CompTIA A+ Core 1 (220-1201)NetworkingMedium
A network administrator is troubleshooting a file transfer issue between an old application server and a client. The application uses unencrypted FTP to transfer files. Which pair of ports should the administrator verify are open on the firewall for FTP control and data connections?
- A20 and 21
- B25 and 110
- C80 and 443
- D22 and 23
Show answer & explanationAnswer & explanation
Correct answer: A. 20 and 21
FTP uses two ports: TCP 21 for the control connection (commands) and TCP 20 for the data connection (file transfer) in active mode. These must both be permitted for FTP to function correctly through a firewall.
Why the other options are wrong
- B. 25 is SMTP and 110 is POP3, both email protocols.
- C. 80 and 443 are HTTP and HTTPS web ports.
- D. 22 is SSH and 23 is Telnet, unrelated to FTP.
FTP Ports 20/21
File Transfer Protocol uses TCP port 21 for control commands and TCP port 20 for the actual data transfer.
- FTP is unencrypted; FTPS or SFTP should be used for security
- Port 21 handles commands like login and directory listing
- Port 20 handles the actual file data in active mode
Memory trick: Twenty carries data, twenty-one gives commands.