Telnet is one of those tech terms you may occasionally hear, but not in an ad or a feature laundry list of any product you may buy. That’s because it’s a protocol, or a language used to talk to computers and other machines; not only that, but Telnet is actually ancient in Internet terms, dating back from 1973.
So what is Telnet, and what is it good for, anyway?
A Concise Definition
Wikipedia’s terse definition of Telnet is:
Telnet is a network protocol used on the Internet or local area networks to provide a bidirectional interactive text-oriented communications facility using a virtual terminal connection.
Wow, that’s a mouthful. Let’s break it down for the rest of us, term by term. If there’s a term you already know, feel free to skip it.
- Network protocol: That’s basically a language, a way for machines to talk to one another.
- Bidirectional: That means Telnet is not one-way; it can be used to send and receive information.
- Interactive: That means Telnet basically expects a live user on one end of the line. Telnet is not usually used for computers to talk autonomously with each other, but was built from the ground up to be human-readable.
- Text-oriented: Telnet is a text-only protocol; you won’t see graphics or fancy images while working with Telnet, nor will you be able to transfer files with Telnet.
- Virtual terminal: Historically, a terminal was a “dumb” computer, with only a keyboard and a screen and no powerful built-in processing facilities. Modern computers can take on the role of a terminal (i.e, open a communications session with another computer), but they are not “real” terminals (their hardware is more powerful). Thus, they are virtual terminals.
Now that we have gone over these, go back and read the Wikipedia definition again. Does it make more sense?
To sum it up in simple terms, Telnet is used to communicate with other computers and machines in a text-based manner. A telnet session looks something like this:
That’s not very visually exciting, but this single screenshot shows all the elements in the definition. You can see that I’m communicating with a network host, and communication is bidirectional and interactive (the host displays text, and then awaits an Enter key press to continue). No image is in sight, so that covers the “text-oriented” part. Last but not least, you can see that the Telnet session is actually running in a Windows 7 window, which means my computer is a “virtual” terminal.
The Most Important Thing You Should Know About Telnet
The one thing you should know about Telnet is that it is not a secure protocol. When you log into a remote host using Telnet, your username and password are sent “in the clear” – meaning, in plain text and not encrypted in any way. That means your credentials can be (relatively) easily intercepted and used to gain access to that device. For this reason (and many others) Telnet has been largely replaced by the more secure SSH protocol.
So What Is It Good For?
So Telnet is text-based, and is not secure. But that doesn’t mean there’s no use for it. There are two common uses for Telnet:
- Configuring network devices: What you see above is a screenshot from my own ADSL router; this is a thoroughly modern router with a Web interface and all, but it also accepts incoming Telnet connections from the local LAN. That means if I ever want to configure it via Telnet, I can.
- Participating in online communities: Telnet’s text-based nature, and the fact that a Telnet session often looks like something from the early Seventies, actually make it ideal for online communities. The Telnet BBS Guide lists 375 different BBSes (bulletin board systems) which you can participate in using Telnet. A typical BBS looks something like this:
What you may find inside varies widely; perhaps it’s ancient and deserted, and perhaps there’s a small and close-knit community of users just waiting to be discovered. Who knows?
And of course, Telnet can also be used for plain old fun:
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