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Network Working Group                                        F. da CruzRequest for Comments: 2839                                    J. AltmanCategory: Informational                             Columbia University                                                               May 2000Internet Kermit ServiceStatus of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2000).  All Rights Reserved.ABSTRACT   This document describes a new file transfer service for the Internet   based on Telnet Protocol for option negotiation and Kermit Protocol   for file transfer and management.  The Internet Kermit Service   provides access to both authenticated and anonymous users.  The use   of Kermit protocol over a Telnet connection provides several   advantages over FTP, including easy traversal of firewalls, transfers   over multiple transports, and security via a combination of supported   Telnet authentication and encryption option negotiations, plus   significant functional benefits.  While this document describes a new   service for the Internet, the clients for this service already exist   on most platforms in the form of Telnet clients that support the   Kermit file transfer protocol.  These clients are available not only   from Columbia University's Kermit Project but also numerous third   parties.TABLE OF CONTENTS1. INTRODUCTION ................................................22. BACKGROUND ..................................................32.1. History ...................................................32.2. Motivation ................................................43. THE INTERNET KERMIT SERVICE MODEL ...........................73.1. Server-Side Kermit Server .................................73.2. Client-Side Kermit Server .................................83.3. Loosely Coupled Operation .................................94. SECURITY CONSIDERATIONS .....................................104.1. AUTHENTICATION ............................................104.1.1. Telnet Authentication ...................................104.1.2. Telnet over TLS option ..................................11da Cruz & Altman             Informational                      [Page 1]

RFC 2839                Internet Kermit Service                 May 20004.1.3. Plaintext Authentication via Kermit REMOTE LOGIN ........114.1.4. Plaintext Authentication via Command Prompt .............114.1.5. Anonymous Login .........................................124.2. ENCRYPTION (PRIVACY) ......................................124.2.1  Telnet Encryption .......................................124.2.2  Telnet Start_TLS ........................................125. SERVICES ....................................................135.1. Features for System Administrators ........................135.2. Features for Users ........................................145.3. User Interface ............................................166. REFERENCES ..................................................187. AUTHORS' ADDRESSES ..........................................198. Full Copyright Statement ....................................20PREFACE   This document describes an Internet Kermit Service (IKS) which   provides an alternative to FTP for the transfer of files.  This   service is based upon both the TELNET protocol and the Kermit file   transfer protocol.1. INTRODUCTION   The Internet Kermit Service:   1. Provides direct access to Kermit file transfer and management      services without requiring the user to first login to a shell      account;   2. Provides Kermit file transfer and management services to anonymous      users;   3. Provides services to all Telnet clients that support Kermit file      transfer protocol via a simple, predictable, scriptable, and      well-documented textual interface;   4. Provides direct and tightly-coupled access to a Kermit server when      requested via the Telnet Kermit Option [TKO].   This memo assumes knowledge of Transmission Control Protocol, the   Telnet Protocol [TEL], the Kermit File Transfer Protocol [KER,PRF],   Telnet Kermit Option [TKO], and the commands and features of Kermit   software [CKB,CMG,K95].   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described inRFC 2119 [BCP].da Cruz & Altman             Informational                      [Page 2]

RFC 2839                Internet Kermit Service                 May 2000   Definitions:   Kermit server      A software program that is ready to accept and act upon commands      in the form of well-defined Kermit packets [KER].   Kermit client      A software program that receives requests through its user      interface from a human user (or a script or other source) and      translates them to command packets, which it sends to a Kermit      server, thus initiating a Kermit protocol transaction such as the      transfer of one or more files.2. BACKGROUND2.1. History   "Kermit" is the name of an extensible platform- and medium-   independent file transfer and management protocol [KER,PRF] and of a   suite of communications software programs that implement it and   integrate it with other communications functions [CMG,CKB,K95].   The Kermit protocol was first developed at Columbia University in New   York City in 1981 for transferring files without errors between   diverse types of computers over potentially hostile communication   links.  Since 1981, the Kermit Project at Columbia University has   expanded the protocol, developed communications software that   implements it upon key platforms, and worked with volunteer   programmers at other sites adapting Kermit protocol to other   platforms or communication methods.  The Kermit Project also serves   as the central point of Kermit software development, support,   information, and distribution throughout the world.   Kermit software is now available for nearly every computer and   operating system in existence.  The major features of the most   popular Kermit programs are:   -  Connection establishment and maintenance for a variety of      connection methods including direct serial, dialup, TCP/IP, X.25,      DECnet, and NETBIOS.   -  Terminal emulation.   -  Error-free transfer of both text and binary files, individually or      in groups.   -  Character-set translation during both terminal emulation and      text-mode file transfer -- a unique feature of Kermit software.da Cruz & Altman             Informational                      [Page 3]

