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 standardize Telnet communication. For this reason, Telnet has been implemented across numerous platforms, based on the specifications of the protocol.
Telnet is provided with various platforms, including UNIX, Windows 95, Windows NT, and Linux.
The command to initiate a Telnet session is usually:
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:
Finally, you can also specify which port to use by putting the port number after the IP address or server name:
telnet 220.127.116.11 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 authorized 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:
|| 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 |