Port 23 is traditionally used by Telnet for unencrypted remote administration. Telnet communicates in plaintext, making it susceptible to eavesdropping, and is therefore considered insecure. SSH on port 22, on the other hand, provides a secure, encrypted method for remote administration. While port 21 is used by FTP, it is for file transfers and not for remote administration, and similarly, while port 80 serves content unencrypted, it is for HTTP traffic, resulting in no relevance to remote administration security concerns.