For FortiGate to FortiExtender connectivity, alternate 'VLAN' mode is supported. It is an alternative for the default CAPWAP mode. While using the default FEX-WAN type interface, all the traffic to and from FortiGate is encapsulated in the CAPWAP data channel. In VLAN mode, the traffic is sent and received on the VLAN interface. Because there is no encapsulation overhead and data traffic is processed in userspace currently, VLAN mode delivers better performance with the requirement that the VLAN interface be directly created on the port on which FortiExtender is connected to FortiGate. It is important to note that in VLAN mode, FortiExtender and FortiGate can be connected directly to each other or via a switch. In case of a switch in between, the switch should be configured to allow the configured VLANs.
Note that VLAN mode must be explicitly enabled, as it is disabled by default on FortiGate, and that all the FEX-WAN interfaces must be deleted before VLAN mode is enabled.
config system global
set fortiextender-vlan-mode enable
Ensure that the VLAN interface is created based on the physical interface of your connected FortiExtender.