RFC 5797
FTP Command and Extension Registry
RFC 5797: FTP Command and Extension Registry 🎀
Okay bestie, this one is by J. Klensin and A. Hoenes (TR-Sys) 🦋. It's a Standards Track document from March 2010, with ISSN 2070-1721, and it updates RFC 959. The header doesn't list anything it obsoletes. It's literally a Request for Comments, so the whole vibe is "here's a proposal, please review it" 💅.
Abstract 🦋
Okay so every version of the FTP spec has added a few new commands 💖, and the early ones are summarized in RFC 959. RFC 2389 came in clutch with a way to specify and negotiate FTP extensions. The number of extensions keeps climbing, both the ones that the mechanism supports and the ones it doesn't 📈. So this spec sets up an IANA registry of FTP Command and Feature names to cut down on naming clashes and the confusion that comes with them. This document is the one that establishes that registry 🎀.
Status of This Memo 🌸
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc5797.
Copyright Notice 💜
Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
Table of Contents 🧚
1. Introduction ....................................................2
2. Registry Definition .............................................2
2.1. Registry Name ..............................................2
2.2. Registry Format ............................................2
2.3. Criteria for Registration ..................................4
2.4. Base FTP Commands ..........................................5
2.5. Obsolete Commands ..........................................5
3. Initial Contents of Registry ....................................6
4. Acknowledgments .................................................8
5. IANA Considerations .............................................9
6. Security Considerations .........................................9
7. References ......................................................9
7.1. Normative References .......................................9
7.2. Informative References .....................................91. Introduction ✨
Okay so every version of the FTP spec has added a few new commands, and the early ones are summarized in RFC 959 [RFC0959]. RFC 2389 [RFC2389] came along with a way to specify and negotiate extensions to the FTP protocol from RFC 959. It works through "FEAT Strings", which identify the extensions the FTP server supports, and the server sends them back in response to a "FEAT" command. The number of extensions keeps growing, and not all of them are supported by FEAT 📈. So an IANA registry is established to reduce the chance of a name conflict and the confusion that follows, and to encourage people to share information 🫶. This specification establishes that registry.
2. Registry Definition 🌸
2.1. Registry Name 💖
The name of this registry is "FTP Commands and Extensions".
2.2. Registry Format 🎀
As specified in this RFC, IANA has established a registry for FTP commands and extensions. Registration requests and registry entries should include the following:
Command Name - The FTP command, either new or modified, used in the extension or with which the extension is used.
Following the long-standing practice of capitalizing command names in FTP specification documents, the command names are entered in all uppercase. For extensions that amend the operation of a command, a plus sign ("+") is appended to the command name. However, if an extension affects the overall command parameter handling and/or transaction processing, instead of being bound to one command (or a small number of commands), the string -N/A- is entered.
The registry entries are intended to be ordered by ascending ASCII collation order of this column (including the + suffix if present).
Extension name - The name of the extension.
FTP extensions predating RFC 2389 [RFC2389], and some extensions published after it, did not specify a keyword to identify the extension in a FEAT response. Some later specifications established FEAT strings with the respective command names as their keywords. In order to provide for keywords for future specifications in such cases, this document establishes 'placeholder' keywords to reserve reasonable feature names for future standardization. Similarly, placeholder keywords are used for the basic FTP commands specified in RFC 959 [RFC0959] and those of its predecessors that are still in use. These placeholder keywords are placed in the registry for convenience; it is not intended that they be returned in FEAT responses.
To compensate for this idiosyncrasy, the column in the registry is entitled "FEAT Code", and to clearly distinguish between the two cases, defined FEAT keywords codes are listed in all uppercase, whereas placeholder keywords (henceforth called "pseudo FEAT codes") are listed in lowercase. Future specifications are allowed to "upgrade" a placeholder to a true keyword unless it is specifically declared 'immutable' below, but otherwise IANA maintains uniqueness of feature names (FEAT codes) based on case-insensitive comparison.
Description - A brief description of the extension and, where appropriate, the command.
FEAT String - (optional in registration requests to IANA)
The string expected to be included in the response to the FEAT command [RFC2389] if the extension is supported.
In many cases, the FEAT string required to identify an extension only consists of the "FEAT Code", making this item redundant. Therefore, this item should only be specified if it is intended to register a FEAT string that contains mandatory elements other than the "FEAT Code" itself.
