Technical Tip: Expected behavior of the FortiGate FortiLink aggregate interface 'split interface' option with multiple FortiSwitches connected to the FortiGate

[Matt_L]

Description	This article explains the behavior of the FortiLink aggregate interface when multiple FortiSwitches are connected to the FortiGate, and the 'split interface' option is enabled.
Scope	FortiOS 7.2, 7.4, 7.6 (including all patches).
Solution	Hovering over the 'i' information icon next to 'FortiLink split interface' in the FortiGate GUI when editing the FortiLink aggregate interface will display the following information: Connect a FortiLink aggregate interface from one FortiGate to more than one FortiSwitch. Note that if the 'FortiLink split interface' option is enabled on the FortiLink interface in the FortiGate, the 'Interface members' section will show that only one of the interface members is up and active. This may lead to concern that there is an issue with the port or ports that are showing down. In the above screenshot, interface x3 shows as down. This is expected behavior as, when the 'FortiLink split interface' option is enabled and multiple FortiSwitch units are connected to the FortiGate, only one link remains active. Note: To enable the FortiLink split interface via the CLI, use the following commands: config system interface     edit <aggregate_name>   (Replace <aggregate_name> with the FortiLink interface name to be configured.)         set fortilink-split-interface enable     end See the following documents for configuration steps for FortiLink: Configuring FortiLink - FortiSwitch 7.2.0 documentation Configuring FortiLink - FortiSwitch 7.4.0 documentation Configuring FortiLink - FortiSwitch 7.6.0 documentation