1. Identify the Problem

The first step in troubleshooting a network is to identify the problem. As a part of this step, you should do the following:

• Gather information about the current state of the network using the network troubleshooting tools that you have available to you.
• Duplicate the problem on a test piece of hardware or software, if possible. This can help you to confirm where your problem lies.
• Question users on the network to learn about the errors or difficulties they have encountered.
• Identify the symptoms of the network outage. For example, do they include complete loss of network connection? Slow behavior on the network? Is there a network-wide problem, or are the issues only being experienced by one user?
• Determine if anything has changed in the network before the issues appeared. Is there a new piece of hardware that’s in use? Has the network taken on new users? Has there been a software update or change somewhere in the network?
• Define individual problems clearly. Sometimes a network can have multiple problems. This is the time to identify each individual issue so that your solutions to one aren’t bogged down by other unsolved problems.

2. Develop a Theory

Once you have finished gathering all the information that you can about the network issue or issues, it’s time to develop a working theory. While you’re producing your theory about the causes of the network issue, don’t be afraid to question the obvious, but remain on the lookout for more serious issues. Sometimes a network outage occurs because someone tripped on a wire or some other simple problem. However, at other times the problems might be related more complicated causes, like a breach in network security.

3. Test the Theory

Using the tools at your disposal, it’s time to test your theory. If your theory is that the network router is defective, try replacing it with another router to see if that fixes the issue. At this stage, it’s important to remember that proving your own theories wrong doesn’t mean that you’ve failed. Instead, it means that it’s time to return to step two, develop a new theory, and then find a way to test that one. Sometimes your first theory may be right, but it’s also common to go through several theories before arriving at the true cause of your network’s issues.

4. Plan of Action

Once you’ve confirmed your theory about the causes of the network issues, you’re in a position to solve them. Come up with a plan of action to address the problem. Sometimes your plan will include just one step. For example, restart the router. In other cases, your plan will be more complex and take longer, such as when you need to order a new part or roll a piece of software back to a previous version on multiple users’ computers.

5. Implement the Solution

Now that you have a plan for fixing the network, it’s time to implement it. There are some solutions that you may be able to do by yourself, while others may require cooperation from other network administrators or users.

6. Verify System Functionality

Once you’ve implemented your solution, be sure to test the network. Make sure that the issue in question has been resolved, but also be on the lookout for other issues that may have arisen from the changes that you made to the network. As part of your verification process, make sure to consult both the network tools at your disposal as well as individual user accounts of their experiences on the network.

7. Document the Issue

If you are a network professional or an enthusiast who is around networks often, then it’s safe to say that this won’t be the last time you encounter this particular issue. Make sure to document each stage of troubleshooting the problem, including the symptoms that appeared on the network, the theory you developed, your strategy for testing the theory and the solution that you came up with to solve the issue. Even if you don’t reference this documentation, it may be helpful to another network engineer at your company in the future and could help to shorten network downtime.

Network Troubleshooting Tools

In addition to user reports and firsthand experience on the network, there are a number of tools available for you to use when it comes to diagnosing and treating network issues. These tools may exist in the computer’s operating system itself, as standalone software applications or as hardware tools that you can use to troubleshoot a network.

Command-Line Tools

On Windows PCs, the command prompt can be accessed by searching for it in the start menu or by typing “cmd” into the Run window. On a Linux system, you can press Ctrl + Alt + T to open the command line.

The following commands can be entered into the command prompt one at a time to reveal specific information about the network status:

• ping — A TCP/IP utility that transmits a datagram to another host, specified in the command. If the network is functioning properly, the receiving host returns the datagram.
• tracert/traceroute —A TCP/IP utility that determines the route data takes to get to a particular destination. This tool can help you to determine where you are losing packets in the network, helping to identify problems.
• nslookup — A DNS utility that displays the IP address of a hostname or vice versa. This tool is useful for identifying problems involving DNS name resolution.
• ipconfig — A Windows TCP/IP utility that verifies network settings and connections. It can tell you a host’s IP address, subnet mask and default gateway, alongside other important network information.
• ifconfig — A Linux or UNIX TCP/IP utility that displays the current network interface configuration and enables you to assign an IP address to a network interface. Like ipconfig on Windows, this command will tell you vital information about the network and its status.
• iptables — A Linux firewall program that protects a network. You can use this tool if you suspect that your firewall may be too restrictive or too lenient.
• netstat — A utility that shows the status of each active network connection. This tool is useful for finding out what services are running on a particular system.
• tcpdump — A utility that is used to obtain packet information from a query string sent to the network interface. It’s available for free on Linux but can be downloaded as a command for Windows.
• pathping — A TCP/IP command that provides information about latency and packet loss on a network. It can help you troubleshoot issues related to network packet loss.
• nmap — A utility that can scan the entire network for various ports and the services that are running on them. You can use it to monitor remote network connections and get specific information about the network.
• route — A command that enables manual updating of the routing table. It can be used to troubleshoot static routing problems in a network.
• arp — A utility that supports the Address Resolution Protocol (ARP) service of the TCP/IP protocol suite. It lets the network admin view the ARP cache and add or delete cache entries. It can be used to address problems having to do with specific connections between a workstation and a host.
• dig — A Linux or UNIX command-line tool that will display name server information. It can be used to troubleshoot problems in DNS name resolution.