Due to space restrictions, and to allow registrants to provide additional information, IANA should present these registration items (if given) in numbered footnotes to the table, not in an additional table column.
Command Type - The type (or 'kind') of the command.
Section 4.1 of RFC 959 [RFC0959] introduced a subdivision of FTP commands into three types: Access control, transfer Parameter {setting}, and Service {execution}. For clarity, and as a service to the user of the registry, this subdivision is extended to all registered FTP commands, using the characteristic initial of the type, a, p, or s, respectively, filed in the registry column titled type. Combinations are allowed, e.g., p/s.
Conformance Requirements - The support expectation for the command.
RFC 959 specifies mandatory-to-implement commands and optional commands. This classification is carried over to all registered commands, using a column titled conf carrying a single character, either m or o, for "mandatory" and "optional", respectively. Similarly, obsoleted or historic entries are left in the registry to avoid conflicts with deployed implementations, and these entries are marked with h (for "historic"). Beyond the initial registrations, Standards Action [RFC5226] is needed to register new "mandatory" entries or to move such entries to "historic".
Reference - A reference to an RFC or other definition of the extension and/or to implementations supporting it (see the next section).
2.3. Criteria for Registration 🦋
This registry is primarily intended to avoid conflicting uses of the same extension names and command keywords for different purposes, not to demonstrate that an extension is somehow "approved". The "Expert Review" method will be used, but the designated expert is expected to check only that at least one of the two criteria that follow are met.
- The extension is documented in a permanent and readily available public specification (this is the same as the "Specification Required" registration policy defined in RFC 5226 [RFC5226]).
- The extension is actually implemented in FTP client and server systems that are generally available (not necessarily either free or unencumbered, but available).
For an extension or command to be marked "mandatory" (m in the conf column), an IETF Standards Track specification is required. An IESG Standards Action is allowed to direct IANA to change the Conformance Requirements listed for any entry.
2.4. Base FTP Commands 👑
The following commands are part of the base FTP specification [RFC0959] and are listed in the registry with the immutable pseudo FEAT code base.
Mandatory commands:
ABOR, ACCT, ALLO, APPE, CWD, DELE, HELP, LIST, MODE, NLST, NOOP,
PASS, PASV, PORT, QUIT, REIN, REST, RETR, RNFR, RNTO, SITE, STAT,
STOR, STRU, TYPE, USEROptional commands:
CDUP, MKD, PWD, RMD, SMNT, STOU, SYSTNote: STD 3 [RFC1123] clarified and updated the status and implementation requirements of these standard FTP commands, and it contains important complementary information for the following commands:
LIST, NLST, PASV, REST, SITE, STOU2.5. Obsolete Commands 🌈
The following commands were specified as experimental in an extension to an early version of the FTP specification [RFC0775], but were later deprecated by RFC 1123 [RFC1123], because Standard FTP [RFC0959] specifies their standard successors. They are listed in the registry with the immutable pseudo FEAT code hist.
XCUP, XCWD, XMKD, XPWD, XRMDImplementation note: Deployed FTP clients still make use of the deprecated commands, and most FTP servers support them as aliases for the standard commands.
The following commands were specified as part of the "FOOBAR" IPng effort in RFC 1545 [RFC1545] and, later, RFC 1639 [RFC1639], and are now obsolete. They are listed in the registry with the immutable pseudo FEAT code hist.
