Jump to content

File Transfer Protocol: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous edit
Content deleted Content added
VisualWikitext
m using AWB
Undid revision 1262461394 by 37.39.146.23 (talk)
 
(550 intermediate revisions by more than 100 users not shown)
Line 1: Line 1:
{{Short description|Standard protocol for transferring files over TCP/IP networks}}
{{redirect|FTP}}
{{Redirect|FTP}}
{{Use dmy dates|date=August 2016}}
{{Infobox networking protocol
| title = File Transfer Protocol
| purpose = [[File transfer]]
| developer = [[Abhay Bhushan]] for RFC 114
| date = {{Start date and age|1971|4|16}}
| osilayer = [[Application layer]]
| ports = 21 for control, 20 for data transfer
| rfcs = RFC 959
}}
{{IPstack}}
{{IPstack}}
{{Internet history timeline}}
The '''File Transfer Protocol''' ('''FTP''') is a standard [[network protocol]] used to transfer [[computer file]]s between [[Client–server model|a client and server]] on a [[computer network]].


FTP is built on a client-server model architecture and uses separate control and data connections between the client and the server.<ref name="for">{{cite book |last=Forouzan |first=B.A. |year=2000 |title=TCP/IP: Protocol Suite |edition=1st |location=New Delhi, India |publisher=Tata McGraw-Hill Publishing Company Limited}}</ref> FTP users may authenticate themselves with a [[clear text|clear-text]] sign-in protocol, normally in the form of a username and password, but can connect anonymously if the server is configured to allow it. For secure transmission that protects the username and password, and encrypts the content, FTP is often [[File Transfer Protocol#Security|secured]] with [[Transport Layer Security|SSL/TLS]] ([[FTPS]]). [[SSH File Transfer Protocol]] (SFTP) is sometimes also used instead, but is technologically different.
The '''File Transfer Protocol''' ('''FTP''') is a standard [[communication protocol]] used for the transfer of [[computer file]]s from a server to a client on a [[computer network]]. FTP is built on a client–server model architecture using separate control and data connections between the client and the server.<ref name="for">{{cite book |last=Forouzan |first=B.A. |year=2000 |title=TCP/IP: Protocol Suite |edition=1st |location=New Delhi, India |publisher=Tata McGraw-Hill Publishing Company Limited}}</ref> FTP users may authenticate themselves with a [[plaintext|plain-text]] sign-in protocol, normally in the form of a username and password, but can connect anonymously if the server is configured to allow it. For secure transmission that protects the username and password, and encrypts the content, FTP is often [[#Security|secured]] with [[Transport Layer Security|SSL/TLS]] ([[FTPS]]) or replaced with [[SSH File Transfer Protocol]] (SFTP).


The first FTP client applications were [[Command-line interface|command-line programs]] developed before [[operating system]]s had [[graphical user interface]]s, and are still shipped with most [[Windows]], [[Unix]], and [[Linux]] operating systems.<ref name="tcpip">{{cite web |last=Kozierok |first=Charles M. |year=2005 |title=The TCP/IP Guide v3.0 |url=http://www.tcpipguide.com/free/t_FTPOverviewHistoryandStandards.htm |publisher=Tcpipguide.com}}</ref><ref name="net+" /> Many FTP clients and automation utilities have since been developed for desktops, servers, mobile devices, and hardware, and FTP has been incorporated into productivity applications, such as [[HTML editor|web page editors]].
The first FTP client applications were [[Command-line interface|command-line programs]] developed before [[operating system]]s had [[graphical user interface]]s, and are still shipped with most [[Windows]], [[Unix]], and [[Linux]] operating systems.<ref name="tcpip">{{cite web |last=Kozierok |first=Charles M. |year=2005 |title=The TCP/IP Guide v3.0 |url=http://www.tcpipguide.com/free/t_FTPOverviewHistoryandStandards.htm |publisher=Tcpipguide.com}}</ref><ref name="net+"/> Many dedicated FTP [[client (computing)|client]]s and automation utilities have since been developed for [[desktop computer|desktops]], servers, mobile devices, and hardware, and FTP has been incorporated into productivity applications such as [[HTML editor]]s and [[file managers]].


An FTP client used to be commonly integrated in [[web browser]]s, where file servers are browsed with the [[Uniform Resource Identifier|URI]] prefix "<code>ftp://</code>". In 2021, FTP support was dropped by [[Google Chrome]] and [[Firefox]],<ref name=":0">{{Cite web|last=Vonau|first=Manuel|date=2021-07-07|title=Firefox follows in Chrome's footsteps and drops FTP support (APK Download)|url=https://www.androidpolice.com/2021/07/14/firefox-90-fully-removes-ftp-support-and-reorganizes-some-settings-apk-download/|access-date=2021-07-12|website=Android Police|language=en-US}}</ref><ref name="chromestatus">{{Cite web|title=Remove FTP support - Chrome Platform Status|url=https://chromestatus.com/feature/6246151319715840|access-date=2021-09-02|website=www.chromestatus.com}}</ref> two major web browser vendors, due to it being superseded by the more secure SFTP and FTPS; although neither of them have implemented the newer protocols.<ref>{{Cite web |last=by |first=Written |date=2020-03-23 |title=Firefox is dropping FTP support |url=https://news.sophos.com/en-us/2020/03/23/firefox-is-dropping-ftp-support/ |access-date=2023-10-13 |website=Sophos News |language=en-US}}</ref><ref>{{Cite web |last=Edwards |first=Benj |date=2022-07-14 |title=Chrome and Firefox Killed FTP Support: Here's an Easy Alternative |url=https://www.howtogeek.com/744569/chrome-and-firefox-killed-ftp-support-heres-an-easy-alternative/ |access-date=2023-10-13 |website=How-To Geek |language=en}}</ref>
==History of FTP server==
The original specification for the File Transfer Protocol was written by [[Abhay Bhushan]] and published as RFC 114 on 16 April 1971. Until 1980, FTP ran on [[Network Control Program|NCP]], the predecessor of TCP/IP.<ref name="tcpip" /> The protocol was later replaced by a TCP/IP version, RFC 765 (June 1980) and RFC 959 (October 1985), the current specification. Several proposed standards amend RFC 959, for example RFC 1579 (February 1994) enables Firewall-Friendly FTP (passive mode), RFC 2228 (June 1997) proposes security extensions, RFC 2428 (September 1998) adds support for [[IPv6]] and defines a new type of passive mode.<ref name="clark">{{cite book |last=Clark |first=M.P. |year=2003 |title=Data Networks IP and the Internet |edition=1st |location=West Sussex, England |publisher=John Wiley & Sons Ltd.}}</ref>


==History of FTP servers==
==Protocol overview==
The original specification for the File Transfer Protocol was written by [[Abhay Bhushan]] and published as {{IETF RFC|114}} on 16 April 1971. Until 1980, FTP ran on [[Network Control Protocol (ARPANET)|NCP]], the predecessor of [[Internet protocol suite|TCP/IP]].<ref name="tcpip" /> The protocol was later replaced by a TCP/IP version, {{IETF RFC|765}} (June 1980) and {{IETF RFC|959}} (October 1985), the current specification. Several proposed standards amend {{IETF RFC|959}}, for example {{IETF RFC|1579}} (February 1994) enables Firewall-Friendly FTP (passive mode), {{IETF RFC|2228}} (June 1997) proposes security extensions, {{IETF RFC|2428}} (September 1998) adds support for [[IPv6]] and defines a new type of passive mode.<ref name="clark">{{cite book |last=Clark |first=M.P. |year=2003 |title=Data Networks IP and the Internet |edition=1st |location=West Sussex, England |publisher=John Wiley & Sons Ltd.}}</ref>

==Protocol overview==


===Communication and data transfer===
===Communication and data transfer===
[[File:Passive FTP Verbindung.svg|thumb|Illustration of starting a passive connection using port 21]]
[[File:Passive FTP Verbindung.svg|thumb|Illustration of starting a passive connection using port 21]]
FTP may run in ''active'' or ''passive'' mode, which determines how the data connection is established.<ref name="slack">{{cite web |title=Active FTP vs. Passive FTP, a Definitive Explanation |url=http://slacksite.com/other/ftp.html |publisher=Slacksite.com |archiveurl=http://webcache.googleusercontent.com/search?q=cache:http://slacksite.com/other/ftp.html |archivedate=2014-12-31}}</ref> In both cases, the client creates a TCP control connection from a random, usually an unprivileged, port N to the FTP server command port 21.
FTP may run in ''active'' or ''passive'' mode, which determines how the data connection is established.<ref name="slack">{{cite web |title=Active FTP vs. Passive FTP, a Definitive Explanation |url=http://slacksite.com/other/ftp.html |publisher=Slacksite.com}}</ref> (This sense of "mode" is different from that of the MODE command in the FTP protocol.)
* In active mode, the client starts listening for incoming data connections from the server on port M. It sends the FTP command PORT M to inform the server on which port it is listening. The server then initiates a data channel to the client from its port 20, the FTP server data port.
* In active mode, the client starts listening for incoming data connections from the server on port M. It sends the FTP command PORT<ref>{{Cite web |last=Weis |first=Olga |date=2022-10-18 |title=FTP Port: Full Guide about FTP and Port Numbers |url=https://mac.eltima.com/ftp-port.html |access-date=2024-03-29 |website=Comprehensive Mac software apps |language=en-US}}</ref> M to inform the server on which port it is listening. The server then initiates a data channel to the client from its port 20, the FTP server data port.
* In situations where the client is behind a [[Firewall (computing)|firewall]] and unable to accept incoming TCP connections, ''passive mode'' may be used. In this mode, the client uses the control connection to send a PASV command to the server and then receives a server IP address and server port number from the server,<ref name="slack"/><ref name="Uftp">{{cite web |last=Parker |first=Don |date=September 2005 |title=Understanding the FTP Protocol |url=http://www.windowsnetworking.com/articles_tutorials/understanding-ftp-protocol.html |publisher=Windowsnetworking.com}}</ref> which the client then uses to open a data connection from an arbitrary client port to the server IP address and server port number received.<ref name="postel">RFC 959 (Standard) File Transfer Protocol (FTP). Postel, J. & Reynolds, J. (October 1985).</ref>
* In situations where the client is behind a [[Firewall (computing)|firewall]] and unable to accept incoming TCP connections, ''passive mode'' may be used. In this mode, the client uses the control connection to send a PASV command to the server and then receives a server IP address and server port number from the server,<ref name="slack"/> which the client then uses to open a data connection from an arbitrary client port to the server IP address and server port number received.<ref name="postel">{{IETF RFC|959}} (Standard) File Transfer Protocol (FTP). Postel, J. & Reynolds, J. (October 1985).</ref>
Both modes were updated in September 1998 to support [[IPv6]]. Further changes were introduced to the passive mode at that time, updating it to ''extended passive mode''.<ref>RFC 2428 (Proposed Standard) Extensions for IPv6, NAT, and Extended Passive Mode. Allman, M. & Metz, C. & Ostermann, S. (September 1998).</ref>
Both modes were updated in September 1998 to support [[IPv6]]. Further changes were introduced to the passive mode at that time, updating it to ''extended passive mode''.<ref>{{IETF RFC|2428}} (Proposed Standard) Extensions for IPv6, NAT, and Extended Passive Mode. Allman, M. & Metz, C. & Ostermann, S. (September 1998).</ref>


