Troubleshooting network problems

By September 8, 2016Troubleshooting

its-not-the-networkYou might not know it, but you don’t need to be a network engineer to perform basic network troubleshooting. Working as a network engineer for many years made me realize how many problems could be addressed by regular users without need to call the help desk or open a ticket.

To back my claim, here is a simple step-by-step procedure that you can follow to determine whether the problem you’ve encountered is caused by your laptop, the network, or the application you’re trying to access. Based on this information, you can easily figure out what needs to be done, saving yourself time and frustration.

What’s the problem?

First of all, we have to define the problem. Ideally, we want to provide as much as accurate information that we can to our friends at the help desk. Saying the Internet is broken or that you can’t connect to the network is not enough.

Here is one first question that you need to answer: “If I open my browser, can I access major websites like google.com and cnn.com?”

    • If you cannot, then keep reading.
    • If you can, but you still have problems accessing one specific application or website, then you can open a ticket to see if help desk can solve it. Most probably is on a part of the network that you don’t have control on, or it’s related to the application itself.

Are you connected?

You need to verify if your Ethernet or WiFi interface is connected to the network. In Windows, the icon that represents the ethernet or wifi connection is located on the bottom right portion of the desktop, while in Mac it’s located on the top right bar.

Windows 10 ethernet interface

widows-ethernet

Mac OS X wifi interface

macosx-wifi

If you are not connected, verify with your support team that the wireless network is active. You can also ask some other users in the same location whether they can connect to the network. If they can, perhaps reboot the workstation and do another test before calling the help desk.

Open the console

Now, open the command prompt to execute some diagnostic commands. If you are using Windows, you have type cmd in the search bar available next to the Start menu icon (Windows 10) or in the Start menu itself (Windows 7 and earlier versions). If you are in Mac Os X, type terminal in the search bar accessible on top right by clicking on the magnifying glass icon.

Do you have an IP address?

An IP address is needed for a computer to communicate with other computers. Also, the IP address uniquely identifies a workstation in a network. In this step, we need to verify that we got an IP address from the DHCP server, which is responsible to dynamically assign IP addresses to clients.

To verify the IP address on your system, type the following commands into the command prompt:

Windows: ipconfig /all

Mac OS X: ifconfig

If your IP address begins with 169.254, then it was auto-configured by the operating system, meaning that communication is missing between your workstation and the DHCP server. If that’s the problem, then tell your support team that you cannot get a DHCP address.

Can you ping the default gateway?

The default gateway host is responsible for transmitting packets to external networks, including the Internet. In this step, we will first get the IP address of your default gateway, and then verify with the PING command that your workstation can reach it.

To get the IP address of the gateway,  type the following command and then hit enter:

Windows: ipconfig /all | find Default Gateway

Mac OS X: netstat -rn | grep default

This command should return an IP address.

Then use the ping command to verify if you can reach the gateway, replacing with the IP address you got using the previous command :

Windows: ping

Mac OS X: ping -c 4

For example, a positive ping command to the gateway 192.168.1.1 will look like:

Windows

Mac OS X

Otherwise, if ping times out, it means that you can’t reach the gateway* and you should communicate this to your help desk.

Windows: Request timed out.

Mac OS X: Request timeout for icmp_seq 0

* Keep in mind that some network administrators may disable or block gateways from responding to ping commands.

Do you have DNS servers configured?

A DNS server enables a computer to translate a website name, like www.google.com, into an IP address. This service, called hostname resolution, is needed because, while humans remember names easily, computers need IP addresses to communicate with one another.

To verify if you can resolve hostnames, you can execute a ping command to google.com. When you execute a ping command to a hostname, the operating system performs a resolution and the IP obtained is displayed in the ping command.

Windows

Mac OS X

If you don’t see an IP address resolved, then you either don’t have a DNS configured, you cannot reach the DNS, or the DNS server is not working.

To figure out what the problem is, first check if you have a DNS configured.

Windows: ipconfig /all | find DNS Servers

Mac OS X: grep nameserver /etc/resolv.conf

If you have one or more DNS servers configured, then verify if you can ping them. If you can’t ping them, report this problem to your help desk. If you can ping them, but you can’t still resolve an IP address as proven in the previous ping command to www.google.com, then you should report this problem to your help desk.

Cheat sheet

network-troubleshooting.001

Here is a quick list of the steps we followed to troubleshoot network connectivity issues you experience in which you can’t connect to any website.

  1. Verify connectivity
  2. Verify IP address
    1. Windows: ipconfig /all
    2. Mac OS X: ifconfig
  3. Verify gateway address
    1. Windows: ipconfig /all | find Default Gateway
    2. Mac OS X: netstat -rn | grep default
  4. Ping gateway address
    1. Windows: ping
    2. Mac OS X: ping -c 4
  5. Verify DNS resolution
    1. Windows: ping www.google.com
    2. Mac OS X: ping -c 4 www.google.com
  6. Verify DNS address
    1. Windows: ipconfig /all | find DNS Servers
    2. Mac OS X: grep nameserver /etc/resolv.conf
  7. Ping DNS address
    1. Windows: ping
    2. Mac OS X: ping -c 4

Closing remarks

I hope this guide will help you start troubleshooting connectivity problems yourself before calling the help desk. If you follow this procedure, you should be able to address the most common configuration problems that prevent you from connecting to the Internet. Also, it will allow you to communicate more precise information to your support stuff so they can better address your tickets.

Relevance to NetBeez

NetBeez is used in a similar way by network administrators to automatically run the tests that I have just illustrated in this article. This is implemented by deploying miniature computers throughout the network that verify that all the pieces and parts of the network infrastructure (DHCP server, gateway, DNS server, …) are available and correctly configured. Should any of the components be unavailable or misconfigured, that miniature computer immediately detects it and alerts the network administrators, without having to rely on human users to discover and report the problem. If you want to learn more, tell your network administrator or support staff to request a product demonstration with one of our engineers, we’d be happy to chat with them.

  • Laurie

    Great breakdown of different things to check and how to do so. Thanks for sharing!