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| Preface |

## Platforms

To a large extent, this book is platform-independent. Because most of the information provided here consists of general principles, most of it should be applicable to you, regardless of what equipment, software, and networking you are using. The most platform-specific issue is what type of system to use as a bastion host. People have successfully built bastion hosts (which we describe in Chapter 5 of this book) using all kinds of computers, including UNIX systems, Windows NT machines, Macintoshes, VMS VAXes, and others.

Having said this, we must acknowledge that there is a strong UNIX orientation to the specific examples in this book. There are several reasons for this. This is a book about building firewalls, and at the present time, the richest source of freely available tools for accomplishing this task is in the UNIX world. As a result, the vast majority of the firewalls being built today use UNIX systems as their bastion hosts (although, of course, many other types of machines may be included in the overall configurations). We expect that this situation may change in the next few years, as more commercial systems become available for many types of systems. Another reason is, of course, that our own experience is primarily in the UNIX world.

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