The server responds over the control connection with [[List of FTP server return codes|three-digit status codes]] in ASCII with an optional text message. For example, "200" (or "200 OK") means that the last command was successful. The numbers represent the code for the response and the optional text represents a human-readable explanation or request (e.g. &lt;Need account for storing file&gt;).<ref name="for" /> An ongoing transfer of file data over the data connection can be aborted using an interrupt message sent over the control connection.
The server responds over the control connection with [[List of FTP server return codes|three-digit status codes]] in ASCII with an optional text message. For example, "200" (or "200 OK") means that the last command was successful. The numbers represent the code for the response and the optional text represents a human-readable explanation or request (e.g. &lt;Need account for storing file&gt;).<ref name="for" /> An ongoing transfer of file data over the data connection can be aborted using an interrupt message sent over the control connection.


FTP needs two ports (one for sending and one for receiving) because it was originally designed to operate on top of [[Network Control Protocol (ARPANET)|Network Control Protocol]] (NCP), which was a [[Simplex communication|simplex protocol]] that utilized two [[List of TCP and UDP port numbers|port addresses]], establishing two connections, for two-way communications. An odd and an even port were reserved for each [[application layer]] application or protocol. The standardization of TCP and UDP reduced the need for the use of two simplex ports for each application down to one duplex port,<ref name="stevens1994v1">{{cite book | last = Stevens | first = W. Richard | title = TCP/IP Illustrated Volume I | location = Reading, Massachusetts, USA | publisher= Addison-Wesley Publishing Company | year = 1994 | isbn = 0-201-63346-9 | volume = 1 }}</ref>{{Rp|15}} but the FTP protocol was never altered to only use one port, and continued using two for backwards compatibility.
While transferring data over the network, four data representations can be used:<ref name="tcpip" /><ref name="net+" /><ref name="clark" />
* [[ASCII]] mode: Used for text. Data is converted, if needed, from the sending host's character representation to [[Extended ASCII|"8-bit ASCII"]] before transmission, and (again, if necessary) to the receiving host's character representation. As a consequence, this mode is inappropriate for files that contain data other than plain text.
* Image mode (commonly called [[Binary data|Binary]] mode): The sending machine sends each file [[byte]] for byte, and the recipient stores the [[bytestream]] as it receives it. (Image mode support has been recommended for all implementations of FTP).
* [[EBCDIC]] mode: Used for plain text between hosts using the EBCDIC character set.
* Local mode: Allows two computers with identical setups to send data in a proprietary format without the need to convert it to ASCII.


===NAT and firewall traversal===
For text files, different format control and record structure options are provided. These features were designed to facilitate files containing [[Telnet]] or [[ASA carriage control characters|ASA]].
FTP normally transfers data by having the server connect back to the client, after the PORT command is sent by the client. This is problematic for both [[Network address translation|NATs]] and firewalls, which do not allow connections from the Internet towards internal hosts.<ref name="ncftp">{{cite web |last=Gleason |first=Mike |year=2005 |title=The File Transfer Protocol and Your Firewall/NAT |url=https://www.ncftp.com/ncftpd/doc/misc/ftp_and_firewalls.html |publisher=Ncftp.com}}</ref> For NATs, an additional complication is that the representation of the IP addresses and port number in the PORT command refer to the internal host's IP address and port, rather than the public IP address and port of the NAT.


There are two approaches to solve this problem. One is that the FTP client and FTP server use the PASV command, which causes the data connection to be established from the FTP client to the server.<ref name="ncftp" /> This is widely used by modern FTP clients. Another approach is for the NAT to alter the values of the PORT command, using an [[application-level gateway]] for this purpose.<ref name="ncftp" />
[[File:FTP model.png|thumb|A model chart of how FTP works]]

===Data types===
While transferring data over the network, five data types are defined:<ref name="tcpip" /><ref name="net+" /><ref name="clark" />
* [[ASCII]] (TYPE A): Used for text. Data is converted, if needed, from the sending host's character representation to [[Extended ASCII|"8-bit ASCII"]] before transmission, and (again, if necessary) to the receiving host's character representation, including [[newline]]s. As a consequence, this mode is inappropriate for files that contain data other than ASCII.
* Image (TYPE I, commonly called [[Binary data|Binary]] mode): The sending machine sends each file [[byte]] by byte, and the recipient stores the [[bytestream]] as it receives it. (Image mode support has been recommended for all implementations of FTP).
* [[EBCDIC]] (TYPE E): Used for plain text between hosts using the EBCDIC character set.
* Local (TYPE L ''n''): Designed to support file transfer between machines which do not use 8-bit bytes, e.g. [[36-bit computing|36-bit systems]] such as DEC [[PDP-10]]s. For example, "TYPE L 9" would be used to transfer data in 9-bit bytes, or "TYPE L 36" to transfer 36-bit words. Most contemporary FTP clients/servers only support L 8, which is equivalent to I.
* [[Unicode]] text files using [[UTF-8]] (TYPE U): defined in an expired [[Internet Draft]]<ref>{{Cite IETF|last=Klensin|first=John|title=FTP TYPE Extension for Internationalized Text|draft=draft-klensin-ftpext-typeu-00|access-date=2020-06-09}}</ref> which never became an RFC, though it has been implemented by several FTP clients/servers.

Note these data types are commonly called "modes", although ambiguously that word is also used to refer to active-vs-passive communication mode (see above), and the modes set by the FTP protocol MODE command (see below).

For text files (TYPE A and TYPE E), three different format control options are provided, to control how the file would be printed:
* Non-print (TYPE A N and TYPE E N) – the file does not contain any carriage control characters intended for a printer
* [[Telnet]] (TYPE A T and TYPE E T) – the file contains Telnet (or in other words, ASCII C0) carriage control characters (CR, LF, etc)
* [[ASA carriage control characters|ASA]] (TYPE A A and TYPE E A) – the file contains ASA carriage control characters
These formats were mainly relevant to [[line printer]]s; most contemporary FTP clients/servers only support the default format control of N.

===File structures===
File organization is specified using the STRU command. The following file structures are defined in section 3.1.1 of RFC959:
* '''F''' or FILE structure (stream-oriented). Files are viewed as an arbitrary sequence of bytes, characters or words. This is the usual file structure on Unix systems and other systems such as CP/M, MS-DOS and Microsoft Windows. (Section 3.1.1.1)
* '''R''' or RECORD structure (record-oriented). Files are viewed as divided into records, which may be fixed or variable length. This file organization is common on mainframe and midrange systems, such as MVS, VM/CMS, OS/400 and VMS, which support [[record-oriented filesystem]]s.
* '''P''' or PAGE structure (page-oriented). Files are divided into pages, which may either contain data or metadata; each page may also have a header giving various attributes. This file structure was specifically designed for [[TENEX (operating system)|TENEX]] systems, and is generally not supported on other platforms. RFC1123 section 4.1.2.3 recommends that this structure not be implemented.

Most contemporary FTP clients and servers only support STRU F. STRU R is still in use in mainframe and minicomputer file transfer applications.

===Data transfer modes===
Data transfer can be done in any of three modes:<ref name="for" /><ref name="tcpip" />
Data transfer can be done in any of three modes:<ref name="for" /><ref name="tcpip" />
* Stream mode: Data is sent as a continuous stream, relieving FTP from doing any processing. Rather, all processing is left up to [[Transmission Control Protocol|TCP]]. No End-of-file indicator is needed, unless the data is divided into [[Record (computer science)|records]].
* Stream mode (MODE S): Data is sent as a continuous stream, relieving FTP from doing any processing. Rather, all processing is left up to [[Transmission Control Protocol|TCP]]. No End-of-file indicator is needed, unless the data is divided into [[Record (computer science)|records]].
* Block mode: FTP breaks the data into several blocks (block header, byte count, and data field) and then passes it on to TCP.<ref name="clark" />
* Block mode (MODE B): Designed primarily for transferring record-oriented files (STRU R), although can also be used to transfer stream-oriented (STRU F) text files. FTP puts each record (or line) of data into several blocks (block header, byte count, and data field) and then passes it on to TCP.<ref name="clark" />
* Compressed mode: Data is compressed using a simple algorithm (usually [[run-length encoding]]).
* Compressed mode (MODE C): Extends MODE B with data compression using [[run-length encoding]].


