Web Service to Test Ports
Good-old grc.com has a good external port tester called ShieldsUp! - https://www.grc.com/
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Test When You Have a Remote Computer Handy
The easiest way to test if a port is listening (i.e. the service or daemon hasn't crashed) if you don't have the proper client program handy is to telnet to the specific tcp/ip port. If you get no response, service is probably down. If you get a connection, service is probably up. Personal uses include testing a IP restricted terminal server from my home linux server through SSH.
In Windows and Linux you can telnet to a specific port with the 2nd parameter. I.e. "telnet [hostname/ip] [port]".
E.g.
Test if pop3 (port 110) server up?
"telnet mymail.mydomain.com 110"
Test if Remote Desktop/Terminal Server (port 3389) server up?
"telnet myterminalserver.mydomain.com 3389"
This only works for TCP/IP! For UDP use... that other thing...
tags: test, diagnose, network, port, telnet, tcpip, remote,