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Network Working Group                                              X. Li
Internet-Draft                                                    C. Bao
Intended status: Informational                                  H. Zhang
Expires: October 13, 2011                         CERNET Center/Tsinghua
                                                              University
                                                          April 11, 2011


                  Address-sharing stateless double IVI
                        draft-xli-behave-divi-02

Abstract

   This document presents the concepts and the implementations of
   address-sharing stateless IVI (stateless 1:N IVI) and the address-
   sharing stateless double IVI (stateless 1:N dIVI).

   The stateless 1:N IVI keeps the features of stateless, end-to-end
   address transparency and bidirectional-initiated communications of
   the original stateless 1:1 IVI, while it can utilize the IPv4
   addresses more effectively.  The stateless 1:N dIVI has above
   features and it does not require the DNS64/DNS46 and ALG supports.

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
   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 October 13, 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



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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   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.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminologies  . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Stateless 1:N IVI  . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Address-sharing algorithm  . . . . . . . . . . . . . . . .  5
     3.2.  Extended address format  . . . . . . . . . . . . . . . . .  5
     3.3.  Protocol translation . . . . . . . . . . . . . . . . . . .  7
     3.4.  Routing  . . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.5.  DNS  . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.6.  ALG  . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.7.  The translator behavior and the IPv6 end system
           requirements . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  Stateless 1:N double IVI . . . . . . . . . . . . . . . . . . .  8
     4.1.  Port number mapping algorithm  . . . . . . . . . . . . . .  8
     4.2.  Double IVI . . . . . . . . . . . . . . . . . . . . . . . .  9
     4.3.  Protocol translation . . . . . . . . . . . . . . . . . . . 10
     4.4.  Home gateway implementation  . . . . . . . . . . . . . . . 10
     4.5.  End system implementation  . . . . . . . . . . . . . . . . 10
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 11
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 12
   Appendix A.  Testing environment and workflow examples . . . . . . 13
     A.1.  The host on the IPv4 Internet initiats communication . . . 14
     A.2.  The address-sharing end system on an IPv6 network
           initiats communication . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15













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1.  Introduction

   The experiences for the IPv6 deployment in the past 10 years strongly
   indicate that for a successful transition, the communication between
   IPv4 and IPv6 address families should be supported.

   Recently, the stateless and stateful IPv4/IPv6 translation methods
   are developed and becoming the IETF standards
   [I-D.ietf-behave-v6v4-framework], [I-D.ietf-behave-v6v4-xlate],
   [I-D.ietf-behave-v6v4-xlate-stateful].  The original stateless IPv4/
   IPv6 translation (stateless 1:1 IVI) is scalable, maintains the end-
   to-end address transparency and support both IPv6 initiated and IPv4
   initiated communications [I-D.ietf-behave-v6v4-framework],
   [I-D.ietf-behave-v6v4-xlate], [I-D.xli-behave-ivi].  But it can not
   use the IPv4 addresses effectively.  The IPv4 address depletion
   problem makes the deployment of the 1:1 IVI stateless IVI difficult.
   The stateful IPv4/IPv6 translation can share the IPv4 addresses among
   IPv6 hosts, but it only supports IPv6 initiated communication
   [I-D.ietf-behave-v6v4-framework],
   [I-D.ietf-behave-v6v4-xlate-stateful].  Rely on session initiated
   states, the stateful translation cannot support the end-to-end
   address transparency and costs more compared with the stateless
   translation.

   In this document, we present concepts and the implementations of the
   address-sharing stateless IVI (stateless 1:N IVI) and the address-
   sharing stateless double IVI (stateless 1:N dIVI).  The basic
   concepts of these techniques are the combination of "Address plus
   port addressing" (A+P) and the IPv4/IPv6 stateless translation (IVI).