Network Troubleshooting Applications

In addition to command-line tools, there are also a number of standalone applications that can be used to determine the status of a network and to troubleshoot issues. Some of these applications may be included in the system that you are working with, while others may need to be installed separately.

• Packet Sniffer — Provides a comprehensive view of a given network. You can use this application to analyze traffic on the network, figure out which ports are open and identify network vulnerabilities.
• Port Scanner — Looks for open ports on the target device and gathers information, including whether the port is open or closed, what services are running on a given port and information about the operating system on that machine. This application can be used to figure out which ports are in use and identify points in a network that could be vulnerable to outside attacks.
• Protocol Analyzer — Integrates diagnostic and reporting capabilities to provide a comprehensive view of an organization’s network. You can use analyzers to troubleshoot network problems and detect intrusions into your network.
• Wi-Fi Analyzer — Detects devices and points of interference in a Wi-Fi signal. This tool can help you to troubleshoot issues in network connectivity over a wireless network.
• Bandwidth Speed Tester — Tests the bandwidth and latency of a user’s internet connection. This application is typically accessed through a third-party website and can be used to confirm user reports about slow connections or download speeds.

Hardware Tools

Command-line tools and applications are software tools for troubleshooting, but some network problems have hardware causes and solutions.

Here are some hardware tools that can help you diagnose and solve network issues:

• Wire Crimpers — A wire crimper (sometimes called a cable crimper) is a tool that attaches media connectors to the ends of cables. You can use it to make or modify network cables.
• Cable Testers — A cable tester (sometimes called a line tester) is a tool that verifies if a signal is transmitted by a given cable. You can use one to find out whether the cables in your network are functioning properly when diagnosing connectivity issues.
• Punch Down Tool — A punch down tool is used in a wiring closet to connect cable wires directly to a patch panel or punch-down block. This tool makes it easier to connect wires than it would be to do it by hand.
• TDR — A time-domain reflectometer (TDR) is a measuring tool that transmits an electrical pulse on a cable and measures the reflected signal. In a functioning cable, the signal does not reflect and is absorbed in the other end. An optical time-domain reflectometer (OTDR) is a similar tool, but used for measuring fiber optic cables, which are becoming more common in modern networks.
• Light Meter — Light meters, also known as optical power meters, are devices used to measure the power in an optical signal.
• Tone Generator — A tone generator is a device that sends an electrical signal through one pair of UTP wires. On the other end, a tone locator or tone probe is a device that emits an audible tone when it detects a signal in a pair of wires. You can use these tools to verify that signals are passing through the wires in your network. They are often used to confirm phone connectivity.
• Loopback Adapter — A loopback adapter is a virtual or physical tool that can be used for troubleshooting network transmission issues. It can be used by utilizing a special connector that redirects the electrical signal back to the transmitting system.
• Multimeter — A multimeter (sometimes called a volt/ohm meter) is an electronic measuring instrument that takes electrical measurements such as voltage, current and resistance. There are hand-held multimeters for fieldwork as well as bench-top models for in-house troubleshooting.
• Spectrum Analyzer — A spectrum analyzer is an instrument that displays the variation of a signal strength against the frequency.

How to Develop Your Network Troubleshooting Skills

These are just a few of the steps you can follow and tools that you can use to troubleshoot an issue in your network. For home networks, many issues can be solved relatively simply, by checking connections, making sure that everything is plugged in and using built-in diagnostic tools.

However, if you want a job working on computer networks, you’ll need to develop your troubleshooting skills to match. Network troubleshooting is an essential skill to have when looking for a job as a network engineer or network administrator, since companies are primarily concerned with minimizing their network downtime.

If you’re looking for a job, an IT certification related to computer networking is essential as proof of your abilities. Keep in mind that certification exams test your skills very closely, so make sure to seek out appropriate network training to properly prepare for your exam and test with confidence.

In order to really develop your skills that will land you the job, it’s important to combine training and certifications with real-world network troubleshooting experience. This experience doesn’t have to come from a job – you can practice your IT skills by tinkering with your own equipment or volunteering with local nonprofits to improve their networks and resolve any issues they’re having.