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Monday, March 22, 2010

The TELNET (Terminal Network) Protocol

TELNET (TErminaL NETwork) is a network protocol used on the Internet or local area networks to provide a bidirectional interactive communications facility.
- Telnet offers users the capability of running programs remotely and facilitates remote administration.
- Telnet is available for practically all operating systems and eases integration in heterogeneous networking environments.
- The Telnet protocol is applied on a TCP connection to send data in ASCII format coded over 8 bits between which the Telnet check sequences come.

Communication is established using TCP/IP and is based on a Network Virtual Terminal (NVT). On the client, the Telnet program is responsible for translating incoming NVT codes to codes understood by the client's display device as well as for translating client-generated keyboard codes into outgoing NVT codes.


The Telnet protocol uses various commands to control the client-server connection. These commands are transmitted within the data stream. The commands are distinguished from the data by setting the most significant bit to 1.

Telnet Options

Options give the client and server a common view of the connection. They can be negotiated at any time during the connection by the use of commands. They are described in separate RFCs.


The use of Telnet for remote logins should be discontinued under all normal circumstances, for the following reasons :
- Telnet, by default, does not encrypt any data sent over the connection (including passwords).
- Telnet have no authentication that would ensure communication is carried out between the two desired hosts and not intercepted in the middle.

Telnet is popular in various application areas:

- Enterprise networks to access host applications, e.g., on IBM Mainframes.
- Administration of network elements, e.g., in commissioning, integration and maintenance of core network elements in mobile communication networks, and many industrial control systems.
- MUD games played over the Internet.
- Internet game clubs.
- Embedded systems.
- Mobile data collection applications.

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