Using telnet


  • Applies to: Grid
    • Difficulty: Easy
    • Time Needed: 10
    • Tools Required: None
  • Applies to: DV
    • Difficulty: Easy
    • Time Needed: 10
    • Tools Required: None
  • Applies to: (ve)
    • Difficulty: Easy
    • Time Needed: 10
    • Tools Required: None

Overview

Telnet is often used when diagnosing problems, to manually "talk" to other services without specialized client software. For example, it is sometimes used in debugging network services such as an SMTP, HTTP, FTP or POP3 server, by serving as a simple way to send commands to the server and examine the responses.

Instructions

In this example, we use port 25 to test SMTP. However, you can use telnet to test any port you wish. Here are a few more examples:

Port NumberDescription
587 Alternative SMTP port
110 POP
22 SSH
143 IMAP

You can find a good detailed list of examples at http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers.

On Mac OS X

  1. On Mac OS X, you have to use the Terminal application located in the Applications/Utilities folder.
  2. Type the following command:
    telnet example.com 25

On Windows XP

  1. Go to the start menu and click on run. In the box type cmd and hit enter. This should open a command prompt window.
  2. Type the following command:
    telnet example.com 25

On Windows Vista

Please try the following:

  1. Go to the start menu. Click on Accessories and select Command Prompt.
  2. Type the following command:
    telnet example.com 25

CAUTION:

By default, Vista doesn't install the Telnet client. The client is for text-based communication with remote systems. You can install it by following these steps:

  1. Click Start and select Control Panel.
  2. Select Programs and Features.
  3. Select Turn Windows features on or off.
  4. Select the Telnet Client option.
  5. Click OK.
  6. A dialog box will appear to confirm installation.

The telnet command should now be available so you can perform the telnet test.

Resources