> I don't see what you're getting at. the outside sites may be running v4
> with a limited number of external addresses ... if they are running v6
> they will have plenty of external addresses.
Not external *IPv4* addresses, they won't - which is what kind of addresses
they need to communicate with other IPv4 sites.
IPv4 vs. IPv6 isn't an either/or - it's quite reasonable for a site
to run IPv4 (with NAT if necessary) alongside IPv6. I expect that
most sites already on the net will do exactly this - use IPv4 with
NAT for traditional applications that NAT supports and use IPv6 for
the other ones.
Keith