Making Linux network bridge transparent for 802.1x packets

Update 17/01/2011: If you are interested in 802.1x bridging, have a look at my Tapping 802.1x Links with Marvin blog post.

802.1x authentication messages are sent in Ethernet frames with destination MAC address set to 01:80:C2:00:00:03. This address belongs to “IEEE 802.1D MAC Bridge Filtered MAC Group Addresses” (01:80:C2:00:00:00 to 01:80:C2:00:00:0F) and such frames are not supposed to be relayed by bridges conforming to IEEE 802.1D [2]. For a number of reasons, you may want these frames to go through your bridge.

Transparent Connection Interception Trick

Now when I have a blog for half a year I figured I should post something. So here goes description of using Linux (Ubuntu in my case) bridge configured to redirect selected TCP connections to intercepting proxy (Burp) and while letting the intercepting proxy communicate with the server. Quite useful when doing pentests of fat clients and appliances communicating over HTTP(S), especially in a situation when you can't tamper with client's /etc/hosts file or use other technique to redirect interesting traffic.

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