Bridges run Spanning Tree Algorithm (STA) to form a tree topology. In the steady

Question

Bridges run Spanning Tree Algorithm (STA) to form a tree topology. In the steady state of STA, only Root Ports and Designated Ports are active; Other ports are blocked. When topology changes, a bridge may hear inferior configuration of original designated router from its blocked port. Before unblocking this port, it should wait for a certain time. Suppose we have a new protocol "STP-", which simply takes away this feature, i.e. the bridge immediately unblocks this port and start announcing its own configuration. Construct a case where "STP" results in an infinite propagation of bridge configuration message AND/OR infinite flooding of data packets upon topology change. Your answer should include: The original topology with all information in the steady state: bridge id, root bridge, root . The changed topology and specification of the changes. Add additional assumptions The way the data packets AND/OR configuration messages are infinitely looping around. port, designated port. when necessary, e.g. the propagation delay on each link Show that the bridge network eventually meltdown under your assumptions.

Explanation / Answer

Introduction

Spanning Tree Protocol (STP) is a Layer 2 protocol that runs on bridges and switches. The specification for STP is IEEE 802.1D. The main purpose of STP is to ensure that you do not create loops when you have redundant paths in your network. Loops are deadly to a network.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

Although this document uses Cisco Catalyst 5500/5000 Switches, the spanning tree principles that the document presents are applicable to almost all devices that support STP.

For the examples, this document used:

A console cable that is suitable for the Supervisor Engine in the switch

Six Catalyst 5509 Switches

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Conventions

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