The telnet URI Scheme
RFC 4248

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Network Working Group                                         P. Hoffman
Request for Comments: 4248                                VPN Consortium
Obsoletes: 1738                                             October 2005
Category: Standards Track

                         The telnet URI Scheme

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document specifies the telnet Uniform Resource Identifier (URI)
   scheme that was originally specified in RFC 1738.  The purpose of
   this document is to allow RFC 1738 to be made obsolete while keeping
   the information about the scheme on standards track.

1.  Introduction

   URIs were previously defined in [RFC2396], which was updated by
   [RFC3986].  Those documents also specify how to define schemes for
   URIs.

   The first definition for many URI schemes appeared in [RFC1738].
   Because that document has been made obsolete, this document copies
   the telnet URI scheme from it to allow that material to remain on
   standards track.

2.  Scheme Definition

   The Telnet URL scheme is used to designate interactive services that
   may be accessed by the Telnet protocol [STD8].

   A telnet URL takes the form:

   telnet://<user>:<password>@<host>:<port>/

Hoffman                     Standards Track                     [Page 1]
RFC 4248                 The telnet URI Scheme              October 2005

   The final "/" character may be omitted.  If :<port> is omitted, the
   port defaults to 23.  The :<password> can be omitted, as well as the
   whole <user>:<password> part.  Few implementations handle the user
   name and password very well, if at all.

   This URL does not designate a data object, but rather an interactive
   service.  Remote interactive services vary widely in the means by
   which they allow remote logins; in practice, the <user> and
   <password> supplied are advisory only: clients accessing a telnet URL
   merely advise the user of the suggested username and password.

   Many RFCs have added various services to the Telnet protocol for
   better authentication, encryption of traffic, or both.  Those RFCs
   have not specified new URI schemes for Telnet to invoke those
   services (along the lines of "https" being a different URI scheme
   from "http").  Some modern telnet clients attempt to invoke those
   more-secure versions of Telnet when resolving a "telnet" URL.

3.  Security Considerations

   There are many security considerations for URI schemes discussed in
   [RFC3986].

   The Telnet protocol normally uses passwords in the clear for
   authentication, and normally offers no privacy.  In normal telnet,
   both the user's identity and their password are exposed without any
   protection; after that, the contents of the entire Telnet session is
   exposed without any protection.

   Many extensions have been made to Telnet to make it more secure in
   different ways.  In particular, [RFC2941] gives a framework based on
   a telnet option that many other security extensions have leveraged
   off of.  These extensions are certainly worthwhile methods for
   reducing the obvious problems with exposing the user's name,
   password, and plaintext of the session in the clear.

   Although some modern telnet clients attempt to invoke those more-
   secure versions of Telnet when resolving a "telnet" URL, other telnet
   clients do not, so a user cannot rely on this type of security unless
   it is explicitly enabled and the results of the security negotiation
   are checked.

Hoffman                     Standards Track                     [Page 2]
RFC 4248                 The telnet URI Scheme              October 2005

4.  Normative References

   [STD8]     Postel, J. and J. Reynolds, "Telnet Protocol
              Specification", STD 8, RFC 854, May 1983.

5.  Informative References

   [RFC1738]  Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
              Resource Locators (URL)", RFC 1738, December 1994.

   [RFC2396]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifiers (URI): Generic Syntax", RFC 2396,
              August 1998.

   [RFC2941]  Ts'o, T. and J. Altman, "Telnet Authentication Option",
              RFC 2941, September 2000.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

Author's Address

   Paul Hoffman
   VPN Consortium
   127 Segre Place
   Santa Cruz, CA  95060
   US

   EMail: paul.hoffman@vpnc.org