Chapter 20. Troubleshooting

The best kind of troubleshooting you can do is no troubleshooting at all, and the best way to minimize troubleshooting is to insist on reliable network designs based on conservative practices. On the other hand, there are a lot of components and devices in a network system, and something is bound to eventually go wrong, even in the best of networks. For those times when your network develops a problem requiring troubleshooting, you need to know how to go about the task of tracking down the failure. There are many ways for things to go wrong in a complex network system. However, the basic approaches to troubleshooting described in this chapter can help you find any problem, no matter how complex the network system may be.

Since reliable network design is the best way to avoid network downtime in the first place, we’ll begin this chapter with some guidelines for building a reliable network. We will describe two important pieces of information you will need when troubleshooting: network documentation, and baselines of network activity so that you have some idea of normal traffic behavior on your network. Knowing how to organize the troubleshooting task can help speed the process. Therefore, we will look at the troubleshooting model, including fault detection and fault isolation. These concepts make it possible for you to isolate a problem in any network, big or small.

After looking at the basic troubleshooting concepts, we’ll take a tour of the common problems ...

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