPv4
   application's packets have to be translated into IPv6 in order to
   communicate with IPv6 applications.

   If the network which host is connecting with is dual stack network,
   then host will behave as what RFC3338 originally described.

   The scenario where destination peer is not reachable with the address
   family a host is provisioned with is not covered by this document, as
   that requires network based protocol translation solution.  However,
   the BIA technology can complement network based protocol translation
   such as [NAT64] and [PNAT] .

   Moreover, since the translation is automatically carried out with the
   help of DNS protocol, most applications do not need to know whether
   target hosts are IPv6 or IPv4 ones.  That is, this allows hosts to
   communicate with other IPv6 hosts using existing IPv4 applications or
   other IPv4 hosts using existing IPv6 applications; thus it seems as
   if peers are always dual stack hosts with applications for both IPv4
   and IPv6.

   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]
   and [RFC3338].

















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2.  Dual Stack Host Architecture Using BIA

   Figure 1 shows the architecture of the host in which BIA is
   installed.


                  +----------------------------------------------+
                  | +-------------------+  +-------------------+ |
                  | |                   |  |                   | |
                  | | IPv4 applications |  | IPv6 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 BIA

   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 translator to communicate with
   other IPv6 hosts using existing IPv4 applications, or communicate
   with other IPv4 hosts using existing IPv4 applications.  The API
   translator consists of 3 modules, an extension name resolver, an
   address mapper and a function mapper.

2.1.  Function Mapper

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

   When detecting the IPv4 socket API functions from IPv4 applications
   in an IPv6 only network, it intercepts the function call and invokes
   new IPv6 socket API functions which correspond to the IPv4 socket API
   functions.  Those IPv6 API functions are used to communicate with the
   target IPv6 hosts.  When detecting the IPv6 socket API functions from



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   the data received from the IPv6 hosts, it works symmetrically in
   relation to the previous case.

   When detecting the IPv6 socket API functions from IPv6 applications,
   in an IPv4 only network, it intercepts the function call and invokes
   new IPv4 socket API functions which correspond to the IPv6 socket API
   functions.  Those IPv4 API functions are used to communicate with the
   target IPv4 hosts.  When detecting the IPv4 socket API functions from
   the data received from the IPv4 hosts, it works symmetrically in
   relation to the previous case.

2.2.  Extension Name Resolver

   It returns a proper answer in response to the IPv4 or IPv6
   application's request.

   When an IPv4 application in an IPv6 only network tries to resolve
   names via the resolver library (e.g. gethostbyname()), BIA intercept
   the function call and instead call the IPv6 equivalent functions
   (e.g. getnameinfo()) that will resolve both A and AAAA records.

   If only AAAA record is available, it requests the address mapper to
   assign an IPv4 address corresponding to the IPv6 address, then
   creates the A record for the assigned IPv4 address, and returns the A
   record to the IPv4 application.

   If both A and AAAA record are available, it doesn't requests the
   address mapper but directly send this A record and AAAA record to
   address mapper to store this relationship, then directly pass this
   this A record to the IPv4 application.

   When an IPv6 application in IPv4 only network tries to resolve names
   via the resolver library (e.g. getnameinfo()), BIA intercept the
   function call and instead call the IPv4 equivalent functions (e.g.
   gethostbyname()) that will resolve both A and AAAA records.

   If the A record is available, it requests the address mapper to
   assign an IPv6 address corresponding to the IPv4 address, then
   creates the AAAA record for the assigned IPv6 address, and returns
   the AAAA record to the IPv6 application.

   If both A and AAAA record are available, it doesn't requests the
   address mapper but directly send this A record and AAAA record to
   address mapper to record this relationship, then directly pass this
   this AAAA record to the IPv6 application.






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2.3.  Address Mapper

   It internally maintains a table of the pairs of an IPv4 address and
   an IPv6 address in an IPv6 only network.  The IPv4 addresses are
   assigned from an IPv4 address pool.  It uses the unassigned IPv4
   addresses (e.g., 0.0.0.1 ~ 0.255.255.255).

   When the extension name resolver or the function mapper requests it
   to assign an IPv4 address corresponding to an IPv6 address, it
   selects and returns an IPv4 address out of the pool, and registers a
   new entry into the table dynamically.  The registration occurs in the
   following 2 cases:

   (1) When the extension name resolver gets only an 'AAAA' record for
   the target host name and there is not a mapping entry for the IPv6
   address.

