Which method in firewall rules explicitly permits certain services?

The method referred to in the context of explicitly permitting certain services in firewall rules is best characterized by the concept of a "Restricted" policy. This approach involves defining specific rules that allow only certain types of traffic while blocking all other types by default. The term "Restricted" highlights that the firewall will accept traffic only for services that are explicitly allowed in its configuration.

In an environment where only predetermined and allowed services are permitted, this method helps to enhance security by minimizing exposure to unnecessary risks. By allowing only specific services, the firewall reduces the attack surface and helps prevent unauthorized access.

The other choices do not align with the concept of explicitly permitting services. "Allow by Default" implies that all services are permitted unless specified otherwise, leading to a more open security posture. "Deny by Default" suggests that all services are blocked until an exception is made, which does not provide explicit allowances but rather a restrictive measure. "Open Policy" indicates a configuration that generally allows a wide range of traffic without explicitly restricting anything, conflicting with the intent of explicitly allowing only certain services.