INTERNET DRAFT                                                 Seungyun Lee
NGTRANS Working Group                                         Myung-Ki Shin
Expires: May 2002                                              Yong-Jin Kim
                                                                       ETRI
                                                              Erik Nordmark
                                                               Alain Durand
                                                           Sun Microsystems
                                                              November 2001

               Dual Stack Hosts using "Bump-in-the-API" (BIA)
                       <draft-ietf-ngtrans-bia-01.txt>


Status of this Memo

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

     Internet Drafts are working documents of the Internet Engineering Task
     Force (IETF), its areas, and working groups. Note that other groups may
     also distribute working documents as Internet-Drafts.

     Internet-Drafts are draft documents valid for a maximum of six months
     and may be updated, replaced, or obsolete by other documents at anytime.
     It is inappropriate to use Internet Drafts as reference material or to
     cite them other than as "work in progress."

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

     The list of Internet-Draft Shadow Directories can be accessed at
     http://www.ietf.org/shadow.html.


Abstract

     This document specifies a mechanism of dual stack hosts using a
     technique called "Bump-in-the-API"(BIA) which allows for the hosts to
     communicate with other IPv6 hosts using existing IPv4 applications. The
     goal of this mechanism is the same as that of the Bump-in-the-stack
     mechanism [BIS], but this mechanism provides the translation method
     between the IPv4 APIs and IPv6 APIs. Thus, the goal is simply achieved
     without IP header translation.



Table of Contents:

     1. Introduction
     2. Applicability and Disclaimer
     2.1 Applicability
     2.2 Disclaimer




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     3. Dual Stack Host Architecture using BIA
     3.1 Function Mapper
     3.2 Name Resolver
     3.3 Address Mapper
     4. Behavior Example
     4.1 Originator Behavior
     4.2 Recipient Behavior
     5. Considerations
     5.1 Socket API Conversion
     5.2 ICMP Messages Handling
     5.3 IPv4 Address Pool and Mapping Table
     5.4 Internally Assigned IPv4 Addresses
     5.5 Mis-match between DNS Result and Peer Applicatin version
     5.6 Implementation Issues
     6. Limitations
     7. Security Considerations
     8. Acknowledgments
     9. References
     Appendix A : API list intercepted by BIA


1. Introduction

     RFC2767 [BIS] 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]. BIS allows hosts to
     communicate with other IPv6 hosts using existing IPv4 applicationns.
     However, this approach is to use an API translator which is inserted
     between 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 implemetation is dependent upon the network interface
     driver.

     This document specifies a new mechanism of dual stack hosts called
     Bump-in-the-API(BIA) technique. The BIA 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. With this mechanism, the
     translation can be simplified without IP header translation.

     Using BIA, the dual stack host assumes that there exists both
     TCP(UDP)/IPv4 and TCP(UDP)/IPv6 stacks on the hosts.

     When IPv4 applications on the dual stack communicate with other IPv6
     hosts, the API translator detects the socket API functions from IPv4
     applications and invokes the IPv6 socket API functions to communicate
     with the IPv6 hosts, and vice versa. In order to support communication
     between IPv4 applications and the target IPv6 hosts, pooled IPv4
     addresses will be assigned through the name resolver in the API
     translator.

     This document uses terms defined in [IPv6],[TRANS-MECH] and [BIS].




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2. Applicability and Disclaimer


2.1 Applicability

     The main purposes of BIA are the same as BIS [BIS]. It makes IPv4
     applications communicate with IPv6 hosts without any modification of
     IPv4 applications.  However, while BIS is for systems with no IPv6
     stack, BIA is for systems with an IPv6 stack, but on which some
     applications are either not yet available on IPv6 or application for
     which source code is not available or lost.  It's good for early
     adopters who do not have all applications handy, but not for mainstream
     production usage.


2.2 Disclaimer

     BIA SHOULD not be used for IPv4 application of which source is
     available.  We strongly recommend that application programers SHOULD use
     this mechanism only when an application source code is not available. As
     well, it SHOULD not be used for excuse not to port software or delaying
     porting.



3. Dual Stack Host Architecture using BIA

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


                 +----------------------------------------------+
                 | +------------------------------------------+ |
                 | |                                          | |
                 | |             IPv4 applications            | |
                 | |                                          | |
                 | +------------------------------------------+ |
                 | +------------------------------------------+ |
                 | |           Socket API (IPv4, IPv6)        | |
                 | +------------------------------------------+ |
                 | +-[ API translator]------------------------+ |
                 | | +-----------+ +---------+ +------------+ | |
                 | | | Name      | | Address | | Function   | | |
                 | | | Resolver  | | Mapper  | | Mapper     | | |
                 | | +-----------+ +---------+ +------------+ | |
                 | +------------------------------------------+ |
                 | +--------------------+ +-------------------+ |
                 | |                    | |                   | |
                 | |    TCP(UDP)/IPv4   | |   TCP(UDP)/IPv6   | |
                 | |                    | |                   | |
                 | +--------------------+ +-------------------+ |
                 +----------------------------------------------+
              Figure 1 Architecture of the dual stack host using BIA




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     Dual stack hosts defined in RFC1933 [TRANS-MECH] 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. The API translator consists of 3
     modules, a name resolver, an address mapper and a function mapper.


3.1 Function Mapper

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

     When detecting the IPv4 socket API functions from IPv4 applications, 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 the data received from the
     IPv6 hosts, it works symmetrically in relation to the previous case.


3.2 Name Resolver

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

     When the IPv4 application sends a query to a name server with A records,
     it detects the query, then creates another query to resolve both A and
     AAAA records for the host name, and sends the query to the server.

     If only the 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 application.

     NOTE: This action is the same as that of the Extension Name Resolver in
     [BIS].


3.3 Address Mapper

     It internally maintains a table of the pairs of an IPv4 address and an
     IPv6 address. The IPv4 addresses are assigned from an IPv4 address pool.
     It uses the unassigned IPv4 addresses (e.g., 0.0.0.0 ~ 0.0.0.255).

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





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     (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.

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


4. Behavior Examples

     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.

     In this section, the meanings of arrows are as follows :

         ---> A DNS message for name resolving created by the
              applications and the name resolver in the API translator.
         +++> An IPv4 address request to and reply from the address mapper
              for the name resolver and the function mapper.
         ===> Data flow by socket API functions created by the
              applications and the function mapper in the API translator.

4.1 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 name server, the 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 name
     resolver requests the address mapper to assign an IPv4 address
     corresponding to the IPv6 address.

     The 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 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 2 illustrates the behavior described above:


      "dual stack"                                                "host6"
      IPv4    Socket |     [ API Translator ]    | TCP(UDP)/IP          Name
      appli-  API    |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 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.|              |
       |        |        |        |        |         |              |

                    Figure 2 Behavior of the originator (1/2)























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

                    Figure 2 Behavior of the originator (2/2)



4.2 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 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 for




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     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:

      "dual stack"                                               "host6"
      IPv4    Socket |     [ API Translator ]    | TCP(UDP)/IP
      appli-  API    |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


5. Considerations

5.1 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, DNS, etc.)  can be translated in API functions.
     Its implementation depends on operating systems.




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


5.2 ICMP Message Handling

     When an application needs ICMP messages values (e.g., Type, Code, etc.)
     sent from a network layer, ICMPv4 message values SHOULD be translated
     into ICMPv6 message values based on [SIIT], and vice versa. It can be
     implemented using raw socket.


5.3 IPv4 Address Pool and Mapping Table

     The address pool consists of the unassigned IPv4 addresses. However, if
     a number of IPv4 applications communicate with IPv6 hosts, the available
     address spaces will be exhausted. As a result, it will be impossible for
     IPv4 applications to communicate with IPv6 hosts. It requires smart
     management techniques for address pool.  For example, it is desirable
     for the mapper to free the oldest entry and re-use the IPv4 address for
     creating a new entry.  This issues is the same as [BIS].


5.4 Internally Assigned IPv4 Addresses

     The IPv4 addresses, which are internally assigned to IPv6 target hosts
     out of the pool, are the unassigned IPv4 addresses (e.g., 0.0.0.0 ~
     0.0.0.255). There is no potential collision with another use of the
     private address space when the IPv4 address flows out from the host.


5.5 Mis-match between DNS result(AAAA) and Peer Application version(v4)

     If a server application you are using supports does not support IPv6
     yet, but runs on an machine that support other IPv6 services and this is
     listed with a AAAA record in the DNS, a client IPv4 application using
     BIA will fail to connect to the server application, because there is a
     mis-match between DNS query result (i.e., AAAA) and a server application
     version(i.e., IPv4).  One of solutions is to try all the addresses
     listed in the DNS and just not fail after the first attempt.  It can be
     applicable by some extensions of name resolver and API translator in
     BIA.  For this, BIA SHOULD do iterated jobs for finding the working
     address used by the other application out of addresses returned by the
     extended name resolver.


5.6 Implementation Issues

     Some operating systems support the pre-load library functions, so it is
     easy to implement the API translator by using it. For example, user can
     replace all existing socket API functions with user-defined socket API
     functions which translate the socket API function. In this case, every




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     IPv4 application has its own translation library using pre-load library
     which will be bound into the application before executing it
     dynamically.

     The 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.



6. Limitations

     This mechanism supports unicast communications only. If it can 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 this kind of IPv6 APIs into IPv4 APIs. Thus, IPv6 inbound
     communication with advanced features may be discarded.


7. Security Considerations

     Since the mechanism use the API translator at the socket API level,
     hosts can utilize the security of network layer (e.g., IPsec) when they
     communicate with IPv6 hosts using IPv4 applications via the mechanism.


8. Acknowledgments

     We would like to acknowledge the implementation contributions by Wanjik
     Lee and i2soft.


9. References


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

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

   [FTP]        Postel, J. and J. Reynolds, "File Transfer Protocol",
                STD 9, RFC 959, October 1985.

   [NAT]        Kjeld B. and P. Francis, "The IP Network Address




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                Translator (NAT)", RFC 1631, May 1994.

   [IPV4]       Postel, J., "Internet Protocol", STD 5, RFC 791,
                September 1981.

   [IPV6]       Deering, S. and R. Hinden, "Internet Protocol, Version 6
                (IPv6) Specification", RFC 2460, December 1998.

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

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

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

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







Authors Addresses


  Seungyun Lee
  ETRI PEC
  161 Kajong-Dong, Yusong-Gu, Taejon 305-600, Korea
  Tel : +82 42 860 5508
  Fax : +82 42 861 5404
  Email : syl@pec.etri.re.kr

  Myung-Ki Shin
  ETRI PEC
  161 Kajong-Dong, Yusong-Gu, Taejon 305-600, Korea
  Tel : +82 42 860 4847
  Fax : +82 42 861 5404
  Email : mkshin@pec.etri.re.kr

  Yong-Jin Kim
  ETRI PEC
  161 Kajong-Dong, Yusong-Gu, Taejon 305-600, Korea
  Tel : +82 42 860 6564
  Fax : +82 42 861 5404
  Email : yjkim@pec.etri.re.kr




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

  Erik Nordmark
  Sun Microsystems, Inc.
  901 San Antonio Road
  Palo Alto, CA 94303, USA
  Tel : +1 650 786 5166
  Fax : +1 650 786 5896
  Email : nordmark@sun.com








































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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()

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

     Most of the socket functions require a pointer to a 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





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