RFC 2839                Internet Kermit Service                 May 2000   -  Remote file management through the client/server protocol.   -  A powerful and portable scripting language allowing complete      automation of any task that can be performed manually.   Kermit's command and script language is consistent across all   platforms and communication methods, thus offering a unified method   for accomplishing a wide range of communication tasks manually or   under script control.   A single Kermit program combines the functions of many different   programs such as uucp, cu, tip, telnet, rlogin, ftp, iconv, and   expect:  it is a Telnet and Rlogin client that can also transfer   files; it is a file transfer program that can also convert character   sets; it is a dialout program that can use dialing directories and   understands country codes and area codes; it is fully scriptable; it   offers both client/server and interactive modes of operation.  In its   desktop versions (particularly for DOS, Windows, and OS/2) it offers   all the features of communications software that are usually lacking   from Internet client software (key mapping, colors, scrollback, mouse   functions, printer control, etc)   Kermit software is widely used throughout the academic, government,   and corporate spheres, both in the USA and internationally.   In addition to the Kermit software developed and/or distributed by   the Kermit Project at Columbia University, hundreds of other software   products -- commercial, shareware, and freeware -- also include some   level of support for the Kermit protocol.  Thus there are hundreds,   perhaps thousands, of independent and interoperable Kermit protocol   implementations based upon the open Kermit protocol specification   [KER].   The Internet has formed the primary mechanism by which users and   developers of Kermit software have collaborated to produce feature   and command sets that continually evolve to meet their needs as   technology changes.2.2. Motivation.   Kermit protocol and software makes connections from one computer to   another and transfers data between them.  Countless people "live" in   Kermit all day long; as a customizable Telnet or Rlogin (or serial   communication) client with a wide selection of terminal emulations   and convenience features, it is their window onto the Internet.da Cruz & Altman             Informational                      [Page 4]

RFC 2839                Internet Kermit Service                 May 2000   Others use it in more creative ways, including some that involve key   parts of the Internet, e.g. in batch or cron jobs that update news or   Web servers or fetch email, or to monitor routers, terminal servers,   and hubs and dial pagers when faults are detected.  It is used by   vendors of telecommunications equipment for remote diagnosis,   patching, and updates.  Telecom managers often use Kermit scripts to   configure PBXs, muxes, routers, or terminal servers.  In the world of   commerce, Kermit is widely used for financial transactions, EDI,   medical claim submission, and so forth.  It is used with mobile   barcode readers in warehousing and inventory applications.  It is   found in US Postal Service sorting and scanning equipment.  It   connects many of the logistics and supply systems throughout the   military.  It is found in fast-food restaurant cash registers,   milling and die-cutting machines, textile looms and cutters, printing   presses, and medical diagnostic equipment.  It was the communications   backbone of the 1994 Brazilian national election -- the largest in   history.   And yet there has never been a strong, explicit connection of Kermit   with the Internet.  In the early years, Kermit acted as a kind of   do-it-yourself network, enabling ordinary users to make connections   that were not already there, and for some years was the predominant   method of connecting a personal computer to the ARPAnet (e.g. by   dialing a TAC).   Nowadays, however, with so many of the world's computers on the   Internet, the role of Kermit software and protocol is changing.   Kermit users on the network would like to have the features,   functions, and interface they are accustomed to -- especially the   automation features -- available for use in settings where presently   only tools like FTP are available -- and even more so in situations   where standard software like FTP can't be used.   An Internet Kermit Service can fill this role, and augment the data   transfer power and flexibility of other Internet applications such as   Web browsers:   -  Like FTP, Kermit provides a service that can be accessed from many      different platforms with a consistent set of commands, but unlike      FTP, these commands include programming constructions such as      variables, arrays, looping and selection mechanisms, and local and      remote procedure calls.   -  Like FTP, Kermit provides both text- and binary-mode data      transfer, as well as file management capabilities.  But Kermit      also offers numerous features lacking from FTP, such asda Cruz & Altman             Informational                      [Page 5]

