Basic Network Troubleshooting

Howdy Everyone! I wanted to go over my process for troubleshooting the local network in a Home or Small Office. This is a simple guide but I feel that it can be applied in most any network environment. When you are troubleshooting, keep the OSI Model in mind and remember that there are multiple protocals that can be in play at each layer!

There are 3 types of IP Addresses that we most commonly encounter.

1. Private IP Address. Addresses that are local to your home network only.
2. Public IP Address. An address that resolves to your home Router/Modem/AIO appliance; reachable from the public internet.
3. CG-NAT Address. An IP Address that cannot be reached directly from the Public Internet but can still provide network connectivity.

When troubleshooting locally, I like to work up the OSI Model starting from Layer 1. Do I have power and solid connectivity? Does my network interface card have any light lights? If the little lights on your network interface card don’t illuminate, you likely do not have a continous connection! Now lets look inside PowerShell on our machine. Keep in mind that we should only see our Private IP space in PowerShell.

Identify Hardware Failure

Ping localhost or 127.0.0.1. This will ping the local network ‘stack’. This confirms that the networking firmware and hardware on your client device function as expected.

1. If the ping fails, restart your client device.
2. If this step continues to fail; suspect failed hardware.

Identify a Gateway Issue

Using the ipconfig output above, we can see our “Gateway” to the internet is 192.168.0.1. Lets ping it to ensure it is responsive.

1. If it does respond, continue to the next step.
2. If it does not respond, reboot your Router/Modem/AIO appliance.
3. If it does not restore after a reboot, engage your Internet Service Provider.

Identify DHCP Issues

If your ipconfig output shows an IPv4 Address of 169.254.X.X - This address is called an APIPA or Automatic Private IP Addressing. This indicates a DHCP server did not reply to a request for an address. You have two options.

• Run ipconfig /release wait 10 seconds, run ipconfig /renew, and check for an IPv4 Address again.
• Reboot the machine.

If this resolved the issue, great! However if it did not…

1. Most users should reboot their Router/Modem/AIO then retry the steps above.
2. If the issue persist, engage your Internet Service Provider.

Identify a possible WAN Issue

At this point, we can assume our local network is working as expected. Let’s head upstream!

In Powershell, lets ping public resource by IP address. Here are some example IP addresses that should work for 99.9% of my readers.

• ping 8.8.8.8
• ping 8.8.4.4
• ping 1.1.1.1
• ping 1.0.0.1
• ping 9.9.9.9

If one or more of these fail to respond consistently or intermittently; you should engage your Internet Service Provider. Be sure to report the results of these ping tests.

Identify possible DNS Issue

Now that we have validated that our network can route TCP/IP traffic, lets introduce a Domain Name Service.

First clear the DNS cache on your device. The command for this in Windows is ipconfig /flushdns. Wait 15 seconds and then run ipconfig /registerdns. Then run the following pings to verify DNS is able to successfully resolve.

• ping google.com
• ping bluebotpc.com
• ping microsoft.com

If these fail, you can attempt to set manaul/custom DNS servers on your machine to bypass your current issue. If everything has been successful to this point, it is highly unlikely you have a network related issue. This guide does not rule out or test for the presents of firewalls.

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