Telnet Basics

A tutorial on telnet for beginners. Explains what telnet is and how to use it.

First of all what is telnet ?
Telnet is a protocol which is part of the TCP/IP suite. It is quite similar to the UNIX rlogin program. Telnet allows you to control a remote computer from your own one. It is terminal emulation software. In the old days harddrives were humonguous and expensive (i am talking waY back here) and there were no personal computers. To make use of existing computers you had to lease hardrive space and use terminals to operate the system. For developers this was great because computing became lots cheaper. You needed a server and many connections could be made. With telnet u can emulate this type of distributed computing and for example operate a supercomputer from a distance.

TCP/IP works with ports and telnet has one also. It's nr 23. It's has several rfc's. Nr 854 dates back to 1983 and is named telnet protocol specification.
With telnet you can do various things like send mail, log in to irc or proxy and even (though hardly anymore) view and modify websites. There are telnet services available allowing you to search through large databases using telnet. With this you use the remote computer's power so it won't presure your precious resources. Usually help or remotehelp are the commands to use to find out what you can and cannot do. If you can't see what you type in then set echo. Once you made a connection you can use the computer as if it was your own. You use command lines for this.
Telnet knows different emulation types. VT-100 is most used. This emulation was used on the video terminals of DEC. There are still VT-100 servers running out there. Scientists use these.

To use telnet you need a client. Windows has telnet built in by default (as does UNIX but that's a different story), but there are third party clients available on the net. You start a telnet session by typing in the command 'telnet server.net 23' where the port number is optional. Since Telnet was based on UNIX (as it is part of TCP/IP which also was based on UNIX) it uses UNIX commands. Basic knowledge would help you here. The port number specifies what services you will use. 23 is the default one. You can log into various services. 80 is the HTTP server for that.
So say you wanted to modify your site from a distance on a leased line. You don't have your fav progs and hardly any time.
/* telnet server.net 80 (leave the /*)
/* GET http://www.server.net/YOURSITE.HTM HTTP/1.1
You can use this method to get the output of a cgi-script as well. The simple request doesn't use the HTTP/1.1 (this is the HTTP version running on the server). If you perform a bad request you usually get some info on the server. Use this to find a the correct versions of services running.
To put files to the server u use the PUT command. Telnet is pretty simillar to FTP which is also part of TCP/IP. There are other commands available like POST, which is used to put larger data files to the server, HEAD to get the sites header and DELETE. This one is obvious isn't it.
You can also use telnet to send raw imails. The port to login to is 25.
First you have to identify your self. This geos like this:
/* telnet mail.server.net 25
/* HELO www.you.net
When you typed this command you'll get some feedback telling you who and what you logged on to. When you login u may get also some feedback telling you things. :`;
After this you tell the server where the mail is from like this:
/* MAIL FROM:you@youradress.net
The server will give you feedback again telling you
/* ...Sender OK