In this chapter, we will focus on how to find and resolve layer-2-based problems with the focus on Ethernet-based issues such as broadcast events and errors and how to find out where they are coming from. We will also focus on LAN protocols such as Spanning Tree, VLANs, and Wireless LAN.

These issues have to be resolved before we go up to layers 3, 4, and the Application layers, since layer 2 problems will be reflected in the upper layer protocols. For example, packet losses in layer 2 will cause retransmissions in TCP, which is a layer 4 protocol, and these can cause slow application response time in the upper layers.