The 5-level Purdue Enterprise Reference Architecture, zones and conduits, and how an Industrial DMZ separates the plant floor from the corporate network.
The Purdue model is the reference architecture nearly every OT security standard (including IEC 62443) builds on — Level 0 sensors and actuators, Level 1 controllers, Level 2 supervisory/HMI, Level 3 site operations, and Levels 4/5 the enterprise IT network, with an Industrial DMZ typically inserted between Level 3 and Level 4. This module works through why traffic should never cross directly from Level 4/5 to Level 0-2, how zones and conduits formalize the model into enforceable security boundaries, and where a historian, jump host, or data diode belongs in the architecture.
By the end of this module you should be able to place a piece of plant equipment at the correct Purdue level and identify which conduit(s) it legitimately needs — the design skill Module 14's manufacturing-plant segmentation project and Module 14's water-utility SCADA hardening project both apply to a full real facility.