Most contemporary FTP clients and servers do not implement MODE B or MODE C; FTP clients and servers for mainframe and minicomputer operating systems are the exception to that.
Some FTP software also implements a [[DEFLATE]]-based compressed mode, sometimes called "Mode Z" after the command that enables it. This mode was described in an [[Internet Draft]], but not standardized.<ref>{{cite IETF |title=Deflate transmission mode for FTP |draft=draft-preston-ftpext-deflate-03.txt |first=J. |last=Preston |year=2005 |month=January |publisher=[[Internet Engineering Task Force|IETF]] |accessdate=27 January 2016}}</ref>


Some FTP software also implements a [[DEFLATE]]-based compressed mode, sometimes called "Mode Z" after the command that enables it. This mode was described in an [[Internet Draft]], but not standardized.<ref>{{cite IETF |title=Deflate transmission mode for FTP |draft=draft-preston-ftpext-deflate-03 |first=J. |last=Preston |date=January 2005 |publisher=[[Internet Engineering Task Force|IETF]] |access-date=27 January 2016}}</ref>
===Login===
FTP login utilizes a normal username and password scheme for granting access.<ref name="tcpip" /> The username is sent to the server using the USER command, and the password is sent using the PASS command.<ref name="tcpip" /> If the information provided by the client is accepted by the server, the server will send a greeting to the client and the session will commence.<ref name="tcpip" /> If the server supports it, users may log in without providing login credentials, but the same server may authorize only limited access for such sessions.<ref name="tcpip" />


[[GridFTP]] defines additional modes, MODE E<ref>{{Cite web|last=Allcock|first=W.|date=April 2003|title=GridFTP: Protocol Extensions to FTP for the Grid|url=https://ogf.org/documents/GFD.20.pdf}}</ref> and MODE X,<ref>{{Cite web|last=Mandrichenko|first=I.|date=May 4, 2005|title=GridFTP v2 Protocol Description|url=https://ogf.org/documents/GFD.47.pdf}}</ref> as extensions of MODE B.
===Anonymous FTP===
A host that provides an FTP service may provide [[Anonymity|anonymous]] FTP access.<ref name="tcpip" /> Users typically log into the service with an 'anonymous' (lower-case and case-sensitive in some FTP servers) account when prompted for user name. Although users are commonly asked to send their [[email]] address instead of a password,<ref name="net+">{{cite book |last=Dean |first=Tamara |title=Network+ Guide to Networks |publisher=Delmar |year=2010 |location= |pages=168–171}}</ref> no verification is actually performed on the supplied data.<ref name="rfc16">RFC 1635 (Informational) How to Use Anonymous FTP. P. & Emtage, A. & Marine, A. (May 1994).</ref> Many FTP hosts whose purpose is to provide software updates will allow anonymous logins.<ref name="net+" />


===Additional commands===
===NAT and firewall traversal===
More recent implementations of FTP support the ''Modify Fact: Modification Time'' (MFMT) command, which allows a client to adjust that [[file attribute]] remotely, enabling the preservation of that attribute when uploading files.<ref>{{cite web |title=MFMT FTP command |url=https://support.solarwinds.com/SuccessCenter/s/article/MFMT-FTP-command |website=support.solarwinds.com |date=2018-10-11}}</ref><ref>{{cite web |title=FTP Commands: DSIZ, MFCT, MFMT, AVBL, PASS, XPWD, XMKD {{!}} Serv-U |url=https://www.serv-u.com/resources/tutorial/dsiz-mfct-mfmt-avbl-pass-xpwd-xmkd-ftp-command |website=www.serv-u.com |language=en}}</ref>
FTP normally transfers data by having the server connect back to the client, after the PORT command is sent by the client. This is problematic for both [[Network address translation|NATs]] and firewalls, which do not allow connections from the Internet towards internal hosts.<ref name="ncftp">{{cite web |last=Gleason |first=Mike |year=2005 |title=The File Transfer Protocol and Your Firewall/NAT |url=http://www.ncftp.com/ncftpd/doc/misc/ftp_and_firewalls.html |publisher=Ncftp.com}}</ref> For NATs, an additional complication is that the representation of the IP addresses and port number in the PORT command refer to the internal host's IP address and port, rather than the public IP address and port of the NAT.


To retrieve a remote file timestamp, there's ''MDTM'' command. Some servers (and clients) support nonstandard syntax of the ''MDTM'' command with two arguments, that works the same way as ''MFMT''<ref>{{cite web |title=MDTM FTP command |url=https://support.solarwinds.com/SuccessCenter/s/article/MDTM-FTP-command |website=support.solarwinds.com |date=2018-10-11}}</ref>
There are two approaches to this problem. One is that the FTP client and FTP server use the PASV command, which causes the data connection to be established from the FTP client to the server.<ref name="ncftp" /> This is widely used by modern FTP clients. Another approach is for the NAT to alter the values of the PORT command, using an [[application-level gateway]] for this purpose.<ref name="ncftp" />


==Login==
===Differences from HTTP===
[[File:1st-ftp-southpole-1994.jpg|thumb|A computer at [[Amundsen–Scott South Pole Station]] logging into an FTP server and transferring a file, in 1994]]
[[Hypertext Transfer Protocol|HTTP]] essentially fixes the bugs in FTP that made it inconvenient to use for many small ephemeral transfers as are typical in web pages.
FTP login uses normal username and password scheme for granting access.<ref name="tcpip" /> The username is sent to the server using the USER command, and the password is sent using the PASS command.<ref name="tcpip" /> This sequence is unencrypted "on the wire", so may be vulnerable to a network [[sniffing attack]].<ref>{{cite web|last1=Prince|first1=Brian|title=Should Organizations Retire FTP for Security?|url=https://www.securityweek.com/should-organizations-retire-ftp-security/|website=Security Week|date=24 January 2012 |access-date=14 September 2017}}</ref> If the information provided by the client is accepted by the server, the server will send a greeting to the client and the session will commence.<ref name="tcpip" /> If the server supports it, users may log in without providing login credentials, but the same server may authorize only limited access for such sessions.<ref name="tcpip" />


===Anonymous FTP===
FTP has a stateful control connection which maintains a current working directory and other flags, and each transfer requires a secondary connection through which the data are transferred. In "passive" mode this secondary connection is from client to server, whereas in the default "active" mode this connection is from server to client. This apparent role reversal when in active mode, and random port numbers for all transfers, is why firewalls and NAT gateways have such a hard time with FTP. HTTP is stateless and multiplexes control and data over a single connection from client to server on well-known port numbers, which trivially passes through NAT gateways and is simple for firewalls to manage.
A host that provides an FTP service may provide [[Anonymity|anonymous]] FTP access.<ref name="tcpip" /> Users typically log into the service with an 'anonymous' (lower-case and case-sensitive in some FTP servers) account when prompted for user name. Although users are commonly asked to send their [[email]] address instead of a password,<ref name="net+">{{cite book |last=Dean |first=Tamara |title=Network+ Guide to Networks |publisher=Delmar |year=2010 |pages=168–171}}</ref> no verification is actually performed on the supplied data.<ref name="rfc16">{{IETF RFC|1635}} (Informational) How to Use Anonymous FTP. P. & Emtage, A. & Marine, A. (May 1994).</ref> Many FTP hosts whose purpose is to provide software updates will allow anonymous logins.<ref name="net+" />


==Software support==
Setting up an FTP control connection is quite slow due to the round-trip delays of sending all of the required commands and awaiting responses, so it is customary to bring up a control connection and hold it open for multiple file transfers rather than drop and re-establish the session afresh each time. In contrast, HTTP originally dropped the connection after each transfer because doing so was so cheap. While HTTP has subsequently gained the ability to reuse the TCP connection for multiple transfers, the conceptual model is still of independent requests rather than a session.
[[File:FileZilla.png|thumb|[[FileZilla]] client running on Windows, one of the best known FTP client software]]


=== File managers ===
When FTP is transferring over the data connection, the control connection is idle. If the transfer takes long enough, the firewall or NAT may decide that the control connection is dead and stop tracking it, effectively breaking the connection and confusing the download. The single HTTP connection is only idle between requests and it is normal and expected for such connections to be dropped after a time-out.
Many file managers tend to have FTP access implemented, such as [[File Explorer]] (formerly Windows Explorer) on [[Microsoft Windows]]. This client is only recommended for small file transfers from a server, due to limitations compared to dedicated client software.<ref>[https://helpdesk.egnyte.com/hc/en-us/articles/201637914-FTP-Access-through-Windows-Explorer FTP Access through Windows Explorer]</ref> It does not support [[SSH File Transfer Protocol|SFTP]].<ref>{{Cite web |title=CSC373/406: SSH [2011/03/27-29] |url=https://fpl.cs.depaul.edu/jriely/373/lectures/class-01-014.html |access-date=2023-10-13 |website=fpl.cs.depaul.edu}}</ref>


