From OpenNMS

OpenNMS has a number of [[Manual:Features features]. They can be broken up into three main areas:

1. Service Monitoring: One major task of any network management solution is to be able to determine the availability of network services. Different tools approach this in different fashions, and OpenNMS uses the concept of "synthetic transactions" which try to mimic the user experience.

For example, in order to test if a DNS server is running, OpenNMS will request a DNS lookup from the device.