An In-Depth Look at the File Transfer Protocol
The File Transfer Protocol is one of the workhorses of the Internet, although it has been surpassed by HTTP over the past several years. FTP is interesting in that it uses two separate connections: a command connection and a data connection.
Like HTTP and SMTP, FTP is text based and uses numeric response codes. One of the neat features of the text-based protocols is that you can use them with the Telnet program. If you want to try out the FTP protocol, for example, you can Telnet to port 21 on a machine that is running an FTP server.
To log on to an FTP server, you must specify a username and password. You specify the username with the USER command:
You specify the password with ...