I've just stumbled upon something pretty weird, at least for me at this moment.
When i've finished setting up my openBSD 5.5 server, along with the isc-dhcp43-server port. I tried to see if i could find this service by doing a nmap-scan from a client.
But somehow the command listed below fails to find the open port (67), although the service is actually and providing ip-addresses.
Am i missing something here?
sudo nmap -Pn -p1-1024 [ip-address]
EDIT: I've also tried to scan the server using the -sU parameter, but even then it returns that the host is down. So i think it's safe to imply that finding a dhcp server does require to send out a dhcp-request packet, and that just port scanning doesn't suffice.
sudo nmap -Pn -sU -p1-1024 [ip-address]
Upon digging a bit deeper, i read that nmap should be able to send a dhcp-discover packet.
sudo nmap -Pn -sU -p1-1024 --script=dhcp-discover [ip-address] -vv
But on my system this returns the following error.
Unknown datalink type 138.
I will investigate this further tomorrow!