RE: ocean: do not boil

[Erik Nordmark <Erik.Nordmark@Sun.COM>]

> >  - NAT-PT ensures, using the DNS ALG, that the host only receives AAAA 
> > records,
> >    thus the host doesn't do anything special.
> 
> And, if the application tries to send to an IPv4 address?  Would it just
> fail with "no route to address", or something like that?

I think so; at least I don't recall seeing this case discussed.

> Right, and this is the part that raises my concerns...  In order for a
> dual-stack node to exist in this environment, it would need to have two
> different "modes" of operation -- one where all A records are translated
> to AAAA records (if behind NAT-PT), and one where the A records result
> in IPv4 traffic (when on an IPv4 network).  How would the node decide
> which "mode" it should be using?

One way is to determine the mode based on whether the node has an
IPv4 address. Thus the node tries to use DHCPv4 to get an IPv4 address
and if that fails it assumes it is IPv6 only and operates in the nat65 mode.
Of course, if the IPv4 address can be assigned using autonet (i.e. link-local
IPv4 addresses), then this needs to be taken into account when trying to
automate this mode selection.
But operationally I suspect always assigning IPv4 addresses, whether link-local
or private RFC 1918 space, and using an IPv4 NAT is simpler since there is one
less mode to worry about.

  Erik