About Opentopia
Opentopia Directory Encyclopedia Tools

TELNET

Encyclopedia : T : TE : TEL : TELNET

TELNET is a network protocol used on the Internet or local area network LAN connections. IETF document STD 8 (aka [RFC 854] and [RFC 855]) states:

The purpose of the TELNET Protocol is to provide a fairly general, bi-directional, eight-bit byte oriented communications facility.

It is typically used to provide user oriented command line login sessions between hosts on the Internet. The name is derived from the words telephone network, since the program is designed to emulate a single terminal attached to the other computer.

By extension, "telnet" also refers to the program which provides the client part of the protocol. TELNET clients have been available on most Unix systems for many years and are available for virtually all types of computers. Most network equipment and OSs with a TCP/IP stack support some kind of Telnet service server for their remote configuration (including ones based on Windows NT). However with recent advancements SSH has become more dominant in remote access for Unix-based machines.

On many systems, the "telnet" client program may also be used to make interactive raw-TCP sessions and is used to communicate to services such as POP3 servers without specialized client software. Although on UNIX other commands such as nc (netcat) or socat are generally better suited for this kind of (testing) usage, as they can be called with arguments to not send any terminal control handshaking characters.

"To telnet" is also used as a verb meaning to establish or use a TELNET connection, as in, "To change your password, telnet to the server and run the passwd command".

It is also a means to connect to the new style Telnet Bulletin Board Systems (that once upon a time were dialup in the 1980s and 1990s) that allow for nostalgia over TCP/IP as well as most supporting all of the well known and other commonly used protocols on the Internet today as a full blown multi-protocol server suite.

Contents

Protocol details

TELNET is a client-server protocol, based on TCP, and clients generally connect to port 23 on the host providing the service programs, it is also possible to use a TELNET program to establish an interactive TCP connection of the protocol and a means of defining and implementing extensions. There are many extensions, some of which have been adopted as Internet Standards. IETF STD document numbers from 27 to 32 define various TELNET extensions (most of which are extremely common). Of the remaining extensions the most useful ones are probably those that are on the IETF standards track as proposed standards; details can be found in STD 1.

Security

There are three main reasons why TELNET is not recommended for modern systems from the point of view of computer security:

In environments where security is important, such as on the public Internet, TELNET should not be used. TELNET sessions are unencrypted. This means that anybody who has access to any router, switch, or gateway located on the network between the two hosts where telnet is being used can intercept the TELNET packets passing by and easily obtain login and password information (and whatever else is typed) with any of several common utilities like tcpdump and Wireshark.

These flaws have seen the usage of the TELNET protocol drop rapidly in favor of a more secure and functional protocol called SSH, released in 1995. SSH provides all functionality present in telnet, with the addition of strong encryption to prevent sensitive data such as passwords from being intercepted, and public key authentication, to ensure that the remote computer is actually who it claims to be.

Experts in computer security, such as SANS Institute, and the members of the comp.os.linux.security newsgroup recommend that the use of TELNET for remote logins should be discontinued under all normal circumstances.

When TELNET was initially developed in 1969, most users of networked computers were in the computer departments of academic institutions, or at large private and government research facilities. In this environment, security was not nearly as much of a concern as it became after the bandwidth explosion of the 1990s. With the exponential rise in the number of people with access to the Internet, and by extension, the number of people attempting to crack into other people's servers, TELNET should generally not ever be used on networks with Internet connectivity.

Current status

While the TELNET protocol itself has been mostly superseded, the TELNET clients are still used to manually "talk" to other services. It is sometimes used in debugging network services such as an SMTP or HTTP server, by serving as a simple way to send commands to the server and examine the responses. TELNET can also be used as a rudimentary IRC client if you know the protocol well enough.

TELNET is also heavily used for MUD games played over the Internet, as well as talkers, MUSH es, MUCKs and MOOes. By using image-to-ASCII algorithms, it can also be used for primitive "video" streaming. Recently, [ASCII-WM] offered live broadcasts of the 2006 World Cup.

TELNET clients

Multiplatform

Windows

Free with Source Code

Non-free Source Code

Macintosh

TELNET servers

Free with Source Code

See also

External links

 

From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.

Search Titles
0123456789
ABCDEFGHIJ
KLMNOPQRST
UVWXYZ?

E-mail this article to:

Personal Message: