Sets up in the ircd's configuration which irc servers will be a "hub server" - those which have many server connections coming off of them...

Format:
H:hostmask:*:server name

In cyclone at least, there's also (in no particular order) a K:Line, Q:Line, C:Line, N:Line, X:Line, A:Line, M:Line, Y:Line, I:Line, U:Line, L:Line, O:Line and a P:Line. There's also a G:Line