FTP or file transfer protocol is a commonly used protocol for exchanging files over any network that supports the TCP/IP protocol (such as the Internet or an intranet). There are two computers involved in an FTP transfer: a server and a client. The FTP server, running FTP server software, listens on the network for connection requests from other computers. The client computer, running FTP client software, initiates a connection to the server. Once connected, the client can do a number of file manipulation operations such as uploading files to the server, download files from the server, rename or delete files on the server and so on. Any software company or individual programmer is able to create FTP server or client software because the protocol is an open standard. Virtually every computer platform supports the FTP protocol. This allows any computer connected to a TCP/IP based network to manipulate files on another computer on that network regardless of which operating systems are involved (if the computers permit FTP access). There are many existing FTP client and server programs, and many of these are free. The internet protocol suite is the set of communications protocols that implement the protocol stack on which the Internet and most commercial networks run. ... The application layer is the seventh level of the seven-layer OSI model. ... The domain name system (DNS) stores and associates many types of information with domain names, but most importantly, it translates domain names (computer hostnames) to IP addresses. ... Secure Sockets Layer (SSL) and Transport Layer Security (TLS), its successor, are cryptographic protocols which provide secure communications on the Internet for such things as e-mail, Internet faxing, and other data transfers. ... Trivial File Transfer Protocol (TFTP) is a very simple file transfer protocol, with the functionality of a very basic form of FTP; it was first defined in 1980. ... Hypertext Transfer Protocol (HTTP) is the method used to transfer or convey information on the World Wide Web. ... The Internet Message Access Protocol (commonly known as IMAP4, and previously called Internet Mail Access Protocol) is an application layer Internet protocol that allows a local client to access e-mail on a remote server. ... IRC redirects here. ... The Network News Transfer Protocol or NNTP is an Internet application protocol used primarily for reading and posting Usenet articles, as well as transferring news among news servers. ... The Network Time Protocol (NTP) is a protocol for synchronising the clocks of computer systems over packet-switched, variable-latency data networks. ... In computing, local e-mail clients use the Post Office Protocol version 3 (POP3), an application-layer Internet standard protocol, to retrieve e-mail from a remote server over a TCP/IP connection. ... Session Initiation Protocol (SIP) is a protocol developed by IETF MMUSIC Working Group and proposed standard for initiating, modifying, and terminating an interactive user session that involves multimedia elements such as video, voice, instant messaging, online games, and virtual reality. ... Simple Mail Transfer Protocol (SMTP) is the de facto standard for e-mail transmission across the Internet. ... The simple network management protocol (SNMP) forms part of the internet protocol suite as defined by the Internet Engineering Task Force. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... TELNET is a network protocol used on the Internet or local area network LAN connections. ... The BitTorrent logo BitTorrent is the name of a peer-to-peer (P2P) file distribution protocol, and is the name of a free software implementation of that protocol. ... The Real-time Transport Protocol (or RTP) defines a standardized packet format for delivering audio and video over the Internet. ... In computing, rlogin is a Unix software utility that allows users to log in on another host via a network, communicating via TCP port 513. ... The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ... The User Datagram Protocol (UDP) is one of the core protocols of the Internet protocol suite. ... The Datagram Congestion Control Protocol (DCCP) is a message-oriented transport layer protocol that is currently under development in the IETF. Applications that might make use of DCCP include those with timingconstraints on the delivery of data such that reliable in-order delivery, when combined with congestion control, is likely... The Stream Control Transmission Protocol (SCTP) is a transport layer protocol defined in 2000 by the IETF Signaling Transport (SIGTRAN) working group. ... Transport layer protocol designed originally as part of the Plan 9 from Bell Labs operating system and used to carry 9P. Its main features are: Reliable datagram service In-sequence delivery Internetworking using IP Low complexity, high performance Adaptive timeouts The original paper describing IL: [1] Categories: Computer stubs ... In computer networking, the Reliable User Datagram Protocol (RUDP) is a transport layer protocol designed at Bell Labs for the Plan 9 operating system. ... The network layer is level three of the seven level OSI model. ... The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ... Internet Protocol version 4 is the fourth iteration of the Internet Protocol (IP) and it is the first version of the protocol to be widely deployed. ... Internet Protocol version 6 (IPv6) is a network layer IP standard used by electronic devices to exchange data across a packet-switched internetwork. ... The Internet Control Message Protocol (ICMP) is one of the core protocols of the Internet protocol suite. ... The Internet Group Management Protocol is a communications protocol used to manage the membership of Internet Protocol multicast groups. ... In computer networking, the Address Resolution Protocol (ARP) is the method for finding a hosts hardware address when only its IP address is known. ... Reverse address resolution protocol (RARP) is a protocol used to resolve an IP address from a given hardware address (such as an Ethernet address). ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Ethernet is a large and diverse family of frame-based computer networking technologies for local area networks (LANs). ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Token-Ring local area network (LAN) technology was developed and promoted by IBM in the early 1980s and standardised as IEEE 802. ... In computing, the Point-to-Point Protocol, or PPP, is commonly used to establish a direct connection between two nodes. ... The Serial Line Internet Protocol (SLIP) is a mostly obsolete encapsulation of the Internet Protocol designed to work over serial ports and modem connections. ... In computer networking, fiber-distributed data interface (FDDI) is a standard for data transmission in a local area network that can extend in range up to 200 km (124 miles). ... Asynchronous Transfer Mode (ATM) is a cell relay network protocol which encodes data traffic into small fixed-sized (53 byte; 48 bytes of data and 5 bytes of header information) cells instead of variable sized packets (sometimes known as frames) as in packet-switched networks (such as the Internet Protocol... Dynamic synchronous Transfer Mode , or DTM for short, is a network protocol. ... In the context of computer networking, frame relay (also found written as frame-relay) consists of an efficient data transmission technique used to send digital information quickly and cheaply in a relay of frames to one or many destinations from one or many end-points. ... SMDS, which stands for Switched Multi-megabit Data Services, was a connectionless service used to connect LANs, MANs and WANs to exchange data. ... The Internet protocol suite is the set of communications protocols that implement the protocol stack on which the Internet runs. ... An intranet is a private computer network that uses Internet protocols, network connectivity, and possibly the public telecommunication system to securely share part of an organizations information or operations with its employees. ... The tower of a personal computer. ... In information technology, a server is a computer system that provides services to other computing systems—called clients—over a network. ... In computing, a client is a system that accesses a (remote) service on another computer by some kind of network. ... Computer software (or simply software) refers to one or more computer programs and data held in the storage of a computer for some purpose. ... In computing, an operating system (OS) is the system software responsible for the direct control and management of hardware and basic system operations. ...

