Chapter 10 Install and System Administration for FortiOS 5.0 : Interfaces : Software switch : Soft switch example
  
Soft switch example
For this example, the wireless interface (WiFi) needs to be on the same subnet as the DMZ1 interface to facilitate wireless syncing from an iPhone and a local computer. The synching between two subnets is problematic. By putting both interfaces on the same subnet the synching will work. The software switch will accomplish this.
 
In this example, the soft switch includes a wireless interface. Remember to configure any wireless security before proceeding. If you leave this interface open without any password or other security, it leaves open access to not only the wireless interface but to any other interfaces and devices connected within the software switch.
See Also
Clear the interfaces and back up the configuration
Merge the interfaces
Final steps
Software switch
Virtual Switch