RFC 2839                Internet Kermit Service                 May 2000      character-set translation, flexible file selection mechanisms,      attribute preservation, and so on (seeSection 5.3 for a longer      list).   -  Unlike standard FTP, Kermit can transfer data through multiple      firewalls, proxies, and network address translators (NATs) on a      single port.   -  Unlike FTP, Kermit can transfer data across a combination of      transports (e.g. dial-up to a terminal server and thence to an      Internet host).   -  Authentication and data transfer can take place over secure      connections (mutually authenticated and encrypted) using      established Telnet authentication and encryption options.   -  Unlike traditional Kermit use over Telnet, anonymous access is      possible, and the considerable overhead of the intervening Telnet      server and pseudoterminal service is eliminated.   Until now the primary obstacles to an Internet Kermit Service have   been:   -  Issues of authentication, privacy, and anonymous access.  These      have been addressed in our implementation, as describedSection 4      of this document.   -  Issues of coordination and control.  A Kermit software program can      be in any of several "modes": at its command prompt or menu,      awaiting commands from the user; in terminal mode, in which the      user's keystrokes are sent to the remote computer or service; or      in protocol mode, in which two Kermit programs communicate via      well-defined Kermit packets [KER].  Commands or operations valid      in one mode do not necessarily work in another.  Until now, it has      been the user's responsibility to switch modes at one or both ends      of the connection as needed.  A companion document [TKO] to this      one specifies a mechanism to closely couple the client and server      via Telnet protocol negotiations, allowing each to know the      other's state and to switch to the appropriate mode automatically      so a valid and useful relationship obtains at all times.   -  Lack of a standard TCP port.  The "registered" port 1649 was      assigned by IANA for this purpose (27 September 1995) and is named      "Kermit". (renamed from "Inspect".)da Cruz & Altman             Informational                      [Page 6]

RFC 2839                Internet Kermit Service                 May 20003. THE INTERNET KERMIT SERVICE MODEL   The Internet Kermit Service (IKS) uses a standard Telnet [TEL]   connection, in which all Telnet rules apply.  Unlike FTP, which   requires additional TCP connections, IKS uses a single channel for   both signaling and data transfer.  The connection is multiplexed via   (a) Telnet options, and (b) Kermit protocol messages.  This allows   existing Telnet clients that also support the Kermit protocol,   whether or not they support the Telnet Kermit Option [TKO], to use   the IKS and take advantage of all relevant Telnet options including   authentication and encryption.   The system Internet services daemon (e.g. inetd) waits for a   connection on the Kermit socket (1649) and then starts the IKS on the   new connection.  The IKS performs the familiar Telnet negotiations   including the Telnet Kermit option.  Unlike a standard Telnet server,   the IKS does not support the ability to present the user with an   interactive system shell.  The Kermit socket is used only for file   transfer and management functions provided by Kermit file transfer   protocol and the Kermit script language.   Once the connection is established, the Telnet Kermit Option is   negotiated in both directions.  The results determine which of the   following configurations is used by the Telnet client and Server:    . Server-side Kermit Server (SKS)    . Client-side Kermit Server (CKS)    . No Kermit Server (NKS)   Different procedures and functions apply to each configuration.  The   configuration may be changed at any time by Telnet Kermit Option   subnegotiations, which assure that the Telnet client and server are   always in compatible states.   The three configurations are described in the following sections.3.1. Server-Side Kermit Server   In the Server-Side Kermit Server (SKS) configuration, the Telnet   server is the Kermit server and the Telnet client is the Kermit   client.  This configuration is used when both Telnet client and IKS   support the Telnet Kermit Option and the IKS sends WILL KERMIT to the   Telnet client and receives DO KERMIT from the Telnet client [TKO].   In this case, the IKS immediately starts a Kermit server and reports   this to the Telnet client with a Telnet KERMIT START-SERVER   subnegotiation.da Cruz & Altman             Informational                      [Page 7]

