10.3. Types of Firewalls

Firewall is really a generic term that covers many different types of devices used to separate network traffic. Most firewalls are simply a server, with a hardened operating system, and a software-based firewall providing the protection. Some firewalls, known as embedded firewalls, have the operating system and firewall programmed directly onto the system CPU.

Three types of firewalls will be covered in this section:

  1. Packet filtering

  2. Stateful packet filtering

  3. Application proxy

The most basic type is the packet filtering firewall. A packet filtering firewall sits between the public and the private network, as shown in Figure 10.1. All network traffic, both ingress and egress, has to pass through the firewall.

The firewall ...

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