NSCA = Nagios Service Check Acceptor.

NSCA is a Nagios service that allows you to receive check results from remote machines and applications with Nagios. The check results are received and submitted to Nagios as Passive checks.

This can reduce the load on the Nagios server as it is not initiating the checks and hence only does work when results are received from remote clients.

This can be also be used for remote devices that are not always online, check results are only received when the remote device is able to send them, hence Nagios won't complain about a device it can't contact because it's not actively checking the remote device, it's passively receiving results.

This means that there are two parts that make this work: