[Dnsmasq-discuss] Answering DHCPINFORM from other interfaces

richardvoigt at gmail.com richardvoigt at gmail.com
Mon Oct 19 05:45:14 BST 2009

On Sun, Oct 18, 2009 at 10:41 AM, Sergei Zhirikov <sfzhi at yahoo.com> wrote:
> richardvoigt at gmail.com wrote:
>> On Sat, Oct 17, 2009 at 1:18 PM, Sergei Zhirikov <sfzhi at yahoo.com> wrote:
>>> Michael Rack wrote:
>>>> You have to setup a bridge on your linux-router and assign every dynamic
>>>> created ppp-interface to that.
>>>>       brctl addif br0 pppx
>>>> Configure DNSMASQ to listen on the bridges interface.
>>>>       interface=br0
>>>>       bind-interfaces
>>>> And well, you're done.
>>>> Cheers,
>>>> Michael.
>>> Thanks for the suggestion, Michael.
>>> I have tried it, but unfortunately it doesn't work :(.
>>> The command "brctl addif br0 ppp0" fails with "can't add ppp0 to bridge br0: Invalid argument". It looks like point-to-point interfaces can not be added to a bridge (I tried also with a TUN device, just to see if it could be added, and got the same error message).
>> Did you create a bridge first?
>> brctl addbr br0
> Of course, I did :)
>> What is the output of
>> brctl show
> # brctl show
> bridge name     bridge id               STP enabled     interfaces
> br0             8000.000000000000       no
> I don't think it is meant to work with PPP interfaces.

Right, since ppp doesn't use an ethernet physical address (MAC
address) the bridge can't learn which endpoints are through which

I'm not sure how the remote peer can generate DHCPINFORM messages when
it got its address through the PPP protocol and not through DHCP at
all.  That seems really wrong, what if you had a PPP server configured
to issue addresses from its own pool, without any DHCP involved?  Are
the DHCP messages actually coming from a host or interface beyond the
far end of the tunnel (i.e. not the ppp interface on the remote

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