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 (C) The Internet Society (2005).
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.
URIs were previously defined in [RFC2396], which was updated by
[RFC3986]. Those documents also specify how to define schemes for
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
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:
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
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
Hoffman Standards Track [Page 2]RFC 4248 The telnet URI Scheme October 20054. 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,