Question 220
A policy enforcement gateway temporarily loses its authorization service. Business policy says a new unauthenticated session must never be admitted while the control plane is unavailable. Which failure mode is required?
Explanation
Correct Answer
This preserves the deny-by-default authorization boundary during loss of the decision component, with a separately approved recovery procedure. Zero-trust decisions depend on resource, identity and device context, not permanent trust arising from network location; the point making a decision and the point enforcing it can be separate. The case turns on a policy enforcement gateway temporarily loses its authorization service; “Fail closed by denying new sessions until authorization can be evaluated” addresses that precise condition. “Fail open and admit new sessions based on their source IP addresses” is not equivalent because network location does not replace an explicit authorization decision when the policy service is unavailable.
Incorrect Answers
An old permit for one subject cannot safely authorize new callers or changed request contexts. Architecture controls differ by layer: application-aware filtering, network isolation, secure access and load distribution address different failure or abuse paths. In the reported situation, a policy enforcement gateway temporarily loses its authorization service. The effective mechanism is “Fail closed by denying new sessions until authorization can be evaluated”: this preserves the deny-by-default authorization boundary during loss of the decision component, with a separately approved recovery procedure.
Network location does not replace an explicit authorization decision when the policy service is unavailable. The evidence is a policy enforcement gateway temporarily loses its authorization service. Architecture controls differ by layer: application-aware filtering, network isolation, secure access and load distribution address different failure or abuse paths. By contrast, “Fail closed by denying new sessions until authorization can be evaluated” operates on the specific concern: this preserves the deny-by-default authorization boundary during loss of the decision component, with a separately approved recovery procedure.
Unrestricted admission defeats the stated no-new-unauthenticated-session requirement and removes evidence. Telemetry provides evidence and may trigger a response; it does not automatically deny a transaction or remediate its cause. Here the decisive fact is a policy enforcement gateway temporarily loses its authorization service. “Fail closed by denying new sessions until authorization can be evaluated” matches that requirement because this preserves the deny-by-default authorization boundary during loss of the decision component, with a separately approved recovery procedure.






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