Case Study: Redundancy at Layer 2 Using Switches
It's often possible to build redundancy into a network at the data link layer rather than the network layer. One example of this is the FDDI ring, which has two physical paths between each station on the ring. Another possibility is to use switches running the Spanning-Tree Algorithm to choose between redundant paths.
For example, in the network in Figure 3-16 there are actually eight paths from Router G to the FDDI ring, but Router G would see only two of them. Spanning tree running between Switches C and D would block some ports to eliminate any loops.
Figure 3-16. Redundancy at Layer 2
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