DHCP giving out IPs that are already in use

Hey Dev. Team!

I don’t know if this is a bug or a feature but today our Neth-Server 7 started giving out IP addresses to new PCs, that are already used manually. I’ve set static DHCP addresses for the existing PC farm by MAC addresses via the WEBUI. Now, a couple of new computers tried to connect via DHCP automatic IP request and the server dished out already used IP addresses for them. Took me a while to figure out why did we have internet connection errors… Almost teared out all my hair. How is this possible? What other information do I have to pass you in order to think about the issue?



Had you the same IP on two different pc at the same time (duplicate ip)?
AFAIK, the dhcp server (dnsmasq) checks if the ip is in use before giving it to the client.
Could you show /var/log/messages and the output of the command db hosts show at the moment of the problem? Please highlight the relevant IP addresses.

Unfortunately I can’t get you neither the log files, nor the output of the command. I’m not allowed to do it. But I can tell you that the output of the command is all our equipment connected to the server, both the reserved equipment and the ones using DHCP. But there is no duplication now.

Also, in the messages log, I was able to find 2 lines that were causing the issues. A very simple form of the lines are:

Nov 30 08:04:11 firewall dnsmasq-dhcp[5573]: DHCPACK(enp2s10) X.Y.Z.28 17:6a:54:XX:X:XX old-workstation
Nov 30 08:24:00 firewall dnsmasq-dhcp[5573]: DHCPACK(enp2s10) X.Y.Z.28 28:dd:bd:XX:X:XX new-laptop

As you can see, the old laptop booted up and since it has a reserve IP, it received it (X.Y.Z.28). Later a new PC was booting with DHCP settings and it received the exact same IP. And this was the confusion all about. :confused:

Could you check also /var/lib/dnsmasq/dnsmasq.leases?
cat /var/lib/dnsmasq/dnsmasq.leases | perl -nwe 's/^(\d+)/localtime($1)/e; print' | less
Here some docs:

Just thinking out loud. Did you check the MAC addresses of the clients? Could there be a MAC set in the driver so duplicate MAC addresses exist?

Yes, I’ve. If you check the log lines I’ve pasted, you can see that the MAC addresses are different.

The issues is resolved by giving all the equipment static IP addresses so far, but this still bugs me a lot.

Please, answer my question above. Thanks.