   The stateless 1:N IVI is the extensions of the stateless 1:1 IVI.  It
   is the solution for the following scenarios
   [I-D.ietf-behave-v6v4-framework].

   o  Scenario 1: An IPv6 network to the IPv4 Internet.

   o  Scenario 2: The IPv4 Internet to an IPv6 network.

   o  Scenario 5: An IPv6 network to an IPv4 network.

   o  Scenario 6: An IPv4 network to an IPv6 network.

   The stateless 1:N IVI and the stateless 1:N dIVI keep all the
   advantages of stateless 1:1 IVI and can use the IPv4 addresses more
   effectively.  In addition, stateless 1:N dIVI can work without DNS64/
   DNS46 and ALG.





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2.  Terminologies

   This document uses the terminologies defined in
   [I-D.ietf-behave-v6v4-framework].

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


3.  Stateless 1:N IVI

   The stateless 1:N IVI is shown in the following figure.


              --------
            //        \\        -----------
           /            \      //          \\
          /              +----+              \        ------------
          |              |XLAT|               |------ End System 1
          |  The IPv4    +----+  An IPv6      |       ------------
          |  Internet    +----+  Network      |       ------------
          |              |DNS |  (address     |------ End System N
          \              +----+   subset)    /        ------------
           \            /      \\          //
            \\        //         ----------
              --------
                         <====>


                        Figure 1: Stateless 1:N IVI

   Where the XLATE is the IPv4/IPv6 translator perform 1:N translation
   between IPv4 and IPv6; DNS is the DNS46 and DNS64 for providing the
   authoritative and resolving services; the End System 1 and End System
   N, etc are the IPv6-only hosts which can restrict their transport-
   layer number port range when communicating with the IPv4 Internet.

   In order to share the IPv4 address among IPv6 hosts, the port number
   multiplexing technique is used [I-D.xli-behave-ivi].  The basic idea
   is similar to the ones used in NAT and A+P. This is to say that a
   single IPv4 address can be shared for multiple IPv6 hosts under the
   condition that these individual hosts can only use a subset of the
   65,536 port numbers when communicating with the IPv4 Internet.  For
   example, if the port multiplexing ratio is 128, each host with IPv4-
   translatable address can use 512 concurrent port numbers when
   communicating with IPv4 Internet.  Note that there is no port number
   restriction when these IPv6 hosts communicate with the IPv6 Internet.



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3.1.  Address-sharing algorithm

   The stateless 1:N IVI is shown in the following figure.


                                             .-------|Host0| A1/(P%N)+0
                                            /
        ------                   -----     |
      /  The   \    ------     /  An   \   |
     |  IPv4    |--|1:N   |---|  IPv6   |------------|Host1| A1/(P%N)+1
      \Internet/   |XLATE |    \Network/   |
        ------      ------       -----     |
                                           |\
                                           |  -------|Host2| A1/(P%N)+2
                                           |
                                           |
                                            \
                                              -------|HostK| A1/(P%N)+K


                        Figure 2: Stateless 1:N IVI

   In the above figure, the Host0, Host1, Host2, ..., HostK are sharing
   the same IPv4 address A1, but port number range for different hosts
   are not overlapped.  Therefore, when these IPv6 hosts communicate
   with the IPv4 Internet via the translator, it looks like a single
   host with IPv4 address A1 communicating with the IPv4 Internet.

   We use the Modulus Operator to define the port number range.  If the
   multiplexing ratio is N, then:

   o  For host K, the allowed port number (P) are P=j*N + K-1, where
      j=0, 1, ..., (65536-N)/N.

   o  For the destination port number (P), the packets will be sent to
      host K=(P%N) (% is the Modulus Operator).

   For example: If N=256, then host K=5 is only allowed to use port
   numbers 5, 261, 517, 773, ..., 65,285 as the source port, while the
   packets with these port numbers as the destination port number will
   be send to host K=5.

3.2.  Extended address format

   In order to perform the stateless translation (IVI) between the IPv4
   and IPv6, both IPv4-mapped and IPv4-translatable address are required
   [I-D.ietf-behave-v6v4-framework].  We use the reserved 16-bits to
   encode the range of the port number [RFC6052].



