This is what the overly complex ipcompare.c does. Well actually not quite; it's both overly complex and inflexible. A nice rewrite so we had a find_ip() along the lines of find_player() would be good.

It is a bit trickier though as multiple players or rather sockets may be associated with one IP (range) so presumably rather than returning a pointer to an existing one of these structures find_ip() should create and return it's own temp linked list to a structure of all the matches it finds.