Both the native file managers for [[KDE]] on Linux ([[Dolphin (file manager)|Dolphin]] and [[Konqueror]]) support FTP as well as SFTP.<ref>{{Cite web |title=FTP |url=https://docs.kde.org/stable5/en/konqueror/konqueror/ftp.html |access-date=2023-10-13 |website=docs.kde.org}}</ref><ref>{{Cite web |last=Cohen |first=Brent |date=2023-07-26 |title=How To Connect to FTP/SFTP in Dolphin {{!}} DeviceTests |url=https://devicetests.com/connect-ftp-sftp-dolphin |access-date=2023-10-13 |language=en-US}}</ref>
==Web browser support==
[[File:Primitive FTPd screenshot.png|left|thumb|198x198px|Primitive FTPd on Android, actively running an FTP and SFTP server]]
Most common [[web browser]]s can retrieve files hosted on FTP servers, although they may not support protocol extensions such as [[FTPS]].<ref name="net+" /><ref name="matthews">{{cite book |last=Matthews |first=J. |year=2005 |title=Computer Networking: Internet Protocols in Action |edition=1st |location=Danvers, MA |publisher=John Wiley & Sons Inc.}}</ref> When an FTP—rather than an HTTP—[[Uniform Resource Locator|URL]] is supplied, the accessible contents on the remote server are presented in a manner that is similar to that used for other web content. A full-featured FTP client can be run within [[Firefox]] in the form of an extension called [[FireFTP]].
On [[Android (operating system)|Android]], the My Files file manager on [[Samsung Galaxy]] has a built-in FTP and [[SSH File Transfer Protocol|SFTP]] client.<ref>{{Cite web |last=Staff |first=Moyens |date=2022-02-28 |title=Samsung My Files vs Google Files: Which File Manager is Better on Galaxy Phones |url=https://uk.moyens.net/android/samsung-my-files-vs-google-files-which-file-manager-is-better-on-galaxy-phones/ |access-date=2023-10-13 |website=Moyens I/O |language=en-GB}}</ref>


===Syntax===
===Web browser===
For a long time, most common [[web browser]]s were able to retrieve files hosted on FTP servers, although not all of them had support for protocol extensions such as [[FTPS]].<ref name="net+" /><ref name="matthews">{{cite book |last=Matthews |first=J. |year=2005 |title=Computer Networking: Internet Protocols in Action |edition=1st |location=Danvers, MA |publisher=John Wiley & Sons Inc.}}</ref> When an FTP—rather than an HTTP—[[URL]] is supplied, the accessible contents on the remote server are presented in a manner that is similar to that used for other web content.
FTP URL syntax is described in RFC 1738, taking the form: <code>ftp://[user[:password]@]host[:port]/url-path</code> (the bracketed parts are optional).

Google Chrome removed FTP support entirely in Chrome 88, also affecting other [[Chromium]]-based browsers such as [[Microsoft Edge]].<ref>{{cite web|url=https://www.omgubuntu.co.uk/2021/01/linux-release-roundup-chrome-lightworks-more|date=2021-01-26|access-date=2021-01-30|website=omgubuntu.co.uk|title=Linux Release Roundup: GParted, Lightworks, Google Chrome + More|first1=Joey|last1=Sneddon}}</ref> Firefox 88 disabled FTP support by default, with Firefox 90 dropping support entirely.<ref>{{cite web|date=2021-04-19|title=See what's new in Firefox: 88.0 Firefox Release|url=https://www.mozilla.org/en-US/firefox/88.0/releasenotes/|access-date=2021-04-20|website=mozilla.org}}</ref><ref name=":0" />

[[FireFTP]] is a discontinued browser extension that was designed as a full-featured FTP client to be run within [[Firefox]], but when Firefox dropped support for FTP the extension developer recommended using [[Waterfox]].<ref>{{Cite web |title=FireFTP - The Free FTP Client for Waterfox |url=https://fireftp.net/ |url-status=dead |archive-url=https://web.archive.org/web/20220301212656/https://fireftp.net/ |archive-date=2022-03-01 |website=FireFTP.net}}</ref> Some browsers, such as the text-based [[Lynx (web browser)|Lynx]], still support FTP.<ref>{{Cite web |title=URL Schemes Supported in Lynx |url=https://lynx.invisible-island.net/lynx_help/lynx_url_support.html |access-date=2023-07-06 |website=Lynx website}}</ref>

====Syntax====
FTP URL syntax is described in {{IETF RFC|1738}}, taking the form: <code>ftp://[user[:password]@]host[:port]/[url-path]</code> (the bracketed parts are optional).


For example, the URL <nowiki>ftp://public.ftp-servers.example.com/mydirectory/myfile.txt</nowiki> represents the file ''myfile.txt'' from the directory ''mydirectory'' on the server ''public.ftp-servers.example.com'' as an FTP resource. The URL <nowiki>ftp://user001:secretpassword@private.ftp-servers.example.com/mydirectory/myfile.txt</nowiki> adds a specification of the username and password that must be used to access this resource.
For example, the URL <nowiki>ftp://public.ftp-servers.example.com/mydirectory/myfile.txt</nowiki> represents the file ''myfile.txt'' from the directory ''mydirectory'' on the server ''public.ftp-servers.example.com'' as an FTP resource. The URL <nowiki>ftp://user001:secretpassword@private.ftp-servers.example.com/mydirectory/myfile.txt</nowiki> adds a specification of the username and password that must be used to access this resource.


More details on specifying a username and password may be found in the browsers' documentation (e.g., [[Firefox]]<ref>{{cite web |url=http://support.mozilla.com/en-US/kb/Accessing+FTP+servers#FTP_servers_that_require_a_username_and_password |title=Accessing FTP servers &#124; How to &#124; Firefox Help |publisher=Support.mozilla.com |date=2012-09-05 |accessdate=2013-01-16}}</ref> and [[Internet Explorer]]<ref>{{cite web |url=http://support.microsoft.com/kb/135975 |title=How to Enter FTP Site Password in Internet Explorer |publisher=Support.microsoft.com |date=2011-09-23 |accessdate=2015-03-28}} Written for IE versions 6 and earlier. Might work with newer versions.</ref>). By default, most web browsers use passive (PASV) mode, which more easily traverses end-user firewalls.
More details on specifying a username and password may be found in the browsers' documentation (e.g., [[Firefox]]<ref>{{cite web |url=https://support.mozilla.org/en-US/kb/Accessing%20FTP%20servers#w_ftp-servers-that-require-a-username-and-password |title=Accessing FTP servers &#124; How to &#124; Firefox Help |publisher=Support.mozilla.com |date=2012-09-05 |access-date=2013-01-16}}</ref> and [[Internet Explorer]]<ref>{{Cite web |url=https://support.microsoft.com/en-us/kb/135975 |title=How to Enter FTP Site Password in Internet Explorer |access-date=13 February 2020 |archive-date=2 July 2015 |archive-url=https://web.archive.org/web/20150702005840/https://support.microsoft.com/en-us/kb/135975 |url-status=dead }} Written for IE versions 6 and earlier. Might work with newer versions.</ref>). By default, most web browsers use passive (PASV) mode, which more easily traverses end-user firewalls.

Some variation has existed in how different browsers treat path resolution in cases where there is a non-root home directory for a user.<ref>{{cite web |url=https://jkorpela.fi/ftpurl.html |title=FTP URLs |author=Jukka “Yucca” Korpela |publisher="IT and communication" (jkorpela.fi) |date=1997-09-18 |access-date=2020-01-26}}</ref>

===Download manager===
Most common [[download manager]]s can receive files hosted on FTP servers, while some of them also give the interface to retrieve the files hosted on FTP servers. [[DownloadStudio]] allows not only download a file from FTP server but also view the list of files on a FTP server.<ref>{{cite web |url=http://www.conceiva.com/products/downloadstudio/features.asp |title=DownloadStudio - Internet Download Manager And Download Accelerator - Features |author= |publisher=Conceiva |date= |access-date=2021-10-19}}</ref>

===Other===
[[LibreOffice]] declared its FTP support deprecated from 7.4 release, this was later removed in 24.2 release.<ref>{{Cite web |url=https://wiki.documentfoundation.org/ReleaseNotes/7.4 |title=LibreOffice 7.4: Release Notes |publisher=The Document Foundation's Wiki |accessdate=2022-09-10 }}</ref><ref>{{Cite web |url=https://wiki.documentfoundation.org/ReleaseNotes/24.2 |title=ReleaseNotes/24.2 |publisher=The Document Foundation's Wiki |accessdate=2024-03-24 }}</ref>


==Security==
==Security==
FTP was not designed to be a secure protocol, and has many security weaknesses.<ref name="nurdle" /> In May 1999, the authors of RFC 2577 listed a vulnerability to the following problems:
FTP was not designed to be a secure protocol, and has many security weaknesses.<ref name="nurdle">{{cite web |title=Securing FTP using SSH |url=https://nurdletech.com/linux-notes/ftp/ssh.html |publisher=Nurdletech.com}}</ref> In May 1999, the authors of {{IETF RFC|2577}} listed a vulnerability to the following problems:
*[[Brute force attack]]
* [[Brute-force attack]]
*[[FTP bounce attack]]
* [[FTP bounce attack]]
*[[Packet capture]]
* [[Packet capture]]
* Port stealing (guessing the next open port and usurping a legitimate connection)
*Port stealing{{elucidate|date=August 2015}}
*[[Spoofing attack]]
* [[Spoofing attack]]
* Username enumeration
*[[Username]] protection{{elucidate|date=August 2015}}
* [[Denial-of-service attack|DoS or DDoS]]


FTP does not encrypt its traffic; all transmissions are in clear text, and usernames, passwords, commands and data can be read by anyone able to perform packet capture ([[Packet analyzer|sniffing]]) on the network.<ref name="tcpip" /><ref name="nurdle" /> This problem is common to many of the Internet Protocol specifications (such as [[SMTP]], [[Telnet]], POP and IMAP) that were designed prior to the creation of encryption mechanisms such as [[Transport Layer Security|TLS]] or SSL.<ref name="clark" />
FTP does not encrypt its traffic; all transmissions are in clear text, and usernames, passwords, commands and data can be read by anyone able to perform packet capture ([[Packet analyzer|sniffing]]) on the network.<ref name="tcpip" /><ref name="nurdle" /> This problem is common to many of the Internet Protocol specifications (such as [[SMTP]], [[Telnet]], [[Post Office Protocol|POP]] and [[Internet Message Access Protocol|IMAP]]) that were designed prior to the creation of encryption mechanisms such as [[Transport Layer Security|TLS]] or SSL.<ref name="clark" />


