I'm in the process of adding servers to our Nagios system using the nsclient. On two servers which are both terminal servers on the local network the host check passes but the service checks timeout due to socket timeout.
I have checked each server and confirmed that port 12489 is open and bound to the right NIC. No firewall is installed on the server and TCP/IP filtering on the NICs is not enabled. From the Nagios server I can ping the terminal server but when I nmap it by IP address, all ports except for 3389 are filtered. I don't know what could be causing this as there are many other servers on the same LAN not experiencing this issue. It seems this filtering action of port 12489 is what is preventing Nagios from doing the service checks. But I can't tell what is doing the filtering.
Could something in terminal services be causing this?