The page below is from the manual of PRTG, our quick-to-install and easy-to-use network monitoring software
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PRTG Manual: Dependencies
Using dependencies, you can pause sensor monitoring based on the status of another sensor to avoid false alarms and incorrect downtime recording. A dependency stops the monitoring of one sensor or a set of sensors as soon as a specific sensor is in Down status. This means, for example, that you can stop monitoring remote network services when the corresponding firewall is down due to connection problems.
When using the auto-discovery function, the Ping Sensor on a device is by default set as the master object for this device. This means that monitoring for the entire device is paused if the Ping sensor is in Down status. Usually, it makes little sense to monitor any other parameters while the Ping sensor indicates that the device can't even be reached.
To view the list of dependencies, choose Devices | Dependencies and the corresponding dependencies path from the main menu. From there you can also access the Dependencies Graph that visualizes all dependencies within your network.