| FAQ Article: What is Telnet? |
Telnet is a program that comes by default with Windows and most Unix/Linux distributions. Put simply - Telnet allows you to connect to other computer systems (using ports). A port is basically a door into a computer, which by default will be closed/shut, but will be opened if your computer needs to use it (usually software applications are responsible for opening up ports on your PC).
You might not realise it - but your computer connects to ports on many different systems all over the Internet everytime you surf the net. In fact, your computer will have connected to port 80 on www.wangproducts.com so that you could view this page! (port 80 is the default HTTP port).
Ever wondered how web pages get into your web browser? well - your computer connects to the web server (for example www.wangproducts.com) on port 80 (default HTTP port). It then sends data into the port specifying various information and the web page we would like to retrieve. The web server software running on port 80 then sends the web page you requested back to your PC - and your web browser displays it. The software listening on a port is usually called a "daemon".
Telnet is a basic utility that will allow you to manually connect to any system on any port you wish. Some common port numbers are:
- Port 21 - (FTP) - used for FTP file transfer connections
- Port 25 - (SMTP) - used for sending email
- Port 110 (POP3) - used for receiving email
- Port 80 (HTTP) - used by web servers to serve web pages
I've skipped TONS of ports there, but those are 4 very common ports. For a better list of ports - try a google search for "port list".
So, would you like to telnet to somewhere? :) - ok, how about we telnet to a free unix shell provider, just so you can get a taste for how telnet connects you to other systems on the net.
In the example below we will telnet to mail.virgin.net on port 25 (SMTP mail port). After connecting, you will see the welcome banner that the mail server software sends back to your system to show you are connected and that it is waiting for your commands:
- In Windows, go to the start menu and choose "Run..." (if you are a unix/linux user, just open a new shell)
- Type "telnet mail.virgin.net 25" (without the quotes)
- Your system will now connect to theirs, and you will see a welcome banner like "220 n064.sc1.cp.net ESMTP Service (7.0.043) ready"
We will use Telnet more throughout our later FAQs - it really is a very useful tool.
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Posted on: 19-08-1999
Article has been viewed 9046 times
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