Reading

Cisco Ethernet Overview
Ethernet Switch Tutorial
Linux Bridging
Understanding the Spanning Tree Protocol
Configuring Spanning Trees

Tasks

The focus of this lab is on local area networks. Local area networks enable end hosts to communicate, and for end hosts to connect to Internet uplinks. While many different LAN technologies and protocols have been developed over the years, Ethernet is the most widely used today, and is the focus of this lab. Note that communications in local area networks takes place at layer 2 (data link) of the protocol stack and is therefore concerned with Medium Access Control (MAC) and MAC addresses as opposed to layer 3 (network) and IP addresses which will be the subject of lab #4.

You will gain experience with LANs by conducting two different experiments in this lab. The first will be to create a LAN bridge using a Linux host. This portion of the lab will require that you become familiar with the brctl tool which interacts with the bridge kernel module available in the standard linux kernel. In the lab, you will configure a Linux host to act as a communications bridge between two hosts.

While bridging is important in terms of enabling multiple LANs to be connected, LAN switching is the dominate mechanism for LANs. Switches enable on-to-one communication between end hosts, obviating the need for traditional shared medium access methods. Furthermore, modern switch devices offer a host of configuration and management capabilities that enable devices to be tuned for specific environments. The second part of this lab will give you an introduction to LAN switching and require you to configure and test a commonly used switch in several different ways.

Tools

In addition to the recommended readings above, you will need to familiarize yourself with the brctl utility that is available in Linux. Use the Linux MAN pages to learn the syntax details of this utility.

Topology

You will build a network that has the following topology in the first half of this lab:

Questions

Please enter the answers to these questions into your lab notebooks before you start the lab.

1. How does Ethernet implement multiple access on a shared bus?

2. Explain the difference between a switch and a hub. When would one be preferable over another?

3. What is an Ethernet collision domain and why is it an important consideration in Ethernet LAN design?

4. How is the Spanning Tree Algorithm used in LANs?

5. What is a forwarding loop? How does it occur?

6. Design a topology of 5 switches/bridges that would cause a forwarding loop. Draw this topology in your lab notebook and explain where the loop would occur.