IDS: Scan for "outsider" Pcs on network

[dhamm () jackofallgames com]

Is there a way to setup a scan and be notified of an intruding pc that is physically plugged into the network? When you 
have an enviroment with a large amount of network jacks, it's hard to make sure the ones no longer in use are turned 
off, and that no "visitors" have sat down to use your network connections, esp. if you have a large amount of 
contractors in and out. It got me to searching the net, and so far I have found one cemmercial product that can do it, 
but nothing else. Any suggestions?

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