What is telnet used for?

Answer 1

Telnet is a simple IP/IPS telephony tool used to access text-based content such as MUCKs, MUDs, MU*s, BBS (Bulletin Board Systems), and other pre-World Wide Web content.

One can interface with MainFrame, VAX, and VMS systems, as well as UNIX and Windows systems.

To quote Wikipedia:

"TELNET (TELe-NETwork) is a network protocol used on the internet or local area networks to provide a bidirectional interactive text-oriented communications facility via a virtual terminal connection."

Originally, computers were what we now call "mainframes", and all users connected through them via a Dumb Terminal - a small monitor and keyboard which was connected with a hardwired cable to the mainframe itself. Mainframes could have several of these Dumb Terminals connected at once, each with one user. You could only use the computer that the terminal was directly hardwired to.

After the invention of the ARPANET and the IP protocol, which allowed for computer to talk to each other over telephone cables, some method for connecting to a different computer was needed. That is, a person might be connected to a specific computer via a dumb terminal, but want to log into a completely different machine. TELNET was invented to perform this function: by using TELNET, the software emulated a hardwired terminal connection to the other computer (this was called a "virtual" terminal connection). Telnet was implement both as a client (which the user ran) and a server (which the computer ran, waiting for connection requests). It has been implemented on virtually every computer system which supports IP networking.

These days, telnet is still used primarily for that purpose: to provide a text-based remote log-in capability. Perhaps the most common usage is for logging into various network equipment (routers, switches, modem banks, terminal servers, etc.) to perform administrative tasks. However, as telnet passes on communications in the clear, it has been superceded by SSH (which encrypts all communications) for most virtual terminal use.

Another common usage of the Telnet client program is to talk directly to certain server daemon processes, enabling the user to pass raw commands to these server daemons, primarily for debugging and test purposes. Thus, a Telnet client can talk directly to a mail daemon, an http (web) daemon, the syslog daemon, and even to some file-sharing daemons. In this case, no virtual terminal is created; rather, the user can pass plain text commands to the server daemon in question, just as a normal service request would do.