Overview

FTP is commonly run on two ports, 20 and 21, and runs exclusively over TCP. The FTP server listens on port 21 for incoming connections from FTP clients. A connection on this port forms the control stream, on which commands are passed to the FTP server. For the actual file transfer to take place, a different connection is required. Depending on the transfer mode, the client (active mode) or the server (passive mode) can listen for the incoming data connection. Before file transfer begins, the client and server also negotiate the port of the data connection. In case of active connections (where the server connects to the client to transfer data), the server binds on port 20 before connecting to the client. For passive connections, there is no such restriction. It has been suggested that this article or section be merged into Computer port (software). ... The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ...

While data is being transferred via the data stream, the control stream sits idle. This can cause problems with large data transfers through firewalls which time out sessions after lengthy periods of idleness. While the file may well be successfully transferred, the control session can be disconnected by the firewall, causing an error to be generated. Look up Data stream in Wiktionary, the free dictionary. ... It has been suggested that Understanding Firewalls be merged into this article or section. ...

When FTP is used in a UNIX environment, there is an often-ignored but valuable command, "reget" (meaning "get again") that will cause an interrupted "get" command to be continued, hopefully to completion, after a communications interruption. The principle is obvious - the receiving station has a record of what it got, so it can spool through the file at the sending station and re-start at the right place for a seamless splice. The converse would be "reput" but is not available. Again, the principle is obvious: The sending station does not know how much of the file was actually received, so it would not know where to start.

Objectives of FTP

The objectives of FTP, as outlined by its RFC, are: In internetworking and computer network engineering, Request for Comments (RFC) documents are a series of memoranda encompassing new research, innovations, and methodologies applicable to Internet technologies. ...

1. To promote sharing of files (computer programs and/or data).
2. To encourage indirect or implicit use of remote computers.
3. To shield a user from variations in file storage systems among different hosts.
4. To transfer data reliably and efficiently.

A remote computer is a computer to which a user does not have physical access, but which he or she can access/manipulate via some kind of network from a local computer (one which the user does have physical access to). ... In general, data consist of propositions that reflect reality. ...

