File Transfer Protocol
FTP allows users to transfer files from one host to another. FTP is a TCP-based connection-oriented protocol, and it uses port 21 to open the connection and port 20 to transfer data. FTP uses clear-text authentication. FTP clients can be configured for two modes of operation: PORT (active) mode and PASV (passive) mode. Figure 3-1 shows FTP modes of operation between an FTP client and FTP server for both the active and passive mode.
Figure 3-1 Overview of FTP Operation and Operating Modes