11.9.1 Network Troubleshooting

Learn to troubleshoot common network, wireless, and VoIP issues.

Before troubleshooting, you should have a clear baseline. The baseline of your network should define how the network operates when nothing is wrong with it. This will help you isolate and begin work on issues much quicker. Other information could include:

• network speed
• available services
• connected devices

Basic Checks

Run these simple checks to avoid extensive time wasted.

• network cable is plugged into the computer, wall jack, and network switch
• verify that the cable actually works using a cable tester or check for link activity lights
• verify that all network equipment (routers, switches, servers) are turned on and operational

Slow Speeds

Identify exactly what is running slow. Is it the network itself? Is it just a specific resource hosted on the server? If so, then you can focus on fixing the transfer speeds of that device. Otherwise, you need to find out what's causing the high latency. A common cause of this is called port flapping. Port flapping happens when a port on a network switch is continuously turning on and off several times per second. Reseating or replacing the network cable where the port is located should resolve the issue. If it doesn't, replacing the switch may be necessary.

You should also make sure that the network infrastructure actually supports the speeds we're expecting. This includes making sure that the correct cabling and devices support our projected speeds. If there is a switch that runs below our expected speeds, that means the entire network is being dragged down to that speed.

On each device, verify that there aren't any background tasks that could be overwhelming the connection, and that the network adapter drivers are up to date.

Limited Connectivity

This just means something on the network can't be accessed. This could be a shared resource, a Dynamic-Host-Configuration-Protocol or a DNS server. The first troubleshooting thing you can do is to ping the loopback address to ensure that the installed network interface device is working properly. You can then ping the host's IP address to ensure that the network configuration is correct.

From there, you ping various devices that stretch further and further outside the local network, like the default gateway (ensures you can communicate with other devices on the local network) or a DNS server (communicate with systems outside the network).

Ensure that you have a valid IP address (any address that isn't assigned by Automatic-Private-IP-Addressing).

VoIP Issues

Make sure that Quality-of-Service is configured to priorities VoIP packets. Ensure that there isn't unnecessary latency on our network due to port flapping or background tasks (also malware but we're assuming you aren't dumb). Ensure that excessive jitter isn't a result of weird QoS settings or misconfigured VoIP endpoints with jitter buffers (not necessary to have them, but if you do it could be another source of issues when using VoIP).

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