When a FortiGate is configured in transparent mode, it functions as a Layer 2 bridge or switch. By default, all physical interfaces are placed into a single virtual switch, effectively making them part of the same broadcast domain. In this mode, the FortiGate inspects and forwards Ethernet frames based on their destination MAC address. It does not modify the source or destination MAC addresses of the original frames as they pass through, making its presence on the network "transparent" to other devices. This allows the FortiGate to be inserted into an existing network without requiring any changes to the IP addressing scheme.

B. The primary advantage of transparent mode is that it can be deployed without altering the existing network's IP address schema, making this statement false.

C. Transparent mode operates at Layer 2, forwarding frames based on a MAC address table. Static routes, a Layer 3 concept, are not required for traffic forwarding through the device.

1. FortiOS Administration Guide 7.0.0

System > Operation Mode > Transparent mode

Page 218: "In Transparent mode

the FortiGate is installed between the internal network and the router. In this mode

the FortiGate acts as a transparent bridge

forwarding frames without modifying the MAC addresses." This directly supports option D.

2. FortiOS Administration Guide 7.0.0

System > Operation Mode > Transparent mode

Page 218: "When you install a FortiGate in Transparent mode

you do not have to change the IP addresses of the computers on the private network." This directly refutes option B.

3. FortiOS Administration Guide 7.0.0

System > Operation Mode > Example: Transparent mode

Page 220: "When you change the operating mode to Transparent

the FortiGate configuration is reset and the FortiGate restarts. All physical interfaces are now part of the default virtual switch

root." This supports option A

as a virtual switch groups interfaces into a single broadcast domain.

4. FortiOS Administration Guide 7.0.0

System > Operation Mode > Transparent mode

Page 218: "The FortiGate unit functions like a bridge

and traffic is not routed." This refutes the premise of option C

which implies Layer 3 routing is the primary forwarding mechanism.