Common solutions to this problem include:
Common solutions to this problem include:
Line 83: Line 140:


===FTP over SSH=== <!-- This section is linked from [[OpenSSH]] -->
===FTP over SSH=== <!-- This section is linked from [[OpenSSH]] -->
FTP over SSH is the practice of tunneling a normal FTP session over a Secure Shell connection.<ref name="nurdle">{{cite web |title=Securing FTP using SSH |url=http://www.nurdletech.com/linux-notes/ftp/ssh.html |publisher=Nurdletech.com}}</ref> Because FTP uses multiple [[Transmission Control Protocol|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 protect only that channel; when data is transferred, the FTP software at either end sets up new TCP connections (data channels) and thus have no [[confidentiality]] or [[integrity protection]].
FTP over SSH is the practice of tunneling a normal FTP session over a Secure Shell connection.<ref name="nurdle"/> Because FTP uses multiple [[Transmission Control Protocol|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 protect only that channel; when data is transferred, the FTP software at either end sets up new TCP connections (data channels) and thus have no [[confidentiality]] or [[integrity protection]].


Otherwise, it is necessary for the SSH client software to have specific knowledge of the FTP protocol, to monitor and rewrite FTP control channel messages and autonomously open new [[packet forwarding]]s for FTP data channels. Software packages that support this mode include:
Otherwise, it is necessary for the SSH client software to have specific knowledge of the FTP protocol, to monitor and rewrite FTP control channel messages and autonomously open new [[packet forwarding]]s for FTP data channels. Software packages that support this mode include:
* Tectia ConnectSecure (Win/Linux/Unix)<ref>http://ssh.com/index.php/products/tectia-pci-point-to-point-encryption.html</ref> of [[SSH Communications Security]]'s software suite
* Tectia ConnectSecure (Win/Linux/Unix)<ref>{{cite web|url=https://www.ssh.com/manuals/mft-events-product/63/ssh-solutions-your-business-components.html|title=Components of the Information Assurance Platform (section Tectia ConnectSecure)|website=ssh.com|archive-url=https://web.archive.org/web/20200731160323/https://www.ssh.com/manuals/mft-events-product/63/ssh-solutions-your-business-components.html|archive-date=2020-07-31}}</ref> of [[SSH Communications Security]]'s software suite

FTP over SSH should not be confused with [[SSH File Transfer Protocol]] (SFTP).


==Derivatives==
==Derivatives==
Line 92: Line 151:
===FTPS===
===FTPS===
{{Main article|FTPS}}
{{Main article|FTPS}}
Explicit FTPS is an extension to the FTP standard that allows clients to request FTP sessions to be encrypted. This is done by sending the "AUTH TLS" command. The server has the option of allowing or denying connections that do not request TLS. This protocol extension is defined in RFC 4217. Implicit FTPS is an outdated standard for FTP that required the use of a SSL or TLS connection. It was specified to use different ports than plain FTP.
Explicit FTPS is an extension to the FTP standard that allows clients to request FTP sessions to be encrypted. This is done by sending the "AUTH TLS" command. The server has the option of allowing or denying connections that do not request TLS. This protocol extension is defined in {{IETF RFC|4217}}. Implicit FTPS is an outdated standard for FTP that required the use of a SSL or TLS connection. It was specified to use different ports than plain FTP.


===SSH File Transfer Protocol===
===SSH File Transfer Protocol===
{{Main article|SSH File Transfer Protocol}}
{{Main article|SSH File Transfer Protocol}}
The SSH file transfer protocol (chronologically the second of the two protocols abbreviated SFTP) transfers files and has a similar command set for users, but uses the [[Secure Shell]] protocol (SSH) to transfer files. Unlike FTP, it encrypts both commands and data, preventing passwords and sensitive information from being transmitted openly over the network. It cannot interoperate with FTP software.
The SSH file transfer protocol (chronologically the second of the two protocols abbreviated SFTP) transfers files and has a similar command set for users, but uses the [[Secure Shell]] protocol (SSH) to transfer files. Unlike FTP, it encrypts both commands and data, preventing passwords and sensitive information from being transmitted openly over the network. It cannot interoperate with FTP software, though some FTP client software offers support for the SSH file transfer protocol as well.


===Trivial File Transfer Protocol===
===Trivial File Transfer Protocol ===
{{Main article|Trivial File Transfer Protocol}}
{{Main article|Trivial File Transfer Protocol}}
Trivial File Transfer Protocol (TFTP) is a simple, lock-step FTP that allows a client to get from or put a file onto a remote host. One of its primary uses is in the early stages of [[Network booting|booting from a local area network]], because TFTP is very simple to implement. TFTP lacks security and most of the advanced features offered by more robust file transfer protocols such as File Transfer Protocol. TFTP was first standardized in 1981 and the current specification for the protocol can be found in RFC 1350.
Trivial File Transfer Protocol (TFTP) is a simple, lock-step FTP that allows a client to get a file from or put a file onto a remote host. One of its primary uses is in the early stages of [[Network booting|booting from a local area network]], because TFTP is very simple to implement. TFTP lacks security and most of the advanced features offered by more robust file transfer protocols such as File Transfer Protocol. TFTP was first standardized in 1981 and the current specification for the protocol can be found in {{IETF RFC|1350}}.


===Simple File Transfer Protocol===
===Simple File Transfer Protocol===
<!--Simple File Transfer Protocol redirects here-->
<!--Simple File Transfer Protocol redirects here-->
Simple File Transfer Protocol (the first protocol abbreviated SFTP), as defined by RFC 913, was proposed as an (unsecured) file transfer protocol with a level of complexity intermediate between TFTP and FTP. It was never widely accepted on the [[Internet]], and is now assigned Historic status by the [[Internet Engineering Task Force|IETF]]. It runs through port 115, and often receives the initialism of ''SFTP''. It has a command set of 11 commands and support three types of data transmission: [[ASCII]], [[Binary file|binary]] and continuous. For systems with a [[word size]] that is a multiple of 8 bits, the implementation of binary and continuous is the same. The protocol also supports login with user ID and password, hierarchical folders and file management (including ''rename'', ''delete'', ''upload'', ''download'', ''download with overwrite'', and ''download with append'').
Simple File Transfer Protocol (the first protocol abbreviated SFTP), as defined by {{IETF RFC|913}}, was proposed as an (unsecured) file transfer protocol with a level of complexity intermediate between TFTP and FTP. It was never widely accepted on the [[Internet]], and is now assigned Historic status by the [[Internet Engineering Task Force|IETF]]. It runs through port 115, and often receives the initialism of ''SFTP''. It has a command set of 11 commands and support three types of data transmission: [[ASCII]], [[Binary file|binary]] and continuous. For systems with a [[word size]] that is a multiple of 8 bits, the implementation of binary and continuous is the same. The protocol also supports login with user ID and password, hierarchical folders and file management (including ''rename'', ''delete'', ''upload'', ''download'', ''download with overwrite'', and ''download with append'').


==FTP commands==
==FTP commands==
{{main article|List of FTP commands}}
{{Main article|List of FTP commands}}


==FTP reply codes==
==FTP reply codes==
{{main article|List of FTP server return codes}}
{{main article|List of FTP server return codes}}
Below is a summary of [[List of FTP server return codes|FTP reply codes]] that may be returned by an FTP [[Server (computing)|server]]. These codes have been standardized in RFC 959 by the IETF. The reply code is a three-digit value. The first digit is used to indicate one of three possible outcomes&nbsp;— success, failure, or to indicate an error or incomplete reply:
Below is a summary of [[List of FTP server return codes|FTP reply codes]] that may be returned by an FTP [[Server (computing)|server]]. These codes have been standardized in {{IETF RFC|959}} by the IETF. The reply code is a three-digit value. The first digit is used to indicate one of three possible outcomes&nbsp;— success, failure, or to indicate an error or incomplete reply:
* 2yz&nbsp;&ndash; Success reply
* 2yz&nbsp;&ndash; Success reply
* 4yz or 5yz &ndash; Failure reply
* 4yz or 5yz &ndash; Failure reply
Line 127: Line 186:


==See also==
==See also==
{{columns-list|colwidth=20em|
* [[Comparison of FTP client software]]
* [[Comparison of FTP client software]]
* [[Comparison of FTP server software]]
* [[Comparison of FTP server software packages]]
* [[Comparison of file transfer protocols]]
* [[Curl-loader]] – FTP/S loading/testing open-source software
* [[Curl-loader]] – FTP/S loading/testing open-source software
* [[DTXT]]
* [[File eXchange Protocol]] (FXP)
* [[File eXchange Protocol]] (FXP)
* [[File Service Protocol]] (FSP)
* [[File Service Protocol]] (FSP)
* [[FTAM]]
* [[FTAM]]
* [[FTPFS]]
* [[FTPFS]]
* [[List of file transfer protocols]]
* [[List of FTP commands]]
* [[List of FTP commands]]
* [[List of FTP server return codes]]
* [[List of FTP server return codes]]
Line 141: Line 202:
* [[Shared file access]]
* [[Shared file access]]
* [[TCP Wrapper]]
* [[TCP Wrapper]]
}}


