RFC 2765 (rfc2765) - Page 3 of 26
Stateless IP/ICMP Translation Algorithm (SIIT)
Alternative Format: Original Text Document
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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