What Is a Firewall? When most people think of a firewall, they think of a device that resides on the network and controls the traffic that passes between network segments | What Is a Firewall When most people think of a firewall they think of a device that resides on the network and controls the traffic that passes between network segments such as the firewall in Figure 1-1 a network-based firewall . However firewalls can also be implemented on systems themselves such as with Microsoft Internet Connection Firewall ICF in which case they are known as host-based firewalls. Fundamentally both types of firewalls have the same objective to provide a method of enforcing an access control policy. Indeed at the simplest definition firewalls are nothing more than access control policy enforcement points. Figure 1-1. A Network Firewall Enforcing Access Controls Firewalls enable you to define an access control requirement and ensure that only traffic or data that meets that requirement can traverse the firewall in the case of a network based firewall or access the protected system in the case of a host-based firewall . Figure 1-1 illustrates how you can use a network-based firewall to allow only traffic that is permitted to access protected resources. What Can Firewalls Do Chapter 2 Firewall Basics and all of Part II How Firewalls Work examine the details of how different types of firewalls work before delving into more detail however you need to understand from a broad design perspective what firewalls can and cannot do. All firewalls or at least all fire-walls that you should be considering implementing share some common traits and functionality that help define what a firewall can do. Fundamentally firewalls need to be able to perform the following tasks Manage and control network traffic Authenticate access Act as an intermediary Protect resources Record and report on events Firewalls Manage and Control Network Traffic The first and most fundamental functionality that all firewalls must perform is to manage and control the network traffic that is allowed to access the protected network or host. Firewalls typically do so by inspecting the .
