In a multi-tenancy setup on FortiGate, you can assign a FortiSwitch port to a VDOM in two primary ways:

Switch the FortiLink Interface to the Target VDOM (A): This method involves configuring the FortiLink interface, which is the dedicated interface used to manage FortiSwitch units from FortiGate, to operate within a specific VDOM. This effectively assigns all ports on the FortiSwitch, managed through that FortiLink interface, to the designated VDOM.

Create a Virtual Port Pool on the FortiGate CLI (C): Virtual port pools are created on FortiGate and allow ports from FortiSwitch to be grouped and assigned to a VDOM. This method is more granular and flexible, as it allows specific ports on the FortiSwitch to be dedicated to different VDOMs without requiring the entire switch or FortiLink interface to be dedicated to a single VDOM.