y chance in the first place. You have helped me become a better writer, and I cannot thank you enough. I would like to thank Rachel Head, the copyeditor who made the first edition a much more readable book. I would like to thank all the wonderful people at O'Reilly. Writing this book was a great experience, due in large part to the people I worked with at O'Reilly. I would like to thank my good friend, John Tocado, who once told me, "If you want to write, then write!" This book is proof that you can change someone's life with a single sentence. You'll argue that I changed my own life, and that's fine, but you'd be wrong. When I was overwhelmed with the amount of remaining work to be done, I seriously considered giving up. Your words are the reason I did not. Thank you. I cannot begin to thank everyone else who has given me encouragement. Living and working with a writer must, at times, be maddening. Under the burden of deadlines, I've no doubt been cranky, annoying, and frustrating, for which I apologize. My purpose for the last year has been the completion of this book. All other responsi- bilities, with the exception of health and family, took a back seat to my goal. Realizing this book's publication is a dream come true for me. You may have dreams yourself, for which I can offer only this one bit of advice: work toward your goals, and you will realize them. It really is that simple. Preface xxiii CHAPTER 1 What Is a Network? Before we get started, I would like to define some terms and set some ground rules. For the purposes of this book (and your professional life, I hope), a computer network can be defined as "two or more computers connected by some means through which they are capable of sharing information." Don't bother looking for that in an RFC because I just made it up, but it suits our needs just fine. There are many types of networks: local area networks (LANs), wide area networks (WANs), metropolitan area networks (MANs), campus area networks (CANs), Ether- net networks, Token Ring networks, Fiber Di