What it means when the PING sensor is down

There are numerous reasons for a PING sensor to fail, the most common one is that the sent packet either did not reach the server or the returning packet was not delivered back to the machine running bello network monitoring. This can be caused by connection problems (line or router failures), routing problems, or simply because a firewall between the server and the monitoring machine has rejected the packet because PINGs are not allowed by the firewall's rules.

Note: When monitoring a remote server a small amount of lost PINGs (1-2%) should usually not be considered harmful.