This! "Enforce LACP Active" must be disabled on the Meraki LAG / AGGR. Unless you unplug / disable the ports it may take up to 30s after the change was synchronized with the switches.   I changed the Fortigates' LAG's LACP Algorythm setting to "L2" as well. (edit LAGport // set algorithm L2 // end)   With this I am happy to report my FG120-HA-Cluster is playing nicely with the MS425-16 Stack acting as the core switch.   LAG1 connects Forti-A-X3&X4 to Meraki-A-1&B-1 LAG2 connects Forti-B-X3&X4 to Meraki-A-2&B-2   Since Forti-A und Forti-B are not connected to the same LAG on the Meraki Stack, there is no need for "set lacp-ha-secondary disable" / "set lacp-ha-slave disable". ... View more

Indeed. If you check the diag output, your Fortigate will think the participating links are up, and balance accordingly (L4 = IP & Port). Have you tried setting the Forti LAG algorithm to L2 or L3? ... View more

What (loadbalancing) algorithm did you set on your Fortigate LAG? The default L4? You can check via CLI: "diagnose netlink aggregate name TheLAGsNameHere" or "config system interface" "edit TheLAGsNameHere" "get" ("show" gives insufficient infos) ... View more

How is it, that this *still* can't be changed? ... View more