Chapter 9 High Availability for FortiOS 5.0 : Solving the High Availability problem : Fortinet redundant UTM protocol (FRUP)
  
Fortinet redundant UTM protocol (FRUP)
An extension to the FGCP combines switching HA and firewall HA into a single unified design. This feature is available on the FortiGate-100D and will be expanded to other models in future releases.
A FRUP setup consists of 2 (and only 2) identical FortiGate-100D units. The setup supports dual redundant HA links between the units for sharing session and configuration data.
FRUP requires redundant external routers where:
One FortiGate unit has a primary connection to one of the routers and a backup connection to the other.
The other FortiGate unit has the opposite configuration.
See “Configuring FRUP” for an example configuration.