Behave Working Group                                             J. Kato
Internet-Draft                                              A. Matsumoto
Intended status: Standards Track                             T. Fujisaki
Expires: September 6, 2010                                           NTT
                                                           March 5, 2010


                  Checksum-Neutral Prefix NAT for IPv6
                  draft-kato-behave-prefix-nat-01.txt

Abstract

   This document describes a use-case of IPv6-to-IPv6 network address
   translation, and a translation mechanism for smaller network.  To be
   used typically in a network where IPv6 /64 prefix is advertiesed, a
   network address translation mechanism is proposed that is based on
   Interface Identifier rewriting to be checksum neutral.

Status of this Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 4
   2.  Proposal of Address Translation using Interface Identifier  . . 4
     2.1.  Address Translation Example . . . . . . . . . . . . . . . . 4
   3.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7







































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1.  Introduction

   The IPv6-to-IPv6 translation mechanism proposed in NAT66 document.
   NAT66 document [I-D.mrw-behave-nat66].  This assumes that a network
   is assigned /48 or larger address block.  This is because the
   mechanism uses 16 bits of IPv6 address for subnetting to make the
   translation neutral to address translation.

   However, in some environment, a network cannot get such a large
   address space.  Then, we propose another IPv6-to-IPv6 translation
   mechanism that can be used in a network with /48 or smaller address
   block and that is neutral to transport layer checksum.  This
   mechanism also has a characteristics of one-to-one mapping, to keep
   the end-to-end transparency as much as possible.


2.  Proposal of Address Translation using Interface Identifier

   A IPv6 address translation mechanism for smaller network is proposed
   in this section.  This translation mechiansm is one-to-one mapping
   based, and is Interface Identifier rewriting based, to make it
   checksum neutral.

   Regarding the prefix part of an IPv6 address, it is simply replaced
   with the predefined external/internal prefix value.  Regarding the
   Interface Identifier part, the modified value is chosen so that the
   address translation does not have an impact on transport layer
   checksum, which is almost the same technique adopted in NAT66
   [I-D.mrw-behave-nat66].

2.1.  Address Translation Example

   Example network structure is described below.


















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               external network: 2001:0DB8:1111:0001::/64
      ------+----------------------
            |
            |
            o eth0 2001:0DB8:1111:0001::1
       +----+-----+
       | NAT66BOX |
       +----+-----+
            o eth1 FD00:0203:1111:0405::1
            |
            |
      ---+--+----------------------
         |      internal network: FD00:0203:1111:0405::/64
         |
         |
         o eth0 FD00:0203:1111:0405:0200:1111:1011:1234
   +-----+-----+
   | IPv6 host |
   +-----+-----+

                              example network

   When IPv6 host sends a packet destined to external network, NAT66BOX
   receives the following IPv6 packet.

   dst IPv6 address:  (somewhere in external network)
   src IPv6 address:  fd00:0203:1111:0405:0200:1111:1011:1234

   NAT66BOX performs the following address translation to the source
   address of the IPv6 packet, and forward the packet to the upstream.
   Here, it is assumed that the function cksum(x) calculates the 16-bit
   one's complement sum as defined in RFC1071 [RFC1071].

      1.  Calculates the difference between to-be-translated prefix
      checksum and translated prefix checksum.

         cksum(FD01:0203:1111:0405) => 0x141B
         cksum(2001:0DB8:1111:0001) => 0x3ECB


      2.  Gets the difference of the two prefixes based on one's
      complement sum.

         0x3ECB - 0x141B = 0x2AB0







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      3.  Gets the difference of the least significant 16 bits of the
      to-be-translated IPv6 address and the difference of the prefixes'
      checksums calculated at 2.

        0x1234 - 0x2AB0 = 0xE783


      4.  Puts the value of 3 to the least significant 16 bits of the
      translated address Interface Identifier, and gets the translated
      address.

          2001:0DB8:1111:0001:0200:1111:1011:E783

   In the same way, translation of incoming packet from external network
   can be processed.


3.  Discussion

   The mechanism describes here ignores the meaning U/L bit described in
   [RFC4291].  As the Interface Identifier part of the translated
   address is not assured of uniqueness, the U/L bit should not be set
   to 1.

   The workarounds for this issue are to have per-session translation
   table, to administrate the addresses of hosts in local network and
   make all of them use addresses with U/L bit 0.


4.  IANA Considerations

   This document has no actions for IANA.


5.  Security Considerations

   TBD


6.  References

6.1.  Normative References

   [I-D.mrw-behave-nat66]
              Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Address
              Translation (NAT66)", draft-mrw-behave-nat66-02 (work in
              progress), March 2009.



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   [RFC1071]  Braden, R., Borman, D., Partridge, C., and W. Plummer,
              "Computing the Internet checksum", RFC 1071,
              September 1988.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

6.2.  Informative References


Authors' Addresses

   Jun-ya Kato
   NTT PF Lab
   Midori-Cho 3-9-11
   Musashino-shi, Tokyo  180-8585
   Japan

   Phone: +81 422 59 2939
   Email: kato@nttv6.net


   Arifumi Matsumoto
   NTT PF Lab
   Midori-Cho 3-9-11
   Musashino-shi, Tokyo  180-8585
   Japan

   Phone: +81 422 59 3334
   Email: arifumi@nttv6.net


   Tomohiro Fujisaki
   NTT PF Lab
   Midori-Cho 3-9-11
   Musashino-shi, Tokyo  180-8585
   Japan

   Phone: +81 422 59 7351
   Email: fujisaki@syce.net











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