[sneak]

CTCP messages still go through the server. DCC (direct client connection) are the p2p connections you are thinking of, but they of course don’t work behind nat.

I was behind NAT when I first got on IRC in ‘98. I set it up with ipfwadm.

[anyfoo]

Ah you are right, I mixed CTCP and DCC up. The former was also used to set up the latter I think? (Among other things.)

I joined IRC in the early 90s, there was no NAT then, packet filtering was uncommon, and practically nothing on the Internet was encrypted. It was a very different time.