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CCNA 3 v3.0 Module 7 Spanning Tree Protocol

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Objectives

• Redundant topologies

• Spanning Tree Protocol

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Redundant topologies

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Redundancy

Redundant networking topologies are designed to ensure that networks continue to function in the presence of single points of failure.

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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.

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Simple Redundant Switched Topology

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Broadcast Storm

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Multiple Frame Transmissions

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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.

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Spanning Tree Protocol

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Using Bridging Loops for Redundancy

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Spanning-Tree Protocol

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Spanning Tree Link Costs

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A Spanning Tree

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Spanning-Tree Operation

• One root bridge per network.

• One root port per nonroot bridge.

• One designated port per segment.

• Nondesignated ports are unused.

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Bridge Protocol Data Unit

Bridge protocol data unit (BPDU)

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Bridge IDs

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Spanning-Tree Port States

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Spanning-Tree Recalculation

A switched internetwork has converged when all the switch and bridge ports are in either the forwarding or blocked state.

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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

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Rapid Spanning-Tree Port Designations

The Rapid Spanning Tree Protocol, IEEE 802.1w, will eventually replace the Spanning Tree Protocol, IEEE 802.1D.