The course is aimed at presenting the main aspects of network security and at providing practical examples and knowledge of some common tools. The course includes the analysis of some important classes of vulnerabilities and of corresponding countermeasures. Management strategies and limitations of current solutions are discussed. Firewall technologies represent a relevant part of the course. The evolution and characteristics of these technologies are analysed, as well as their application in complex industrial scenarios. In general, the goal of the course is to provide a wide analytical perspective of the network security field combined with the description of low-level techniques.