Since last week, I could not connect to 2 remote desktop servers which are in a different city. The error message was “Remote Desktop can’t connect to the remote computer for one of these reasons:”

With many years experience, I could tell it’s network related issue. As the issue happening, the servers were still in production and remote users were still running applications and accessing files on the server. I could still remote manage the servers. I restarted the remote desktop related services and stop the Windows firewall service but still didn’t help.

But the network team checked the routers and firewall settings and found no issue. I could also remote desktop connect to the other PCs in the same remote network as the servers were. So the router and firewall between my current network and remote network have no issue.

When I used telnet command to test service port, I got below error message.

G:\>telnet 192.168.1.11 3389
Connecting To 192.168.1.11…Could not open connection to the host, on port 3389: Connect failed

It still looked like a network issue or the port number was not correct. Good news was I still could use Registry Editor and ‘connect Network Registry’ menu to connect the remote server.

The port number for RDP was not designed to be changed, and the only way to do so is through editing registry: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal SErver\WinStations\RDP-Tcp\PortNumber

Wow, the PortNumber was not 3389! That’s why I could not connect to it. I used the port number I saw and I successfully connected the server via remote desktop connection.

Now I have a question Who and Why it has been changed?