Port 22 is used for SSH (Secure Shell), which is a secure and encrypted protocol for remote access to a server.
Port 23 is used for Telnet, which is an insecure and unencrypted protocol for remote access. Port 990 is used for FTPS (File Transfer Protocol Secure), which is a secure and encrypted protocol for file transfer. The administrator should open port 22 and close port 23 to enable SSH and disable Telnet, as SSH is more secure and reliable than Telnet. The administrator does not need to open port 990, as FTPS is not required for making configuration changes123.
References = 1: Remote Desktop - Allow access to your PC from outside your network(https://learn.microsoft.
com/en-us/windows-server/remote/remote-desktop-services/clients/remote-desktop-allow-outside-access) 2:
Test remote network port connection in Windows 10 - Winaero(https://winaero.com/test-remote-network-port- connection-in-windows-10/) 3: Windows Command to check if a remote server port is opened?
(https://superuser.com/questions/1035018/windows-command-to-check-if-a-remote-server-port-is-opened)