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| Preface |

## Acknowledgments

When we set out to write this book, we had no idea that it would consume so much time and energy. We would never have succeeded without the help of many people.

Special thanks to Ed DeHart and Craig Hunt. Ed worked with Brent in the early stages of this book and wrote the foreword to it; we appreciate all that he has done to help. TCP/IP is essential for understanding the basics of firewall construction, and Craig Hunt, author of TCP/IP Network Administration has kindly let us excerpt much of that book's Chapters 1 and 2 in this book's Appendix C so readers who do not already have a TCP/IP background can get a jump start.

Thanks to all those who reviewed drafts of the book before publication and made helpful suggestions: Fred Avolio, Steve Bellovin, Niels Bjergstrom, Rik Farrow, Simson Garfinkel, Eliot Lear, Evi Nemeth, Steve Simmons, Steve Romig, Gene Spafford, Phil Trubey, and Mark Verber. Thanks as well to Eric Allman for answering many Sendmail questions and Paul Traina for answering many Cisco questions.

Thanks to all the people at O'Reilly & Associates who turned this manuscript into a finished book: to Mary Anne Weeks Mayo, the wonderful and patient project manager/copyeditor for the book; Len Muellner, Ellen Siever, and Norm Walsh who converted the book from Word to SGML and contributed their tool-tweaking prowess; Chris Reilley who created the many excellent diagrams; Edie Freedman who designed the cover and Nancy Priest who designed the interior layout; John Files and Juliette Muellner who assisted with production; Seth Maislin who prepared the index; and Sheryl Avruch and Kismet McDonough-Chan who did the final quality control on the book.

Brent says: I would like to extend personal thanks to my friends and family, for keeping me going for a year and a half while I worked on the book; to my staff at Great Circle Associates, for keeping my business going; to the many hundreds of folks who've attended my Internet Security Firewalls Tutorial, for providing the impetus for this whole endeavor (and for keeping my bills paid!); and to the many thousands of subscribers to the Firewalls mailing list on the Internet, for providing a stimulating environment to develop many of the ideas found in this book. I also owe a lot of thanks to Debby Russell, our editor at O'Reilly & Associates, for all her help and guidance, and to our technical reviewers, for all their wonderful comments and suggestions. Most of all, though, I'd like to thank my very good friend and coauthor, Elizabeth Zwicky, without whose collaboration and encouragement this book probably never would have been finished, and certainly wouldn't have been as good.

Elizabeth says: My thanks go to my friends, my family, and my colleagues at Silicon Graphics, for an almost infinite patience with my tendency to alternate between obsessing about the book and refusing to discuss anything even tangentially related to it. I'd like to particularly thank Arnold Zwicky, Diana Smetters, Greg Rose, Eliot Lear, and Jeanne Dusseault for their expert moral support (often during similar crises of their own). But the most thanks for this effort have to go to Debby and Brent, for giving me a chance to be part of an unexpected but extremely rewarding project.

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