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KNOWLEDGE HUB

The Purdue Model: the map we still use to segment OT

The 1990s reference model that remains the starting point for segmenting industrial networks — and why it needs nuance today.

What it is

The Purdue Enterprise Reference Architecture (PERA) originated in the 1990s at Purdue University as a model for organizing manufacturing enterprise architecture. The OT security community adopted it as a reference map for segmenting industrial networks by risk level and function.

Why it matters

Before Purdue, it was common to find the plant floor connected directly to the corporate network with no clear boundary. The model gave a whole generation of engineers a shared vocabulary — 'Level 2', 'industrial DMZ' — for designing and auditing segmentation.

How it's structured

• Level 0 — Physical process: sensors, actuators, the actual process.
• Level 1 — Basic control: PLCs, RTUs, real-time controllers.
• Level 2 — Supervisory: HMI, local SCADA, operator stations.
• Level 3 — Site operations: historians, MES, OT domain servers.
• DMZ zone (3.5): the mandatory boundary between OT and IT — no traffic should cross directly from Level 3 to Level 4.
• Level 4 — Business logistics: ERP, corporate IT.
• Level 5 — Enterprise: corporate network, internet.

Best practices

• Use the industrial DMZ religiously — it's the single piece that most prevents lateral movement between IT and OT.
• Treat Purdue as a starting point, not dogma: document where your real architecture diverges and why.
• Combine it with 62443's zones and conduits to have both the map (Purdue) and the required security level per zone (62443).

Common mistakes

• Assuming the model still fully applies to architectures with IIoT, cloud, and remote maintenance — today it needs adaptation, not abandonment.
• Drawing the Purdue diagram once and never validating it against the real network again.
• Confusing 'having the diagram' with 'having the segmentation' — the drawing doesn't enforce the firewall rules.