When constructing a firewall, a variety of firewall criteria can be used. The ability of the firewall to protect the system from unwanted access is the first requirement. The firewall should be able to prevent unauthorized users from accessing the system's resources. The ability of the firewall to protect the system from illegal traffic is the second requirement. Unauthorized traffic entering or exiting the system should be blocked by the firewall. The ability of the firewall to safeguard the system from unauthorized alterations is the third requirement. Unauthorized users should not be able to make changes to the system's settings, and unauthorized users should not be able to change the system's resources. The fourth requirement is the firewall's ability to defend the system from threats. The firewall should be able to prevent unauthorized users from launching attacks on the system and block attacks on the system.