Overview

Introduction

The Configure, Verify, and Troubleshoot Spanning Tree Protocols module provides you with the instructions and Cisco hardware to develop your hands on skills in understanding the configuration of STP and its related protocols. This module includes the following activities:

  • Configuring Spanning Tree Protocol
  • Examining and configuring ports, their STP roles as well as their STP states
  • Configuring Rapid Per VLAN Spanning Tree Plus or RPVST+

Exercise 1 - Spanning Tree Protocol

The purpose of the Spanning Tree Protocol, or STP is to allow for the physical redundancy of connections while preventing logical layer 2 loops from forming in a network. This can occur when two switches are connected together using multiple connections. In fact, it doesn’t have to be two switches, you could, for example, have a hundred switches in your network, and then somebody places a hub under their desk or in a meeting room and connects two of its interfaces to your infrastructure. One connection may go to NYCORE1 in the network; the other connection may go to NYCORE2. This would cause a loop to occur.

STP's role is to find these loops and take appropriate action against one of the interfaces where the loop has occurred. There are many examples of what happens when a loop occurs in a network, the classic example being when an ARP packet consumes vast amounts of bandwidth because the switches don’t yet know about all the devices connected to them.

In this exercise, you will learn how to determine the outcome of the default STP topology between three switches, how to manipulate this configuration and how to verify that your manipulations have been implemented.

Exercise 2 - STP and Ports

STP prevents the creation of loops by giving various roles to ports. These roles are determined by their location relative to the root bridge.

In this exercise, you will examine the port roles, learn how to configure the ports such that certain roles are given to specific ports, and you will learn about the different STP states and the process ports go through in order to determine their roles.

Exercise 3 - Rapid Per VLAN Spanning Tree Plus

STP comes in different flavors. Up until now, you have been using Per VLAN Spanning Tree plus or PVST+. This is the default configuration of all Cisco switches. An additional spanning tree flavor that is often used is Rapid PVST+ or RPVST+. It is also often referred to simply as Rapid Spanning Tree or RSTP. As its name suggests, it converges much faster than PVST+.

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