RFC 2839                Internet Kermit Service                 May 2000   The SKS configuration is appropriate when the user wishes to interact   only with the Telnet client's commands or menus.   If authentication was not performed with one of the Telnet   Authentication Option protocols, the Kermit server rejects all Kermit   protocol operations (except REMOTE LOGIN, REMOTE HELP, REMOTE EXIT,   BYE, or FINISH -- that is, the ones that request help, that log in,   that close the connection, or that change the status of the   connection) until:   - A Kermit REMOTE LOGIN command successfully authenticates the user;   - The login retry limit is reached;   - A Kermit BYE or REMOTE EXIT command is received, which closes the      connection;   - A Kermit FINISH command or a Telnet KERMIT REQ-KERMIT-STOP      subnegotiation is received to request the IKS exit from Kermit      server mode.  At this point, the IKS can either exit and close the      connection or issue an interactive login prompt, depending on how      it was started or configured by the system administrator.   Once the user is authenticated:   - The Telnet client configures itself for Kermit client/server      operation, with itself as the Kermit client, communicating with      the server only by Kermit packets, and optionally adjusting its      menus or commands to eliminate functions (such as terminal      emulation) that make no sense in this context.   - The relationship persists until the Telnet client and IKS agree to      terminate the Kermit server via Kermit protocol commands (BYE,      FINISH, or REMOTE EXIT), or by Telnet Kermit Option      subnegotiation, or by closing the connection.3.2. Client-Side Kermit Server   In the Client-Side Kermit Server (CKS) configuration, the Telnet   server is the Kermit client, and the Telnet client is the Kermit   server.  This configuration is used when the IKS has sent WONT KERMIT   or SB KERMIT STOP-SERVER, and the Telnet Client has sent WILL KERMIT   and SB KERMIT START-SERVER, indicating that it is prepared to accept   and process Kermit protocol packets.   In the CKS configuration, the Telnet client assumes the role of   Kermit server by virtue of its ability to recognize and process   Kermit protocol packets in its terminal emulator.  Thus the Telnetda Cruz & Altman             Informational                      [Page 8]

RFC 2839                Internet Kermit Service                 May 2000   client must not send WILL KERMIT or the KERMIT START-SERVER   subnegotiation unless its terminal emulator is capable of recognizing   Kermit packets.   If the IKS is at top command level (as opposed to executing a   script), or when it reaches top level after finishing a script, it   issues its interactive command prompt.   At this point, the user may type commands or send scripted commands   to the IKS command prompt.  When a data-transfer command (such as   SEND) is issued by the user at the IKS prompt, a Kermit packet is   transmitted and recognized by the Telnet client, causing it to   automatically perform the requested action (e.g. receive a file), and   then resume its previous mode (terminal emulation or script   execution) when the data transfer is complete.   Thus, in the CKS configuration, data transfers are initiated by the   IKS rather than by the Telnet client.  This configuration is useful   when the user prefers the command interface or repertoire of the   server to that of the client.   If the IKS sends a Telnet KERMIT START-SERVER subnegotiation, the   relationship switches automatically to Server-Side Kermit Server   (Section 3.1), in which the Telnet client is the Kermit client and   the Telnet server is the Kermit server.   If the Telnet client sends a KERMIT STOP-SERVER subnegotiation, the   connection switches to No Kermit Server (Section 3.3) and the IKS   issues its command prompt.  At this point, neither side is a Kermit   server, and both sides may optionally disable Kermit protocol   commands.  Subsequent user action can designate one side or the other   as the Kermit server, as desired.3.3. No Kermit Server   If both Telnet client and IKS send WONT KERMIT or SB KERMIT STOP-   SERVER, or if the Kermit client and server are connected across   multiple hosts or transports, thus precluding end-to-end Telnet   negotiation, a Kermit server is not known to be available.  In the   KERMIT STOP-SERVER case, the Kermit partners can later switch back to   SKS or CKS, but in the other two cases, there is no such signaling   and loose coupling characterizes the entire session.   In the No Kermit Server (NKS) configuration, the IKS presents a   command prompt to the Telnet client.  As in the Client-Side Kermit   Server configuration, plain-text commands are issued to the IKS.da Cruz & Altman             Informational                      [Page 9]

