All these questions should only be solved and proved through engineering method and technology realization . in this dissertation , the author tried to illustrate the purpose and aims of internet security by giving a new idea of the boundary of traditional lan . using the ppdr theory , also combining with a real instance and the monitor - auditing software already developed , the author proved the validity and the applicability of this theory model both theoretically and practically . furthermore , illustrated how the security technology strategy is formed and applied by using the reasoning method of system engineering science , hence , advanced a good instance as to how to thoroughly fulfil the internet security engineering 本论文通过对传统的内联网系统边界和区域定义的充分理解和重新认识，对网络安全的目的、目标进行了描述，并运用p ~ 2dr理论模型，结合所参与的一个网络安全工程实例和已开发完成的内联网监控审计软件，从理论和实践两方面证明该理论模型和对一些定义理解的正确性和可实现性，以系统工程学的思维方式阐述了安全策略的形成过程和实现方法，对网络安全工程实际应用提出了可资借鉴的实例。
