Chapter 9 High Availability for FortiOS 5.0 : Full mesh HA : Example: full mesh HA configuration : How packets travel from the internal network through the full mesh cluster and to the Internet
  
How packets travel from the internal network through the full mesh cluster and to the Internet
If the cluster is operating in active-passive mode and 620_ha_2 is the primary unit, all packets take the following path from the internal network to the internet:
1. From the internal network to Sw4. Sw4 is the active connection to 620_ha_2; which is the primary unit. The primary unit receives all packets.
2. From Sw4 to the 620_ha_2 port3 interface. Active connection between Sw4 and 620_ha_2. Port3 is the active member of the redundant interface.
3. From 620_ha_2 port3 to 620_ha_2 port1. Active connection between 620_ha_2 and Sw2. Port1 is the active member of the redundant interface.
4. From Sw2 to the external router and the Internet.