Net::IP::Match::Regexp allows you to check an IP address against one or
more IP ranges.  It employs Perl's highly optimized regular expression
engine to do the hard work, so it is very fast.  It is optimized for
speed by doing the match against a regexp which implicitly checks the
broadest IP ranges first.  An advantage is that the regexp can be
computed and stored in advance (in source code, in a database table,
etc) and reused, saving much time if the IP ranges don't change too
often.  The match can optionally report a value (e.g. a network name)
instead of just a boolean, which makes module useful for mapping IP
ranges to names or codes or anything else.

WWW: http://search.cpan.org/dist/Net-IP-Match-Regexp/