Nagios Remote Plugin Executor (NRPE) is a daemon for running check commands on remote computers. It is designed explicitly to allow the central Nagios server to trigger checks on other machines in a secure manner.
NRPE offers a very good security mechanism along with encryption mechanisms. It is possible to specify a list of machines that can run checks via NRPE and which plugins can be run along with aliases that should be used by the central Nagios server.
The main difference is that the communication overhead is much smaller than for the SSH checks. This means that both the central Nagios server and the remote machine need less CPU time to perform a check. This is mainly important for Nagios servers that deal with a lot of checks that are performed remotely on machines. If the SSH overhead compared to NRPE is only 1 second, then for performing 20,000 checks, we can save 5.5 hours that would be spent on negotiations.