>From Steve Gibson's website: (www.grc.com) Port 113 is associated with the Internet's Ident/Auth (Identification / Authentication) service. When a client program in your computer contacts a remote server for services such as POP, IMAP, SMTP, or IRC, that remote server sends back a query to the "Ident" server running in many systems listening for these queries on port 113. Essentially, the remote server is asking your system to identify itself . . . and you. This means that port 113 is often probed by attackers as a rich source of your personal information.
You may recall, from my explanation of Stealthed ports, that attempting to connect to a stealthed port is both costly and painful for the contact initiator � which is why it's so cool to stealth our machines. But the problem with simple stealthing of port 113 is that we don't want to hurt the servers we are trying to contact when they turn around and send us their IDENT query. If they get no response at all from their port 113 query, our connection to them (which initiated their query in the first place) will be delayed or perhaps completely abandoned. Note that not all servers generate IDENT queries. So, depending upon your ISP, stealthing port 113 may not be any problem for you. However, you'll note that requirements for port 113 are common enough that most mature firewalls (BlackICE Defender, AtGuard, NIS2K, etc.) include built-in default rules allowing IDENT queries to pass through. These rules result in the IDENT's status being "closed" rather than "stealth." So what can you do? You may be able to remove or disable your firewall's default rule for IDENT (port 113) and run it in full stealth mode without trouble. If you do this, keep on the lookout for trouble connecting to less common servers, like IRC, which might have problems that you haven't encountered before. Or, you can leave the default rule in place and live with your system's IDENT service port being visible to the outside world. Be aware that this provides a means for intruders to detect an otherwise stealthed computer. And they'll know you're running a firewall since other things are stealthed, but not port 113. Or, you can switch to the very latest, highest technology, and best adaptive firewall which is smart enough to stealth this port against random probes, while still showing it as "closed" to queries from valid servers . .
