File Transfer Protocol FTP

What Is File Transfer Protocol FTP?

File Transfer Protocol--or FTP--is a language and methodology behind the transmission of information between computers. FTP is an intrinsic part of the Internet Protocol Suite--TCP/IP--that defines the current structure of the Internet. The Internet Protocol Suite is composed of four layers: the link layer, the Internet layer, the transport layer and the application layer. FTP is part of the application layer.

Function

·         FTP allows data duplication between two or more remote connections operating in a client-server relationship. The target machine, the server, transmits data to the requesting machine, the client. Multiple clients can access the server simultaneously. In addition to downloading information from the server, clients with appropriate levels of access can upload files back to the server machine. To facilitate the data transfer process, two connections are made between the client and the server. The first connection--on port 21--is the control connection, or protocol interpreter connection. The server will "listen" for incoming control connections here from clients. The second connection--on port 20--is the data connection. It is formed once a control connection is established and data transmission requests are sent and acknowledged.

Features

·         The File Transfer Protocol features several data representation modes, including ASCII and binary--or "image"--modes. Binary mode is a perfect duplicate of each byte, while ASCII mode converts characters into 8-bit ASCII before transmission. ASCII mode should not be used to copy files that include numeric data. In addition to these data modes, FTP programs often allow two types of connection modes, passive and active. Passive connection mode exists for clients that cannot accept incoming TCP connections; active connection mode allows the client to send the port and IP address it wishes to use for the connection.

What Is an FTP Server?

FTP Server

File Transfer Protocol (FTP) is a TCP protocol for uploading and downloading files between computers. FTP works on a client/server model. The server component is called an FTP daemon. It continuously listens for FTP requests from remote clients. When a request is received, it manages the login and sets up the connection. For the duration of the session it executes any of commands sent by the FTP client.

Access to an FTP server can be managed in two ways:

·         Anonymous

·         Authenticated

In the Anonymous mode, remote clients can access the FTP server by using the default user account called "anonymous" or "ftp" and sending an email address as the password. In the Authenticated mode a user must have an account and a password. User access to the FTP server directories and files is dependent on the permissions defined for the account used at login. As a general rule, the FTP daemon will hide the root directory of the FTP server and change it to the FTP Home directory. This hides the rest of the file system from remote sessions.

      Command Purpose

! Runs the specified command on the local computer.

? Displays descriptions for ftp commands. Identical to help.

append Appends a local file to a file on the remote computer, using the current file type setting.

ascii Sets the file transfer type to ASCII, the default.

bell Toggles a bell to ring after each file transfer command is completed. By default, the bell is off.

binary Sets the file transfer type to binary.

bye Ends the FTP session with the remote computer and exits ftp.

cd Changes the working directory on the remote computer.

close Ends the FTP session with the remote server and returns to the command interpreter.

debug Toggles debugging. When debugging is on, each command sent to the remote computer is printed, preceded by the string --->. By default, debugging is off.

delete Deletes files on remote computers.

dir Displays a list of a remote directory's files and subdirectories.

disconnect Disconnects from the remote computer, retaining the ftp prompt.

get Copies a remote file to the local computer, using the current file transfer type.

glob Toggles filename globbing. Globbing permits use of wildcard characters in local file or path names. By default, globbing is on.

hash Toggles hash-mark (#) printing for each 2048 bytes data block transferred. By default, hash-mark printing is off.

help Displays descriptions for FTP commands.

lcd Changes the working directory on the local computer. By default, the current directory on the local computer is used.

literal Sends arguments, verbatim, to the remote FTP server. A single FTP reply code is expected in return.

ls Displays an abbreviated list of a remote directory's files and subdirectories.

mdelete Deletes multiple files on remote computers.

mdir Displays a list of a remote directory's files and subdirectories. Allows you to specify multiple files.

mget Copies multiple remote files to the local computer using the current file transfer type.

mkdir Creates a remote directory.

mls Displays an abbreviated list of a remote directory's files and subdirectories.

mput Copies multiple local files to the remote computer, using the current file transfer type.

open Connects to the specified FTP server.

prompt Toggles prompting. During multiple file transfers, ftp provides prompts to allow you to selectively retrieve or store files; mget and mput transfer all files if prompting is turned off. By default, prompting is on.

put Copies a local file to the remote computer, using the current file transfer type.

pwd Prints the current directory on the remote computer.

quit Ends the FTP session with the remote computer and exits ftp.