The emphasis here is on more complicated network defenses that require careful design and setup - both design and implementation of the order of the day here. The authors caution mention the threat they see in various situations, go into some detail about how the threat appeared, and explain what configuration changes you can make to your perimeter defenses to resist the threat of the Wall. - David Topics covered: Means of protecting private networks from external security threats. The authors go into detail about the meaning attackers' use of security holes in common Internet services, and show how pairs of the holes or at least limit the damage that can be done through them. With coverage of Unix, Linux, and Windows NT, the authors detail their philosophy of firewall design and general security policy.