How do I 'break' an unwanted Internet connection?
 

I was looking at the 'Active Connections' on Firestarter. Most of them I was aware of and approved, but there were a couple I didn't understand. Had to reboot to get rid of them. Is there a command I could issue to break such a connection? Hopefully one that needs only the port # or ip address since that's all the info Firestarter is giving me.

Could you give us some examples of connections you didn't want?

Well, you could just kill the process that is using the port. That may or may not be a good thing.

To find out what process is using a given network connection:

As root, try running "netstat -np" or "lsof -i". Depending on how many connections you have you will probably need to pipe the output to a pager (pg, more, less, etc.) This will give you the process id and program name of the thing that's using the connection. Non-root users cannot get this information AFAIK.

Sounds like you need dsniff, a package that basically sniffes network connections, but also comes with 2 useful tools you might want to take a look at:

* tcpkill - kills specified in-progress TCP connections.
* tcpnice - slow down specified TCP connections via "active" traffic shaping.

There is also a tool called 'cutter' which cuts off active ip connections, but I haven't used it. Just google for it.

Hope this helps.

Ooh! that sounds like exactly what I need. I was trying to get the problem to reoccur, so I could be a little more specific about the connections I didn't want, but it hasn't yet. It will tho, and I'm sure that the process involved is going to be java, which is also controlling connections I want to keep. Thus haertig's kill suggestion above is probably not going to work. His suggested troubleshooting commands work nicely, tho.

All I want to do is slam the door on specific connected ports.

another easy way to track connections is netstat.
"netstat -l" shows listening sockets
"netstat -p" shows pid of whats on the socket
"netstat -c" will scroll the connections continuos
those are just the couple i know off the top of my head reading man netstat should help if you need anything else.