tailieunhanh - Why Do You Need a Firewall?

A firewall is a piece of software or hardware that filters all network traffic between your computer, home network, or company network and the Internet. It is our position that everyone who uses the Internet needs some kind of firewall protection. This chapter tells you what a firewall does and sets down the basic questions that you should ask as you are evaluating spe- cific firewalls. | 04 540483 5 28 03 9 26 AM Page 9 Chapter 1 Why Do You Need a Firewall In This Chapter Understanding what a firewall does Connecting to the Internet Figuring out Internet protocols Understanding how a firewall works Identifying hackers Setting rules 1. . . . .ID f you want to find out about firewalls you bought the right book. Before we start exploring the gory details of how firewalls work and how to configure them we use this chapter to lay the groundwork. If you are already familiar with how the Internet works and how you connect to it and if you have a basic understanding of firewalls then you can skip this chapter. If these topics are new to you if you want to refresh your knowledge of any of these topics or if you want to get an overview of what a firewall is then read on. Defining a Firewall A firewall is a piece of software or hardware that filters all network traffic between your computer home network or company network and the Internet. It is our position that everyone who uses the Internet needs some kind of firewall protection. This chapter tells you what a firewall does and sets down the basic questions that you should ask as you are evaluating specific firewalls. Not too long ago only construction workers and architects asked the question Why do we need a firewall Before the term firewall was used for a component of a computer network it described a wall that was designed to 04 540483 5 28 03 9 26 AM Page 10 10 Part I Introducing Firewall Basics contain a fire. A brick and mortar firewall is designed to contain a fire in one part of a building and thus prevent it from spreading to another part of the building. Any fire that may erupt inside a building stops at the firewall and won t spread to other parts of the building. A firewall in a computer network performs a role that is very similar to that of a firewall in a building. Just as a firewall made out of concrete protects one part of a building a firewall in a network ensures that .