Linux Firewalls - Michael Rash [2]
Cover and Interior Design:
Octopod Studios
Developmental Editor:
William Pollock
Technical Reviewer:
Pablo Neira Ayuso
Copyeditors:
Megan Dunchak and Bonnie Granat
Compositors:
Christina Samuell and Riley Hoffman
Proofreaders:
Karol Jurado and Riley Hoffman
Indexer:
Nancy Guenther
For information on book distributors or translations, please contact No Starch Press, Inc. directly:
No Starch Press, Inc. 555 De Haro Street, Suite 250, San Francisco, CA 94107 phone: 415.863.9900; fax: 415.863.9950; info@nostarch.com; www.nostarch.com
Library of Congress Cataloging-in-Publication Data
Rash, Michael.
Linux firewalls : attack detection and response with iptables, psad, and fwsnort / Michael Rash.
p. cm.
Includes index.
ISBN-13: 978-1-59327-141-1
ISBN-10: 1-59327-141-7
1. Computers--Access control. 2. Firewalls (Computer security) 3. Linux. I. Title.
QA76.9.A25R36 2007
005.8--dc22
2006026679
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The information in this book is distributed on an "As Is" basis, without warranty. While every precaution has been taken in the preparation of this work, neither the author nor No Starch Press, Inc. shall have any liability to any person or entity with respect to any loss or damage caused or alleged to be caused directly or indirectly by the information contained in it.
ACKNOWLEDGMENTS
Linux Firewalls was made possible with the help of a host of folks at every step along the way. I'd particularly like to thank the people at No Starch Press for the efforts they put forth. William Pollock, Bonnie Granat, Megan Dunchak, and Christina Samuell all contributed many hours of expert editing, and the book is higher quality as a result. To Pablo Neira Ayuso, thanks for helping to make Netfilter and iptables what they are today, and for handling the technical edit of the material in this book. Ron Gula, CTO of Tenable Network Security, and Raffael Marty, chief security strategist of Splunk, both contributed constructive criticism, and they were kind enough to endorse the book before it was published. I also wish to thank Richard Bejtlich, founder of TaoSecurity, for writing an excellent foreword. Richard, your books are an inspiration. My parents, James and Billie Mae, and my brother, Brian, all deserve a special thank you for their constant encouragement. Finally, many thanks go to my wife, Katie. This book would not have been possible without you.
FOREWORD
When hearing the term firewall, most people think of a product that inspects network traffic at the network and transport layers of the OSI Reference Model and makes pass or filter decisions. In terms of products, dozens of firewall types exist. They are differentiated by the data source they inspect (e.g., network traffic, host processes, or system calls) and the depth to which they inspect those sources. Almost any device that inspects communication and decides whether to pass or filter it could be considered a firewall product.
Marcus Ranum, inventor of the proxy firewall and the implementer of the first commercial firewall product, offered a definition of the term firewall in the mid-1990s when he said, "A firewall is the implementation of your Internet security policy." [1] This is an excellent definition because it is product-neutral, timeless, and realistic. It applies equally well to the original firewall book, Firewalls and Internet Security by William R. Cheswick and Steven M. Bellovin (Addison-Wesley Professional, 1994), as it does to the book you're reading now.
In the spirit of Ranum's definition, a firewall could also be considered a policy enforcement system. Devices that inspect and then pass or filter network traffic