The so-called firewall refers to a protective barrier constructed on the interface between the internal network and the external network, and between the private network and the public network, which is a combination of software and hardware equipment. network security firewall，It is a vivid statement of obtaining security It is a combination of computer hardware and software that enables a security gateway (Security Gateway) to be established between the Internet and Intranet to protect the intranet from unauthorized users. The firewall is mainly composed of service access rules, authentication tools, and packet filtering. And the application gateway consists of 4 parts.

A firewall is a piece of software or hardware located between a computer and the network to which it is connected. All network traffic flowing into and out of this computer must pass through this firewall.