Network redundancy is a key to maintaining network reliability. Multiple physical links between devices provide redundant paths. The network can then continue to operate when a single link or port has failed. Redundant links can also share the traffic load and increase capacity.
Multiple paths need to be managed so that Layer 2 loops are not created. The best paths are chosen, and an alternate path is immediately available in case a primary path fails. Spanning Tree Protocol (STP) is used to create one path through a Layer 2 network.
This chapter focuses on the protocols used to manage these forms of redundancy. It also covers some of the potential redundancy problems and their symptoms.