Chapter 9 High Availability for FortiOS 5.0 : Configuring and connecting HA clusters : Example: Transparent mode active-active HA configuration : Example Transparent mode HA network topology
  
Example Transparent mode HA network topology
Figure 193 shows a Transparent mode FortiGate-620B HA cluster consisting of two FortiGate‑620B units (620_ha_1 and 620_ha_2) installed between the Internet and internal network. The topology includes a router that performs NAT between the internal network and the Internet. The cluster management IP address is 10.11.101.100.
Figure 193: Transparent 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.