Criticisms of FTP

1. Passwords and file contents are sent in clear text, which can be intercepted by eavesdroppers. There are protocol enhancements that circumvent this.
2. Multiple TCP/IP connections are used, one for the control connection, and one for each download, upload, or directory listing. Firewall software needs additional logic to account for these connections.
3. It is hard to filter active mode FTP traffic on the client side by using a firewall, since the client must open an arbitrary port in order to receive the connection. This problem is largely resolved by using passive mode FTP.
4. It is possible to abuse the protocol's built-in proxy features to tell a server to send data to an arbitrary port of a third computer; see FXP.
5. FTP is a high latency protocol due to the number of commands needed to initiate a transfer.
6. No integrity check on the receiver side. If transfer is interrupted the receiver has no way to know if the received file is complete or not. It is necessary to manage this externally for example with MD5 sums or cyclic redundancy checking.

A password is a form of secret authentication data that is used to control access to a resource. ... In data communications, cleartext is the form of a message or data which is transferred or stored without cryptographic protection. ... Eavesdropping is the intercepting of conversations by unintended recipients. ... It has been suggested that Understanding Firewalls be merged into this article or section. ... It has been suggested that this article or section be merged into Computer port (software). ... In information technology, a server is a computer system that provides services to other computing systems—called clients—over a network. ... File eXchange Protocol (FXP) is a method of data transfer which uses the FTP protocol to transfer data from one remote server to another without routing this data through the clients connection. ... In cryptography, MD5 (Message-Digest algorithm 5) is a widely-used cryptographic hash function with a 128-bit hash value. ... A cyclic redundancy check (CRC) is a type of hash function used to produce a checksum – a small, fixed number of bits – against a block of data, such as a packet of network traffic or a block of a computer file. ...

Security problems

The original FTP specification is an inherently insecure method of transferring files because there is no method specified for transferring data in an encrypted fashion. This means that under most network configurations, user names, passwords, FTP commands and transferred files can be "sniffed" or viewed by anyone on the same network using a packet sniffer. This is a problem common to many Internet protocol specifications written prior to the creation of SSL such as HTTP, SMTP and Telnet. The common solution to this problem is to use either SFTP (SSH File Transfer Protocol), or FTPS (FTP over SSL), which adds SSL or TLS encryption to FTP as specified in RFC 4217. Packet sniffers (also known as network or protocol analyzers or Ethernet sniffers) are computer software (usually) or computer hardware that can intercept and log traffic passing over a digital network or part of a network. ... Secure Sockets Layer (SSL) and Transport Layer Security (TLS), its successor, are cryptographic protocols which provide secure communications on the Internet. ... HTTP (for HyperText Transfer Protocol) is the primary method used to convey information on the World Wide Web. ... Simple Mail Transfer Protocol (SMTP) is the de facto standard for email transmission across the Internet. ... TELNET is a network protocol used on the Internet or local area network LAN connections. ... In computing, the SSH File Transfer Protocol or SFTP is a network protocol that provides file transfer and manipulation functionality over any reliable data stream. ... FTPS is a name used to encompass a number of ways in which FTP software can perform secure file transfers. ... Secure Sockets Layer (SSL) and Transport Layer Security (TLS), its successor, are cryptographic protocols which provide secure communications on the Internet. ... Secure Sockets Layer (SSL) and Transport Layer Security (TLS), its successor, are cryptographic protocols which provide secure communications on the Internet for such things as e-mail, Internet faxing, and other data transfers. ... In cryptography, encryption is the process of obscuring information to make it unreadable without special knowledge. ...

FTP return codes

Main article: List of FTP server return codes

FTP server return codes indicate their status by the digits within them. A brief explanation of various digits' meanings are given below:

• 1yz: Positive Preliminary reply. The action requested is being initiated but there will be another reply before it begins.
• 2yz: Positive Completion reply. The action requested has been completed. The client may now issue a new command.
• 3yz: Positive Intermediate reply. The command was successful, but a further command is required before the server can act upon the request.
• 4yz: Transient Negative Completion reply. The command was not successful, but the client is free to try the command again as the failure is only temporary.
• 5yz: Permanent Negative Completion reply. The command was not successful and the client should not attempt to repeat it again.
• x0z: The failure was due to a syntax error.
• x1z: This response is a reply to a request for information.
• x2z: This response is a reply relating to connection information.
• x3z: This response is a reply relating to accounting and authorization.

For other uses, see Syntax (disambiguation). ...

