Net::CIDR::Set represents sets of IP addresses and
allows standard set operations (union, intersection,
membership test etc) to be performed on them.

In spite of the name it can work with sets consisting
of arbitrary ranges of IP addresses - not just CIDR blocks.

Both IPv4 and IPv6 addresses are handled - but they may not
be mixed in the same set. 

WWW: http://search.cpan.org/dist/Net-CIDR-Set/