Chapter 7 Firewall for FortiOS 5.0 : Multicast forwarding : Configuring FortiGate multicast forwarding : Adding multicast security policies
  
Adding multicast security policies
You need to add security policies to allow packets to pass from one interface to another. Multicast packets require multicast security policies. You add multicast security policies from the CLI using the config firewall multicast-policy command. As with unicast security policies, you specify the source and destination interfaces and optionally the allowed address ranges for the source and destination addresses of the packets.
You can also use multicast security policies to configure source NAT and destination NAT for multicast packets.
Keep the following in mind when configuring multicast security policies:
The matched forwarded (outgoing) IP multicast source IP address is changed to the configured IP address.
Source and Destination interfaces are optional. If left blank, then the multicast will be forwarded to ALL interfaces.
Source and Destination addresses are optional. If left un set, then it will mean ALL addresses.
The nat keyword is optional. Use it when source address translation is needed.