Chapter 23. Firewalls
A firewall (see Figure 23-1) is a computer that sits between your internal network and the rest of the network and attempts to prevent bad things from happening (such as internal users sending company secrets outside, or outside people breaking into systems inside) without preventing good things from happening (such as employees accessing information available externally). It is sometimes called other things, like a security gateway, or various more colorful names thought up by frustrated network users when it prevents them from doing what they want to do.
Figure 23-1. Firewall
Why is a firewall needed? It isn’t if the systems ...