Tag Archives: troubleshooting - Page 2

How to “ping” a port

Most of us would be familiar with the simple ICMP based ‘ping’ command which allows us to test for a basic response from some network connected device. While great for basic troubleshooting it does not allow us to confirm if the particular host at the other end is responding on TCP or UDP ports where the majority of services are likely to be provided.

Ping isn’t the be all and end all of network troubleshooting, if a firewall blocks inbound ICMP traffic then a ping will not succeed which can produce a false perception that the host is down as it is not responding to the ping, however other services could still be responding fine.

Alternatively while ping may come back fine with a response it doesn’t indicate if a web server is responding on port 80 for HTTP requests, the web server may have failed and no longer be responding.

So if ping is ICMP based, can we hit a TCP or UDP port for response instead? The answer is yes, let’s take a look.

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How to test network connectivity with telnet

This post is a follow on from my post last week regarding how to install the telnet client. The telnet client is simple yet extremely powerful in helping us gain a quick idea of where a problem may lie with TCP connectivity, it’s one of my first go to tools to use when testing a network connection to a server.

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How to enable the telnet client in Windows 8.1

By default the telnet client in Microsoft’s Windows operating systems is disabled, this is unfortunate as it is an extremely useful tool which can be used for testing TCP connectivity to external hosts on a specified port.

This is great when you’re trying to troubleshoot network connectivity problems, for example, say we have a web server which should be listening on port 80 to serve HTTP traffic but we are not able to load a web page, by using telnet to connect to the web server on port 80 we can verify the connectivity.

It may be that the connectivity is fine but there is a problem with the web server, or that the web server is stopped and the port is not listening at all, for instance. With telnet we can get a better understanding of what’s going on.

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