[Dnsmasq-discuss] Defending IP address

[Geoff Back]

Hi Johan,

On 05/05/2023 08:40, Johan Vromans wrote:
> Hi,
>
> I have a number of IoT devices. Occasionally, when they try to set up the
> DHCP lease, some of them send wrong packets. The device effectively claims
> the IP address of the DHCP server. From the system log:
>
>     May  4 05:39:59 srv1 dhcpcd[449]: eth0: hardware address
>     xx:xx:xx:xx:xx::ce claims 192.168.1.10
>
> where 192.168.1.10 is the address of the DHCP server.
>
> If a second package arrives within 10 seconds,
>
>     May  4 05:40:08 srv1 dhcpcd[449]: eth0: hardware address
>     xx:xx:xx:xx:xx::e7 claims 192.168.1.10
>
> dnsmasq shuts down the network connection
Actually, it is dhcpcd that drops the address, not dnsmasq.

> dhcpcd[449]: eth0: 10 second defence failed for 192.168.1.10
> dnsmasq-dhcp[24169]: DHCPRELEASE(eth0) 192.168.1.96 xx:xx:xx:xx:xx::e7 
> avahi-daemon[373]: Withdrawing address record for 192.168.1.10 on eth0.
> avahi-daemon[373]: Leaving mDNS multicast group on interface eth0.IPv4 with
> address 192.168.1.10. avahi-daemon[373]: Interface eth0.IPv4 no longer
> relevant for mDNS. dhcpcd[449]: eth0: deleting route to 192.168.1.0/24
> dhcpcd[449]: eth0: deleting default route via 192.168.1.1
>
> and slowly the LAN collapses.
>
> How can I prevent dnsmasq from EVER giving up its own IP address?

Set static IP on the interface and do not run dhcpcd.  The problem is
with dhcpcd releasing the address, not with dnsmasq.

Cheers,

Geoff.

>
> -- Johan
>
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