You cannot use the FRITZ!Box as a wireless extender. If you would like to use the FRITZ!Box with a router from another manufacturer, you can use an an existing Wi-Fi network in the FRITZ!Box for the internet connection. In this case, the FRITZ!Box still functions as a router and and provides its own network with its own network address range.

If you want to extend the Wi-Fi range of a router from another manufacturer, you can use a FRITZ!Repeater. FRITZ!Repeaters behave like conventional wireless devices towards wireless routers and can therefore be used with all commercially available routers.