Unlike data communications of the past today s networks consist of numerous devices that handle the data as it passes from the sender to the receiver. However security concerns are frequently raised in circumstances where interconnected computers use a network not controlled by any one entity or organization. Introduction to Network Security examines various network protocols focusing on vulnerabilities exploits attacks and methods to mitigate an attack. The book begins with a brief discussion of network architectures and the functions of layers in a typical network. It then examines vulnerabilities and attacks divided into four categories: header- protocol- authentication- and traffic-based. The author next explores the physical network and transport layers of each network as well as the security of several common network applications. The last section recommends several network-based security solutions that can be successfully deployed. This book uses a define-attack-defend methodology for network security. The author briefly introduces the relevant protocols and follows up with detailed descriptions of known vulnerabilities and possible attack methods. He delineates the threats against the protocol and presents possible solutions. Sample problems and lab experiments based on the concepts allow readers to experiment with attacks and assess the effectiveness of solutions. Two appendices provide further clarification and a companion website is offered which supplements the material. While most of the books available on this subject focus solely on cryptographic techniques to mitigate attacks this volume recognizes the limitations of this methodology and considers a wider range of security problems and solutions. By focusing on a practical view of network security and examining actual protocols readers can better understand the vulnerabilities and develop appropriate countermeasures.