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Using Telnet


Introduction to Telnet

Telnet is a protocol for emulating a remote terminal, which means that it can be used to run commands entered on a keyboard at a remote machine. The tool Telnet is an implementation of the Telnet protocol, which means that it translates the protocol specifications into programming language to create a program that can emulate a terminal.

Telnet operates in a client/server environment, meaning that the remote machine is configured as a server, and consequently waits for the other machine to request a service from it. Therefore, since the remote machine is sending data to be displayed, the user feels like he/she is working directly on the remote machine. In UNIX, the service is provided by what is called a daemon, a small task that runs in the background. The Telnet daemon is called Telnetd.

Protocols and implementation

Telnet is also a protocol, a set of rules and procedures which have been defined in order to standardise Telnet communication. For this reason, Telnet has been implemented across numerous platforms, based on the specifications of the protocol.

Running Telnet

Telnet is provided with various platforms, including UNIX, Windows 95, Windows NT, and Linux.
The command to initiate a Telnet session is usually: 

telnet server_name

server_name represents the name or IP address of the remote machine that the user wants to connect to. You can also give its IP address, for example: 

telnet 125.64.124.77

Finally, you can also specify which port to use by putting the port number after the IP address or server name: 

telnet 125.64.124.77 80

Commands in Telnet

Once you are connected to the remote machine, you will be asked to provide a login and password for security reasons, to keep access restricted to authorised individuals only. Indeed, the reason Telnet is such a powerful protocol is that it allows commands to be run remotely. The commands that can be run in a Telnet session are defined by the network administrator. They tend to be UNIX commands, as most Telnet servers run UNIX. The standard commands are:

Command Description
? show help
close Close Telnet session
display Show connection settings onscreen (type of terminal & port)
environ For defining the operating system's environmental variables
logout For logging out
mode Switches between the transfer modes ASCII (transferring a file as text) and BINARY (transferring a file in binary)
open Opens another connection from the current one
quit Leaves the Telnet application
set Changes the connection settings
unset Loads the default connection settings
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