Please mirror, because more people should have a copy of this: https://3e.org/vvannot This is Vinge's annotated copy of A Fire Upon the Deep. It has all his comments and discussion with editors and early readers. It provides an absolutely fascinating insight into his writing process and shows the depth of effort he put into making sure everything made sense.
The key insight always was hexapodia.
(I'm glad someone linked to this. I actually bought the annotated edition a while back and was reading it back in the Palm Pilot era, I think, but I've lost it and never quite finished it. So I'm happy to see it and have no qualms for myself about grabbing it.)