What is STP? 37
As an example, Figure 5 shows a network containing three LAN segments 
separated by three bridges. With this configuration, each segment can 
communicate with the others using two paths. Without STP enabled, this 
configuration creates loops that cause the network to overload. 
Figure 5   A network configuration that creates loops
Figure 6 shows the result of enabling STP on the bridges in the 
configuration. STP detects the duplicate paths and prevents, or blocks, 
one of them from forwarding traffic, so this configuration will work 
satisfactorily. STP has determined that traffic from LAN segment 2 to LAN 
segment 1 can only flow through Bridges C and A, because, for example, 
this path has a greater bandwidth and is therefore more efficient. 
Figure 6   Traffic flowing through Bridges C and A