   (2) When the function mapper gets a socket API function call from the
   data received and there is not a mapping entry for the IPv6 source
   address.

   It internally maintains a table of the pairs of an IPv4 address and
   an IPv6 address in an IPv6 only network.  The IPv6 addresses are
   assigned from unassigned IPv6 address pool as well. (to be assigned
   by IANA).

   When the extension name resolver or the function mapper requests it
   to assign an IPv6 address corresponding to an IPv4 address, it
   selects and returns an IPv6 address out of the pool, and registers a
   new entry into the table dynamically.  The registration occurs in the
   following 2 cases:

   (1) When the extension name resolver gets only an 'A' record for the
   target host name and there is not a mapping entry for the IPv4
   address.

   (2) When the function mapper gets a socket API function call from the
   data received and there is not a mapping entry for the IPv4 source
   address.

   NOTE: This is the same as that of the Address Mapper in [RFC2767].










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3.  Behavior Examples -- dual stack network and IPv6 only peer

   This section describes behaviors of the proposed dual stack host
   called "dual stack", which communicates with an IPv6 host called
   "host6" using an IPv4 application on dual stack network.  There are
   several reasons to upgrade IPv4 applications to support IPv6 such as
   charging, codec et al, and this is out of scope of this document.

   In the following sections, the meanings of arrows are as follows:

      ---> A DNS message for name resolving created by the applications
      and the extension name resolver in the API translator.

      +++> An IPv4 or IPv6 address request to and reply from the address
      mapper for the extension name resolver and the function mapper.

      ===> Data flow by socket API functions created by the applications
      and the function mapper in the API translator.

3.1.  Originator Behavior

   This sub-section describes the behavior when the "dual stack" sends
   data to "host6".

   When an IPv4 application sends a DNS query to its extension name
   server, the extension name resolver intercepts the query and then
   creates a new query to resolve both A and AAAA records.  When only
   the AAAA record is resolved, the extension name resolver requests the
   address mapper to assign an IPv4 address corresponding to the IPv6
   address.

   The extension name resolver creates an A record for the assigned IPv4
   address and returns it to the IPv4 applications.

   In order for the IPv4 application to send IPv4 packets to host6, it
   calls the IPv4 socket API function.

   The function mapper detects the socket API function from the
   application.  If the result is from IPv6 applications, it skips the
   translation.  In the case of IPv4 applications, it requires an IPv6
   address to invoke the IPv6 socket API function, thus the function
   mapper requests an IPv6 address to the address mapper.  The address
   mapper selects an IPv4 address from the table and returns the
   destination IPv6 address.  Using this IPv6 address, the function
   mapper invokes an IPv6 socket API function corresponding to the IPv4
   socket API function.

   When the function mapper receives an IPv6 function call,it requests



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   the IPv4 address to the address mapper in order to translate the IPv6
   socket API function into an IPv4 socket API function.  Then, the
   function mapper invokes the socket API function for the IPv4
   applications.

   Figure 2 illustrates the behavior described above:


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



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


                   Figure 2: Behavior of the originator

3.2.  Recipient Behavior

   This subsection describes the recipient behavior of "dual stack".
   The communication is triggered by "host6".

   "host6" resolves the address of "dual stack" with 'AAAA' records
   through its extension name server, and then sends an IPv6 packet to
   the "dual stack".

   The IPv6 packet reaches the "dual stack" and the function mapper
   detects it.

   The function mapper requests the IPv4 address to the address mapper
   in order to invoke the IPv4 socket API function to communicate with
   the IPv4 application.  Then the function mapper invokes the
   corresponding IPv4 socket API function for the IPv4 applications
   corresponding to the IPv6 functions.

   Figure 3 illustrates the behavior described above:










