防火墙是在内部网络 (如互联网 )与外部网络 (如内联网 )之间实施安全防范的系统，是一种访问控制机制，用于确定哪些内部服务允许外部访问以及允许哪些外部服务访问内部服务。 一、防火墙的基本准则 1.一切未被允许的就是禁止的 基于这个准则，防火墙应封锁所有信息流，然 A firewall is a system that enforces security between an internal network (such as the Internet) and an external network (such as an intranet). It is an access control mechanism that determines which internal services allow external access and which external services allow access to internal services. First, the basic principles of the firewall 1. All is not allowed is forbidden Based on this criterion, the firewall should block all information flow, of course