[Dnsmasq-discuss] DHCP over a wireless bridge

Albert ARIBAUD albert.aribaud at free.fr
Wed Jan 8 05:45:27 GMT 2014

Le 08/01/2014 03:11, John Kaye a écrit :
> Hi All,
> I'm developing a transparent wireless bridge for a client who
> manufactures printers. The printers connect through the Ethernet side of
> the bridge and the wireless side of the bridge associates with an AP.
> The AP will reject frames from the printers because their source address
> is different from the source address that is associated with the AP; to
> resolve that, ebtables is used to snat the source address of the frames
> from the printers, and everything flows.
> Everything flows nicely when the printers are configured with static
> IPs. When the printers are configured to use DHCP, the AP never delivers
> an IP, even though it receives a discovery request from the printers. I
> assume the AP doesn't respond because the DCHP DISCOVER frame has the
> client mac address encoded within it, which doesn't match the address
> that it is associated with, so it's ignored. Does that sound correct?
> To enable the printers to get IP addresses from the AP, it would seem
> that a DHCP relay proxy of some sort would need be to implemented to run
> on the bridge. The proxy would relay DHCP requests to the AP and return
> addresses to the printers. Does that sounds feasible?
> If my assumptions are correct, can dnsmasq be configured as a DHCP relay
> proxy? If so, are there examples of how it can be done?
> If my assumptions are not correct (which I imagine they are),  are there
> other options?
> I truly appreciate any guidance. My networking knowledge is limited,
> though it is growing by leaps and bounds!
> Cheers,
> -John

I am not sure I understand your requirements fully, but I have a setup 
similar to yours, or more exactly, I have a setup where DHCP clients are 
on one side of a wireless link and the dnsmasq server is on the other 
side, and I did not have to snat because I did not experience this:

	"he AP will reject frames from the printers because their
	"source address is different from the source address that is
	"associated with the AP"

Can you elaborate on the symptom (the "rejection"): what do you try, 
what do you expect and what do you actually see that makes you conclude 
the AP has "rejected" the printer's frames?


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