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   The IPv4-mapped addresses are used to represent IPv4 addresses in
   IPv6, as shown in the following figure.


     | 0                 |32 |40            |72         |88       127|
     -----------------------------------------------------------------
     |    LIR            |FF | IPv4 addr    | all 0                  |
     -----------------------------------------------------------------

                   Figure 3: IPv4-mapped address format

   Note that we use the address format and the prefix (e.g. 2001:db8:
   ff00::/40) defined in [I-D.xli-behave-ivi].  There is no port number
   coding required for the IPv4-mapped address.

   The IPv4-translatable addresses are used to represent IPv6 addresses
   in IPv4, we defined the extended IPv4-translatable as shown in the
   following figure.


     | 0                 |32 |40            |72         |88       127|
     -----------------------------------------------------------------
     |    LIR            |FF | IPv4 addr    |Port Coding| all 0      |
     -----------------------------------------------------------------

            Figure 4: Extended IPv4-translatable address format

   Where, we use reserved 16-bits to encode the port number range based
   on the Modulus Operator.

   The most significant 4 bits define the multiplexing ratio and the
   least significant 12 bits define the index of the host, as shown in
   the following figure.


















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      (4 bits) | Index Range(12 bits) | Multx ratio    | # of  Ports
     -----------------------------------------------------------------
          0               000-000               1              65,536
          1               000-001               2              32,768
          2               000-003               4              16,384
          3               000-007               8               8,192
          4               000-00f              16               4,096
          5               000-01f              32               2,048
          6               000-03f              64               1,024
          7               000-07f             128                 512
          8               000-0ff             256                 256
          9               000-1ff             512                 128
          A               000-3ff           1,024                  64
          B               000-7ff           2,048                  32
          C               000-fff           4,096                  16
      -----------------------------------------------------------------

               Figure 5: Transport layer port number coding

3.3.  Protocol translation

   The protocol translation is defined in [I-D.ietf-behave-v6v4-xlate].

3.4.  Routing

   The routing follows the general IPv4/IPv6 routing principle, i.e.
   "more specifics win", same as the original stateless 1:1 IVI.
   [I-D.xli-behave-ivi].

3.5.  DNS

   The DNS handling is referring to DNS64 [I-D.ietf-behave-dns64] and
   DNS46 [I-D.xli-behave-ivi].

3.6.  ALG

   The ALG related issue is discussed in
   [I-D.ietf-behave-v6v4-framework].

3.7.  The translator behavior and the IPv6 end system requirements

   For the stateless 1:N IVI, the IPv6 end systems are required to
   follow the port number range defined by the extended IPv4-
   translatable address format when communicating with the IPv4
   Internet.  The behaviors of the stateless 1:N translator are:






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   o  If the packets are from the IPv4 Internet to an IPv6 network, the
      IPv4 source addresses are translated to the IPv4-mapped addresses
      and the source port numbers are unchanged; the IPv4 destination
      addresses are translated to the extended IPv4-translatable
      addresses based on the destination port number and the destination
      port numbers are unchanged.

   o  If the packets are from an IPv6 network to the IPv4 Internet, the
      IPv6 source addresses and the source port numbers are checked, if
      the source port number matches the port number range defined by
      the extended IPv4-translatable address format, the IPv6 source
      addresses (which are the IPv4-translatable addresses) are
      translated to the IPv4 addresses and the source port numbers are
      unchanged; the destination IPv6 addresses (which are the IPv4-
      mapped addresses) are translated to the IPv4 destination addresses
      and the destination port numbers are unchanged.  However, if the
      source port numbers do not match the port number range defined by
      the extended IPv4-translatable address format, the packets will be
      dropped.

   Therefore, the IPv6 end systems must follow the port number range
   defined by the extended IPv4-translatable addresses.  The behavior of
   the IPv6 end system when communicating with the IPv4 Internet are:

   o  If the IPv6 end system is used as a server, different well-known
      ports will be served by different IPv6 hosts.

   o  If the IPv6 end system is used as a client, the end system must
      generate the source port numbers in the range defined by the
      extended IPv4-translatable address format.  This can be done by
      modification of the end system, or via a port number mapping
      device (home gateway).


