Change MTU to support Jumbo Frames in FortiOS

This info is quite hard to come across and Fortigate don’t have it in their GUI from FortiOS v5.0+, SSH into your Fortigate’s CLI and enter the following (it can be done on both software aggregated and standard interfaces):

config system interface
edit [interfacename]
    set mtu-override enable
    set mtu 9208
end
end

Confirm your MTU size change has worked on the given interface by plugging directly into it (test MTU in accordance to my guide here).

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