> > But isn't it possible to have a router convert from an IPv6 address
> > with provider bits to an IPv4 address by simply stripping all but the

> You can't strip a non-zero part of IPv6 address, as this would cause
> transport layer pseudo-header checksum to fail.

Unless you recalulate the checksum. There are products out now
that do similar things (like map a large set of private ip addresses to
a single class C).

You're absolutely correct -- Network Address Translation (NAT) boxes
do this. Moreover, the use of NAT boxes allows to significantly
reduce the problem of IPv4 address space depletion (as sites that
use NAT boxes can use private address space out of RFC1597),
so that we wouldn't run out of IPv4 addresses any time soon.