LPRT, LPSV3. Initial Contents of Registry ✨
okay bestie, so the registry didn't start out empty 🥹 as a favour to people using it and to authors of existing specs, every FTP command and feature published in RFCs after STD 3 [RFC1123] (up to when this was written) got added the moment the registry was created. iconic of them 💅
these pseudo FEAT codes were assigned, following Section 2:
base— FTP standard commands [RFC0959]hist— Historic experimental commands [RFC0775], [RFC1639]secu— FTP Security Extensions [RFC2228]feat— FTP Feature Negotiation [RFC2389]nat6— FTP Extensions for NAT/IPv6 [RFC2428]
and here's the full table 🎀 every row is one command, with its FEAT code, description, type, conf column and the RFC numbers + notes:
+-------+------+-------------------+------+------+------------------+
| cmd | FEAT | description | type | conf | RFC#s/References |
| | Code | | | | and Notes |
+-------+------+-------------------+------+------+------------------+
| ABOR | base | Abort | s | m | 959 |
| ACCT | base | Account | a | m | 959 |
| ADAT | secu | Authentication/ | a | o | 2228, 2773, 4217 |
| | | Security Data | | | |
| ALLO | base | Allocate | s | m | 959 |
| APPE | base | Append (with | s | m | 959 |
| | | create) | | | |
| AUTH | secu | Authentication/ | a | o | 2228 |
| | | Security | | | |
| | | Mechanism | | | |
| AUTH+ | AUTH | Authentication/ | a | o | 2773, 4217 #2 |
| | | Security | | | |
| | | Mechanism | | | |
| CCC | secu | Clear Command | a | o | 2228 |
| | | Channel | | | |
| CDUP | base | Change to Parent | a | o | 959 |
| | | Directory | | | |
| CONF | secu | Confidentiality | a | o | 2228 |
| | | Protected Command | | | |
| CWD | base | Change Working | a | m | 959 |
| | | Directory | | | |
| DELE | base | Delete File | s | m | 959 |
| ENC | secu | Privacy Protected | a | o | 2228, 2773, 4217 |
| | | Command | | | |
| EPRT | nat6 | Extended Port | p | o | 2428 |
| EPSV | nat6 | Extended Passive | p | o | 2428 |
| | | Mode | | | |
| FEAT | feat | Feature | a | m #1 | 2389 |
| | | Negotiation | | | |
| HELP | base | Help | s | m | 959 |
| LANG | UTF8 | Language (for | p | o | 2640 |
| | | Server Messages) | | | |
| LIST | base | List | s | m | 959, 1123 |
| LPRT | hist | Data Port | p | h | 1545, 1639 |
| | | {FOOBAR} | | | |
| LPSV | hist | Passive Mode | p | h | 1545, 1639 |
| | | {FOOBAR} | | | |
| MDTM | MDTM | File Modification | s | o | 3659 |
| | | Time | | | |
| MIC | secu | Integrity | a | o | 2228, 2773, 4217 |
| | | Protected Command | | | |
| MKD | base | Make Directory | s | o | 959 |
| MLSD | MLST | List Directory | s | o | 3659 |
| | | (for machine) | | | |
| MLST | MLST | List Single | s | o | 3659 |
| | | Object | | | |
| MODE | base | Transfer Mode | p | m | 959 |
| NLST | base | Name List | s | m | 959, 1123 |
| NOOP | base | No-Op | s | m | 959 |
| OPTS | feat | Options | p | m #1 | 2389 |
| PASS | base | Password | a | m | 959 |
| PASV | base | Passive Mode | p | m | 959, 1123 |
| PBSZ | secu | Protection Buffer | p | o | 2228 |
| | | Size | | | |
| PBSZ+ | PBSZ | Protection Buffer | p | o | 4217 |
| | | Size | | | |
| PORT | base | Data Port | p | m | 959 |
| PROT | secu | Data Channel | p | o | 2228 |
| | | Protection Level | | | |
| PROT+ | PROT | Data Channel | p | o | 4217 |
| | | Protection Level | | | |
| PWD | base | Print Directory | s | o | 959 |
| QUIT | base | Logout | a | m | 959 |
| REIN | base | Reinitialize | a | m | 959 |
| REST | base | Restart | s/p | m | 959, 1123 |
| REST+ | REST | Restart (for | s/p | m | 3659 #3 |
| | | STREAM mode) | | | |
| RETR | base | Retrieve | s | m | 959 |
| RMD | base | Remove Directory | s | o | 959 |
| RNFR | base | Rename From | s/p | m | 959 |
| RNTO | base | Rename From | s | m | 959 |
| SITE | base | Site Parameters | s | m | 959, 1123 |
| SIZE | SIZE | File Size | s | o | 3659 |
| SMNT | base | Structure Mount | a | o | 959 |
| STAT | base | Status | s | m | 959 |
| STOR | base | Store | s | m | 959 |
| STOU | base | Store Unique | a | o | 959, 1123 |
| STRU | base | File Structure | p | m | 959 |
| SYST | base | System | s | o | 959 |
| TYPE | base | Representation | p | m | 959 #4 |
| | | Type | | | |
| USER | base | User Name | a | m | 959 |
| XCUP | hist | {precursor for | s | h | 775, 1123 |
| | | CDUP} | | | |
| XCWD | hist | {precursor for | s | h | 775, 1123 |
| | | CWD} | | | |
| XMKD | hist | {precursor for | s | h | 775, 1123 |
| | | MKD} | | | |
| XPWD | hist | {precursor for | s | h | 775, 1123 |
| | | PWD} | | | |
| XRMD | hist | {precursor for | s | h | 775, 1123 |
| | | RMD} | | | |
| -N/A- | TVFS | Trivial Virtual | p | o | 3659 |
| | | File Store | | | |
+-------+------+-------------------+------+------+------------------+
Table 1and the notes that go with it 📝
- #1 While an IETF Standards Action would be required to make the FEAT mechanism [RFC2389] mandatory, implementation of that extension mechanism is clearly required in conjunction with any extension or feature that depends on it.
