Passive checks are sent to Nagios via the external command pipe. As it is a named pipe on a specific machine, the main problem is that all passive check results need to be sent from this machine.

For many Nagios installations, this causes a problem. Very often, a check needs to be done on one or more remote hosts. This requires some mechanism to pass results from the machines that perform the tests to the computers running the Nagios daemon, which will process the results.

This is why Nagios Service Check Acceptor (NSCA) was developed. It is a client-server application that allows the passing of service and host check results over the network. This protocol allows the use of encryption, so the results are sent securely.

NSCA is an application that allows the sending of results directly to the Nagios external command pipe. NSCA consists of two parts — the server and the client. The part responsible for receiving check results and passing them to Nagios is the server. This listens...