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One of my server pairs is running icinga and a dhcp server on each of them in HA mode for redundancy reasons. I've been trying to monitor the dhcp service using the nagios check_dhcp plugin. With the servers checking themselves, however, I mostly got many CRITICAL: No DHCPOFFERs were received replies.

After some extended research, I finally stumbled over a thread named check_dhcp ignores DHCP replies [sf#1090549] in the associated github issues. This described the issue as follows:

Checking a DHCP server which runs on the local host currently is not possible with check_dhcp (though it might work if the DHCP server was compiled to use normal sockets, as opposed to the LPF/BPF/whatever interfaces it usually uses).

With this in mind, I ended up monitoring the dhcp cluster from another server pair. That doesn't really make me very happy and I hope I can find another solution in the future.