Chapter 12. Troubleshooting

Table of Contents

12.1. Introduction to Troubleshooting
12.2. Troubleshooting at the Ethernet Layer
12.3. Troubleshooting at the IP Layer
12.4. Handling and Diagnosing Routing Problems
12.5. Identifying Problems with TCP Sessions
12.6. DNS Troubleshooting

Invariably, troubles and misconfigurations creep into networks. New devices get connected and added to a network. Old devices are removed, and something seemingly unrelated breaks. Troubleshooting is really a test in discerning patterns.

My favored method for solving problems is to start with the simplest elements, verifying correct operation and proceeding to the next layer or element until I have isolated the problem element. If you are lucky, you'll know from a symptom where the problem is likely to be, but more often, you'll have to start at the bottom of the networking hierarchy, and verify each other layer.