TCP port 23 is used by:

TCP port 23 is used by:

• A. SSH
• B. Telnet
• C. FTP
• D. SMTP

Answer: (B)

Understanding well-known TCP ports helps you map numeric ports to the services that typically run on them. The well-known port range (0–1023) is reserved for standard services, and port 23 is assigned to Telnet. Telnet provides a remote command-line session over TCP, but it sends everything in plaintext, making it insecure compared to modern alternatives. That’s why SSH, which uses port 22 and provides encrypted communication, is preferred today. Other common ports include SSH on 22, FTP on 20/21, and SMTP on 25. So, the service associated with port 23 is Telnet.

Understanding well-known TCP ports helps you map numeric ports to the services that typically run on them. The well-known port range (0–1023) is reserved for standard services, and port 23 is assigned to Telnet. Telnet provides a remote command-line session over TCP, but it sends everything in plaintext, making it insecure compared to modern alternatives. That’s why SSH, which uses port 22 and provides encrypted communication, is preferred today. Other common ports include SSH on 22, FTP on 20/21, and SMTP on 25. So, the service associated with port 23 is Telnet.