Chapter 7 Firewall for FortiOS 5.0 : Security policies : IPv6 Policies
  
IPv6 Policies
IPv6 security policies are created both for an IPv6 network, and a transitional network. A transitional network is a network that is transitioning over to IPv6, but must still have access to the Internet or must connect over an IPv4 network.
These policies allow for this specific type of traffic to travel between the IPv6 and IPv4 networks. The IPv6 options for creating these policies is hidden by default. You must enable this feature in System > Config > Settings.