A variation on the tunnelling IPv6 through IPv4 is using an IPSec VPN tunnel between to FortiGate devices. FortiOS supports IPv6 over IPSec. In this sort of scenario, 2 networks using IPv6 behind FortiGate units are separated by the Internet, which uses IPv4. An IPSec VPN tunnel is created between the 2 FortiGate units and a tunnel is created over the IPv4 based Internet but the traffic in the tunnel is IPv6. This has the additional advantage of make the traffic secure as well.