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 "dual stack"                                               "host6"
   IPv4    Socket |     [ API Translator ]    | TCP(UDP)/IP
   appli-  API    |Ext Name  Address  Function| (v6/v4)
   cation         |Resolver  Mapper   Mapper  |
    |        |        |        |        |         |              |
   <<Receive data from "host6".>>       |         |              |
    |        |        |        |        |         |              |
    |      An IPv6 Socket function call.|<========|==============|
    |        |        |        |        |         |              |
    |        |        |        |<+++++++|  Request IPv4 addresses|
    |        |        |        |        |  corresponding to the IPv6
    |        |        |        |        |  addresses.            |
    |        |        |        |        |         |              |
    |        |        |        |+++++++>| Reply with the IPv4 addresses.
    |        |        |        |        |         |              |
    |        |        |        |        |<<Translate IPv6 into IPv4.>>
    |        |        |        |        |         |              |
    |<=======|========|========|========|  An IPv4 function call |
    |        |        |        |        |         |              |
   <<Reply an IPv4 data to "host6".>>   |         |              |
    |        |        |        |        |         |              |
    |========|========|========|=======>|  An IPv4 function call |
    |        |        |        |        |         |              |
    |        |        |        |        |<<Translate IPv4 into IPv6.>>
    |        |        |        |        |         |              |
    |        |        |        |<+++++++|  Request IPv6 addresses|
    |        |        |        |        |  corresponding to the IPv4
    |        |        |        |        |  addresses.            |
    |        |        |        |        |         |              |
    |        |        |        |+++++++>| Reply with the IPv6 addresses.
    |        |        |        |        |         |              |
    |      An IPv6 Socket function call.|=========|=============>|
    |        |        |        |        |         |              |


            Figure 3: Behavior of Receiving data from IPv6 host















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4.  Behavior Examples -- IPv6 only network and dual-stack peer

   This section describes behaviors of the proposed dual stack host
   called "dual stack", which communicates with a dual-stack peer called
   "host46" using an only IPv4 application while provisioned only with
   IPv6 network connectivity.

4.1.   Originator Behavior

   This subsection describes the originator behavior of "dual stack."
   The communication is triggered by "dual stack."

   The application sends a query to its extension name server to resolve
   'A' records for "host46."

   The resolver snoops the query, then creates another query for 'AAAA'
   to resolve both 'A' and 'AAAA' records for the host name, and sends
   it to the server.

   If both the 'A' and 'AAAA' records are resolved, so the resolver does
   not need to request the mapper to allocate any IPv4 addresses from
   its pool, but only to store the mapping between received
   destination's IPv4 and IPv6 addresses. the resolver can return 'A'
   record to the application as is.

   If only 'AAAA' records is resolved, so the resolver need to request
   the address mapper to allocate any IPv4 addresses from its pool, then
   the resolver creates an 'A' record and passes it to the application.

   In order for the IPv4 application to send IPv4 packets to host6, it
   calls the IPv4 socket API function.

   The function mapper detects the socket API function from the
   application.  If the result is from IPv6 applications, it skips the
   translation.  In the case of IPv4 applications, it requires an IPv6
   address to invoke the IPv6 socket API function, thus the function
   mapper requests an IPv6 address to the address mapper.  The address
   mapper selects an IPv4 address from the table and returns the
   destination IPv6 address.  Using this IPv6 address, the function
   mapper invokes an IPv6 socket API function corresponding to the IPv4
   socket API function.

   When the function mapper receives an IPv6 function call,it requests
   the IPv4 address to the address mapper in order to translate the IPv6
   socket API function into an IPv4 socket API function.  Then, the
   function mapper invokes the socket API function for the IPv4
   applications.




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   Figure 4 illustrates the behavior described above:


  "dual stack"                                                "host46"
 IPv4    Socket |     [ API Translator ]    | TCP(UDP)/IP          Name
 appli-  API    |Ext Name  Address  Function| (v6/v4)             Server
 cation         |Resolver  Mapper   Mapper  |
  |        |        |        |        |         |              |       |
  |        |        |        |        |         |              |       |
  |--------|------->|  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.>>      |
  |        |        |        |        |         |              |



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  |  An IPv6 Socket API function call.|<========|==============|
  |        |        |        |        |         |              |
  |        |        |        |        |<<Translate IPv6 into IPv4.>>
  |        |        |        |        |         |              |
  |        |        |        |<+++++++|  Request IPv4 addresses|
  |        |        |        |        |  corresponding to the  |
  |        |        |        |        |  IPv6 addresses.       |
  |        |        |        |        |         |              |
  |        |        |        |+++++++>| Reply with the IPv4 addresses.
  |        |        |        |        |         |              |
  |<=======|========|========|========|  An IPv4 Socket function call.
  |        |        |        |        |         |              |


                   Figure 4: Behavior of the originator

4.2.   Recipient Behavior

   The recipient behaviour is exactly the same as in 3.2.
































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5.  Behavior Examples -- IPv4 only network and IPv4 only peer

   This section describes action of the proposed dual stack host called
   "dual stack," which communicates with an IPv4 peer called "host4"
   using an IPv6 application.

