Re: unable to manage Fortiswitch 108E
I am assuming you are trying to use FortiLink between Fortigate and Fortiswitch. If so, in releases FortiSwitchOS 3.3.0 and beyond, the FortiSwitch models support FortiLink auto-discovery, which is automatic detection of the port connected to the FortiGate. You can use any of the switch ports for FortiLink, but they may not be set/enabled by default.
Use the following FortiSwitch CLI commands to configure a port for FortiLink auto-discovery:
config switch interface
set auto-discovery-fortilink enable
Hope that this is helpful.