Which port must be opened to allow remote administration of a Unix server if the technician cannot connect?

Opening TCP port 22 is essential for allowing remote administration of a Unix server because this port is used for SSH (Secure Shell) protocol. SSH is a secure method for accessing a remote computer over a network, and it is widely used in Unix and Linux server environments for secure command-line interface connections.

When a technician attempts to connect to a Unix server remotely and cannot, ensuring that TCP port 22 is open would typically resolve the issue, as it facilitates encrypted and secure communication, which is critical for remote administration tasks.

The other port options mentioned serve different purposes: TCP port 21 is used for FTP (File Transfer Protocol), which is not secure; UDP port 69 is associated with TFTP (Trivial File Transfer Protocol), a simpler and unsecured version of FTP; and TCP port 3389 is used for RDP (Remote Desktop Protocol), which is typically used for Windows environments rather than Unix systems. Thus, TCP port 22 is the appropriate choice for remote administration of Unix servers.