ther parties involved have been changed. Cisco equipment is used for the examples within this book and, with very few excep- tions, the examples are TCP/IP-based. You may argue that a book of this type should include examples using different protocols and equipment from a variety of vendors, and, to a degree, that argument is valid. However, a book that aims to cover the breadth of technologies contained herein, while also attempting to show examples of these technologies from the point of view of different vendors, would be quite an impractical size. The fact is that Cisco Systems (much to the chagrin of its competitors, I'm sure) is the premier player in the networking arena. Likewise, TCP/IP is the protocol of the Internet, and the protocol used by most networked devices. Is it the best protocol for the job? Perhaps not, but it is the protocol in use today, SO it's what I've used in all my examples. Not long ago, the Cisco CCIE exam still included Token Ring Source Route Bridging, AppleTalk and IPX. Those days are gone, however, indicating that even Cisco understands that TCP/IP is where everyone is heading. I have included a chapter on IPv6 in this edition, since it looks like we're heading that way eventually. WAN technology can include everything from dial-up modems (which, thankfully, are becoming quite rare) to T1, DS3, SONET, MPLS, and SO on. We will look at many of these topics, but we will not delve too deeply into them, for they are the subject of entire books unto themselves-some of which may already sit next to this one on your O'Reilly bookshelf. Again, all the examples used in this book are drawn from real experiences, most of which I faced myself during my career as a networking engineer, consultant, manager, and director. I have run my own company and have had the pleasure of working with some of the best people in the industry. The solutions presented in these chapters are the ones my teams and I discovered or learned about in the process of resolving the issues we encountered. I faced a very t