2 High Availability for Vcontroller and CPMHow High Availability WorksWhen High Availability is active, a Primary appliance sends a“heartbeat” to a Secondary appliance. This heartbeat tells theSecondary appliance that the primary appliance is still “alive,” orup. If the primary appliance fails, the heartbeat ceases. When theSecondary appliance detects three consecutive missed heartbeats,it assumes all processing tasks.High Availability ModesThere are two High Availability modes: Active/Standby and Active/Active.Active/StandbyIn Active/Standby mode, when a primary appliance fails thepassive appliance comes online with a full copy of the state tableand VPN tunnels, to provide maximum uptime and networkavailability. Active/Standby is available for all models that havean HA interface. In this mode, both appliances are configuredwith the same system name, IP address, and configurationinformation.Active/ActiveIn Active/Active mode, the paired appliances process traffic inparallel, and use transparent state failover. In the case of a failure,all processing and traffic transitions seamlessly to the appliancethat is still working. System configuration, security policies, activeconnections, and VPN tunnels are shared between the two activeappliances. Both appliances are sending and receiving packets, soprocessing throughput is potentially doubled. If one appliancefails, the other is fully aware of the state of all connections and cancontinue carrying the load without dropping any packets.Active/Active mode requires the purchase of an upgradedsoftware license.