notacomputergeek

There have been several times in my career that I have come across faulty network interface ports or bad ethernet cables/connections and they can be difficult to diagnose. Symptoms usually appear when network devices go offline, come back online, go offline, etc. Here are a few steps and inexpensive tools that can help the process. Obviously, your local data cabling vendor has far more sophisticated tools if you want to hire them.

In a network environment, I like to start with installing PRTG Network Monitor Freeware Edition (www.paessler.com) on a computer (server, if available) that constantly monitors devices on the network using the Ping sensor. PTRG is free for up to 100 sensors, so if your network is small, this is a great, inexpensive tool. PRTG can be installed any time, so it’s best to have it in place before problems occur.

For those of you who don’t know, the ping network command basically sends a command to the device (by IP address or name) and says “are you there?, are you there?, are you there?” in perpetuum. If it doesn’t get a proper response, the PRTG software can send you an email. That’s how you know something went offline. The port on the device should respond with “yes, I’m here”, but sometimes there is no response, or it responds with “blah, blah, blah” – uff-dah!

One tool I like to use is the Klein Tools Scout Pro 3 (Amazon US $75) ethernet cable tester for testing cables and connections. There are better testers available, but this one is a good value. One of my frustrations with cable installers or DIY installers is that sometimes nothing is labeled, so you have no idea where the other end of an ethernet cable goes.

Now, on to a problem I encountered recently. The first step to diagnosing is to determine how widespread is the problem. Is it one user, all users, or a specific department having the issue? In this case, the PRTG Ping sensors (on the server and a local desktop) were showing devices all over the network going up and down. Eventually, no one had consistent access to the server, but the internet was working for most. Looks like this is affecting everyone trying to access the server files. Here is a look at a portion of the network.

I opened two command prompts on a Desktop computer and started pinging the Router and the Server. The Router responded fine, but the Server did not. Using the ping command on the Server to the Router showed sporadic success, so the problem is likely near the Server. This really does depend on your network and where your switches are located, so it helps if you have a network map. Sometimes network drivers need to be reloaded or even updated, so I rebooted the Server and still had problems.

The next step was to use our Klein tool and test the cable going from the server to a nearby switch. It tested fine. I then moved the Server ethernet cable to different ports on the Switch, but still had the same sporadic connectivity. Next, I had a spare switch, so after I swapped it out, we still had connectivity issues. It’s likely not a bad switch. There was a Laptop connected to a docking station next to the Server and the docking station ethernet cord was connected to the same Switch as the Server. Pinging the Server from the laptop still had connectivity issues, but I’m narrowing down the problem.

I rebooted the docking station – still had problems. Because of my experience with these particular docking stations (Dell WD19S), I unplugged the ethernet cable from the docking station, plugged it directly into the laptop, and Boom!, all my pings started working properly in <1ms. I had found my problem – the ethernet port on the docking station must be bad and spewing garbage (“blah, blah, blah”) over the network. I like the Dell WD19S docking stations, but I’ve seen many of their network interface ports go bad.

There are so many more sophisticated network diagnostic tools, but this article is intended for semi-technical people who aren’t afraid to try. It’s really just a process of elimination using some simple tools. So, the next time you’re experiencing network issues, I hope at least some parts of this will help.