I was vague about the years to avoid having to do too much research for mere nostalgia, but there was a transition in there from "just MIT-MULTICS and MIT-ATHENA" to "MIT-MULTICS.ARPA" and then eventually having .EDU names as well. (The same sort of nostalgia that leads me to use 10/8 for home and office nets just so I can put some interesting machine on 10.0.0.6.) (And it turns out searching for "10.0.0.6 imp 6" (multics was imp 6 port 0) turns up https://www.google.com/books/edition/ARPANET_Directory/M6opA... in the "in 1982 information was in books" department...)