==References==
==References==
{{reflist|2}}
{{Reflist}}


==Further reading==
==Further reading==
* RFC 697 – CWD Command of FTP. July 1975.
* {{IETF RFC|697}} – CWD Command of FTP. July 1975.
* RFC 959 – (Standard) File Transfer Protocol (FTP). J. Postel, J. Reynolds. October 1985.
* {{IETF RFC|959}} – (Standard) File Transfer Protocol (FTP). J. Postel, J. Reynolds. October 1985.
* RFC 1579 – (Informational) Firewall-Friendly FTP. February 1994.
* {{IETF RFC|1579}} – (Informational) Firewall-Friendly FTP. February 1994.
* RFC 1635 – (Informational) How to Use Anonymous FTP. May 1994.
* {{IETF RFC|1635}} – (Informational) How to Use Anonymous FTP. May 1994.
* RFC 1639 – FTP Operation Over Big Address Records (FOOBAR). June 1994.
* {{IETF RFC|1639}} – FTP Operation Over Big Address Records (FOOBAR). June 1994.
* RFC 1738 – Uniform Resource Locators (URL). December 1994.
* {{IETF RFC|1738}} – Uniform Resource Locators (URL). December 1994.
* RFC 2228 – (Proposed Standard) FTP Security Extensions. October 1997.
* {{IETF RFC|2228}} – (Proposed Standard) FTP Security Extensions. October 1997.
* RFC 2389 – (Proposed Standard) Feature negotiation mechanism for the File Transfer Protocol. August 1998.
* {{IETF RFC|2389}} – (Proposed Standard) Feature negotiation mechanism for the File Transfer Protocol. August 1998.
* RFC 2428 – (Proposed Standard) Extensions for IPv6, NAT, and Extended passive mode. September 1998.
* {{IETF RFC|2428}} – (Proposed Standard) Extensions for IPv6, NAT, and Extended passive mode. September 1998.
* RFC 2577 – (Informational) FTP Security Considerations. May 1999.
* {{IETF RFC|2577}} – (Informational) FTP Security Considerations. May 1999.
* RFC 2640 – (Proposed Standard) Internationalization of the File Transfer Protocol. July 1999.
* {{IETF RFC|2640}} – (Proposed Standard) Internationalization of the File Transfer Protocol. July 1999.
* RFC 3659 – (Proposed Standard) Extensions to FTP. P. Hethmon. March 2007.
* {{IETF RFC|3659}} – (Proposed Standard) Extensions to FTP. P. Hethmon. March 2007.
* RFC 5797 – (Proposed Standard) FTP Command and Extension Registry. March 2010.
* {{IETF RFC|5797}} – (Proposed Standard) FTP Command and Extension Registry. March 2010.
* RFC 7151 - (Proposed Standard) File Transfer Protocol HOST Command for Virtual Hosts. March 2014.
* {{IETF RFC|7151}} – (Proposed Standard) File Transfer Protocol HOST Command for Virtual Hosts. March 2014.
*[http://www.iana.org/assignments/ftp-commands-extensions/ftp-commands-extensions.xhtml IANA FTP Commands and Extensions registry] &ndash; The official registry of FTP Commands and Extensions
* [https://www.iana.org/assignments/ftp-commands-extensions/ftp-commands-extensions.xhtml IANA FTP Commands and Extensions registry] &ndash; The official registry of FTP Commands and Extensions

== External links ==
* {{Wikibooks-inline|Communication Networks/File Transfer Protocol}}
* [//servertest.online/ftp FTP Server Online Tester] Authentication, encryption, mode and connectivity.
* Anonymous FTP Servers by Country Code [[Top-level domain|TLD]] (2012): {{Cite web|url=https://www.jumpjet.info/Offbeat-Internet/Public/FTP/url.htm|title=Offbeat Internet - Public Access - FTP|website=www.jumpjet.info|access-date=2020-01-16|date=2012|archive-url=https://web.archive.org/web/20230328113445/https://www.jumpjet.info/Offbeat-Internet/Public/FTP/url.htm|archive-date=2023-03-28|url-status=dead}}


{{Wikibooks|Communication Networks/File Transfer Protocol}}
{{URI scheme}}
{{URI scheme}}
{{Authority control}}
{{Use dmy dates|date=August 2016}}


[[Category:File Transfer Protocol| ]]
[[Category:File Transfer Protocol| ]]
[[Category:Application layer protocols]]
[[Category:Clear text protocols]]
[[Category:Clear text protocols]]
[[Category:Network file transfer protocols]]
[[Category:Computer-related introductions in 1971]]
[[Category:History of the Internet]]
[[Category:History of the Internet]]
[[Category:Application layer protocols]]
[[Category:Internet Standards]]
[[Category:Internet Standards]]
[[Category:Network file transfer protocols]]
[[Category:OS/2 commands]]
[[Category:Unix network-related software]]
[[Category:Unix network-related software]]
[[Category:1980 introductions]]
[[Category:File sharing]]

Latest revision as of 20:33, 11 December 2024

"FTP" redirects here. For other uses, see FTP (disambiguation).

File Transfer Protocol
Communication protocol
PurposeFile transfer
Developer(s)Abhay Bhushan for RFC 114
IntroductionApril 16, 1971; 53 years ago (1971-04-16)
OSI layerApplication layer
Port(s)21 for control, 20 for data transfer
RFC(s)RFC 959
Internet protocol suite
Application layer
Transport layer
Internet layer
Link layer
Internet history timeline

Early research and development:

Merging the networks and creating the Internet:

Commercialization, privatization, broader access leads to the modern Internet:

Examples of Internet services:

The File Transfer Protocol (FTP) is a standard communication protocol used for the transfer of computer files from a server to a client on a computer network. FTP is built on a client–server model architecture using separate control and data connections between the client and the server.[1] FTP users may authenticate themselves with a plain-text sign-in protocol, normally in the form of a username and password, but can connect anonymously if the server is configured to allow it. For secure transmission that protects the username and password, and encrypts the content, FTP is often secured with SSL/TLS (FTPS) or replaced with SSH File Transfer Protocol (SFTP).

The first FTP client applications were command-line programs developed before operating systems had graphical user interfaces, and are still shipped with most Windows, Unix, and Linux operating systems.[2][3] Many dedicated FTP clients and automation utilities have since been developed for desktops, servers, mobile devices, and hardware, and FTP has been incorporated into productivity applications such as HTML editors and file managers.

An FTP client used to be commonly integrated in web browsers, where file servers are browsed with the URI prefix "ftp://". In 2021, FTP support was dropped by Google Chrome and Firefox,[4][5] two major web browser vendors, due to it being superseded by the more secure SFTP and FTPS; although neither of them have implemented the newer protocols.[6][7]

History of FTP servers

[edit]

The original specification for the File Transfer Protocol was written by Abhay Bhushan and published as RFC 114 on 16 April 1971. Until 1980, FTP ran on NCP, the predecessor of TCP/IP.[2] The protocol was later replaced by a TCP/IP version, RFC 765 (June 1980) and RFC 959 (October 1985), the current specification. Several proposed standards amend RFC 959, for example RFC 1579 (February 1994) enables Firewall-Friendly FTP (passive mode), RFC 2228 (June 1997) proposes security extensions, RFC 2428 (September 1998) adds support for IPv6 and defines a new type of passive mode.[8]

Protocol overview

[edit]

Communication and data transfer

[edit]
Illustration of starting a passive connection using port 21

FTP may run in active or passive mode, which determines how the data connection is established.[9] (This sense of "mode" is different from that of the MODE command in the FTP protocol.)

  • In active mode, the client starts listening for incoming data connections from the server on port M. It sends the FTP command PORT[10] M to inform the server on which port it is listening. The server then initiates a data channel to the client from its port 20, the FTP server data port.
  • In situations where the client is behind a firewall and unable to accept incoming TCP connections, passive mode may be used. In this mode, the client uses the control connection to send a PASV command to the server and then receives a server IP address and server port number from the server,[9] which the client then uses to open a data connection from an arbitrary client port to the server IP address and server port number received.[11]

Both modes were updated in September 1998 to support IPv6. Further changes were introduced to the passive mode at that time, updating it to extended passive mode.[12]

The server responds over the control connection with three-digit status codes in ASCII with an optional text message. For example, "200" (or "200 OK") means that the last command was successful. The numbers represent the code for the response and the optional text represents a human-readable explanation or request (e.g. <Need account for storing file>).[1] An ongoing transfer of file data over the data connection can be aborted using an interrupt message sent over the control connection.

FTP needs two ports (one for sending and one for receiving) because it was originally designed to operate on top of Network Control Protocol (NCP), which was a simplex protocol that utilized two port addresses, establishing two connections, for two-way communications. An odd and an even port were reserved for each application layer application or protocol. The standardization of TCP and UDP reduced the need for the use of two simplex ports for each application down to one duplex port,[13]: 15  but the FTP protocol was never altered to only use one port, and continued using two for backwards compatibility.

NAT and firewall traversal

[edit]

FTP normally transfers data by having the server connect back to the client, after the PORT command is sent by the client. This is problematic for both NATs and firewalls, which do not allow connections from the Internet towards internal hosts.[14] For NATs, an additional complication is that the representation of the IP addresses and port number in the PORT command refer to the internal host's IP address and port, rather than the public IP address and port of the NAT.

