Do need an extra rule for hosts that are reachable over a dyndns name?
Actually not, if you defined the dns name as ip address in the host properties.
We need to check if the core uses the right dns name as address while doing the check.
The check command uses the $HOSTADDRESS$ macro which is filled by the address directive in the nagios config files (if you are using nagios as core for your OMD site). To verify the correct address, run the following command:
The output should show you