Due Care implies that not only has a party not been negligent or careless, but also that he/she has been guilty of no violation of law in relation to the subject mater or transaction which constitutes the cause of action. Due Care and Reasonable Care are used interchangeably. The definitions of Due Care given in the other answers re from Blacks Law Dictionary, Abridged Fifth Edition, West Publishing Company, St. Paul Minnesota, 1983.

A "fail-closed" approach means that in the event of a failure, such as a firewall malfunction or outage, the default behavior is to block all traffic or deny access. This prioritizes security by ensuring that, in the absence of normal operation, the firewall will still enforce a security posture that restricts access and protects the network from potential threats.