This book is used as the text book for my college course. The examples are ridiculous, the exercises are nuts, and the definitions are strange. "This book is not intended to be read in sequence, from beginning to end." (from the book's introduction) Maybe the book isn't meant to be read at all. There is better information from O'Reilly and Cisco. Search for "firewall" on O'Reilly's site and you'll get better information than whats in this book and you'll save $75. Get "The Best Damn Firewall Book Period" instead of this, Amazon sells it for $37 and it gets 4 stars.