Life has more than its share of rules. We just can't seem to get away from them. When it comes to firewalls, rules play an important part, too. A firewall enforces rules about what network traffic is allowed to enter or leave your personal computer or network. Most firewalls come with some preconfigured rules, but most likely you will have to add more rules. After the rules are in place, a firewall examines all network traffic and drops the traffic if the rules prohibit it. A large part of administering a firewall consists of configuring rules, such as the following:

• Allow everyone to access all Web sites.
• Allow outgoing e-mail from the internal mail server.
• Drop all outgoing network traffic unless it matches the first two rules.
• Allow incoming Web requests to the public Web server.
• Drop all incoming network traffic except for connections to the public Web server.
• Log all connection attempts that were rejected by the firewall.
• Log all access to external Web sites.

Configuring rules for a home network can be very easy. You may merely have to define a rule that allows all outgoing network traffic and another one that allows no connections to be established from the outside. Setting up the rules for a large corporation with many Web servers, thousands of users, and many departments (each with different needs for accessing the Internet) can be much more complicated.