Bridge with a tweak...

Hi list,

I have a question regarding bridges in general, and my bridge in particular. I want to take all the packages flowing one way over the bridge (say eth0->eth1) and pack them in my own packet- structure (extra headers added, and the content modulated for further wireless transportation), and all the packages flowing in the other direction (say eth1->eth0) needs to be "de- packed" (stripped of my custom headers, and demodulated).

What I'm basically doing is trying to make my software radio (connected to one of the network- devices) work as a wireless network adapter, but with my own signaling- scheme, but I don't want to use the same computer for the radio, as for "browsing the web", since the radio- part is a bit on the heavy side to the processor.

Is there an easy way to do this? Where would you start? I have been looking at the code for the kernel- module, but haven't really got any really useful clues from it.

Any pointers towards where to start looking, poking and dragging would be greatly appreciated.

BR
Mattias Kjellsson

Yes... you modify the particular interface, not the bridge. For example, you can place a tun/tap interface into the bridge (instead of eth1) to receive all packets passing through the bridge into a user-mode application. If you get the user-mode solution fully working but the performance is not high enough, then you could make a kernel module. And the vlan or IP tunneling code would be the best place to start, since they add and remove headers already. But user-mode is much easier both to write and to debug, so start with tun/tap.

Note that because of the switching code, you'll not get any packets arriving on your interface besides ARP until you get bidirectional communications working (well, maybe some broadcast UDP like DHCP REQUEST).