> I disagree. What problem does NAT solve, other than allowing people to cut corners and not deploy IPv6?

It by default ensures that machines inside a network are not reachable from the outside world. It gives you one address to the outside world which made IP blocks for abuse work quite well and enabled a lot of other users.

Sure, it's a bit of a pain for UDP communication but given the common NAT behaviours not completely terrible. If it was defined a bit clearer NAT would not have been that controversial.

So does a firewall, in a much less complicated way.

NATs are not terribly complex and most consumer grade firewalls are significantly worse than a simple NAT is.

Well, it allowed us to keep growing the internet before we had IPv6, for one thing.

You might want to look at when IPv6 was designed. It's quite a bit older than you might think.

Designed is very different from available in any form. If I couldn't buy a router that supports it with any amount of money, NAT was my only answer. This was the existing state of the world for a long time.

Wasn't IPv6 already out before we ran out of IPv4 addresses? In which case NAT is just a kluge for the lazy who didn't want to deploy IPv6.

One can't control those that must deploy IPv6 first. That's the problem NAT solves. Developing NAT was likely not easy; consider how many implementations f it up anyway.