Amazon.com (ISBN 1565921240, Paperback)

Simply put, a firewall is a way to restrict access between the Internet and your company's internal network. It enables you to get out to the Net while keeping unauthorized people from breaking into your systems. This is a solid, definitive text for building Internet firewalls that every system administrator who is connecting to the Net should own. Written in down-to-earth yet detailed style, you're guided through the entire process of designing, building and maintaining firewalls. The preface gives the best reason for using this book to build firewalls: "In any society, a small percentage of people are malicious." Indeed.