If you are working on a physical security plan for a data center and focusing on building and access control, what layer of the plan would this relate to?

Layer 1 represents the outermost site perimeter security such as fencing, vehicle barriers, and security checkpoints.

Layer 2 covers the building exterior, including its physical walls, doors, and entry points from outside.

Layer 3 corresponds to the building interior and access control mechanisms in the standard four-layer model. This layer encompasses physical controls such as mantraps, card readers, biometrics, and interior locked doors that regulate who can move through the facility to reach sensitive areas.

Layer 4 is the innermost layer focused on individual cabinet, rack, and equipment-level physical security.

A five-layer classification does not exist in the standard four-layer data center security model.