An Overview to Troubleshooting a Computer Network


A computer network is a group of computers that use a set of common communication protocols for sharing resources over digital interconnections. For computers to communicate, they have to be connected to a network. Troubleshooting is the process of identifying, locating and correcting problems. Experienced network administrators can often rely on instinct to troubleshoot. However, there are structured techniques that can be used to determine the most probable cause and solution in network administration.

A network today, however, can consist of various devices connected to a network – local and remote.

As a network administrator working in an IT firm, it’s only a matter of time before troubles creeps up and all eyes are on you to remedy the issue. This article will attempt to list some common troubleshooting guides for you to get a network up and running in no time.

When troubleshooting, proper documentation must be maintained. This document states all the steps taken in troubleshooting, even the ones that did not solve the issue. This documentation should include as much information as possible about the following:

  • The problem encountered
  • Steps taken to determine the cause of the problem
  • Steps to correct the problem and ensure that it will not reoccur

Structured Troubleshooting Methods

According to CISCO Networking Academy; There are several structured troubleshooting approaches that can be used. Which one to use will depend on the situation and includes the following points with their stated advantages and disadvantages:

In bottom-up troubleshooting, you start with the physical layer and the physical components of the network as shown in the figure, and move up through the layers of the OSI model until the cause of the problem is identified.
Bottom-up troubleshooting is a good approach to use when the problem is suspected to be a physical one. Most networking problems reside at the lower levels, so implementing the bottom-up approach is often effective.
The disadvantage with the bottom-up troubleshooting approach is it requires that you check every device and interface on the network until the possible cause of the problem is found.

The top-down troubleshooting starts with the end-user applications and moves down through the layers of the OSI model until the cause of the problem has been identified.
End-user applications of an end system are tested before tackling the more specific networking pieces. Use this approach for simpler problems, or when you think the problem is with a piece of software.
The disadvantage with the top-down approach is it requires checking every network application until the possible cause of the problem is found.

In divide-and-conquer troubleshooting, you start by collecting user experiences of the problem, document the symptoms and then, using that information, make an informed guess as to which OSI layer to start your investigation. When a layer is verified to be functioning properly, it can be assumed that the layers below it are functioning. The administrator can work up the OSI layers. If an OSI layer is not functioning properly, the administrator can work down the OSI layer model.
For example, if users cannot access the web server, but they can ping the server, then the problem is above Layer 3. If pinging the server is unsuccessful, then the problem is likely at a lower OSI layer.

This is one of the most basic troubleshooting techniques. The approach first discovers the traffic path all the way from source to destination. The scope of troubleshooting is reduced to just the links and devices that are in the forwarding path. The objective is to eliminate the links and devices that are irrelevant to the troubleshooting task at hand. This approach usually complements one of the other approaches.

This approach is also called swap-the-component because you physically swap the problematic device with a known, working one. If the problem is fixed, then the problem is with the removed device. If the problem remains, then the cause may be elsewhere.

This approach is also called the spot-the-differences approach and attempts to resolve the problem by changing the nonoperational elements to be consistent with the working ones. You compare configurations, software versions, hardware, or other device properties, links, or processes between working and nonworking situations and spot significant differences between them.

Educated Guess
This approach is also called the shoot-from-the-hip troubleshooting approach. This is a less-structured troubleshooting method that uses an educated guess based on the symptoms of the problem. Success of this method varies based on your troubleshooting experience and ability. Seasoned technicians are more successful because they can rely on their extensive knowledge and experience to decisively isolate and solve network issues.

Steps to Troubleshoot a Network
Steps to Troubleshoot a Network.
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Credits to the CISCO Networking Academy and dnsstuff