Chapter 11 IPsec VPN for FortiOS 5.0 : IPv6 IPsec VPNs : Configuring IPv6 IPsec VPNs : Security policies
  
Security policies
To complete the VPN configuration, you need a security policy in each direction to permit traffic between the protected network’s port and the IPsec interface. You need IPv6 policies unless the VPN is IPv4 over IPv6.