OK, "NAT is evil" is probably my catch phrase and I have put it on t-shirts and coasters and all sorts.
But WTF - I am today accessing IPv4-only internet hosts via NAT from IPv6. We finally got totd (Trick or treat daemon) working and I finally got the basics of our carrier grade IPv6/4 NAT gateway working in the FireBrick FB6000.
TOTD basically acts as a DNS proxy that answers AAAA (IPv6) queries when the host only has IPv4 by mapping the answer to a specific block of IPv6 space (2001:8b0:6464:: in this case).
The FireBrick FB6000 does the clever IPv4/6 session tracking and mapping.
I have yet to sort traceroutes, but pings work. Traceroutes will be hard as it means mapping all of the ICMP and ICMPv6 code/types. And we still have to fully handle fragments. But we do have a TCP MRU fixup so that basically everything just works. And over the next few days we expect full ICMP support and MTU and fragment issues resolved.
It's on the A&A status page, but anyone can try as we have not actually locked it down. It will be locked down at the first sign of abuse, don't worry. DNS 2001:8b0:6464::1 and 2001:8b0:6464::2 and you are surfing an IPv6-only internet.
I mean, just, well, WOW!!!