DDNS is the abbreviation for the Dynamic Domain Name System. It is a domain service that permits network customers to connect with the wireless router that works through its registered domain name. For the ASUS DDNS service to work correctly, you need to get a public IP address. If your wireless router sits behind any other gateway or firewall, it may get a private IP address (192.168.x.x, 10.x.x.x, or 172.16.x.x). In this case, the Asus router Ddns not working.