[Bridge] Making a bridge work without source address spoofing

Stephen Hemminger shemminger at osdl.org
Mon Jul 25 09:39:37 PDT 2005

On Wed, 14 Jul 2004 12:38:18 -0500
"Saxer, John -ACDSD" <John.Saxer at itt.com> wrote:

> So, I agree, the curent wireless card I have been given does not
> allow source address spoofing, but I still would like to use
> bridging. I wonder if anyone has tried modifying the bridge code to
> encapsulate the actual packet in some way so that the desired source
> address can be preserved?
> I am thinking of something like duplicating the ETH header, adding it
> to the beginning of the packet, so that there are 2 headers. I know
> that the wireless card strips the header off, adding its own header,
> and so it would strip off the extra one, leaving the original
> unchanged. Then, when the packet arrives, I would add software to
> strip the wireless header off again, leaving me with the original
> packet again!

It won't work the data is sequential.

You could hack up a  your custom wireless driver to custom bridge code.
At which point you might as well forget bridging and just do routing
or tunneling.

> I guess I am thinking that I could add this "extra" header processing
> in the wireless driver. Do you think this might work?

Why bother? The point of the bridge is to be transparent.  If you
don't want it to be transparent?

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