在当今的计算机世界，因特网无孔不入。为应付“不健全”的因特网，人们创建了几种安全机制，例如：访问控制、认证表，以及最重要的方法之一：防火墙。-In today' s computer world, the Internet pervasive. To cope with the " no sound"　of the Internet, people have created several security mechanisms, such as: access control, authentication tables, and one of the most important way: the firewall.