Purdue Model (Purdue Enterprise Reference Architecture)

The Purdue Model is a reference architecture that organizes an industrial network into layered zones: from the physical process and field devices at the bottom, up through control systems, supervisory/SCADA systems, a demilitarized zone (DMZ), and finally business/enterprise IT systems at the top. It's the most widely referenced framework for deciding where to draw network segmentation boundaries between OT and IT, and for reasoning about how far an intruder could reach if one layer were compromised.