Building Internet Firewalls .

By D. Brent Chapman & Elizabeth D. Zwicky; ISBN 1-56592-124-0, 517 pages.
First Edition, November 1995.

It is scarcely possible to enter a bookstore, read a magazine or a newspaper, or listen to a news broadcast without seeing or hearing something about the Internet in some guise. It's become so popular that it no longer requires explanations when mentioned in nontechnical publications, and it gets mentioned plenty, in magazines ranging from The New Yorker to Bead and Button . While nontechnical publications are obsessed with the Internet, the technical publications have moved on and are obsessed with security. It's a logical progression; once the first excitement of having a superhighway in your neighborhood wears off, you're bound to notice that not only does it let you travel, it lets a very large number of strangers show up where you are, and not all of them are people you would have invited.

Both views are true: The Internet is a marvelous technological advance that provides access to information, and the ability to publish information, in revolutionary ways. But it's also a major danger that provides the ability to pollute and destroy information in revolutionary ways. This book is about one way to balance the advantages and the risks - to take part in the Internet while still protecting yourself.

Later in this chapter, we describe different models of security people have used to protect their data and resources on the Internet. Our emphasis in this book is on the network security model and, in particular, the use of Internet firewalls. A firewall is a form of protection that allows a network to connect to the Internet while maintaining a degree of security. The section later in this chapter called "What is an Internet Firewall?" describes the basics of firewalls and summarize what they can - and cannot - do to help make your site secure. Before we discuss what you can do with a firewall, though, we want to describe briefly why you need one. What are you protecting on your systems? What types of attacks and attackers are we seeing today? What types of security can you use to protect your site?

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