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Purdue Enterprise Reference Architecture (Purdue Model & ISA-95)

Demarcating Levels 0 through 5, industrial network segmentation, and secure OT/IT convergence.

Executive Overview

The Purdue Model (formalized in ISA-95) is the structural cornerstone of industrial control systems architecture. It segregates physical equipment, real-time controllers, supervisory HMIs, and corporate ERP systems into disciplined hierarchical zones.

1. The Six Purdue Levels (Level 0 to Level 5)

The Purdue Model structures industrial networks into discrete functional tiers:

  • Level 0 (Physical Process): Physical equipment, sensors, valves, motors, transformers, and switchgear.
  • Level 1 (Basic Control): Microprocessors executing cyclic logic: PLCs, RTUs, and distributed I/O blocks.
  • Level 2 (Area Supervisory Control): Operator HMIs, alarms, batch controls, and SCADA engineering consoles.
  • Level 3 (Site Operations & MES): Process historians, plant scheduling, laboratory systems, and batch records.
  • Level 3.5 (Industrial DMZ): Security boundary with jumpboxes, dual firewalls, and data proxies.
  • Level 4/5 (Enterprise IT): Corporate ERP (SAP), business email, Active Directory, and Internet egress.

Frequently Asked Questions

Why is Level 3.5 (IDMZ) critical in modern OT security?

It completely terminates network sessions between corporate IT and control systems, preventing ransomware and malicious packets from laterally jumping into real-time controllers.

AI Summary

The Purdue Model (formalized in ISA-95) is the structural cornerstone of industrial control systems architecture. It segregates physical equipment, real-time controllers, supervisory HMIs, and corporate ERP systems into disciplined hierarchical zones.