ath client bridge

Andrew Atrens atrens at
Wed Oct 19 07:26:43 PDT 2005

Andrew Thompson wrote:
> On Wed, Oct 19, 2005 at 11:01:30AM +0200, Jiri Mikulas wrote:
>>I have problem to setup bridging box with ath in client mode and if_bridge
>>When card is in AP mode, everything is ok, but if I want to run card in
>>client mode, bridging is not working.
>>Here are my testing steps: (it's quite long, so I prefer put URL there :) )
> Bridging on the client side of a wireless connection is not supported
> and has to do with the 801.11 frame format. The problem is that the
> client only registers its own MAC address with the AP, so the bridged
> clients do not get a reply (as far as I understand).

Yah, the 802.11 header only has room for three addresses.

The AP uses them as -


(in this case src is the *real* src of the packet hence the AP itself can bridge)

The client uses -


(in this case src *must* be the client mac, hence the client can't bridge packets
  from other macs)

There is a four address version of the packet header, but as I recall the fourth
address is used by TKIP.

So it's a problem with 802.11 standard. I think that's why they came up with WDS.
I think there's some support for WDS in MadWiFi, but not yet in the BSD stack(s).

Another thing that you *could* do - that I'm actually working on for DragonFly, is
to add support for bridging GIF interfaces. Or, if it was possible add support
for directly bridging across IPsec - I think even transport mode support would suffice,
as long as in either case the AP and client were endpoints for the IPsec connection.


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