5.1.  Originator Behavior

   This sub-section describes the behavior when the "dual stack" sends
   data to "host4".

   When an IPv6 application sends a DNS query to its extension name
   server, the extension name resolver intercepts the query and then
   creates a new query to resolve both A and AAAA records.

   When only the A record is resolved, the extension name resolver
   requests the address mapper to assign an IPv6 address corresponding
   to the IPv4 address.  The extension name resolver creates an AAAA
   record for the assigned IPv6 address and returns it to the IPv6
   applications.

   When both the A and AAAA record are resolved, the extension name
   resolver doesn't need to requests the address mapper to assign an
   IPv6 address corresponding to the IPv4 address.  It just need store
   the mapping information between A and AAAA record then the extension
   name resolver directly pass this AAAA record to the IPv6
   applications.

   In order for the IPv6 application to send IPv6 packets to host4, it
   calls the IPv6 socket API function.

   The function mapper detects the socket API function from the
   application.  If the result is from IPv4 applications, it skips the
   translation.  In the case of IPv6 applications, it requires an IPv4
   address to invoke the IPv4 socket API function, thus the function
   mapper requests an IPv4 address to the address mapper.  The address
   mapper selects an IPv6 address from the table and returns the
   destination IPv4 address.  Using this IPv4 address, the function
   mapper invokes an IPv4 socket API function corresponding to the IPv6
   socket API function.

   When the function mapper receives an IPv4 function call,it requests
   the IPv6 address to the address mapper in order to translate the IPv4
   socket API function into an IPv6 socket API function.  Then, the
   function mapper invokes the socket API function for the IPv6
   applications.

   Figure 5 illustrates the behavior described above:



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  "dual stack"                                                "host4"
 IPv6    Socket |     [ API Translator ]    | TCP(UDP)/IP          Name
 appli-  API    |Ext Name  Address  Function| (v6/v4)             Server
 cation         |Resolver  Mapper   Mapper  |
  |        |        |        |        |         |              |       |
 <<Resolve an IPv6 address for "host4".>>       |              |       |
  |        |        |        |        |         |              |       |
  |--------|------->|  Query of 'AAAA' records for host4.      |       |
  |        |        |        |        |         |              |       |
  |        |        |--------|--------|---------|--------------|------>|
  |        |        |  Query of 'A' records and 'AAAA' for host4       |
  |        |        |        |        |         |              |       |
  |        |        |<-------|--------|---------|--------------|-------|
  |        |        |  Reply with the 'A' record.              |       |
  |        |        |        |        |         |              |
  |        |        |<<The 'A' record is resolved.>>           |
  |        |        |        |        |         |              |
  |        |        |+++++++>|  Request one IPv6 address       |
  |        |        |        |  corresponding to the IPv4 address.
  |        |        |        |        |         |              |
  |        |        |        |<<Assign one IPv address.>>      |
  |        |        |        |        |         |              |
  |        |        |<+++++++|  Reply with the IPv6 address.   |
  |        |        |        |        |         |              |
  |        |        |<<Create 'AAAA' record for the IPv6 address.>>
  |        |        |        |        |         |              |
  |<-------|------ Reply with the 'AAAA' record.|              |
  |        |        |        |        |         |              |
  |        |        |        |        |         |              |
 <<Call IPv6 Socket API function >>   |         |              |
  |        |        |        |        |         |              |
  |========|========|========|=======>|An IPv6 Socket API function Call
  |        |        |        |        |         |              |
  |        |        |        |<+++++++|  Request IPv4 addresses|
  |        |        |        |        |  corresponding to the  |
  |        |        |        |        |  IPv6 addresses.       |
  |        |        |        |        |         |              |
  |        |        |        |+++++++>| Reply with the IPv4 addresses.
  |        |        |        |        |         |              |
  |        |        |        |        |<<Translate IPv6 into IPv4.>>
  |        |        |        |        |         |              |
  |  An IPv4 Socket API function call.|=========|=============>|
  |        |        |        |        |         |              |
  |        |        |        |        |<<Reply an IPv4 data    |
  |        |        |        |        |  to dual stack.>>      |
  |        |        |        |        |         |              |
  |  An IPv4 Socket API function call.|<========|==============|
  |        |        |        |        |         |              |



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  |        |        |        |        |<<Translate IPv4 into IPv6.>>
  |        |        |        |        |         |              |
  |        |        |        |<+++++++|  Request IPv6 addresses|
  |        |        |        |        |  corresponding to the  |
  |        |        |        |        |  IPv4 addresses.       |
  |        |        |        |        |         |              |
  |        |        |        |+++++++>| Reply with the IPv6 addresses.
  |        |        |        |        |         |              |
  |<=======|========|========|========|  An IPv6 Socket function call.
  |        |        |        |        |         |              |


                   Figure 5:  Behavior of the originator

5.2.  Recipient Behavior

   This subsection describes the recipient behavior of "dual stack".
   The communication is triggered by "host4".

