Debian Network Tap
From NSMWiki
There are two pages of interest here.
The first provides assistance for setting up a passive bridge tap in Debian Linux. The passive bridge tap can potentially sniff network traffic at whatever speed the pair of network interface cards can achieve.
http://www.altsec.info/active-network-tap.html
The second features detailed instructions for building an ethernet 10/100 passive network tap, usually for under around US$25.00.
