This updated report provides an overview of firewall technology, and helps organizations plan for and implement effective firewalls. It explains the technical features of firewalls, the types of firewalls that are available for implementation by organizations, and their security capabilities. Organizations are advised on the placement of firewalls within the network architecture, and on the selection, implementation, testing, and management of firewalls. Other issues covered in detail are the development of firewall policies, and recommendations on the types of network traffic that should be prohibited. The appendices contain helpful supporting material, including a glossary and lists of acronyms and abreviations; and listings of in-print and online resources. Illus.