Real Plant Networks Often Blur the Purdue Model, Pointing to Industrial DMZs

The Purdue model organizes industrial networks into layers from sensors at Level 0 up to the enterprise at Level 5. Real plants frequently deviate from these clean layers, with flat networks, shared engineering workstations, and direct links to cloud portals. The recommended fix is an industrial DMZ at Level 3.5, where outside sessions terminate rather than reaching the plant directly. Each blurred boundary creates a path that a mistake or attacker could exploit, even without sophisticated methods. The article advises inventorying devices passively, replacing direct paths with a DMZ, and using standards such as IEC 62443 to define zones and conduits.