RFC 2839                Internet Kermit Service                 May 2000   In the loosely coupled NKS configuration, the Telnet client does not   know the state of the Telnet server, and so can not automatically   adjust its commands and menus to present only valid choices, or   automatically change its state to complement the server's; it is the   user's responsibility to assure that the "mode" (command prompt,   terminal emulation, server command wait) of each Kermit partner is   appropriate for each action.  Thus an Internet Kermit Server appears   as an ordinary remote Kermit program to any Telnet client that does   not implement the Telnet Kermit Option, or in which this feature is   disabled or can not be used.   The NKS configuration allows successful manual operation of the IKS   through Telnet clients that do not support the Telnet Kermit Option.   The Telnet client might or might not support Kermit "autodownload"   and "autoupload"; if it does not, then the user is forced to manually   issue command on both sides of the connection in the traditional and   familiar manner [CKB,CMG,K95].4. SECURITY CONSIDERATIONS4.1. AUTHENTICATION   Authentication is provided via one or more of the following methods:    - The Telnet AUTHENTICATION option;    - The Telnet START_TLS option;    - Plaintext userid/password verification.4.1.1. Telnet Authentication option   The use of one of the many Telnet authentication option methods   removes the need to transmit passwords in plaintext across public   networks.  In addition, the exchange of user authentication   information often provides a shared secret that can be used with the   Telnet Encryption Option protocols to encrypt the connection in one   or both directions.   Telnet authentication may also be used in conjunction with the Telnet   START_TLS option to negotiate end user identity over the encrypted   and host authenticated TLS channel.   The IKS currently supports Kerberos 4, Kerberos 5, Secure Remote   Password and Microsoft NTLM authentication methods via the Telnet   AUTH option.da Cruz & Altman             Informational                     [Page 10]

RFC 2839                Internet Kermit Service                 May 20004.1.2. Telnet over TLS option   The Telnet START_TLS option provides for the negotiation and   establishment of a TLS version 1 session after the initial telnet   connection.  The TLS connection provides host to client   authentication via the use of X.509 certificate chains.  TLS also   supports optional client to host authentication using host verified   X.509 certificates which may be used to authenticate a userid   provided by the client or be mapped to a userid based upon properties   of the certificate.4.1.3. Plaintext Authentication via Kermit REMOTE LOGIN   In the Server-Side Kermit Server configuration, if the client is not   yet authenticated, the client must log in using a REMOTE LOGIN   command, in which a Kermit packet containing user ID and password in   clear text is sent from the Telnet client to the Telnet server, which   then calls upon local mechanisms to authenticate the user.  Any   packets other than login (or REMOTE HELP, REMOTE EXIT, FINISH, or   BYE) packets are rejected (returned with an error message) until the   user is authenticated.  If the number of unsuccessful login attempts   exceeds the limit, the connection is closed.  Many Kermit client   programs support this login method already.   This method should be avoided whenever possible.  If plaintext   passwords are used, they should only be sent after the Telnet START-   TLS option has been negotiated (see 4.2.2).  Otherwise, passwords are   open to packet sniffing.4.1.4. Plaintext Authentication via Command Prompt   In the Client-Side Kermit Server and No Kermit Server configurations,   the server presents the user with a plain-text interactive interface   that begins with the server issuing "Username:" and "Password:"   prompts, just as if the user were logging in to a multiuser   timesharing system such as VMS or UNIX.  When a password is not   required an empty response can be given.  Invalid username-password   combinations result in a new series of prompts up to the login retry   limit, and then disconnection.   This method should be avoided whenever possible.  If plaintext   passwords are used, they should only be sent after the Telnet START-   TLS option has been negotiated (see 4.2.2).  Otherwise, passwords are   open to packet sniffing.da Cruz & Altman             Informational                     [Page 11]