- #2 FEAT String for [RFC4217]:
AUTH TLS. FEAT String for [RFC2773]:AUTH KEA-SKIPJACK - #3 FEAT String:
REST STREAM - #4 FEAT String:
TYPE {semicolon-separated list of supported types}
4. Acknowledgments 🫶
any work to update or extend FTP depends on the base spec in RFC 959, and the editors, Jon Postel and Joyce Reynolds, get big thank-yous for it 💜 the option-negotiation mechanism from RFC 2389 (plus all the features that came after it) is the reason this registry is relevant at all, and those authors deserve credit too ✨
Barry Leiba and Alexey Melnikov gave a bunch of suggestions on earlier versions, and most of them made it in 🙌
Anthony Bryan caught a few typos 🙈
Scott Bradner suggested a clarification to the "Expert Review" text 🧚
the authors are also super grateful for the comments and support from FTP implementers and lots of IETF participants 🌈 and the IESG comments helped shape this document and registry so they're more useful 🦋
5. IANA Considerations 🍓
IANA set up the registry described in Section 2, using the initial contents from Section 3, and it includes the bodies of Sections 2.4 and 2.5 as explanatory text in the registry's preface 📖
new entries should be added when FTP extensions get approved or defined in RFCs, or when extensions that are already in use and well-documented are identified. so basically the registration requirement is a slightly relaxed version of "Specification Required" [RFC5226] with Expert Review 💅 see Section 2.3 for the specifics and exceptions.
6. Security Considerations 🔥
okay this section is short but it's giving confidence 😌 creating this registry gives better documentation and protection against interoperability problems, and it introduces no new security issues ✨
7. References 📚
7.1. Normative References
[RFC0959] Postel, J. and J. Reynolds, "File Transfer Protocol",
STD 9, RFC 959, October 1985.
[RFC2389] Hethmon, P. and R. Elz, "Feature negotiation mechanism for
the File Transfer Protocol", RFC 2389, August 1998.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.7.2. Informative References
[RFC0775] Mankins, D., Franklin, D., and A. Owen, "Directory
oriented FTP commands", RFC 775, December 1980.
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
[RFC1545] Piscitello, D., "FTP Operation Over Big Address Records
(FOOBAR)", RFC 1545, November 1993.
[RFC1639] Piscitello, D., "FTP Operation Over Big Address Records
(FOOBAR)", RFC 1639, June 1994.
[RFC2228] Horowitz, M., "FTP Security Extensions", RFC 2228,
October 1997.
[RFC2428] Allman, M., Ostermann, S., and C. Metz, "FTP Extensions
for IPv6 and NATs", RFC 2428, September 1998.
[RFC2773] Housley, R. and P. Yee, "Encryption using KEA and
SKIPJACK", RFC 2773, February 2000.
[RFC4217] Ford-Hutchinson, P., "Securing FTP with TLS", RFC 4217,
October 2005.Authors' Addresses 🎀
John C Klensin
1770 Massachusetts Ave, Ste 322
Cambridge, MA 02140
USA
Phone: +1 617 245 1457
EMail: john+ietf@jck.com
Alfred Hoenes
TR-Sys
Gerlinger Str. 12
Ditzingen D-71254
Germany
EMail: ah@TR-Sys.dethat's the whole RFC 5797 🌈✨ the registry is set up, the table is populated, and now you know exactly how FTP feature stuff fits together 👑
📦 where this page comes from
- ietf: rfc5797 2010-03
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms