On Friday 03 August 2007, Keith Moore wrote:
NAT isn't the only answer to the question "I can't
get IPv4 addresses, what do I do?" Using IPv6 and
a proxy to reach the IPv4 world is much, much
cleaner. And it also works from v4 to v6. We
really should start advocating this as the
preferred transition mechanism.
NAT and proxies are not mutually exclusive. There
are advantages to having a proxy that can forward
TCP and UDP traffic from an outside address/port to
an inside address/port and vice versa; there are
also advantages to a NAT that can do the same thing
on a per-packet level. But a good, explicit protocol
and API for doing each would be welcome. It would
also be useful if the forwarder/NAT had explicit
means of communicating the "external" source and
destination address/port to the "internal" host -
say via the same control protocol used to establish
and maintain the address binding.
FWIW, there's a protocol that would give you the same
functionality as a NAT while preserving end-to-end
transparency of the network (i.e. IPv4 packets won't
be modified between the internal host on the IPv6-only
network and its IPv4 correspondent outside in the IPv4
Internet). It would also let the internal host to know
what address/port pair it was using to communicate,
without change to the application.
That's Ream-Specific IP [RFC3102][RFC3103].
That would make it relatively easy
to, say, have a server inside an IPv6-only network
establish presence on an IPv4 network provided by an
ISP, while still allowing the application to see the
real IPv4 source address (say for logging or spam
filtering).
Yes, that was pretty easy on an RSIP-enabled server on
an IPv6-only network connected to the IPv4 world via
an RSIP gateway, e.g. /etc/init.d/inetd start on the
server!
Last but not least, provided that an IKE implementation
would be modified to work hand-in-hand [RC3104] with
RSIP, it would also be possible to support end-to-end
IPv4 IPsec while one or both ends are on an IPv6 only
network.
--julien
[RFC3102] Realm Specific IP: Framework
[RFC3103] Realm Specific IP: Protocol Specification
[RFC3104] RSIP Support for End-to-end IPsec
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