What does TCP port 23 primarily support?

TCP port 23 primarily supports Telnet, which is a protocol used for diagnosing and configuring network devices by allowing remote access to systems over a network. Telnet operates on a client-server model and uses a text-based interface, enabling users to log into remote devices as if they were sitting right in front of them. It's important to note that Telnet does not encrypt its data transmissions, which can make it less secure than other protocols.

In the context of the other options: FTP (File Transfer Protocol) typically uses ports 20 and 21, SSH (Secure Shell) operates on port 22 and provides a secure alternative to Telnet, and SFTP (SSH File Transfer Protocol) also utilizes port 22 and offers a secure file-transfer capability. Since these protocols are designed to serve different functions, they do not utilize port 23, confirming that the primary function of port 23 is indeed to support Telnet.