Hmm, your question seems to require a list of the IP's. You can do this fairly easily on the server side with (whatever your OS's equivalent) the FreeBSD netstat -an command. Parsing the output for IP-Octet.IP-Octet.IP-Octet.IP-Octet.23 (23 being the telnet port) should not be to hard. There are even a couple CPAN modules that will help with easy IP Addr parsing.

Doing it this way is going to be much easier than a client side solution, IMHO.

"Nothing is sure but death and taxes" I say combine the two and its death to all taxes!