In the domain of information technologies, certification exams are widespread as a mechanism for validation of expertise in specific domains of knowledge. CompTIA is an organization recognized by the ANSI, created to respond to the demand for certification of information technology. The CompTIA Security + certification is internationally recognized validation of skills related to computer security. The absence of ontologies for semantic markup of learning objects in the domain of this certification exam in the context of the Semantic Web, is the main motivation for the development of this proposal. This article presents a proposal to the domain ontology of this Network Security certification exam is developed, reaching the formal modeling Protege subdomain of Firewalls.