Abstract: Rules and dianoetic machines that are the key technologies of firewall are studied in this paper. The rule formalization definition, abstract model of dianoetic machine, and dianoetic algorithm in the enhanced packet filtering firewalls are proposed. The relevant dianoetic machine is designed and implemented accordingly. The research results are validated while the applications of the firewall are illustrated. Finally, the advantages of the firewall are summarized and the research directions in the future are indicated.