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Objectives • Redundant topologies • SpanningTree Protocol
Redundancy Redundant networking topologies are designed to ensure that networks continue to function in the presence of single points of failure.
Redundant Topologies • A goal of redundant topologies is to eliminate network outages caused by a single point of failure. • All networks need redundancy for enhanced reliability.
Media Access Control Database Instability In a redundant switched network, it is possible for switches to learn the wrong information. A switch can learn that a MAC address is on a port when it is not.
Spanning-Tree Operation • One root bridge per network. • One root port per nonroot bridge. • One designated port per segment. • Nondesignated ports are unused.
Bridge Protocol Data Unit Bridge protocol data unit (BPDU)
Spanning-Tree Recalculation A switched internetwork has converged when all the switch and bridge ports are in either the forwarding or blocked state.
Rapid Spanning-Tree Protocol • The standard and protocol introduce the following: • Clarification of port states and roles • Definition of a set of link types that can go to forwarding state rapidly • Allowing switches, in a converged network, to generate their own BPDUs rather than relaying root bridge BPDUs
Rapid Spanning-Tree Port Designations The Rapid SpanningTree Protocol, IEEE 802.1w, will eventually replace the SpanningTree Protocol, IEEE 802.1D.