Chapter 1 What’s New for FortiOS 5.2.1 : IPsec VPN : Internet Key Exchange (IKE) : Multiple Interfaces
  
Multiple Interfaces
An IPsec policy can now contain multiple source and destination interfaces. This feature is supported for combinations of IPsec interfaces, physical interfaces, and zones (including those with a combination of physical and IPsec interfaces).
It is not supported for SSL VPN interfaces.