ZyXEL Communications ZyWALL Series Support Note page 8

Step 4: Enable 6 to 4 tunnel.
(1) Go to Configuration > Interface > Tunnel > Click Add button
(2) Select the 6to4 in that Tunnel Mode
(3) Check the Prefix in the 6tp4 tunnel Parameter
(4) Select the WAN1 interface as the gateway in the Gateway Setting
After these configuration steps, connect your computer to the device and check that
your computer received an IPv6 IP address from tunnel.