Failures at the core layer cause widespread outages. It is critical to have written policies and proceduresin place to govern how changes are approved, tested, installed, and documented. Plan a back-outstrategy to return the network to its previous state in case changes are not successful.Network ConvergenceThe choice of a routing protocol for the core layer is determined by the size of the network and thenumber of redundant links or paths available. A major factor in choosing a protocol is how quickly itrecovers from a link or device failure.