There are two approaches to solve this problem. One is that the FTP client and FTP server use the PASV command, which causes the data connection to be established from the FTP client to the server.[14] This is widely used by modern FTP clients. Another approach is for the NAT to alter the values of the PORT command, using an application-level gateway for this purpose.[14]

A model chart of how FTP works

Data types

[edit]

While transferring data over the network, five data types are defined:[2][3][8]

  • ASCII (TYPE A): Used for text. Data is converted, if needed, from the sending host's character representation to "8-bit ASCII" before transmission, and (again, if necessary) to the receiving host's character representation, including newlines. As a consequence, this mode is inappropriate for files that contain data other than ASCII.
  • Image (TYPE I, commonly called Binary mode): The sending machine sends each file byte by byte, and the recipient stores the bytestream as it receives it. (Image mode support has been recommended for all implementations of FTP).
  • EBCDIC (TYPE E): Used for plain text between hosts using the EBCDIC character set.
  • Local (TYPE L n): Designed to support file transfer between machines which do not use 8-bit bytes, e.g. 36-bit systems such as DEC PDP-10s. For example, "TYPE L 9" would be used to transfer data in 9-bit bytes, or "TYPE L 36" to transfer 36-bit words. Most contemporary FTP clients/servers only support L 8, which is equivalent to I.
  • Unicode text files using UTF-8 (TYPE U): defined in an expired Internet Draft[15] which never became an RFC, though it has been implemented by several FTP clients/servers.

Note these data types are commonly called "modes", although ambiguously that word is also used to refer to active-vs-passive communication mode (see above), and the modes set by the FTP protocol MODE command (see below).

For text files (TYPE A and TYPE E), three different format control options are provided, to control how the file would be printed:

  • Non-print (TYPE A N and TYPE E N) – the file does not contain any carriage control characters intended for a printer
  • Telnet (TYPE A T and TYPE E T) – the file contains Telnet (or in other words, ASCII C0) carriage control characters (CR, LF, etc)
  • ASA (TYPE A A and TYPE E A) – the file contains ASA carriage control characters

These formats were mainly relevant to line printers; most contemporary FTP clients/servers only support the default format control of N.

File structures

[edit]

File organization is specified using the STRU command. The following file structures are defined in section 3.1.1 of RFC959:

  • F or FILE structure (stream-oriented). Files are viewed as an arbitrary sequence of bytes, characters or words. This is the usual file structure on Unix systems and other systems such as CP/M, MS-DOS and Microsoft Windows. (Section 3.1.1.1)
  • R or RECORD structure (record-oriented). Files are viewed as divided into records, which may be fixed or variable length. This file organization is common on mainframe and midrange systems, such as MVS, VM/CMS, OS/400 and VMS, which support record-oriented filesystems.
  • P or PAGE structure (page-oriented). Files are divided into pages, which may either contain data or metadata; each page may also have a header giving various attributes. This file structure was specifically designed for TENEX systems, and is generally not supported on other platforms. RFC1123 section 4.1.2.3 recommends that this structure not be implemented.

Most contemporary FTP clients and servers only support STRU F. STRU R is still in use in mainframe and minicomputer file transfer applications.

Data transfer modes

[edit]

Data transfer can be done in any of three modes:[1][2]

  • Stream mode (MODE S): Data is sent as a continuous stream, relieving FTP from doing any processing. Rather, all processing is left up to TCP. No End-of-file indicator is needed, unless the data is divided into records.
  • Block mode (MODE B): Designed primarily for transferring record-oriented files (STRU R), although can also be used to transfer stream-oriented (STRU F) text files. FTP puts each record (or line) of data into several blocks (block header, byte count, and data field) and then passes it on to TCP.[8]
  • Compressed mode (MODE C): Extends MODE B with data compression using run-length encoding.

Most contemporary FTP clients and servers do not implement MODE B or MODE C; FTP clients and servers for mainframe and minicomputer operating systems are the exception to that.

Some FTP software also implements a DEFLATE-based compressed mode, sometimes called "Mode Z" after the command that enables it. This mode was described in an Internet Draft, but not standardized.[16]

GridFTP defines additional modes, MODE E[17] and MODE X,[18] as extensions of MODE B.

Additional commands

[edit]

More recent implementations of FTP support the Modify Fact: Modification Time (MFMT) command, which allows a client to adjust that file attribute remotely, enabling the preservation of that attribute when uploading files.[19][20]

To retrieve a remote file timestamp, there's MDTM command. Some servers (and clients) support nonstandard syntax of the MDTM command with two arguments, that works the same way as MFMT[21]

Login

[edit]
A computer at Amundsen–Scott South Pole Station logging into an FTP server and transferring a file, in 1994

FTP login uses normal username and password scheme for granting access.[2] The username is sent to the server using the USER command, and the password is sent using the PASS command.[2] This sequence is unencrypted "on the wire", so may be vulnerable to a network sniffing attack.[22] If the information provided by the client is accepted by the server, the server will send a greeting to the client and the session will commence.[2] If the server supports it, users may log in without providing login credentials, but the same server may authorize only limited access for such sessions.[2]

Anonymous FTP

[edit]

A host that provides an FTP service may provide anonymous FTP access.[2] Users typically log into the service with an 'anonymous' (lower-case and case-sensitive in some FTP servers) account when prompted for user name. Although users are commonly asked to send their email address instead of a password,[3] no verification is actually performed on the supplied data.[23] Many FTP hosts whose purpose is to provide software updates will allow anonymous logins.[3]

Software support

[edit]
FileZilla client running on Windows, one of the best known FTP client software

File managers

[edit]

Many file managers tend to have FTP access implemented, such as File Explorer (formerly Windows Explorer) on Microsoft Windows. This client is only recommended for small file transfers from a server, due to limitations compared to dedicated client software.[24] It does not support SFTP.[25]

Both the native file managers for KDE on Linux (Dolphin and Konqueror) support FTP as well as SFTP.[26][27]

Primitive FTPd on Android, actively running an FTP and SFTP server

On Android, the My Files file manager on Samsung Galaxy has a built-in FTP and SFTP client.[28]

Web browser

[edit]

For a long time, most common web browsers were able to retrieve files hosted on FTP servers, although not all of them had support for protocol extensions such as FTPS.[3][29] When an FTP—rather than an HTTP—URL is supplied, the accessible contents on the remote server are presented in a manner that is similar to that used for other web content.

Google Chrome removed FTP support entirely in Chrome 88, also affecting other Chromium-based browsers such as Microsoft Edge.[30] Firefox 88 disabled FTP support by default, with Firefox 90 dropping support entirely.[31][4]

FireFTP is a discontinued browser extension that was designed as a full-featured FTP client to be run within Firefox, but when Firefox dropped support for FTP the extension developer recommended using Waterfox.[32] Some browsers, such as the text-based Lynx, still support FTP.[33]

Syntax

[edit]

FTP URL syntax is described in RFC 1738, taking the form: ftp://[user[:password]@]host[:port]/[url-path] (the bracketed parts are optional).

For example, the URL ftp://public.ftp-servers.example.com/mydirectory/myfile.txt represents the file myfile.txt from the directory mydirectory on the server public.ftp-servers.example.com as an FTP resource. The URL ftp://user001:secretpassword@private.ftp-servers.example.com/mydirectory/myfile.txt adds a specification of the username and password that must be used to access this resource.

More details on specifying a username and password may be found in the browsers' documentation (e.g., Firefox[34] and Internet Explorer[35]). By default, most web browsers use passive (PASV) mode, which more easily traverses end-user firewalls.

Some variation has existed in how different browsers treat path resolution in cases where there is a non-root home directory for a user.[36]

Download manager

[edit]

Most common download managers can receive files hosted on FTP servers, while some of them also give the interface to retrieve the files hosted on FTP servers. DownloadStudio allows not only download a file from FTP server but also view the list of files on a FTP server.[37]

Other

[edit]

LibreOffice declared its FTP support deprecated from 7.4 release, this was later removed in 24.2 release.[38][39]

Security

[edit]

FTP was not designed to be a secure protocol, and has many security weaknesses.[40] In May 1999, the authors of RFC 2577 listed a vulnerability to the following problems:

FTP does not encrypt its traffic; all transmissions are in clear text, and usernames, passwords, commands and data can be read by anyone able to perform packet capture (sniffing) on the network.[2][40] This problem is common to many of the Internet Protocol specifications (such as SMTP, Telnet, POP and IMAP) that were designed prior to the creation of encryption mechanisms such as TLS or SSL.[8]

Common solutions to this problem include:

  1. Using the secure versions of the insecure protocols, e.g., FTPS instead of FTP and TelnetS instead of Telnet.
  2. Using a different, more secure protocol that can handle the job, e.g. SSH File Transfer Protocol or Secure Copy Protocol.
  3. Using a secure tunnel such as Secure Shell (SSH) or virtual private network (VPN).

FTP over SSH

[edit]

FTP over SSH is the practice of tunneling a normal FTP session over a Secure Shell connection.[40] 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 protect only that channel; when data is transferred, the FTP software at either end sets up new TCP connections (data channels) and thus have no confidentiality or integrity protection.

Otherwise, it is necessary for the SSH client software to have specific knowledge of the FTP protocol, to monitor and rewrite FTP control channel messages and autonomously open new packet forwardings for FTP data channels. Software packages that support this mode include:

FTP over SSH should not be confused with SSH File Transfer Protocol (SFTP).

Derivatives

[edit]

FTPS

[edit]
Main article: FTPS

Explicit FTPS is an extension to the FTP standard that allows clients to request FTP sessions to be encrypted. This is done by sending the "AUTH TLS" command. The server has the option of allowing or denying connections that do not request TLS. This protocol extension is defined in RFC 4217. Implicit FTPS is an outdated standard for FTP that required the use of a SSL or TLS connection. It was specified to use different ports than plain FTP.

SSH File Transfer Protocol

[edit]
Main article: SSH File Transfer Protocol

The SSH file transfer protocol (chronologically the second of the two protocols abbreviated SFTP) transfers files and has a similar command set for users, but uses the Secure Shell protocol (SSH) to transfer files. Unlike FTP, it encrypts both commands and data, preventing passwords and sensitive information from being transmitted openly over the network. It cannot interoperate with FTP software, though some FTP client software offers support for the SSH file transfer protocol as well.

