RFC 2765 (rfc2765) - Page 3 of 26

Stateless IP/ICMP Translation Algorithm (SIIT)

RFC 2765                          SIIT                     February 2000


      hosts in the new network are configured with IPv4 addresses.  But
      these new IPv6 devices might occasionally need to communicate with
      some IPv4 nodes out on the Internet.

   -  An existing network where a large number of IPv6 devices are
      added.  The IPv6 devices might have both an IPv4 and an IPv6
      protocol stack but there is not enough global IPv4 address space
      to give each one of them a permanent IPv4 address.  In this case
      it is more likely that the routers in the network already route
      IPv4 and are upgraded to dual routers.

   However, there are other potential solutions in this area:

   -  If there is no IPv4 routing inside the network i.e., the cloud
      that contains the new devices, some possible solutions are to
      either use the translators specified in this document at the
      boundary of the cloud, or to use Application Layer Gateways (ALG)
      on dual nodes at the cloud's boundary.  The ALG solution is less
      flexible in that it is application protocol specific and it is
      also less robust since an ALG box is likely to be a single point
      of failure for a connection using that box.

   -  Otherwise, if IPv4 routing is supported inside the cloud and the
      implementations support both IPv6 and IPv4 it might suffice to
      have a mechanism for allocating a temporary address IPv4 and use
      IPv4 end to end when communicating with IPv4-only nodes.  However,
      it would seem that such a solution would require the pool of
      temporary IPv4 addresses to be partitioned across all the subnets
      in the cloud which would either require a larger pool of IPv4
      addresses or result in cases where communication would fail due to
      no available IPv4 address for the node's subnet.

   This document specifies an algorithm that is one of the components
   needed to make IPv6-only nodes interoperate with IPv4-only nodes.
   Other components, not specified in this document, are a mechanism for
   the IPv6-only node to somehow acquire a temporary IPv4 address, and a
   mechanism for providing routing (perhaps using tunneling) to and from
   the temporary IPv4 address assigned to the node.

   The temporary IPv4 address will be used as an IPv4-translated IPv6
   address and the packets will travel through a stateless IP/ICMP
   translator that will translate the packet headers between IPv4 and
   IPv6 and translate the addresses in those headers between IPv4
   addresses on one side and IPv4-translated or IPv4-mapped IPv6
   addresses on the other side.






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