How to Troubleshoot Port Forwarding via Firewall

A business uses UTT router to connect to the Internet, and wants a server (IP Address: to open Web service (Protocol: TCP; Port: 3389) for access from Internet. Port forwarding enabled but access is not available from the Internet.
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. Logit the router Web GUI and check the Port Forwarding settings at Network > NAT.
2. Check the connection status of the Network.
3. Run cmd, test telnet WAN IP + port, press enter, port 3389 is not available. (Here is a public under the test.)
4. Test WAN IP is pingable, Internet access is available.
5. Test ping from the server, but is unable to reach.
6. Check the Access Control at Firewall
Disable Access Control