[kazinator]

The first NAT I used in the middle 90's was IP Masquerading in the Linux kernel, by Pauline Middelink. That had a firewall.

[kstrauser]

Same, but ISTR we had some Cisco gear where NAT (or PAT as they insisted; yes, I know difference; no, no one cared) had a different license or hardware requirement or something from firewall rules.