Chapter 12. Troubleshooting

Table of Contents

1. Introduction to Troubleshooting
2. Troubleshooting at the Ethernet Layer
3. Troubleshooting at the IP Layer
4. Handling and Diagnosing Routing Problems
5. Identifying Problems with TCP Sessions
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.