RE: ocean: do not boil

[Erik Nordmark <Erik.Nordmark@sun.com>]

Overall these are good questions.
However, some details are muddled due to us having both NAT-PT and NAT64
and they work slightly differently. Example below.

There is also a larger issue to keep in mind when comparing NATv4 and 
transition specific NATs (whether NAT-PT, nat64, or something else).
Presumably there is a gradual evolution of the ALG support in NATv4
boxes (special support for special application protocols).
There is a danger in having a separate transition specific NAT in that
it might lag behind the NATv4 ALG support. Hence folks might get less
things to work with the transition specific NAT until IPv6 sales volume
makes the transition specific NAT be ahead of NATv4 in terms of
special ALGs.
For that reason it might make to look very hard at the use of off the shelf
NATv4 technology combined with an IPv6 router.

> How will hosts know that they are running in a NAT-PT environment,
> and that they shouldn't send IPv4 traffic?  Will they default to
> using IPv4-mapped addresses whenever they don't have IPv4 addresses
> configured?  What would be the implications of this behaviour
> (if any) in the event of a DHCP failure on an IPv4-only or IPv4/IPv6
> network that is running these same implementations?

 - NAT-PT ensures, using the DNS ALG, that the host only receives AAAA records,
   thus the host doesn't do anything special.

 - A host with NAT64 support would receive A records thus presumably it
   would determine to send using IPv6 based on the fact that it doesn't
   have any configured IPv4 addresses (or no IPv4 routers in the routing
   table, or an implementation specific knob).

    Erik