(Sorry, my German-speaking brain won't create thoughts at the moment. [:(])
INVALID_ID_INFORMATION means that you must either use a different L2TP/IPsec client that expects IPsec responses from the private IP on your UTM'S External interface, or you must bridge the Fritzbox so that the UTM can have your public IP on its External interface.
I prefer the SSL VPN. It works great with my iPhone (free OpenVPN app in the AppStore) and on PCs with the Sophos SSL VPN Client that's easily installed from the UTM. I know that some European ISPs block some UDP, but I prefer to change the SSL VPN Protocol to UDP to speed up the connection and to avoid conflict with other uses of TCP 443.
(Sorry, my German-speaking brain won't create thoughts at the moment. [:(])
INVALID_ID_INFORMATION means that you must either use a different L2TP/IPsec client that expects IPsec responses from the private IP on your UTM'S External interface, or you must bridge the Fritzbox so that the UTM can have your public IP on its External interface.
I prefer the SSL VPN. It works great with my iPhone (free OpenVPN app in the AppStore) and on PCs with the Sophos SSL VPN Client that's easily installed from the UTM. I know that some European ISPs block some UDP, but I prefer to change the SSL VPN Protocol to UDP to speed up the connection and to avoid conflict with other uses of TCP 443.