I still have one IP address lodged in my memory from 25+ years ago - sable, the university's key Unix server for students, on which I learned so much about Unix and the 1990s Internet.

(I'm not sure if I'd faced DNS issues that meant I needed to know that - but it was a time when dialup ISPs told you what to manually configure for your DNS rather than it being automatically assigned, so it all seemed a bit chunkier.)