A FortiGate is operating in NAT/Route mode and configured with two virtual LAN (VLAN) sub- interfaces added to the same physical interface. Which statement about the VLAN IDs in this scenario is true?

Even if VLAN sub-interfaces belong to different VDOMs, if they are on the same physical interface, they still require unique VLAN IDs to avoid conflicts in traffic tagging and forwarding.

Each VLAN sub-interface configured on a FortiGate in NAT/Route mode, when attached to the same physical interface, must be assigned a distinct VLAN ID. This uniqueness is critical for the FortiGate to correctly identify, tag, and route traffic for each logical VLAN segment.

The requirement for unique VLAN IDs is independent of the IP address subnet assignment; two sub-interfaces on the same physical port cannot share a VLAN ID regardless of whether their IP addresses are in the same subnet.

Similar to C, the IP address configuration (same or different subnets) does not override the fundamental requirement that each VLAN sub-interface must have a unique VLAN ID for proper operation on a shared physical interface.