About FortiLink split interface

Split interface is for attaching 2 switches directly to FortiGate… and employs Spanning Tree. So unless your switches are interlinked, both ports will always be active.

If both interfaces are to the same switch, then split interface should be disabled, and the 802.3ad trunk will come up.

Also note that the Config won’t stay permanent on the switch — it’ll get overwritten by the Config from FortiGate if you were trying to admin-shut them via ssh to the switch…