VLAN Trunking and MAC Address Learning

A FortiGate port becomes a trunk when 2 or more VLANs are configured on this port, in the same or different forwarding domains.

When trunks are configured on a FortiGate, it is essential to create forwarddomains, in order to avoid packets looping back on the VLANs of the trunk. This will confine all broadcasts and multicast traffic between the interfaces belonging to a same forward domain.

In the case where a trunk port is configured with a VLAN in a different forwarding domains, the MAC address of the network device connected to this port learns the FDB of each forwarding domain. This is Independent VLAN Learning (IVL).