• Firewalls operate by examining a data packet and performing a comparison with some predetermined logical rules. The logic is based on a set of guidelines programmed in by a firewall administrator, or created dynamically and based on outgoing requests for information. This logical set is most commonly referred to as firewall rules, rule base, or firewall logic. Most firewalls use packet header information to determine whether a specific packet should be allowed to pass through or should be dropped. In order to better understand more complex rules, it is important to be able to create simple rules and understand how they interact.