CLI magic: Tcpdump
Don't worry, I'm not going to try to turn you into to a network security analyst or administrator. But if you're interested in what's happening under the hood on your Internet connection, I'll be happy to introduce you to an old and respected command-line tool. Come on, pull that many-pixeled GUI quilt off of you and meet me at the CLI for a look at tcpdump.
Most distributions include tcpdump out of the box, and most require that you run it as root. So as super user, simply enter tcpdump at the command line. It will take the default values and go, pumping out packets as they are received.
By Joe Barr at Linux.com
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