Spanning tree causing a problem with the DL or on the Core? What does
your STP configuration look like for other switches that are working?
Are other working switches connected to the the same DL ?
Did you read on Fortilink over layer 3? You create a layer 3 vlan id and
pass it through the 3rd switch to the Fortiswitches as an interface on
the Fortilink Interface from the Gate.
https://docs.fortinet.com/document/fortiswitch/7.4.4/fortilink-guid...
diag switch-controller mac-cache show It will show you each switch
(Serial Number) then what vlan id , prot and mac address of the device
if connected. It also shows when it was last seen on the port.