RFC 2839                Internet Kermit Service                 May 20004.1.5. Anonymous Login   When the username is "anonymous" or "ftp", the IKS behaves like an   anonymous ftp server, in a manner appropriate to the underlying   platform.  In UNIX, for example, access is restricted to a designated   area of the file system.  A password might or might not be required,   according to the preference of the site administrator.   If privacy is desired the Telnet START-TLS option should be used (see   4.2.2).4.2.  ENCRYPTION (PRIVACY)   As the Internet becomes ever more public and susceptible to   eavesdropping, it becomes increasingly necessary to provide methods   for private access to services.  Telnet provides two such mechanisms:    . Telnet Encryption option    . Telnet START-TLS option4.2.1.  Telnet Encryption option   The Telnet Encryption option, although it has never achieved RFC   status, has been used for years in conjunction with the Telnet Auth   option in Telnet clients and servers that support Kerberos 4,   Kerberos 5, Secure Remote Password, and others.  The IKS currently   supports the following encryption methods under the Telnet Encryption   option:    .  cast128_ofb64    .  cast5_40_ofb64    .  des_ofb64    .  cast128_cfb64    .  cast5_40_cfb64    .  des_cfb644.2.2. Telnet over TLS option   Transport Layer Security (TLS), the successor to Secure Sockets Layer   (SSL), provides methods to implement Server authentication, Client   authentication, and Transport Layer encryption.  Unlike Telnet   Encryption, Start-TLS does not require the use of Telnet   Authentication in order to provide a private channel.  This means   that it can be used in conjunction with plaintext passwords and   anonymous connections.da Cruz & Altman             Informational                     [Page 12]

RFC 2839                Internet Kermit Service                 May 20005. SERVICES   The Internet Kermit Service includes features for both users and   system administrators.  The IKS is incorporated into  the 7.0 release   of Columbia University's C-Kermit software, which is the "master"   Kermit software program in terms of features and command language.   An overview of C-Kermit can be found at:http://www.columbia.edu/kermit/ckermit.htmlhttp://www.kermit-project.org/ckermit.html   When C-Kermit is employed as an Internet Kermit Service, it may offer   all its functions to "real" users (those who are authenticated as   specific users), and a safe subset of its functions to anonymous   users.   The Internet Kermit Service resembles an FTP server in that it   performs its own authentication and uses a well-defined protocol to   communicate with its client, but differs from the FTP server by also   offering (at the system manager's discretion) an interactive user   interface to the Telnet client when it is in terminal mode.  It also   differs from FTP in restricting all protocol messages and data   transfer to a single socket connection.   An IKS has been deployed at Columbia University for worldwide public   access to the Kermit FTP site:     telnet://kermit.columbia.edu:1649/     telnet://ftp.kermit-project.org:1649/5.1. Features for System Administrators   The system administrator can supply IKS configuration parameters as   command-line options or in a configuration file, or both in   combination.  Such parameters include:    . Whether anonymous logins are allowed.    . The file system or root directory to which anonymous users are      restricted.    . Specification of permissions and other attributes to be assigned      to files uploaded by anonymous users.    . Whether to make session entries in system logs.da Cruz & Altman             Informational                     [Page 13]

RFC 2839                Internet Kermit Service                 May 2000    . Specific services to disable: reception of files, sending of      files, sending of email, printing, changing of directories,      getting directory listings, deleting files, etc (see next      section).    . Whether access to the interactive command prompt is allowed.5.2. Features for Users   The IKS supports a wide range of services, including, but not limited   to, the following:    . Authentication as a real user or anonymously.    . Transmission of files to which read access is allowed.    . Reception of files into directories or devices to which write      access is allowed.    . The ability to display a file on the client's screen.    . Ability to list files.    . Ability to change its working (default) directory.    . Ability to delete files to which write or delete access is      allowed.    . Ability to rename and copy files    . Ability to create and remove directories.    . The ability to route received files to a specified printer, or to      send them as email to a specified address list.    . Client control of server parameter settings, within limits      established by the server system administrator.    . Transmission of variables from client to server or vice versa.    . Remote and local script execution.    . Remote and local procedure execution.da Cruz & Altman             Informational                     [Page 14]

