This is actually a more SNMP related question.
We are monitoring remote site servers through IP and Port Mapping. The remote site firewall doesn't allow ICMP packages. So we setup monitors only through SNMP ports. It's working well. It can monitor CPU, Memory, drive space and etc. But the problem comes when the device goes down. Which SNMP object should I set as dependency for all those SNMP monitors? Or there is other TCP/UDP protocol I can use to monitor the simple status of the device?
Just monitor for the status of SNMP being up or down, not for a particular OID. Set this monitor to be a bit more aggressive in its timing parameters and set it as the dependency.