Methods to activate firewall mechanism have been introduced in this research. The purpose is to build stronger protection for the intranet from the threats of Internet. The foundation of the work is the threat reduction strategies that are derived from formalizing and identifying the interaction between internal users and external parties. Internet access model is developed to facilitate this task. Mechanism of active firewall are divided into two main process i.e. initialisation and runtime process. The former process deals with the mechanism to start up and bring the active firewall into a point of its operation. Three approaches are introduced, namely open condition, close condition and lattice-based method. The open condition and close ...