The most difficult system administration issue to address is network security. When you connect your computer to the rest of the world via a network such as the Internet, someone could find an opening.
A way to protect your network from unauthorized users accessing hosts on your network is to use a firewall, or a secure gateway system. A firewall is a dedicated system separating two networks, each of which approaches the other as not trusted—it is a secure host that acts as a barrier between your internal network and outside networks. The firewall has two primary functions: It acts as a gateway to pass data between the networks, and it acts as a barrier to block the passage of data to and from the network. In addition, ...