In recent years packet-filtering firewalls have seen some impressive technological advances (e.g., stateful inspection, transparency, performance, etc.) and wide-spread deployment. In contrast, fire-wall and security management technology is lacking. In this paper we present Firmato, a firewall management toolkit, with the following distinguishing properties and components: (1) an entity-relationship model containing, in a unified form, global knowledge of the security policy and of the network topology; (2) a model definition language, which we use as an interface to define an instance of the entity-relationship model; (3) a model compiler, translating the global knowledge of the model into firewall-specific configuration files; and (4) a graphical firewall rule illustrator. We implemented a prototype of our toolkit to work with several commercially available fire-wall products. This prototype was used to control an operational firewall for several months. We believe that our approach is an important step toward streamlining the process of configuring and managing firewalls, especially in complex, multi-firewall installations.