[Dnsmasq-discuss] Multiple interfaces responding to DHCP requests

[Geert Stappers]

On Thu, May 13, 2021 at 09:31:21PM +0100, Nick Howitt wrote:
> On 13/05/2021 19:26, Geert Stappers via Dnsmasq-discuss wrote:
> > On Thu, May 13, 2021 at 01:05:07PM +0100, Nick Howitt wrote:
> > > I am trying to help someone who has a set up with three LAN's, all on
> > > different subnets and all acting as DHCP servers. He is getting an odd
> > > result that when a device on the enp2s0 LAN requests an IP, both enp2s0 and
> > > enp3s0 respond with IP's. I've never seen this before and my own server does
> > > not act this way.
> > > 
> > >      ...
> > > 
> > >  From the dnsmasq log:
> > > May  8 11:23:39 dnsmasq-dhcp[7226]: DHCPDISCOVER(enp2s0) de:ad:c0:de:ca:fe
> > > May  8 11:23:39 dnsmasq-dhcp[7226]: DHCPOFFER(enp2s0) 192.168.1.214 de:ad:c0:de:ca:fe
> > > May  8 11:23:42 dnsmasq-dhcp[7226]: DHCPDISCOVER(enp3s0) de:ad:c0:de:ca:fe
> > > May  8 11:23:42 dnsmasq-dhcp[7226]: DHCPOFFER(enp3s0) 192.168.168.215 de:ad:c0:de:ca:fe
> > > 
> > >      ...
> > > 
> > > I have a similar dual LAN set up and it works as expected with each
> > > LAN only responding with its own LAN DHCP settings.
> > 
> > That means the "problem" is outside dnsmasq.
> > 
> > 
> > > Thanks,
> > > 
> > 
> > Feel welcome to report back.
> 
> OK, but if the problem is outside dnsmasq, why does dnsmasq log two
> DHCPDISCOVERs and DHCPOFFERs? Could he have a networking problem with the
> two LAN's bridged somewhere?

Yes


> Perhaps I can ask him to unplug the cable to
> enp3s0 and see if the problem goes away.

It is surely an usefull trouble shoot check.



Groeten
Geert Stappers
-- 
Silence is hard to parse