Internet Services from KKoncepts

If you are running an IPCop firewall (or similar firewall - Debian and Ubuntu you can install this program) and need to check who is taking up all your bandwidth, there is a command line utility in IPCop that will do this for you - iftop

Log into ipcop using ssh as root and run iftop - It is shows the ip address that uses the greatest bandwidth at the moment and since it started. There is no man page in ipcop - you can try this Iftop manual page