How to Troubleshoot Port Forwarding via User Authentication

A business uses UTT router to connect to the Internet, and wants a server (IP Address: to open Web service (Protocol: TCP; Port: 80) for access from Internet. Port forwarding enabled but access is not available from the Internet while PCs inside of the network can access the server.
1. a UTT Business Router (hereinafter shorted as “the Router"), such as UTT router N518W, AC750W, AC750GW, AC1220GW, ER518, ER840G and ER4240G. Firmware Version: 3.0.0 or above
2. a PC/laptop connected to the Router wirelessly or through an Ethernet cable
1. Login the router Web GUI and check the Port Forwarding settings at Network > NAT.
2. Run command line instruction and test port 9000. (use telnet + WAN IP + port number to check your ISP/Router/Firewall is not blocking port, operation based on Windows 10)
3. Check Authentication Settings at User Management > User Authentication, Neither Mandatory PPPoE Authentication or Web Authentication enabled, external port will be inactive.
4. Configure Authentication Free with server IP.
5. Enable Authentication Free.