RFC 2839                Internet Kermit Service                 May 2000   File transfer features include:    . Kermit text-mode transfers incorporate not only record-format      conversion, but also character-set translation;    . Kermit can switch automatically between text and binary mode on a      per-file basis when sending groups of files.    . A selection of file collision options, including "make backup copy      of existing file and accept incoming file", "reject incoming      file", "accept incoming file only if newer than existing file",      etc.    . Numerous methods for selecting the files to be transferred,      including pattern matching, lists of filenames (or patterns),      exception lists, date and/or size ranges, etc.    . Filename conversion and file renaming.    . Automatic directory creation if elected and enabled.    . Standard mechanisms for directory traversal, allowing transmission      of entire directory trees or other file hierarchies even between      unlike file systems such as VMS, UNIX, and Windows.    . Atomic file movement: optionally, the source file can be deleted      (or renamed, or moved) when and only when it has been transferred      successfully.    . Kermit can retain file attributes including time stamps and      permissions (at the user's or system administrator's discretion),      even between unlike platforms;    . Recovery of interrupted transfers from the point of failure.    . File-transfer pipes and filters.   Script programming features include:    . Macros with parameter substitution.    . Built-in and user-defined variables and arrays, with global or      local scope.da Cruz & Altman             Informational                     [Page 15]

RFC 2839                Internet Kermit Service                 May 2000    . Built-in and user-defined functions.  Built-in functions include:          - String functions          - Arithmetic functions          - Date / time functions          - File functions    . Input search for multiple simultaneous targets.    . IF-ELSE, WHILE, FOR, SWITCH, GOTO, C-like block structure.    . Every command returns a completion status that may be tested and      used as a basis for subsequent actions.5.3. User Interface   The Internet Kermit Service uses the Kermit command and script   language, as implemented in Columbia University's C-Kermit   communication software [CKB].  This program and its command language   are portable to all known varieties of UNIX, as well as to Windows   95/98/NT, OS/2, Digital (Open)VMS, Stratus VOS, Data General AOS/VS,   Plan 9, OS-9, QNX, the Commodore Amiga, and other platforms.  The   C-Kermit command language is a superset of that of other Kermit   software programs including MS-DOS Kermit for DOS and Windows 3.x,   IBM Mainframe Kermit for VM/CMS, MVS/TSO, CICS, and MUSIC, PDP-11   Kermit for RT-11, RSTS/E, RSX-11, and IAS, and dozens of other Kermit   programs.   It is far beyond the scope of this document to enumerate, let alone   describe, the commands and services of C-Kermit; this is the subject   of a 600-page book [CKB], augmented by hundreds of pages of online   material.  A brief overview is included here.   Commands are based on English words.  There is no plan at present to   support other natural languages (Italian, Portuguese, Norwegian,   Russian, Hebrew, Japanese, Cherokee, etc) as alternative bases for   command words, since this would reduce the portability of scripts.   However, since the command language includes a macro capability,   macros may be defined to provide selected commands in different   languages if desired.   Certain commands can apply either locally or remotely, for example   "CD" (Change Directory).  The convention is to prefix the command   with the word REMOTE if it is to apply remotely.  Example: "cd foo"   changes to the "foo" directory on the computer where the command was   given; "remote cd foo" sends a Kermit packet to the Kermit server   requesting it to change its directory to "foo".  The commands in this   category include:da Cruz & Altman             Informational                     [Page 16]

