Computer Networking: Internet Protocols in Action

Chapter 1.1. Examining a Quiet Network with Ethereal

INTRODUCTION

If you use network software like web browsers or e-mail clients, then you know they require a network connection to work properly. However, do you know what kind of messages they send over the Internet? For example, what does your computer say to a remote web server in order to retrieve a web page and how does your computer direct your e-mail to the person to whom you have addressed it?

You can examine the details of network conversations using a tool called a network protocol analyzer. A network protocol analyzer is a piece of software that can record each packet sent over the network and display them in a human-readable format. On a busy network, this can be a lot of information so network protocol analyzers typically provide summary statistics about all packets and allow users to filter out unwanted data or search for specific packets of interest.

Throughout this book, we are going to use an open source network protocol analyzer called Ethereal. This first chapter will give you a basic introduction to Ethereal. Once you have mastered the basics of Ethereal, we will be ready to use it as a tool for exploring the details of network protocols like HTTP, SMTP, TCP, UDP, IP and many more.

You will learn the most from each exercise if you install Ethereal on your local computer and follow along as you read. Ethereal is available for most platforms, including Windows, Mac, and Unix/Linux. We have also included the source ...