The firewalls use hello message and heartbeats to verify that the peer device is responsive and operational. Hello messages are sent from one peer to the other at the configured Hello Interval to verify the state of the device. The heartbeat is an ICMP ping to the HA peer over the control link, and the peer responds to the ping to establish that the devices are connected and responsive. For details on the HA timers that trigger a failover, see HA Timers. (The HA timers for the CN-Series firewall are the same as that of the PA-5200 Series firewalls).