Anonymous FTP

Many sites that run FTP servers enable so-called "anonymous ftp". Under this arrangement, users do not need an account on the server. The user name for anonymous access is typically 'anonymous' or 'ftp'. This account does not need a password. Although users are commonly asked to send their email addresses as their passwords for authentication, usually there is trivial or no verification, depending on the FTP server and its configuration. Internet Gopher has been suggested as an alternative to anonymous FTP, as well as Trivial File Transfer Protocol. The term FTP server can mean one of two things: a computer responsible for serving any kind of files, via the File Transfer Protocol to FTP clients which can also web browsers; a software program that implements the FTP protocol and is working as a daemon serving any kind of... ... A user in computing context is one who uses a computer system. ... E-mail, or email, is short for electronic mail and is a method of composing, sending, and receiving messages over electronic communication systems. ... Gopher is a distributed document search and retrieval network protocol designed for the Internet. ... Trivial File Transfer Protocol (TFTP) is a very simple file transfer protocol, with the functionality of a very basic form of FTP; it was first defined in 1980. ...

Data format

While transferring data over the network, two modes can be used

1. ASCII mode
2. Binary mode

The two types differ in the way they send the data. When a file is sent using an ASCII-type transfer, the individual letters, numbers, and characters are sent using their ASCII character codes. The receiving machine saves these in a text file in the appropriate format (for example, a Unix machine saves it in a Unix format, a Macintosh saves it in a Mac format). Hence if an ASCII transfer is used it can be assumed plain text is sent, which is stored by the receiving computer in its own format. Translating between text formats entails substituting the end of line and end of file characters used on the source platform with those on the destination platform, e.g. a Windows machine receiving a file from a Unix machine will replace the carriage returns with carriage return-line feed pairs. ASCII transfer is also marginally faster, as the highest-order bit is dropped from each byte in the file.[1] There are 95 printable ASCII characters, numbered 32 to 126. ... Look up binary in Wiktionary, the free dictionary. ... Computer files can be divided into two broad categories: binary and text. ... Originally, carriage return was the term for the key, lever, or mechanism on a typewriter that would cause the cylinder on which the paper was held (the carriage) to return to the left side of the paper after a line of text had been typed, and would often move it... In computing, line feed (LF) is a control character indicating that one line should be fed out. ...

Sending a file in binary mode is different. The sending machine sends each file bit for bit and as such the recipient stores the bitstream as it receives it. Any form of data that is not plain text will be corrupted if this mode is not used. BIT is an acronym for: Bangalore Institute of Technology Bilateral Investment Treaty Bhilai Institute of Technology - Durg Birla Institute of Technology - Mesra Battles in Time (Doctor Who magazine) Category: ...

By default, most FTP clients use ASCII mode. Some clients try to determine the required transfer-mode by inspecting the file's name or contents.

FTP and web browsers

Most recent web browsers and file managers can connect to FTP servers, although they may lack the support for protocol extensions such as FTPS. This allows manipulation of remote files over FTP through an interface similar to that used for local files. This is done via an FTP URL, which takes the form ftp(s)://<ftpserveraddress>  (e.g., [2]). A password can optionally be given in the URL, e.g.:   ftp(s)://<login>:<password>@<ftpserveraddress>:<port>. Most web-browsers require the use of passive mode FTP, which not all FTP servers are capable of handling. Some browsers allow only the downloading of files, but offer no way to upload files to the server. Icons for Web browser shortcuts on an Apple computer (Safari, Internet Explorer, and Firefox). ... A file manager is a computer program that provides a user interface to work with file systems. ... FTPS is a name used to encompass a number of ways in which FTP software can perform secure file transfers. ... A Uniform Resource Locator, URL (spelled out as an acronym, not pronounced as earl), or Web address, is a standardized address name layout for resources (such as documents or images) on the Internet (or elsewhere). ...

FTP over SSH

FTP over SSH refers to the practice of tunneling a normal FTP session over an SSH connection. In computing, Secure shell, or SSH, is both a computer program and an associated network protocol designed for logging into and executing commands on a remote computer. ...

Because FTP uses multiple TCP connections (unusual for a TCP/IP protocol that is still in use), it is particularly difficult to tunnel over SSH. With many SSH clients, attempting to set up a tunnel for the control channel (the initial client-to-server connection on port 21) will only protect that channel; when data is transferred, the FTP software at either end will set up new TCP connections (data channels) which will bypass the SSH connection, and thus have no confidentiality, integrity protection, etc. The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ... Confidentiality has been defined by the International Organization for Standardization (ISO) as ensuring that information is accessible only to those authorized to have access and is one of the cornerstones of Information security. ... In telecommunication, the term data integrity has the following meanings: The condition that exists when data is unchanged from its source and has not been accidentally or maliciously modified, altered, or destroyed. ...

