wireless-to-wired bridging

Lowell Gilbert freebsd-questions-local at be-well.ilk.org
Sun Feb 13 07:17:33 PST 2005

"Reid Linnemann" <lreid at cs.okstate.edu> writes:

> I'm bridging the devices so that the wired and wireless nets will appear
> to be on the same physical network to eachother.

Well, yes, that's what bridging means.  Why do you want that?  [Is it
a Microsoft thing?]

> I think I was really tired when I wrote my original email.. so let me
> rewrite my hypothesis:
> I am suspicious that, since the wireless interface on the BSD machine
> operates in AP mode, if a wireless client wants to send a packet to
> another wireless client, it must be first sent to the wireless interface
> of the BSD machine, which should theoretically redirect the packet to
> the appropriate host on the wireless net. In the wired network, a switch
> handles this case automagically on the datalink layer before any
> messages can hit the rl1 interface of the BSD router. I've looked at
> the bridge code, and it seems that unless a packet is multicast or
> broadcast it will be copied to the other bridged interfaces but not
> returned to the original caller. Since the packets being sent from one
> wireless client to another are not broadcast, I think that the bridge
> module may be dumping them into the black hole of the wired LAN, and
> they are not being processed and pumped back out through the ath
> interface. Is this a correct assumption? Are there ways I can overcome
> this problem?

On a quick look, I think you might be on the right track.  The
bridging code seems in a number of spots to be built specifically for
Ethernet.  I have always maintained that bridging unlike media was a
hack bound for problems...

You might have more success using dummynet for bridging rather than
trying to fix things in the protocol stack.  

Good luck.
Lowell Gilbert, embedded/networking software engineer, Boston area

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