Cisco Routers for the Desperate, 2nd Edition

Spanning Tree

While Ethernet seems to be a straightforward way to wire an office, it has its problems. The most serious problem is the loop. An Ethernet network needs to have a simple, flat topology, without any loops. A loop will break the network. For example, Figure 8-1 shows a correct Ethernet network. A looped network would look like the one in Figure 8-2.

Figure 8-1. A network without loops

Figure 8-2. A looped network

A looped network without loop protection will regularly, frequently, and reliably crash. Loops are bad.

The spanning tree protocol ...