If you’re executing Pandora FMS under a virtual environment and you’re using a “shared network” (some times called NAT or Host network), the network is not “real” and therefore cannot be calculated. This is easily tested by doing a simple traceroute from the command line (for example google.com). You should see 7-15 steps until it reaches the final endpoint. In a shared network you will only see one step.
If you execute Pandora FMS in “network bridge” mode or on a real host, this will function correctly.