This document begins with an overview of the Internet and common services. It describes Internet-related security problems in detail by examining problems with various TCP/IP services and by examining other factors that have caused the Internet to grow less secure. Chapter 2 discusses firewalls, their benefits as well as their disadvantages, and then the various firewall components, including advanced authentication measures and network access policy. Chapter 3 describes several firewall configurations that illustrate how the firewall components fit together and can be used to implement various policies. Chapter 4 discusses procurement, administrative issues, and other actions sites should take to secure their Internet-connected systems. Appendix A provides pointers to other books and information about firewalls and Internet security. Appendix B contains a collection of frequently asked questions about firewalls that is available on-line (see Appendix B for more information).