Which port must be opened on a server's firewall to allow Remote Desktop access?

To enable Remote Desktop access to a server, it is essential to open port 3389 on the server's firewall. Remote Desktop Protocol (RDP), which allows users to connect to and control a computer remotely, operates over this specific port. Consequently, if port 3389 is blocked by the firewall, attempts to establish a Remote Desktop connection will fail, rendering remote access impossible.

The other ports mentioned serve different functions: Port 80 is commonly used for HTTP traffic, allowing web browsers to access websites, while port 443 is used for HTTPS, providing secure web traffic. Port 21 is the default for FTP, which is used for file transfer operations. None of these ports facilitate Remote Desktop connections, making port 3389 the correct choice for this purpose.