ough decision when writing the second edition of this book. Should I keep the CatOS commands or discard them in favor of newer Nexus NX-OS examples? This decision was tough not only because my inclusion of CatOS resulted in some praise from my readers, but also because as of this writing in early 2011, I'm still seeing CatOS switches running in large enterprise and ecommerce networks. As such, I decided to keep the CatOS examples and simply add NX-OS commands. I have added many topics in this book based mostly on feedback from readers. New topics include Cisco Nexus, wireless, MPLS, IPv6, and Voice over IP (VoIP). Some of these topics are covered in depth, and others, such as MPLS, are purposely light for reasons outlined in the chapters. Topics such as Nexus and VoIP are vast and added significantly to the page count of an already large and expensive book. I have also removed the chapters on server load balancing, both because I was never really happy with those chapters and because I could not get my hands on an ACE module or ap- pliance in order to update the examples. On the subject of examples, I have updated them to reflect newer hardware in every applicable chapter. Where I used 3550 switches in the first edition, I now use 3750s. Where I used PIX firewalls, I now use ASA appliances. I have also included examples from Cisco Nexus switches in every chapter that I felt warranted them. Many chapters therefore have examples from Cat-OS, IOS, and NX-OS. Enjoy them, because I guar- antee that CatOS will not survive into the third edition. Who Should Read This Book This book is intended for anyone with first-level certification knowledge of data net- working. Anyone with a CCNA or equivalent (or greater) knowledge should benefit from this book. My goal in writing Network Warrior is to explain complex ideas in an easy-to-understand manner. While the book contains introductions to many topics, you can also consider it a reference for executing common tasks related to those topics. I am a teacher at heart, and this 