Chapter 9 High Availability for FortiOS 5.0 : Configuring and connecting HA clusters : Example: NAT/Route mode active-passive HA configuration : Example NAT/Route mode HA network topology
  
Example NAT/Route mode HA network topology
Figure 190 shows a typical FortiGate-620B HA cluster consisting of two FortiGate‑620B units (620_ha_1 and 620_ha_2) connected to the same internal (port2) and external (port1) networks.
Figure 190: Example NAT/Route mode HA network topology
Port3 and port4 are the default FortiGate-620B heartbeat interfaces. Because the cluster consists of two FortiGate units, you can make the connections between the heartbeat interfaces using crossover cables. You could also use switches and regular ethernet cables.