In this tutorial I will be explaining the use of Telnet for accessing your cgi webspace shell as well as using it as a very simple and useful diagnostic aid in determining if a server or service is responding to requests.

In the following sections I will explain what Telnet is and show how it can be used for:

• Accessing the shell on a CGI server (port 23)
• Checking a web server (port 80)
• checking a POP3 mail server (port 110)
• Checking a SMTP mail server (port 25)
• checking a Autoturn MX backup mail server (port 79)

The port numbers will become obvious in the section descriptions and are included here as a quick reference.