Validate::Net is a class designed to assist with validation internet
related strings.  It can be used to validate CGI forms, internally by
modules, and in any place where you want to check that an internet
related string is valid before handing it off to a Net::* class.

Whenever a test is false, you can access the reason through the reason
method.

WWW: http://search.cpan.org/dist/Validate-Net/