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TELNET IS TCP

TELNET (TELetype NET work) is a network protocol used on the Internet or local area network LAN connections. It was developed in 1969.

Telnet is TCP/IP protocol (Transmission control protocol/Internet protocol) that provides a standardized means of accessing resources on a remote machine where the initiating machine is treated as local to the remote host. In many implementations Talents can be used to connect to the port number of other servers and to interact with them using a command line. For example, the HTTP (Hyper Text Transfer Protocol) and SMTP (Simple Mail Transfer Protocol) were generated this way.

The Telnet protocol is based on the concept of a network virtual terminal (NVT), which is an imaginary device that represents a lowest common denominator terminal. By basing the protocol on this interface, the client and server machines do not have to obtain information about the each other’s terminal characteristics. Instead each machine initially maps its characteristics to that of an NVT and negotiates options for changes to the NTV or other enhancements, such as changing the character set.

The Network Virtual Terminal

The Network Virtual Terminal (NVT) is a bi–directional character device. The NVT has a printer and keyboard. The printer responds to incoming Data and the keyboard produces out going data which is sent over the telnet connection

Telnet commands use the 7–bit U.S variant of the ASCII character set. A command consists minimally of the 2 byte sequence: the Interpret As Command (IAC) escape character followed by the command code. If the command pertains to option negotiation, that is, one of WILL, WON’T, DO or DONT, then 3 byte contains the option code.


PROTOCOL DETAILS: TELNET is the client server protocol, based on reliable connection oriented transport. Typically this is TCP port 23, but in fact Telnet predates TCP/IP and was originally run on NCP.

 There are many extensions; some of each has been adopted as internet standards. IETF STD documents 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.

SECURITY: There are 3 main reasons why TELNET is not recommended for modern systems from the point of view computer security:

  1. Commonly used TELNET daemons have several vulnerabilities discovered over the years, and probably several more still exist.
  2. TELNET, by default, does not encrypt any data sent over the connection (including pass words), and so it is trivial to eavesdrop on the communications and use the password later for malicious purposes.
  3. TELNET lacks an authentication scheme that makes it possible to ensure that communication is carried out between the two desired hosts, and not intercepted in the middle (see also Man-in-the-middle attacks).

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 be used as a rudimentary IRC client if one knows the protocol well enough. TELNET is still very popular in enterprise networks to access host applications, i.e. on IBM Mainframes.

TELNET is also heavily used for MUD games played over the internet, as well as talkers, MUSHes, MUCKs and MOOes. By using image- to-ASCII algorithms, it cab also be used for primitive “video” streaming. Recently, ASCII-WM offered live broadcasts of the 2006 World Cup.
                                                                                  -Pavana, V SEM