Since NAT for IPv6 is much simpler than for IPv4, a bunch of
the issues associated with IPv4 NAT usage don't exist. Like,
there should be no need for port translation. No need to
time out mappings. For the most part, NAT for IPv6 should be
just a simple substitution of prefix A for prefix B. What,
exactly, are the range of choices that NAT vendors need to agree on?
A couple of things come to mind...
Vendors need to agree on the timeout for mappings and on the
method for substituting prefixes. Even if ignoring port translation
seems obvious, a vendor who is adapting/upgrading old code might
include this in the absence of a standard. Also, an IPv6 NAT could
include features that are not in v4 NAT such as using RFC 3041
algorithms to generate the Interface ID portion of the mapped
address rather than passing the ID through unchanged.
An often used example of how IPv6 is better than IPv4, talks about
how every device can have its own IPv6 address, so that just like
a telephone set, every device can be "called" by any other device.
But if you look into how the telephone system works, many telephone
sets are not available to receive calls. Instead, they are in
communication with a PABX which may or may not forward phone calls
to the phone set. Since an IPv6 NAT device fills an analogous gateway
role in the Internet, one wonders why there is no IPv6 NAT standard
to cover things like local hosts registering with the NAT to receive
packets on a certain port, or local hosts registering a forwarding
address for packets on a certain port.
--Michael Dillon
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