   "host4" resolves the address of "dual stack" with 'A' records through
   its extension name server, and then sends an IPv4 packet to the "dual
   stack".

   The IPv4 packet reaches the "dual stack" and the function mapper
   detects it.

   The function mapper requests the IPv6 address to the address mapper
   in order to invoke the IPv6 socket API function to communicate with
   the IPv6 application.  Then the function mapper invokes the
   corresponding IPv6 socket API function for the IPv6 applications
   corresponding to the IPv4 functions.

   Figure 6 illustrates the behavior described above:


















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   "dual stack"                                               "host4"
   IPv6    Socket |     [ API Translator ]    | TCP(UDP)/IP
   appli-  API    |Ext Name  Address  Function| (v6/v4)
   cation         |Resolver  Mapper   Mapper  |
    |        |        |        |        |         |              |
   <<Receive data from "host4".>>       |         |              |
    |        |        |        |        |         |              |
    |      An IPv4 Socket function call.|<========|==============|
    |        |        |        |        |         |              |
    |        |        |        |<+++++++|  Request IPv6 addresses|
    |        |        |        |        |  corresponding to the IPv4
    |        |        |        |        |  addresses.            |
    |        |        |        |        |         |              |
    |        |        |        |+++++++>| Reply with the IPv6 addresses.
    |        |        |        |        |         |              |
    |        |        |        |        |<<Translate IPv4 into IPv6.>>
    |        |        |        |        |         |              |
    |<=======|========|========|========|  An IPv6 function call |
    |        |        |        |        |         |              |
   <<Reply an IPv6 data to "host4".>>   |         |              |
    |        |        |        |        |         |              |
    |========|========|========|=======>|  An IPv6 function call |
    |        |        |        |        |         |              |
    |        |        |        |        |<<Translate IPv6 into IPv4.>>
    |        |        |        |        |         |              |
    |        |        |        |<+++++++|  Request IPv4 addresses|
    |        |        |        |        |  corresponding to the IPv6
    |        |        |        |        |  addresses.            |
    |        |        |        |        |         |              |
    |        |        |        |+++++++>| Reply with the IPv4 addresses.
    |        |        |        |        |         |              |
    |      An IPv4 Socket function call.|=========|=============>|
    |        |        |        |        |         |              |



           Figure 6: behavior of Receiving data from IPv4 hostr














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6.  Considerations

6.1.  Socket API Conversion

   IPv4 socket API functions are translated into semantically the same
   IPv6 socket API functions and vice versa.  See Appendix A for the API
   list intercepted by BIA.  IP addresses embedded in application layer
   protocols (e.g., FTP) can be translated in API functions.  Its
   implementation depends on operating systems.

   NOTE: Basically, IPv4 socket API functions are not fully compatible
   with IPv6 since the IPv6 has new advanced features.

6.2.  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, and vice versa.
   It can be implemented using raw socket.

6.3.  IPv4 or IPv6 Address Pool and Mapping Table

   The address pool consists of the unassigned IPv4 addresses or
   internal IPv6 addresses.  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.  However, if a
   number of IPv4 applications communicate with IPv6 hosts or IPv6
   applications communicate with IPv4 hosts, the available address
   spaces will be exhausted.  As a result, it will be impossible for
   IPv4 applications to communicate with IPv6 nodes or IPv6 applications
   to communicate with IPv4 nodes.  It requires smart management
   techniques for address pool.  For example, it is desirable for the
   mapper to free the oldest entry and reuse the IPv4 address or IPv6
   address for creating a new entry.  This issues is the same as [BIS].
   In case of a per-node address mapping table, it MAY cause a larger
   risk of running out of address.

6.4.  Internally Assigned IPv4 or IPv6 Addresses

   The IPv4 addresses, which are internally assigned to IPv6 target
   hosts out of the pool, are the unassigned IPv4 addresses (e.g.,
   0.0.0.1 ~ 0.255.255.255).  There is no potential collision with
   another use of the private address space when the IPv4 address flows
   out from the host.

