In our network, we monitor devices that usually should not be reachable. If they go online, something is wrong. A typical example for this would be a scenario of a backup ISDN router going online only if the usual broadband Internet connection fails.
I want to set up a Ping sensor that acts in an inverse / reverse way: It shows a green OK status if a device is not reachable, and a red Error status when a device answers to a Ping.
How can I do that?