I'm posting this message due to the number of times I have been asked about this situation: Is your roommate driving you mad by clogging up your network with downloads of Spanish Simpson's episodes and incomplete movies over KaZaA? Need to stop it?? Here's what KaZaA does. It's default setting is port 1214. So, on your router, block based on the IP (or Mac address) of the computer, or computers you are targeting, on port 1214. Done, right?! Not so fast pard'ner. KaZaA knows to check through from port 1000-4000 in this case. So block those too. Done? Yes, you've slowed it down at this point, quite severely, but only in connection time. If the user sets the time-out a tad higher, or if their machine is particularly quick in connecting, then you're still stuck. This is because... Next, KaZaA will latch onto port 80. You cannot block port 80 safely. Blocking port 1000-4000 is risky enough, but Port 80 is your internet browsing port. On port 80, KaZaA will then begin to interlace itself with your incoming and outgoing 'surf' traffic. This will cripple your browsing capabilities almost completely. The only way to block this is to establish your network's browsing capabilities to a random port (eg: port 5555) via a proxy server setup. NOW you can fully block port 80 and cripple KaZaA for good. Yet, the configuration to setup the proxy server connection, and conficts in blocking ports, could make this much more complex than it seems. Simplest Answer: Just tell your employees/roommates to get rid of KaZaA.. much easier ! Scripts can also be built for W2000, etc, which can block the installation of KaZaA, and/or automatically remove existing versions from your network (we're talking about a corporate network here). Well.. Enjoy blocking your roommates' KaZaA abuse, then play dumb and insist it's the service provider, not the router. It's even more fun to make the blocking disabled for part of the day, so that they continuously get cut-off in the middle of files. : )

Wouldn't stopping inbound port 80 requests be easiest? Unless your roomates are running a webserver on their PC that shouldn't be an issue...

That's a good plan, assuming you don't want any traffic on port 80. That would shut-down any regular internet traffic. The only way to do that is abandon it altogether and setup a proxy server connection for IE/Netscape/whatever to access the internet on some mystery port, that way KaZaA won't really be able to find it.