RFC 2839                Internet Kermit Service                 May 2000     ASSIGN <variable> <value>      Assign a value to a variable.     CD <directory>                 Change working directory.     COPY <files> <destination>     Copy file(s)     DELETE <files>                 Delete file(s)     DIRECTORY [ <pattern> ]        List file(s)     EXIT                           Exit     HELP [ <topic-or-command> ]    Display help text     MKDIR <directory>              Create a directory     PRINT <files>                  Print file(s)     PWD                            Print working directory     RENAME <old> <new>             Rename file(s)     RMDIR <directory>              Remove a directory     SET <parameter> <value>        Change a parameter's value     TYPE <file>                    Display the contents of a file   As a convenience, REMOTE commands also have short synonyms: RASSIGN,   RCD, RCOPY, RDELETE, and so forth.   The basic file transfer commands are:     SEND [ modifiers ] <files>    Send file(s) (to server)     GET [ modifiers ] <files>     Get file(s) (from server)   These commands take a file name, pattern, or list, plus various   optional modifiers, including transfer mode specifiers (text,   binary), file selectors (date, size, exception list), aliasing, name   and path options, disposition specifiers, and so on.   In addition to the commands listed above, the following commands are   sent by the client to the server:     REMOTE QUERY                   Get value of variable or procedure     BYE                            Log out and close the connection     FINISH                         Request the server leave server mode   Like all Kermit client/server commands, these can be disabled if   desired.   Of course there are numerous other commands with purely local effect,   such as the many scripting commands.  These, plus all the commands   above, are fully documented in [CKB].  The repertoire grows over   time, but never in a way that invalidates existing scripts.   The system administrator can allow or forbid access to any of these   features, and to the command language as a whole.  In the latter   case, the IKS may be accessed only as a Kermit server, by giving   commands to the client.da Cruz & Altman             Informational                     [Page 17]

RFC 2839                Internet Kermit Service                 May 20006. REFERENCES   [TKO] Altman, J. and F. da Cruz, "Telnet Kermit Option",RFC 2840,         May 2000.   [BCP] Bradner, S., "Key words for use in RFCs to Indicate Requirement         Levels",BCP 14,RFC 2119, March 1997.   [KER] da Cruz, Frank, "Kermit, A File Transfer Protocol", Digital         Press/ Butterworth Heinemann, Newton, MA (1987).  379 pages,         ISBN 0-932376-88-6.   [CKB] da Cruz, Frank, and Christine M. Gianone, "Using C-Kermit",         Second Edition, Digital Press / Butterworth-Heinemann, Woburn,         MA (1997).  622 pages, ISBN 1-55558-164-1.   [CMG] Gianone, Christine M., "Using MS-DOS Kermit", Second Edition,         Digital Press / Butterworth-Heinemann, Woburn, MA (1992). 345         pages, ISBN 1-55558-082-3.   [K95] Gianone, Christine M., and Frank da Cruz, "Kermit 95", Manning         Publications, Greenwich CT, (1996). 88 pages, ISBN 1-884777-         14-7.   [PRF] Huggins, James K., "Kermit Protocol - Formal Specification and         Verification", in Boerger, E., "Specification and Validation         Methods", Oxford University Press (1995).  ISBN 0-19-853854-5.   [FTP] Postel, J. and J. Reynolds, "File Transfer Protocol (FTP)", STD         9,RFC 959, October 1985.   [TEL] Postel, J. and J. Reynolds, "Telnet Protocol Specification",         STD 8,RFC854, May 1983, et seq.; "Telnet Option         Specification", STD 8,RFC855, May 1983, et seq.   [IAN] Internet Assigned Numbers Authority:http://www.iana.org/numbers.htmlhttp://www.iana.org/assignment/port-numbersda Cruz & Altman             Informational                     [Page 18]

RFC 2839                Internet Kermit Service                 May 20007. AUTHORS' ADDRESSES   Frank da Cruz   EMail: fdc@columbia.edu   Jeffrey E. Altman   EMail:jaltman@columbia.edu   The Kermit Project   Columbia University   612 West 115th Street   New York NY 10025-7799   USAhttp://www.columbia.edu/kermit/http://www.kermit-project.org/da Cruz & Altman             Informational                     [Page 19]

RFC 2839                Internet Kermit Service                 May 20008.  Full Copyright Statement   Copyright (C) The Internet Society (2000).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.da Cruz & Altman             Informational                     [Page 20]