Have a read of this:
Heres what you need to know:
"Set up a cron job on the slave host that periodically (say every minute) runs a script that checks the staus of the Nagios process on the master host (using the check_nrpe plugin on the slave host and the nrpe daemon and check_nagios plugin on the master host). The script should check the return code of the check_nrpe plugin . If it returns a non-OK state, the script should send the appropriate commands to the external command file to enable both notifications and active service checks. If the plugin returns an OK state, the script should send commands to the external command file to disable both notifications and active checks."
Heres a list of what you can pass to the external command file and how to do it:
nagios.org/developerinfo/ext ... ndlist.php
You're going to want to look at "DISABLE_NOTIFICATIONS" , "STOP_EXECUTING_SVC_CHECKS" and their ENABLE and START counterparts. You're going to be passing those commands to the nagios.cmd file in your cron job on the slave.
So heres a quick run down on what you need to do:
-Set up the slave nagios server with Rsync between the plugins directory and the config directory
-Set up NRPE on the master nagios box with a command that runs the check_nagios plugin.
-set up a cron on your slave which runs "check_nrpe -H master.server.net -c check_nagios" then parses those results. Make an if/then statement which will pass DISABLE_NOTIFICATIONS and STOP_EXECUTING_SVC_CHECKS to the nagios.cmd file if everything returns OK, or START_EXECUTING_SVC_CHECKS and ENABLE_NOTIFICATIONS if everything is not ok on the master.
If you don't mind having them both do checks on all hosts, you dont have to bother with the NSCA part. otherwise read up on Distributed monitoring and how to use NSCA. Basically a rundown of that is in your nagios.cfg you define an "OCSP" command which runs after every single service check. This OCSP command points to a script which runs send_nsca which sends your service check results to another nagios server. If you have q's about setting that up after reading the docs let me know