作为内部网络与外部公共网络之间的第一道屏障,防火墙是最先受到人们重视的网络安全产品之一。虽然从理论上看,防火墙处于网络安全的最底层,负责网络间的安全认证与传输,但随着网络安全技术的整体发展和网络应用的不断变化,现代防火墙技术已经逐步走向网络层之外的其他安全层次,不仅要完成传统防火墙的过滤任务,同时还能为各种网络应用提供相应的安全服务。 As the first barrier between the internal network and the external public network, the firewall was one of the first network security products to be valued by people. Although theoretically, the firewall is at the bottom of the network security and is responsible for the security authentication and transmission among the networks. However, with the overall development of network security technology and the ever-changing network applications, the modern firewall technology has gradually moved beyond the network layer Other levels of security, not only to complete the traditional firewall filtering tasks, but also for a variety of network applications to provide the appropriate security services.