From FRITZ! OS 07.10 onwards, if the internet fails, the FRITZ! Box can temporarily use the wireless hotspot of a cell phone as a fallback. The function is hidden under Internet> Access data> Internet provider> Existing access via WLAN . The FRITZ! Box then works as a router itself and provides a network with its own address range. When the Internet is available again, you simply reset the setting. I also had to check the options WLAN> Radio network> 2.4 GHz frequency band active and Internet> Access data> IPv6> IPv6 support active .