The book is thematically divided into three segments: Part I describes the conditions surrounding the operation and security of computer networks; Part II build from there and confronts the reader to the prevailing security situation based on the constant security threat, and Part III - presents readers - the core with most of the practice and the best solution currently in use. This text area start / reference to a comprehensive survey of computer network security concepts, methods, and practices and includes network security tools, policies, and administrative purposes in an integrated manner.