Peer-to-Peer Communication Across Network Address Translators
bford.info(2005)
Follow up from 2008 is this: https://bford.info/pub/net/rfc5128-abs/
Ah that’s cool didn’t realize how old it was. The content seems to have held up well. Showed up in google when researching NAT and imo it’s up there with Tailscale’s article in terms of how well it’s written with the drawings.