Just a tip for anyone interested. My advice is to make sure your servers are Dual Stacked so you won't have to care where the client is coming from. It will just work.
4in6, tunnel IPv4 over IPv6, the reverse of
6in4(6over4), tunnel IPv6 packets over IPv4 to a relay on the other side.
6to4, this automatically generates a IPv6 prefix you can use based on your public IPv4 Address. This breaks if you don't get a public IPv4 address. Which is the case soon since most Local registries will run out of public v4 "soon" and thus start giving users a private address and NAT everything. This transition tech has limited lifetime. Always starts with 2002::/16. It carries the IPv6 traffic over IPv4 like 6in4.
DS-Lite, tunnels your IPv4 over IPv6, you still get NAT from the ISP but the base carrier is IPv6, like 4in6. The benefit from the ISP is that they don't need Public IPv4 to rollout, which is what any starting ISP will need to do starting 2013 because they will get a single /22 for transition purposes only.
6rd, based on the 6to4 mechanism, but the ISP controls the relay which means they can offer a more reliable service, it also works with private IP addresses on the WAN because they can define the relay the client uses. It uses a similar "calculate the local prefix based on the WAN address" as 6to4, but it can have a different prefix from 2002::/16 and is ISP prefix instead.
ISATAP, Teredo, ignore. It's going away. Windows thing. Automatic tunneling mechanism.
NAT64, DNS64, This is what you will use if you have a v6 client, that can not speak IPv4. We'll need this in the near future, mostly for mobile since it's hard to do dual stack there. Otherwise a v6 only device can not reach IPv4 sites. T-Mobile US is running limited scope testing, but most things work fine.
You'll need a black belt in packet capture foo to decode the NAT though. It's positively unreadable. But it's required to go forward.
4rd, rapid IPv4 deployment, but over IPv6. Tunnel your IPv4 over IPv6. This might be used somewhere in the future. This is for ISPs deploying IPv6 only to the client and then to give them a small bit of IPv4 so they can atleast dual stack. It means all equipment between your CPE and the ISP is IPv6 only. Which is something that will happen in 2013+. See DS-Lite which so far the ISPs prefer better.
NAT-PT, NAPT-PT. You mean something like Carrier(Crummy) Grade Nat, or Large Scale(Sucky) NAT.
I feel for anyone that's going to see their internet connection end up like this, sharing a single IP with a few hundred customers and then wondering why the single IP block from the forum just took out a whole lot of customers. All the automatic blocking mechanisms we have today in forum software in the like will wreck havoc with this.
The FBI was complaining about not being ready to track IPv6, that's just silly, they should try and decode connections from such a large NAT and then try to find which of the few hundred users was it.