Telnet was developed in the year of 1969, it was constructed to be a form of remote control to mainframe computers from the distant terminals.
It is a network protocol used on the Internet or local area networks to provide a bidirectional interactive communications facility. Telnet provides access to a command-line interface on a remote host via a virtual terminal connection which consists of an 8-bit byte-oriented data connection over the Transmission Control Protocol (TCP).
The computer being connected to, which accepts the connection, is referred to as the remote computer. The remote computer can be physically located in the next room, the next town or in another country.
TELNET permits a user to log in on any other computer on the network. We can start a remote session by specifying a computer to connect to. From that time until we finish the session, anything we type is sent to the other computer.
The Telnet program runs on the computer and connects your System to a specified server that you wish to access on the network. We can enter commands through the TELecommunication NETwork program and they will be executed as if we were entering them directly on the server console. This enables us to control the server and communicate with other servers on the network. you must log in to a server by entering a valid username and password when start Telnet session. Telnet is a common way to remotely control Web servers.
The term telnet also knew as software that implements the client part of the protocol. TELecommunication NETwork clients have been available on most Unix systems for many years and are available virtually for all platforms. Most of the Operating System’s and networks’ equipment with the TCP/IP protocol stack supports any one kind of telecommunication network services or server for their remote configurations based on a reliable connection-oriented transport.
Generally, this protocol used to establish a connection to TCP port 23, where a getty-equivalent program is listening, although TELecommunication NETwork predates.
The following are common ports to connect the telnet:
Port 21 ~ File Transfer Protocol
Port 22 – SSH Remote Login Protocol
Port 23 – Telnet Server
Port 25 – Simple Mail Transfer Protocol (SMTP)
Port 53 – Domain Name Server (DNS)
Port 69 – Trivial File Transfer Protocol (TFTP)
Port 70 – Gopher
Port 80 – HyperText Transfer Protocol (HTTP)
Port 110 – Post Office Protocol 3 (POP3)
Command Prompt> Telnet <Remote Host or IP address>