Network firewalls are security devices used to stop or mitigate() access to private networks connected to the lnternet, especially intranets. The only traffic allowed on the network is defined via firewall ()-any other traffic attempting to access the network is blocked. Network firewalls sit at the () line of a network, acting as a communications liaison between internal and external devices, When properly configured, a firewall allows users to access any of the resources they need while simultaneously keeping out unwanted accesses. In addition to limiting access to a protected computer and network, a firewall can () all traffic coming into or leaving a network, and manage remote access to a private network through secure authentication certificates and logins. () firewalls examine every packet that passes through the network and then accept or deny it as defined by rules set by the user.
A．Unauthorized
B．a(chǎn)uthorized
C．normal
D．frequent

A．Ports

A．Front

A．Reply

A．Application-layer