Refer to the exhibits.

The output of the status of high availability on the FortiGate shows that the cluster mode is active-passive, which means that only one FortiGate unit is active at a time, while the other unit is in standby mode. The active unit handles all traffic and also sends HA heartbeat packets to monitor the standby unit. The standby unit becomes active if it stops receiving heartbeat packets from the active unit, or if it receives a higher priority from another cluster unit. In active-passive mode, all cluster units share a virtual MAC address for each interface, which is used as the source MAC address for all packets forwarded by the cluster. References:https://docs.fortinet.com/document/fortigate/6.4.0/cookbook/103439/high-availability-with-two-fortigates