[ianburrell]

An alternate to IPv6 would have been to store the NAT addresses in IPv4 somehwere. But the IPv4 options are fragile and normal NAT would likely destroy them. It would still require rewriting all of the networking and software. It would have engrained NAT everywhere and made lots of routing problems, like is that your or mine 10. network.

[tracker1]

That's where the public prefix would be the differentiator... you could only access from external directly over IPv6, but it still represents the same device as the NAT ipv4 address.

Difference is it's all public after, it would ease the transition dramatically, and then you can just use whatever you want internally making /32 the minimal assigned block or whatever the prefix size is.

[ianburrell]

Stop saying IPv6 when talking about new protocol. IPv6 already exists and is better than potential IPv4 extension. There was a window twenty years ago for alternative but now IPv6 is usable and can access IPv4 hosts with NAT64. The only reason for IPv4 is inertia.

Routing would be complicated when have to deal with variable length addresses when half the hosts don't know about them and half the routers remove them. It wouldn't make up for rewriting all the software, we know how hard that was with IPv6.