What is the predefined rule set used by the firewalld service called?

The predefined rule set used by the firewalld service is called Zones. In the context of firewalld, zones are used to define the level of trust for the network connections a system is exposed to. Each zone has its own set of rules that specify what services and ports are allowed or denied, based on the perceived trustworthiness of the connection. For instance, a public zone may have more restrictive rules compared to a home zone where more services might be trusted.

Using zones allows for a more flexible and manageable approach to firewall configuration, as different network interfaces can be assigned to different zones based on the desired security posture. This zoning feature makes it easier for system administrators to quickly apply consistent security rules for various network environments without having to create and maintain complex sets of rules individually.

The other choices, such as Policies, Rules, and Profiles, do not accurately capture the concept of how firewalld organizes its security framework. While they may relate to security configurations, they do not specifically refer to the method firewalld uses to categorize and apply multiple rules efficiently within its structured environment.