CompTIA Network+ (N10-009)Networking ConceptsEasy
A technician is configuring a firewall rule to permit an internal server to send and receive unencrypted file transfer control commands using traditional FTP. Which port must be allowed for the FTP control channel?
- A20
- B21
- C22
- D69
Show answer & explanationAnswer & explanation
Correct answer: B. 21
FTP uses two ports: port 21 for the control channel (commands like login and directory listing) and port 20 for the active-mode data channel. Port 22 is SSH/SFTP, and port 69 is TFTP.
Why the other options are wrong
- A. Port 20 is the FTP data channel, not the control channel.
- C. Port 22 is used by SSH and SFTP, a different protocol.
- D. Port 69 is used by TFTP, a simplified UDP-based file transfer protocol.
FTP Ports (20/21)
File Transfer Protocol uses TCP port 21 for control commands and TCP port 20 for data transfer in active mode.
- Port 21 = control channel
- Port 20 = active mode data channel
- FTP transmits credentials in cleartext
Memory trick: '21 controls, 20 delivers' — control comes first alphabetically and numerically.