How to use a simple Linux utility to see what is hogging your network bandwidth.
The nethogs utility allows you to see what is hogging your bandwidth. Type
sudo apt-get install nethogs to install this.
Then run it like this:
homer@lollinux-machina:~/Documents/Doom2 ☠ $ sudo nethogs eth1
A screen like the one shown below will appear. This will show the programs that are hogging your bandwidth.
This is a very useful command if you want to find a rogue process on your system that has run away and is hammering your bandwidth.