[Dnsmasq-discuss] Shut down caused by device request address.

[Matthias Andree]

Am 22.02.26 um 11:33 schrieb Colin Finnis:
>
> I have been running dnsmasq for some time on a Raspberry PI. I had no 
> problems until about 18 months ago when the DNS would suddenly stop 
> working. I found these types of entries in the syslog.
>
> Feb 21 16:14:07 pilot dnsmasq-dhcp[2061]: DHCPACK(eth0) 192.168.0.242 
> 02:ef:dd:91:3a:f3 Wild-s-S21
>
> Feb 21 16:14:09 pilot dnsmasq-dhcp[2061]: DHCPREQUEST(eth0) 
> 192.168.0.242 02:ef:dd:91:3a:f3
>
> Feb 21 16:14:09 pilot dnsmasq-dhcp[2061]: DHCPACK(eth0) 192.168.0.242 
> 02:ef:dd:91:3a:f3 Wild-s-S21
>
> Feb 21 16:14:09 pilot dhcpcd[377]: eth0: hardware address 
> 02:ef:dd:91:3a:f3 claims 192.168.0.8
>
> Feb 21 16:14:10 pilot dhcpcd[377]: eth0: hardware address 
> 02:ef:dd:91:3a:f3 claims 192.168.0.8
>
> Feb 21 16:14:10 pilot dhcpcd[377]: eth0: 10 second defence failed for 
> 192.168.0.8
>
> Feb 21 16:14:10 pilot dhcpcd[377]: eth0: deleting route to 192.168.0.0/24
>
> Feb 21 16:14:10 pilot dhcpcd[377]: eth0: deleting default route via 
> 192.168.0.1
>
> Feb 21 16:14:10 pilot avahi-daemon[279]: Withdrawing address record 
> for 192.168.0.8 on eth0.
>
> The problem always seems to be associated with Samsung phones and 
> appears to have started after an update to the phone around 18 months 
> ago. I have found what purports to be a solution which requires a 
> setting change on the phone. This is fine for my phone but visitors to 
> my house can cause the same problem and its difficult to get them all 
> to change before the damage is done. It dosnt always happens when the 
> phone is brought into the house, I think it occur when the phone is 
> close to the property and the signal is poor.
>
> As you can see the request is made for an address and the DNS 
> responds. The request is made a second time and immediately the device 
> seems to take over the IP address of the DNS box. DHCPD then goes into 
> some sort of defence mode and avahi withdraws the statically assigned 
> address. I have tried changing the address of the DNS server in case 
> it was just the phone using a random address but that made no 
> difference. I cant run a network monitor on the traffic so I cant see 
> what is happen during this event. It just sems strange behaviour for 
> the phone to suddenly decide its going to usurp the DNS’s IP address.
>
> Im technically savvy having worked in the IT industry for 40 years but 
> cant work out away to either prevent this or stop it happening. The 
> only way at the moment is to reboot the PI. Any help would be appreciated.
>
> Colin Finnis
>

Colin,

you're not reporting your dnsmasq version, and what's utterly unclear to 
me is how the MAC address is both for Wild-s-S21 and dhcpcd? What is the 
setting for the Samsung phone that would prevent this? Give the phone a 
static address?

How come dhcpcd concludes that the shown hardware address is for 
192.168.0.8 if dnsmasq handed out 192.168.0.242 for what appears to be a 
Samsung S21 phone?

What dhcpcd and version is it? Is there a tcpdump or tshark dump or 
something, possibly combined with a dhcpcd debug log, so we could see 
what's up? This does not *obviously* look like a dnsmasq bug.

For an approach to solving this, outside dnsmasq, I wouldn't configure 
"pilot" (the RPi) through DHCP but give it a static address instead, 
possibly also from 192.168.0.* but then also reducing the DHCP address 
pool so its static address isn't part of the pool - and avoid running 
dhcpcd.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/attachments/20260222/ccd9b2ed/attachment-0001.htm>