Trivial File Transfer Protocol

[edit]
Main article: Trivial File Transfer Protocol

Trivial File Transfer Protocol (TFTP) is a simple, lock-step FTP that allows a client to get a file from or put a file onto a remote host. One of its primary uses is in the early stages of booting from a local area network, because TFTP is very simple to implement. TFTP lacks security and most of the advanced features offered by more robust file transfer protocols such as File Transfer Protocol. TFTP was first standardized in 1981 and the current specification for the protocol can be found in RFC 1350.

Simple File Transfer Protocol

[edit]

Simple File Transfer Protocol (the first protocol abbreviated SFTP), as defined by RFC 913, was proposed as an (unsecured) file transfer protocol with a level of complexity intermediate between TFTP and FTP. It was never widely accepted on the Internet, and is now assigned Historic status by the IETF. It runs through port 115, and often receives the initialism of SFTP. It has a command set of 11 commands and support three types of data transmission: ASCII, binary and continuous. For systems with a word size that is a multiple of 8 bits, the implementation of binary and continuous is the same. The protocol also supports login with user ID and password, hierarchical folders and file management (including rename, delete, upload, download, download with overwrite, and download with append).

FTP commands

[edit]
Main article: List of FTP commands

FTP reply codes

[edit]
Main article: List of FTP server return codes

Below is a summary of FTP reply codes that may be returned by an FTP server. These codes have been standardized in RFC 959 by the IETF. The reply code is a three-digit value. The first digit is used to indicate one of three possible outcomes — success, failure, or to indicate an error or incomplete reply:

  • 2yz – Success reply
  • 4yz or 5yz – Failure reply
  • 1yz or 3yz – Error or Incomplete reply

The second digit defines the kind of error:

  • x0z – Syntax. These replies refer to syntax errors.
  • x1z – Information. Replies to requests for information.
  • x2z – Connections. Replies referring to the control and data connections.
  • x3z – Authentication and accounting. Replies for the login process and accounting procedures.
  • x4z – Not defined.
  • x5z – File system. These replies relay status codes from the server file system.

The third digit of the reply code is used to provide additional detail for each of the categories defined by the second digit.

See also

[edit]

References

[edit]
  1. ^ a b c Forouzan, B.A. (2000). TCP/IP: Protocol Suite (1st ed.). New Delhi, India: Tata McGraw-Hill Publishing Company Limited.
  2. ^ a b c d e f g h i j Kozierok, Charles M. (2005). "The TCP/IP Guide v3.0". Tcpipguide.com.
  3. ^ a b c d e Dean, Tamara (2010). Network+ Guide to Networks. Delmar. pp. 168–171.
  4. ^ a b Vonau, Manuel (7 July 2021). "Firefox follows in Chrome's footsteps and drops FTP support (APK Download)". Android Police. Retrieved 12 July 2021.
  5. ^ "Remove FTP support - Chrome Platform Status". www.chromestatus.com. Retrieved 2 September 2021.
  6. ^ by, Written (23 March 2020). "Firefox is dropping FTP support". Sophos News. Retrieved 13 October 2023.
  7. ^ Edwards, Benj (14 July 2022). "Chrome and Firefox Killed FTP Support: Here's an Easy Alternative". How-To Geek. Retrieved 13 October 2023.
  8. ^ a b c d Clark, M.P. (2003). Data Networks IP and the Internet (1st ed.). West Sussex, England: John Wiley & Sons Ltd.
  9. ^ a b "Active FTP vs. Passive FTP, a Definitive Explanation". Slacksite.com.
  10. ^ Weis, Olga (18 October 2022). "FTP Port: Full Guide about FTP and Port Numbers". Comprehensive Mac software apps. Retrieved 29 March 2024.
  11. ^ RFC 959 (Standard) File Transfer Protocol (FTP). Postel, J. & Reynolds, J. (October 1985).
  12. ^ RFC 2428 (Proposed Standard) Extensions for IPv6, NAT, and Extended Passive Mode. Allman, M. & Metz, C. & Ostermann, S. (September 1998).
  13. ^ Stevens, W. Richard (1994). TCP/IP Illustrated Volume I. Vol. 1. Reading, Massachusetts, USA: Addison-Wesley Publishing Company. ISBN 0-201-63346-9.
  14. ^ a b c Gleason, Mike (2005). "The File Transfer Protocol and Your Firewall/NAT". Ncftp.com.
  15. ^ Klensin, John. FTP TYPE Extension for Internationalized Text. I-D draft-klensin-ftpext-typeu-00. Retrieved 9 June 2020.
  16. ^ Preston, J. (January 2005). Deflate transmission mode for FTP. IETF. I-D draft-preston-ftpext-deflate-03. Retrieved 27 January 2016.
  17. ^ Allcock, W. (April 2003). "GridFTP: Protocol Extensions to FTP for the Grid" (PDF).
  18. ^ Mandrichenko, I. (4 May 2005). "GridFTP v2 Protocol Description" (PDF).
  19. ^ "MFMT FTP command". support.solarwinds.com. 11 October 2018.
  20. ^ "FTP Commands: DSIZ, MFCT, MFMT, AVBL, PASS, XPWD, XMKD | Serv-U". www.serv-u.com.
  21. ^ "MDTM FTP command". support.solarwinds.com. 11 October 2018.
  22. ^ Prince, Brian (24 January 2012). "Should Organizations Retire FTP for Security?". Security Week. Retrieved 14 September 2017.
  23. ^ RFC 1635 (Informational) How to Use Anonymous FTP. P. & Emtage, A. & Marine, A. (May 1994).
  24. ^ FTP Access through Windows Explorer
  25. ^ "CSC373/406: SSH [2011/03/27-29]". fpl.cs.depaul.edu. Retrieved 13 October 2023.
  26. ^ "FTP". docs.kde.org. Retrieved 13 October 2023.
  27. ^ Cohen, Brent (26 July 2023). "How To Connect to FTP/SFTP in Dolphin | DeviceTests". Retrieved 13 October 2023.
  28. ^ Staff, Moyens (28 February 2022). "Samsung My Files vs Google Files: Which File Manager is Better on Galaxy Phones". Moyens I/O. Retrieved 13 October 2023.
  29. ^ Matthews, J. (2005). Computer Networking: Internet Protocols in Action (1st ed.). Danvers, MA: John Wiley & Sons Inc.
  30. ^ Sneddon, Joey (26 January 2021). "Linux Release Roundup: GParted, Lightworks, Google Chrome + More". omgubuntu.co.uk. Retrieved 30 January 2021.
  31. ^ "See what's new in Firefox: 88.0 Firefox Release". mozilla.org. 19 April 2021. Retrieved 20 April 2021.
  32. ^ "FireFTP - The Free FTP Client for Waterfox". FireFTP.net. Archived from the original on 1 March 2022.
  33. ^ "URL Schemes Supported in Lynx". Lynx website. Retrieved 6 July 2023.
  34. ^ "Accessing FTP servers | How to | Firefox Help". Support.mozilla.com. 5 September 2012. Retrieved 16 January 2013.
  35. ^ "How to Enter FTP Site Password in Internet Explorer". Archived from the original on 2 July 2015. Retrieved 13 February 2020. Written for IE versions 6 and earlier. Might work with newer versions.
  36. ^ Jukka “Yucca” Korpela (18 September 1997). "FTP URLs". "IT and communication" (jkorpela.fi). Retrieved 26 January 2020.
  37. ^ "DownloadStudio - Internet Download Manager And Download Accelerator - Features". Conceiva. Retrieved 19 October 2021.
  38. ^ "LibreOffice 7.4: Release Notes". The Document Foundation's Wiki. Retrieved 10 September 2022.
  39. ^ "ReleaseNotes/24.2". The Document Foundation's Wiki. Retrieved 24 March 2024.
  40. ^ a b c "Securing FTP using SSH". Nurdletech.com.
  41. ^ "Components of the Information Assurance Platform (section Tectia ConnectSecure)". ssh.com. Archived from the original on 31 July 2020.

Further reading

[edit]
  • RFC 697 – CWD Command of FTP. July 1975.
  • RFC 959 – (Standard) File Transfer Protocol (FTP). J. Postel, J. Reynolds. October 1985.
  • RFC 1579 – (Informational) Firewall-Friendly FTP. February 1994.
  • RFC 1635 – (Informational) How to Use Anonymous FTP. May 1994.
  • RFC 1639 – FTP Operation Over Big Address Records (FOOBAR). June 1994.
  • RFC 1738 – Uniform Resource Locators (URL). December 1994.
  • RFC 2228 – (Proposed Standard) FTP Security Extensions. October 1997.
  • RFC 2389 – (Proposed Standard) Feature negotiation mechanism for the File Transfer Protocol. August 1998.
  • RFC 2428 – (Proposed Standard) Extensions for IPv6, NAT, and Extended passive mode. September 1998.
  • RFC 2577 – (Informational) FTP Security Considerations. May 1999.
  • RFC 2640 – (Proposed Standard) Internationalization of the File Transfer Protocol. July 1999.
  • RFC 3659 – (Proposed Standard) Extensions to FTP. P. Hethmon. March 2007.
  • RFC 5797 – (Proposed Standard) FTP Command and Extension Registry. March 2010.
  • RFC 7151 – (Proposed Standard) File Transfer Protocol HOST Command for Virtual Hosts. March 2014.
  • IANA FTP Commands and Extensions registry – The official registry of FTP Commands and Extensions
[edit]
Retrieved from "https://en.wikipedia.org/enwiki/w/index.php?title=File_Transfer_Protocol&oldid=1262512537"