Palo Alto Networks' path monitoring feature lets you verify connectivity to an IP address or group of IP addresses. It uses ICMP pings as heartbeats to verify that the specified IP address is reachable. You can use path monitoring to monitor the availability of interconnected networking devices like a router or a switch, connectivity to a server, or some other vital device that is in the flow of traffic. In active/passive mode, both firewalls share the same configuration settings, and one actively manages traffic until a path, link, system, or network failure occurs. If the active firewall can't reach certain hosts outside the network, then it will fail over to the passive device.