   The IPv6 addresses, which are internally assigned to IPv4 target
   hosts out of the pool, are the special IPv6 addresses (It need IANA's
   consideration).  There is no potential collision with another use of



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   thosee address space when the IPv6 address flows out from the host.

6.5.  Implementation Issues

   Some operating systems support the preload library functions, so it
   is easy to implement the API translator by using it.  For example,
   the user can replace all existing socket API functions with user-
   defined socket API functions which translate the socket API function.
   In this case, every IPv4 application has its own translation library
   using a preloaded library which will be bound into the application
   before executing it dynamically.

   Some other operating systems support the user-defined layered
   protocol allowing a user to develop some additional protocols and put
   them in the existing protocol stack.  In this case, the API
   translator can be implemented as a layered protocol module.

   In the above two approaches, it is assumed that there exists both
   TCP(UDP)/IPv4 and TCP(UDP)/IPv6 stacks and there is no need to modify
   or to add a new TCP-UDP/IPv6 stack.































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7.  Limitations

   This mechanism supports unicast communications only.  In order to
   support multicast functions, some other additional functionalities
   must be considered in the function mapper module.

   Since the IPv6 API has new advanced features, it is difficult to
   translate such kinds of IPv6 APIs into IPv4 APIs.  Thus, IPv6 inbound
   communication with advanced features may be discarded.










































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8.  ALG related

   BIA host should only perform a minimum of ALG, especially for Host to
   Host Direct scenario to avoid complicated ALG design for various kind
   of appliation.  ALG design is not encouraged for host based
   translation.  It is out of scope of this document, and it will be
   handled in other document like [PNAT-ALG].












































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9.  Security Considerations

   The security consideration of BIA mostly relies on that of NAT-PT .
   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 level, hosts can utilize the
   security of the network layer (e.g., IPsec) when they communicate
   with IPv6 or IPv4 hosts using IPv4 or IPv6 applications via the
   mechanism.  As well, there isn't a DNS ALG as in NAT-PT, so there is
   no interference with DNSSEC.

   The use of address pooling may open a denial of service attack
   vulnerability.  So BIA should employ the same sort of protection
   techniques as NAT-PT does.





































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10.  Acknowledgments

   The authors gratefully acknowledge the many helpful advice from Dan
   Wing and Dave Thaler for initiating this work, thanks mailing list
   discussion from Mohamed Boucadair, Yiu L. Lee, James Woodyatt,
   Lorenzo Colitti, Qibo Niu and Pierrick Seite.  Contributions from
   Gang Chen, Bo Zhou, Dapeng Liu,Hong Liu, Tao Sun et al. in the
   development of this document.

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








































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11.  Normative References

   [ADDRFORMAT]
              Huitema, C., "IPv6 Addressing of IPv4/IPv6 Translators",
              draft-ietf-behave-address-format-00 (work in progress),
              Aug 2009.

   [DNS64]    Bagnulo, M., "DNS64: DNS extensions for Network Address
              Translation from IPv6 Clients to IPv4 Servers",
              draft-ietf-behave-dns64-00 (work in progress), July 2009.

   [NAT64]    Bagnulo, M., "NAT64: Network Address and Protocol
              Translation from IPv6 Clients to IPv4 Servers",
              draft-ietf-behave-v6v4-xlate-stateful-01 (work in
              progress), July. 2009.

   [PNAT]     Huang, Bill., "Prefix NAT: Host based IPv6 translation",
              draft-huang-pnat-host-ipv6-03 (work in progress).

   [PNAT-ALG]
              Wing, D., "Concerns with IPv4 Applications Accessing IPv6
              Servers (NAT46)", draft-wing-behave-v4app-v6server-01
              (work in progress), February 2010.

   [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.

   [RFC2765]  Nordmark, E., "Stateless IP/ICMP Translation Algorithm
              (SIIT)", RFC 2765, February 2000.

   [RFC2766]  Tsirtsis, G. and P. Srisuresh, "Network Address
              Translation - Protocol Translation (NAT-PT)", RFC 2766,
              February 2000.

   [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.




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Appendix A.  API list intercepted by BIA

   The following functions are the API list which SHOULD be intercepted
   by BIA module.

   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 [SOCK-EXT], 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

   BIA MAY intercept inet_ntoa() and inet_addr() and use the address
   mapper for those.  Doing that enables BIA 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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