A user reports being unable to access an FTP server online to download a file.Which of the following may be the cause?

A) Port 80 is blocked on the firewall
B) Port 443 is blocked on the firewall
C) Port 21 is blocked on the firewall
D) Port 110 is blocked on the firewall

Port 21

The network port commonly used by the File Transfer Protocol (FTP) for establishing connections for transferring files between computers.

FTP Server

A server that allows for the transfer of files between computers over a network using the File Transfer Protocol.

Firewall

A security system designed to prevent unauthorized access to or from a private network by controlling incoming and outgoing network traffic based on predetermined security rules.