Question

How can I verify communication over a specific port using the Telnet Client?

 

Prerequisite

Install the Telnet Client on the server from which you want to test your connection.

 

Answer

  1. On the server from which you'd like to test communication, open a Command Prompt
  2. Run the command telnet
  3. Watch to see if you get a response (typically indicated by strings of gibberish) or if the connection fails

Example:

To see if your Site Server machine "mySiteServer" can communicate with the Agent installed on "myAgent" over port 3999, you'd run the command telnet myAgent 3999 from "mySiteServer".

If you receive a response similar to the screenshot below, it indicates communication is open over port 3999 between "mySiteServer" and "myAgent":

https://s3.amazonaws.com/cdn.freshdesk.com/data/helpdesk/attachments/production/69009876516/original/2017-07-03_13_59_23-AccessData_Help_Center_-_Agent.png?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAS6FNSMY2XLZULJPI%2F20210926%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20210926T165714Z&X-Amz-Expires=300&X-Amz-SignedHeaders=host&X-Amz-Signature=5a345c098d4dc183f9c7e801729d55bc869380438bfd8d63a6ce635b61ff3453

If you receive a message like "Connect Failed", there is something between "mySiteServer" and "myAgent" blocking communication over port 3999 (firewall, security software, etc).

 

Overview

The Telnet Client can be used as a sort of super-ping, allowing you to initiate communication to a target over a desired port to look for a response.