Page146

Perimeter Defenses

Perimeter defenses help prevent, detect, and correct unauthorized physical access. Buildings, like networks, should employ defense-in-depth. Any one defense may fail: so critical assets should be protected by multiple physical security controls, such as fences, doors, walls, and locks. The ideal perimeter defense is safe, prevents unauthorized ingress, and when applicable offers both authentication and accountability.

Fences

Fences may range from simple deterrents (such as 3-foot/1-meter tall fencing) to preventive devices, such as an 8-foot (2.4-meter) tall fence with barbed wire on top. Fences should be designed to steer ingress and egress to controlled points, such as exterior doors and gates.

Gates

The gates shown in Table 4.12 range in strength from ornamental (a class I gate designed to deter access) to a class IV gate designed to prevent a car from crashing through (such as gates at airports and prisons). For more information, see ASTM International’s “ASTM F2200” Standard Specification for Automated Vehicular Gate Construction at https://www.astm.org/f2200-20.html.

Table 4.12 Types of Vehicle Gates.

Type	Description
Class I	Residential (home use)
Class II	Commercial/General Access (parking garage)
Class III	Industrial/Limited Access (loading dock for 18-wheeler trucks)
Class IV	Restricted Access (airport or prison)

Gates should be placed at controlled points at the perimeter. Secure sites use fences and topography to steer traffic to these points.