[Dnsmasq-discuss] DHCP over a wireless bridge

Nikita N. nikitan at operamail.com
Wed Jan 8 13:35:15 GMT 2014

Hi Albert :) you didnt mention last time you had a wifi based
configuration too, nice to know! :)
To answer John, if I can try to help, yes, your requirement looks little
unclear to me too.. FYI, Im "playing" too with a wifi loopback bridge
project, and its indeed not very easy to implement from scratch.. ;) Im
running too dnsmasq on the AP side, absolutely DHCP dynamic (nothing
static) but only because the AP is a Linux fully operational dedicated
Running dnsmasq on a AP router bought and used "as is" of course you
cant.. I suspect you need to install your own Linux, lots of infos on
web about that ..
As for me, a common issue Im encountering here is the server/AP "not
hearing" the client frames (even if client/AP are close each other), so
you would need to implement also your own logic for "retransmission" if
that happens in your tests..
Also be very attentive on the option you give to dnsmasq: you pick the
wrong ones, things will not work as you want! :) so you could also post
your dnsmasq.conf here..
Im encountering also other issues, unfortunately, but Im still working
on them.. 

On Tue, Jan 7, 2014, at 09:45 PM, Albert ARIBAUD wrote:
> 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?
> Amicalement,
> -- 
> Albert.
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