Thanks, killians45!
I Googled "
5-4-3 network rule" and found some nice pictures at
this link and
that one. I wondered why I'd never heard of it before, but it's apparently because it's not much of a concern any more. Back in the day when most segments were connected by hubs/repeaters/concentrators it was an issue. With switches and buffering, the rule is somewhat obsolete, but still worth knowing.