Port Party is meant to be a quick-read series highlighting some of the more common things particular ports are used for and exploring around a bit. It is not meant to be exhaustive!
telnet lets you communicate with other computers.
The Dark Days
Long, long ago in the days where computers were as big as rooms and punch cards were the hot new thing there was an issue: what happened when you wanted to have a computer do a certain calculation but you were a lowly grad student or scientist who was at the mercy of the university or government agency when it came to using the computer.
Some old-timers note that it was rough: they'd have to not only have a punch-card ready, but they'd have to submit it to an operator (physically walk over to some person who was in charge of operating the computer!) and then wait in a queue for a while until the results came out and the operator got in touch with you (via phone? via yelling? via grapevine?) and you got your results. And if you messed up and had a bug in the code? Welp. Enjoy your wasted week.
But Out of the Darkness...
Telnet was born in 1969. This allowed individuals to run computers at-a-distance decreased the amount of walking done by computer scientists by a fair bit. This isn't a history lesson, so I'll just note that if you're interested in this sort of thing there's a ton of interesting stories around how this came about and some drama related to putting it into computer systems. Some argue this started (or at least solidified) the client-server relationship.
 Okay, Telnet is not actually the application, it's the protocol, but we use them mostly interchangably these days. Get off my back, dang.
Okay, so we still use it, right?
Ehhhh, sort of. We have things which are better now, like SSH. Telnet, while revolutionary, was created in an age where people weren't too worried about security. But now-a-days, we're pretty worried about that sort of thing.
Fine, what can we still do with it?
Okay, yeah, so there's a few fun things you can still do with telnet, even with the lack-of-security.
- Checking the weather if you, for whatever reason, you only have a shell. Type in
telnetinto your terminal and then the command
o rainmaker.wunderground.com. Once you do this, it'll ask for you where you want to see the weather. If I plug in
chi, it shows me the Chicago weather. Pretty cool!
- A much more interesting use of Telnet is to test if a port at a specific address is open or not. This is pretty neat. There are currently better ways to achieve essentially the same goal but for a quick check it's not bad!
$ telnet 192.168.0.10 25 Trying 192.168.0.10... telnet: Unable to connect to remote host: Connection timed out # Whoops, guess 25 isn't open on 192.168.0.10! $ telnet blog.jsalv.com 443 Trying [blog.jsalv.com]... Connected to blog.jsalv.com. Escape character is '^]'. # Looks like 443 is open on some foolish scrub's domain!
There's a few other things that you might want to do with telnet, including some forums which are still active (!!) but this should at least help you get your feet wet.