Meilleure réponse par roylion15
To avoid these problems of double NAT, you should place your voo modem-router in "bridge mode" and to use only your airport extreme as router.
In this mode, the function "router" of the voo modem-router is deactivated, and it becomes a simple modem, now it is your Apple router which will make its work. You have to deactivate the WiFi on the modem voo and connect only your router on an ethernet port.
To change the modem in "bridge mode", you have to connect in the modem via your Internet browser at http://192.168.0.1 >> login: voo and pass: WPA key behind the modem : In the web interface first deactivate the wifis save the settings then go in the "expert mode" menu and check "bridge mode", the modem is going to reboot and after that you should obtain the public IP on your Airport extreme immediately.
Sorry if my English is not so good ... Regards