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RFC 5797 - FTP Command and Extension Registry


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Internet Engineering Task Force (IETF)                        J. Klensin
Request for Comments: 5797
Updates: 959                                                   A. Hoenes
Category: Standards Track                                         TR-Sys
ISSN: 2070-1721                                               March 2010

                   FTP Command and Extension Registry

Abstract

   Every version of the FTP specification has added a few new commands,
   with the early ones summarized in RFC 959.  RFC 2389 established a
   mechanism for specifying and negotiating FTP extensions.  The number
   of extensions, both those supported by the mechanism and some that
   are not, continues to increase.  An IANA registry of FTP Command and
   Feature names is established to reduce the likelihood of conflict of
   names and the consequent ambiguity.  This specification 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 .....................................9

1.  Introduction

   Every version of the FTP specification has added a few new commands,
   with the early ones summarized in RFC 959 [RFC0959].  RFC 2389
   [RFC2389] established a mechanism for specifying and negotiating
   extensions to the FTP protocol specified in RFC 959, by means of
   "FEAT Strings" identifying extensions supported by the FTP server,
   and sent in response to a "FEAT" command.  The number of extensions
   continues to grow, not all of them supported by FEAT.  An IANA
   registry is established to reduce the likelihood of a conflict of
   names and the consequent ambiguity and to encourage the sharing of
   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 to capitalize command names
      in specification documents for FTP, the command names are entered
      in all uppercase.  For extensions amending 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.

      It is intended to have the registry entries 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.

   1.  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]).

   2.  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, USER

      Optional commands:

      CDUP, MKD, PWD, RMD, SMNT, STOU, SYST

   Note: 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, STOU

2.5.  Obsolete Commands

   The following commands were specified as experimental in an extension
   to an early version of the FTP specification [RFC0775] but 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, XRMD

   Implementation 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, LPSV

3.  Initial Contents of Registry

   As a service to users of the registry and the authors of existing
   specifications, all FTP commands and features published in RFCs after
   STD 3 [RFC1123] and up to the time of this writing were included in
   the registry upon creation.

   The following pseudo FEAT codes have been assigned, according to
   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]

   +-------+------+-------------------+------+------+------------------+
   | 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 1

   Notes:
   #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 specification in
   RFC 959.  The contributions of its editors, Jon Postel and Joyce
   Reynolds, are gratefully acknowledged.  The option-negotiation
   mechanism specified in RFC 2389 (and the accumulation of features
   that followed it) made this registry relevant; the authors of those
   documents are acknowledged as well.

   Barry Leiba and Alexey Melnikov made several suggestions about
   earlier versions of this document, most of which have been
   incorporated.

   Anthony Bryan spotted a few typographical errors.

   Scott Bradner suggested a clarification to the "Expert Review" text.

   The authors appreciate the comments and support for this work
   received from FTP implementers and many IETF participants.  Comments
   from the IESG helped to shape this document and registry to improve
   its utility.

5.  IANA Considerations

   IANA has established the registry described in Section 2 using the
   initial content specified in Section 3 and including the body of
   Sections 2.4 and 2.5 as explanatory text in the preface of the
   registry.

   New entries should be added to this registry when extensions to FTP
   are approved or defined in RFCs or when extensions that are already
   in use and well-documented are identified.  In other words, the
   requirement for registration is a slightly relaxed version of
   "Specification Required" [RFC5226] with Expert Review.  See
   Section 2.3 for specifics and exceptions.

6.  Security Considerations

   The creation of this registry provides improved documentation and
   protection against interoperability problems.  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.de

 

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