4.  Stateless 1:N double IVI

   In general, it is not a good idea to modify the end system in order
   to meet the IPv6 end system requirements of the stateless 1:N IVI.
   Alternatively, we can use the home gateway to map the randomly
   generated source port number to the port number range defined by
   extended IPv4-translatable address format.

4.1.  Port number mapping algorithm

   The port number mapping algorithm is straightforward.  The port
   number mapping device maintains a database of allowed port numbers
   defined by the extended IPv4-translatable address format.  If the
   packets from the end system contains the source port number which do



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   not match the port number range defined by the extended IPv4-
   translatable address format, the home gateway will translate the
   source port number to an allowed one and keep the record in the
   database for translating back the returning packets and all the
   packets in the same session.

   The port number database can be refreshed via the corresponding
   transport layer flags for TCP or via timeout for UDP sessions.

4.2.  Double IVI

   If we can use the home gateway for the port number mapping, then we
   can also use the home gateway (1:1 Xlate) to translate the IPv6
   packets back to IPv4, as shown in the following figure.


           ------                   -----
         /  The   \    ------     /  An   \        -----     -----
        |  IPv4    |--|1:N   |---|  IPv6   |------|1:1  |---|Host1|
         \Internet/   |XLATE |    \Network/       |XLATE|    -----
           ------      ------       -----          -----

                        Figure 6: Double IVI (dIVI)

   The advantage of double IVI is that the DNS64/DNS46 and ALG are not
   required.

   The first IPv4/IPv6 translator (1:N XLATE) is the core network
   translator, the second IPv4/IPv6 translator (1:1 XLATE) is the home
   gateway translator.  The features of these translators are:

   Core network translator:  The core network translator (1:N XLATE) is
      implemented in the border between the IPv6 core network and the
      IPv4 Internet.  It translates the packets between IPv4 and IPv6
      with the 1:N stateless address mapping, same as the one used in
      the stateless 1:N IVI.

   Home gateway translator:  The home gateway translator (1:1 XLATE) is
      implemented between an IPv6 network and user's end system.  It
      translates the packets between IPv4 and IPv6 with 1:1 stateless
      address mapping.  In addition, the home gateway translator maps
      random source port numbers to restricted port number based on the
      extended IPv4-translatable address format and keeps the mapping
      table in database for the port number mapping of the retuning
      packets and all the packets in the same session.  Note that the
      1:1 XLATE is still stateless for the address mapping.





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4.3.  Protocol translation

   The protocol translation is referring to
   [I-D.ietf-behave-v6v4-xlate].  Special MTU and fragmentation actions
   must be taken, due to double translation (more details).

4.4.  Home gateway implementation

   The home gateway implementation is suitable for the ADSL environment,
   as shown in the following figure.

                                              ----     -----
                                           .-|hgw0|---|Host0| A1/(P%N)+0
                                          /   ----     -----
      ------                   -----     |
    /  The   \    ------     /  An   \   |    ----     -----
   |  IPv4    |--|1:N   |---|  IPv6   |------|hgw1|---|Host1| A1/(P%N)+1
    \Internet/   |XLATE |    \Network/   |    ----     -----
      ------      ------       -----     |
                                         |\   ----     -----
                                         |  -|hgw2|---|Host2| A1/(P%N)+2
                                         |    ----     -----
                                         |
                                          \   ----     -----
                                            -|hgwK|---|HostK| A1/(P%N)+K
                                              ----     -----

                Figure 7: dIVI home gateway implementation

   Where Xlate is the IPv4/IPv6 stateless 1:N IVI translator; hgw0,
   hgw1, ..., hgwK are the home gateways performing the port number
   mapping and the 1:1 IPv4/IPv6 translation function; Host0, Host1,
   ..., HostK are dual-stack hosts who share same IPv4 address (A1), and
   have different non-IPv4-translatable IPv6 addresses.

4.5.  End system implementation

   For the wireless mobile Internet environment, it is not difficult to
   modify the operating system of the mobile device, therefore it
   possible to integrate the port number restriction and the IPv4/IPv6
   translation function in the mobile device, which is an IPv6-only host
   to the network and has a dual-stack socket API for the applications
   running on this host.








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                                                -----------
                                             .-|Host0 (hgw)| A1/(P%N)+0
                                            /   -----------
        ------                   -----     |
      /  The   \    ------     /  An   \   |    -----------
     |  IPv4    |--|1:N   |---|  IPv6   |------|Host1 (hgw)| A1/(P%N)+1
      \Internet/   |XLATE |    \Network/   |    -----------
        ------      ------       -----     |
                                           |\   -----------
                                           |  -|Host2 (hgw)| A1/(P%N)+2
                                           |    -----------
                                           |
                                            \   -----------
                                              -|HostK (hgw)| A1/(P%N)+K
                                                -----------

                 Figure 8: dIVI end system implementation


5.  Security Considerations

   There are no security considerations in this document.


6.  IANA Considerations

   This memo adds no new IANA considerations.

   Note to RFC Editor: This section will have served its purpose if it
   correctly tells IANA that no new assignments or registries are
   required, or if those assignments or registries are created during
   the RFC publication process.  From the author's perspective, it may
   therefore be removed upon publication as an RFC at the RFC Editor's
   discretion.


7.  Acknowledgments

   The authors would like to acknowledge the following contributors in
   the different phases of the address-sharing IVI and dIVI development:
   Maoke Chen, Yu Zhai, Wentao Shang, Weifeng Jiang and Yuncehng Zhu.

   The authors would like to acknowledge the following contributors who
   provided helpful inputs: Dan Wing, Fred Baker, Dave Thaler, Randy
   Bush and Kevin Yin.


8.  References



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8.1.  Normative References

   [I-D.ietf-behave-dns64]
              Bagnulo, M., Sullivan, A., Matthews, P., and I. Beijnum,
              "DNS64: DNS extensions for Network Address Translation
              from IPv6 Clients to IPv4 Servers",
              draft-ietf-behave-dns64-11 (work in progress),
              October 2010.

   [I-D.ietf-behave-v6v4-framework]
              Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
              IPv4/IPv6 Translation",
              draft-ietf-behave-v6v4-framework-10 (work in progress),
              August 2010.

   [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.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

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

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              October 2010.

8.2.  Informative References

   [CERNET]   "CERNET Homepage:
              http://www.edu.cn/english_1369/index.shtml".

   [CNGI-CERNET2]
              "CNGI-CERNET2 Homepage:
              http://www.cernet2.edu.cn/index_en.htm".

   [I-D.xli-behave-ivi]
              Li, X., Bao, C., Chen, M., Zhang, H., and J. Wu, "The



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              CERNET IVI Translation Design and Deployment for the IPv4/
              IPv6 Coexistence and Transition", draft-xli-behave-ivi-07
              (work in progress), January 2010.

   [dIVI]     "Test homepage for the dIVI:
              http://202.38.97.114:8056/test.html".


Appendix A.  Testing environment and workflow examples

   We have a testing environment for the address-sharing stateless
   double IVI with 1:N stateless core translator and 1:1 stateless home
   gateway translators (or modified end systems) deployed in the
   [CERNET] (IPv4) and [CNGI-CERNET2] (IPv6).

   The current implementation of the core translator, home gateway
   translator and the modified end systems are implemented in Linux OS,
   with a slightly different Port Coding scheme, as shwon in the
   following figure:


     | 0                 |32 |40            |72     |96     |112  127|
     -----------------------------------------------------------------
     |    LIR            |FF | IPv4 addr    | zero  |   R   |H index |
     -----------------------------------------------------------------

     R:        Port multiplexing ratio
     H index:  Host Index


      Figure 9: Extended IPv4-translatable address format (testing)

   Where bit 96 to 111 is used to represnet the port multiplexing ratio,
   for example, 0100 represents port multiplexing ratio 256; bit 112 to
   127 is used to represent the host index starting from 0 to R-1.

   The testing environment is shown in the following figure.














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                  [2001:DA9:FF3A:C8C0:A00:0:100:0] - 58.200.192.10:4096
                                                ----     -----
                                             .-|hgw0|---|Host0|
                                            /   ----     -----
        ------                   -----     |
      /  The   \    ------     /  An   \   |
     |  IPv4    |--|1:N   |---|  IPv6   |--
      \Internet/   |XLATE |    \Network/   |    ----     -----
        ------      ------       -----      \--|hgw1|---|Host1|
        /    \                                  ----     -----
       |      \   [2001:DA9:FF3A:C8C0:A00:0:100:1] - 58.200.192.10:4097
       |       \
       |        \       --
       |         \ ----|S2|
      --                --
     |C1|              202.38.105.1:80 - [2001:252:ffca:2669:100::]
      --
     125.34.46.137 - [2001:DA9:ff7d:222e:8900::]


                    Figure 10: dIVI testing environment

   In this testing environment, the LIR=2001DA9:ff00::/40 and the port
   multiplexing ratio R=256.  We only show two hosts here, Host0
   (index=0) and Host1 (index=1).  The core translator 1:N XLATE is
   configured with LIR=2001DA9:ff00::/40 and R=256.  The home gateway
   (hgw1) is configured with LIR=2001DA9:ff00::/40, R=256 and index=0,
   while the home gateway (hgw2) is configured with LIR=2001DA9:
   ff00::/40, R=256 and index=1.

   The testing homepage is at [dIVI]

A.1.  The host on the IPv4 Internet initiats communication

   Host C1 (125.34.46.137) in the IPv4 Internet initiates communication
   with address-sharing end system Host0 (http://58.200.192.10:4096) in
   an IPv6 network behind home gateway.














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   On the IPv4 Internet
   Src#p= 125.34.46.137#1856 (#random port)
   Dst#p= 58.200.192.10:4096 (#server port)

   On an IPv6 network
   Src#p= [2001:DA9:ff7d:222e:8900::]#1856 (#random port)
   Dst#p= [2001:DA9:FF3A:C8C0:A00:0:100:0]#4096 (#server port)

   On the address-sharing end system Host0
   Src#p= 125.34.46.137#1856 (#random port)
   Dst#p= 58.200.192.10:4096 (#server port)

                           Figure 11: Example 1

   The returning packets reverse the Src and Dst.

A.2.  The address-sharing end system on an IPv6 network initiats
      communication

   An address-sharing end system Host0 (58.200.192.10) in an IPv6
   network behind home gateway initiates communication with Host S2
   (http://202.38.105.1:80) in the IPv4 Internet

 On the end system Host0
 Src#p= 58.200.192.10:1881 (random port)
 Dst#p= 202.38.105.1:80#80 (server port)

 On an IPv6 network
 Src#p= [2001:DA9:FF3A:C8C0:A00:0:100:0]#8192 (home gateway mapped port)
 Src#p= [2001:252:ffca:2669:100::]#80 (server port)

 On the IPv4 Internet
 Src#p= 58.200.192.10:8192  (home gateway mapped port)
 Dst#p= 202.38.105.1:80#80 (server port)

                           Figure 12: Example 2

   The returning packets reverse the Src and Dst, the home gateway maps
   the "home gateway mapped port (8192)" back to the original "random
   port (1881)".











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Authors' Addresses

   Xing Li
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN

   Phone: +86 10-62785983
   Email: xing@cernet.edu.cn


   Congxiao Bao
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN

   Phone: +86 10-62785983
   Email: congxiao@cernet.edu.cn


   Hong Zhang
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN

   Phone: +86 10-62785983
   Email: neilzh@gmail.com





















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