If the FTP client is configured to use passive mode and to connect to a SOCKS server interface that many SSH clients can present for tunnelling, it is possible to run all the FTP channels over the SSH connection. Alternatively, The GNU licensed software FONC [3] allows both data and control of active and passive FTP connections to be encrypted over ssh tunnels. SOCKS is an Internet protocol that allows client-server applications to transparently use the services of a network firewall. ...

Otherwise, it is necessary for the SSH client software to have specific knowledge of the FTP protocol, and monitor and rewrite FTP control channel messages and autonomously open new forwardings for FTP data channels.

FTP over SSH is sometimes referred to as secure FTP; this should not be confused with other methods of securing FTP, such as with SSL/TLS (FTPS). Other methods of transferring files using SSH which are not related to FTP include SFTP or SCP; in both of these, the entire conversation (credentials and data) is always protected by the SSH protocol. FTPS is a name used to encompass a number of ways in which FTP software can perform secure file transfers. ... In computing, the SSH File Transfer Protocol or SFTP is a network protocol that provides file transfer and manipulation functionality over any reliable data stream. ... Secure Copy or SCP is a means of securely transferring computer files between a local and a remote host or between two remote hosts, using the Secure Shell (SSH) protocol. ...

References

The protocol is standardized in RFC 0959 by the IETF as: Standardization, in the context related to technologies and industries, is the process of establishing a technical standard among competing entities in a market, where this will bring benefits without hurting competition. ... In internetworking and computer network engineering, Request for Comments (RFC) documents are a series of memoranda encompassing new research, innovations, and methodologies applicable to Internet technologies. ... The Internet Engineering Task Force (IETF) is charged with developing and promoting Internet standards. ...

• RFC 959 File Transfer Protocol (FTP). J. Postel, J. Reynolds. Oct-1985. This obsoleted the preceding RFC 765 and earlier FTP RFCs back to the original RFC 114.
• See also RFC 1579 Firewall-Friendly FTP.

See also

• Archie search engine
• List of FTP server return codes
• List of FTP commands
• Ident
• TCP Wrapper

Archie was the first search engine ever invented, designed to index FTP archives, allowing people to find specific files. ... Below is a list of all FTP commands that may be sent to an FTP host. ... The Ident Protocol, specified in RFC 1413, is an Internet protocol that helps identify the user of a particular TCP connection. ... TCP Wrapper is a host-based network ACL system written by Dr. Wietse Venema, used to filter otherwise (yet) unauthenticated network access to Internet protocol services run on (Unix-like) operating systems such as Linux or BSD. Allowing host or subnetwork IP adresses, names and/or ident query replys, to...

FTP-like protocols

• FTPFS
• FTPS, FTP run over SSL
• Simple File Transfer Protocol (SFTP), the historic protocol RFC 913
• SSH file transfer protocol (SFTP), a protocol running over SSH
• Trivial File Transfer Protocol (TFTP)

FTPFS (File Transfer Protocol FileSystem) is an obsoleted Linux kernel module that allows the user to mount a FTP server onto the local filesystem. ... FTPS is a name used to encompass a number of ways in which FTP software can perform secure file transfers. ... The term SFTP has other meanings. ... In computing, the SSH File Transfer Protocol or SFTP is a network protocol that provides file transfer and manipulation functionality over any reliable data stream. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Trivial File Transfer Protocol (TFTP) is a very simple file transfer protocol, with the functionality of a very basic form of FTP; it was first defined in 1980. ...

Software

• Comparison of FTP clients
• List of FTP servers

The following tables compare general and technical information for a number of FTP clients. ... The following is a list of FTP servers. ...

External links

• RFC 959 — File Transfer Protocol (FTP). J. Postel, J. Reynolds. Oct-1985., also RFC0959 in html format
• RFC 1579 — Firewall-Friendly FTP
• RFC 2228 — FTP Security Extensions
• FTP Reviewed — a review of the protocol notably from a security standpoint
• Raw FTP command list
• FTP Sequence Diagram (in PDF format)
• [4] — FTP A free, fast and reliable FTP program ready to download

To meet Wikipedias quality standards, this article or section may require cleanup. ...

Tutorial/overview

• Setting up an FTP Server in WinXP PCSTATS Beginners Guide
• New users guide Useful introduction.
• An Overview of the File Transfer Protocol — explains how the FTP works at the protocol level
• Active vs. Passive FTP explained and illustrated
• Dmoz directory about FTP
• The FTP and Your Firewall — details FTP's problems with firewalls and how to deal with them
• FTP File Transfers Basics of the FTP communication.
• Anonymous FTP Sites List List of currently known anonymous FTP sites.