Hi,

I'm trying to setup a bridge between 2 ethernet interfaces, one on-board and one USB. Essentially, I'm trying to intercept packets coming from one source (connected to me) and transparently pass them along to the other interface, which is connected to the real internet. Basically:

Computer1 <----> (eth0) Me (eth1) <----> Internet

(I swear, it's for networking class to demonstrate a possible way a MITM attack is performed. Educational purposes only, guys).

The issue I'm having is I can tcpdump each interface independently and receive data, but I'm not able to "forward" packets from 1 to another.

Here's what I've done:
# ifconfig eth0 mtu 1500 promisc up
# ifconfig eth1 mtu 1500 promisc up
# brctl addbr br0
# brctl addif eth0
# brctl addif eth1
# echo 1 > /proc/sys/net/ipv4/ip_forward
# for x in $(ls /proc/sys/net/bridge); do echo 0 > $x; done

I feel like there's something obvious I'm missing. What am I doing wrong?


Thanks,
-rabbit

this seems similar:
http://www.linuxquestions.org/questi...lu#post3804866

Hi,

Thanks for the replay, but my goal isn't to masq. the 2 interfaces together. Doing so would modify packets as they pass through my computer. I specifically need a fully transparent setup, where my computer (the bridge) is practically invisible to both parties.


Thanks,
-rabbit

I did it! It's actually a fairly simple procedure once you understand everything. Here are the commands I ran, in order:

And I'm now a transparent bridge between the two wires. You can tap either end with Wireshark/tcpdump to watch the traffic fly through your computer. Hopefully, I can save someone a lot of frustration and time with this.


-rabbit