Network Security, Firewalls, and VPNs, 3rd Edition

Firewall Rules

Firewalls filter traffic using rules or filters. All firewalls, of whatever type—static packet filtering, stateful inspection, application proxy, circuit proxy, or content filtering—use rules to filter traffic. Rules are instructions that evaluate and take action on traffic traversing the network.

Firewall rules are used to control what traffic enters or leaves a secured network area. Depending on where the firewall is positioned, this mechanism can protect the private network from the public Internet or filter traffic between internal subnets or departments. The security administrator or the dedicated firewall administrator configures firewall rules in accordance with the organization’s security policy.

Generally, two main ...