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Note The Remote Desktop Connection Client for  the Mac supports only port 3389. 3389 is the default port. 

I would always recommend that if you use RDP on the net to connect to pc’s,  to always change the port from its default. As with any registry change, if you don’t know what you are doing,  you can mess up the OS badly. Back up the registry before you begin. 

1. Start Registry Editor.
2. Locate and then click the following registry subkey: 

   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\TerminalServer\WinStations\RDP-Tcp\PortNumber

3. On the Edit menu, click Modify, and then click Decimal.
4. Type the new port number, and then click OK.
5. Quit Registry Editor.

Note When you try to connect to this computer by using the Remote Desktop connection, you must type the new port.