I suggest you switching from Net::Irc to POE::Component::IRC as i also saw suggested somewhere else (maybe in old version Net::Irc documentation?).
If you want you can take a look at my bot TriviaHam - Quiz Irc Bot: to authenticate a user i use the "who" field that comes with every IRC message using POE::Component::IRC. From the "who" field you can easily know the IP (i get the nick in the get_nick sub with a simple regular expression, you can do it the other way around, taking just the IP).
Hope this can help.

$|=$_='1g2i1u1l2i4e2n0k',map{print"\7",chop;select$,,$,,$,,$_/7}m{..}g