FTP: File Transfer Protocol

File Transfer Protocol (FTP) enables file sharing between hosts. FTP uses TCP to create a virtual connection for control information and then creates a separate TCP connection for data transfers. The control connection uses an image of the TELNET protocol to exchange commands and messages between hosts.

The key functions of FTP are:

1)to promote sharing of files (computer programs and/or data),

2)to encourage indirect or implicit (via programs) use of remote computers,

3)to shield a user from variations in file storage systems among hosts, and

4)to transfer data reliably and efficiently. FTP, though usable directly by a user at a terminal, is designed mainly for use by programs.

FTP control frames are TELNET exchanges and can contain TELNET commands and option negotiation. However, most FTP control frames are simple ASCII text and can be classified as FTP commands or FTP messages. FTP messages are responses to FTP commands and consist of a response code followed by explanatory text.

FTP has little security protection when performing file transfer: both user password and the data are exposed to public. To make the file transfer more secure, some enhancements have been made on the FTP, including SFTP, SSH protected FTP and BBFTP.

• the data that is transferred, it should only be used to transfer small (1-10KB) files containing sensitive data. Large files that do not contain sensitive information should be transferred via a method that does not encrypt data.

• SSH protected FTP: This transfer method encrypts the passwordinformation but does NOT encrypt the data being transferred. As a result, it should only be used to transfer large (and small) files that do NOT contain sensitive information. File that contain sensitive information should be transferred with SFTP .
• BBFTP: BBFTP only encryptsusernames and passwords, it does NOT encrypt the data being transferred. BBFTP is a non-interactive FTP-like system that supports parallel TCP streams for data transfers, allowing it to achieve bandwidths that are greater than normal FTP. Because of these characteristics, it is the preferred method for transferring large data files over network.

Protocol Structure - FTP (File Transfer Protocol)

Command	Description
ABOR	Abort data connection process.
ACCT <account>	Account for system privileges.
ALLO <bytes>	Allocate bytes for file storage on server.
APPE <filename>	Append file to file of same name on server.
CDUP <dir path>	Change to parent directory on server.
CWD <dir path>	Change working directory on server.
DELE <filename>	Delete specified file on server.
HELP <command>	Return information on specified command.
LIST <name>	List information if name is a file or list files if name is a directory.
MODE <mode>	Transfer mode (S=stream, B=block, C=compressed).
MKD <directory>	Create specified directory on server.
NLST <directory>	List contents of specified directory.
NOOP	Cause no action other than acknowledgement from server.
PASS <password>	Password for system log-in.
PASV	Request server wait for data connection.
PORT <address>	IP address and two-byte system port ID.
PWD	Display current working directory.
QUIT	Log off from the FTP server.
REIN	Reinitialize connection to log-in status.
REST <offset>	Restart file transfer from given offset.
RETR <filename>	Retrieve (copy) file from server.
RMD <directory>	Remove specified directory on server.
RNFR <old path>	Rename from old path.
RNTO <new path>	Rename to new path.
SITE <params>	Site specific parameters provided by server.
SMNT <pathname>	Mount the specified file structure.
STAT <directory>	Return information on current process or directory.
STOR <filename>	Store (copy) file to server.
STOU <filename>	Store file to server name.
STRU <type>	Data structure (F=file, R=record, P=page).
SYST	Return operating system used by server.
TYPE <data type>	Data type (A=ASCII, E=EBCDIC, I=binary).
USER <username>	User name for system log-in.

Standard FTP messages are as follows:

FTP is defined by IETF (http://www.ietf.org ) RFC 959 and updated by 2228, 2640, 2773

http://www.javvin.com/protocol/rfc959.pdf : FILE TRANSFER PROTOCOL (FTP)