If you are involved with implementing and maintaining computer networks, then it indicates that one of your networks will not function as it should at some point. This could be the result of human error, such as a configuration mistake or poor network design. It could be the result of a software or hardware failure. It is possible that someone is launching a malicious attack on your network. Finally, there is a possibility that legitimate users on your own network will, perhaps unintentionally, cause the network to malfunction. In each of these cases, you, as the person responsible for maintaining the network, will be called upon to fix the problem, and your troubleshooting skills will be put to the test.

In this chapter, we will first outline a general procedure for troubleshooting networks. We will then discuss some common networking problems and possible causes. We will also cover the most useful troubleshooting tools available in both pfSense and on the command line of most operating systems. In the final section, we will apply what you learned to troubleshoot a real-world networking problem.

In this chapter, you will learn the following topics:

• Troubleshooting fundamentals
• pfSense troubleshooting tools
• A troubleshooting scenario