This section focuses on the technologies used in various firewalls and how they work. The firewall taxonomy in Figure 2-1 shows the general types of firewalls. | Firewall Technologies This section focuses on the technologies used in various firewalls and how they work. The firewall taxonomy in Figure 2-1 shows the general types of firewalls. This section focuses more on the underlying technologies that devices that fall into those types utilize. In some cases one technology discussed here can fall into multiple types in the taxonomy tree. The focus is on a wide range of firewall technologies including the following Personal firewalls Packet filters Network Address Translation NAT firewalls Circuit-level firewalls Proxy firewalls Stateful firewalls Transparent firewalls Virtual firewalls Now you might be thinking Wait I thought there were three firewall products software based appliance based and integrated. The firewall technologies discussed in this section may be used by any of the three basic physical firewalls. Indeed these technologies simply allow us to define a firewall in a more granular fashion. So for example an appliance firewall can be further quantified as a stateful firewall. Each of these technologies is examined and discussed to provide you with an understanding of the differences between these technologies and by extension the firewall devices that utilize these technologies. Each section focuses predominantly on the operation of the firewall in its function as a network security device. Discussion of the redundancy capabilities performance and management of specific firewalls is not covered. This section provides a brief introduction to some specific firewalls that subsequent chapters cover in greater detail. Personal Firewalls Personal firewalls are designed to protect a single host. They can be viewed as a hardened shell around the host system whether it is a server desktop or laptop. Typically personal firewalls assume that outbound traffic from the system is to be permitted and inbound traffic requires inspection. By default personal firewalls include various profiles that accommodate the typical .
