Sidebar: What Is a Firewall?

A firewall is a dedicated system that sits between your internal network (sometimes called an intranet), and the Internet. The firewall system scrutinizes all offered network traffic and throws away or refuses any packets that would violate the integrity and security of the internal network.

The firewall is invisible to the users on the internal network. Internal workstations simply contact the firewall whenever they want access to the Internet. Users aren't required to use special programs or contact special daemons running on the firewall. The firewall's protective packet filtering is completely transparent.