OT Network Testing for Critical Infrastructure: Purdue, NIST, and Redbot’s Safety-First Approach

At the core of Redbot Security’s OT methodology is the Purdue Enterprise Reference Architecture. While often oversimplified in textbooks, the Purdue model provides a reliable blueprint for how processes, control systems, and enterprise networks should be segmented. More importantly, it reveals how segmentation failures allow attackers to traverse from business IT into critical control zones.

Redbot begins OT testing by mapping assets, data flows, and trust boundaries to their respective Purdue layers, from Level 0 field devices to Level 4 enterprise systems. This mapping provides clarity on where isolation should exist and where it has eroded over time. It also helps identify the conduits, firewalls, remote access channels, and network junctions, through which attackers most often move.

Once the architecture is understood, Redbot evaluates whether segmentation aligns with Purdue’s intent. Many utilities believe they have a strong OT DMZ, only to discover that firewall rules unintentionally allow unrestricted traffic from Level 4 into Level 3 or even Level 2. In other cases, vendor remote access tunnels bypass segmentation entirely, introducing direct pathways into SCADA servers or engineering workstations. Redbot’s testing focuses heavily on these conduits, validating whether the controls actually enforce the separation operators believe exists.

The process extends into protocol-level evaluations inside OT networks. Instead of relying on aggressive scanning, Redbot uses controlled, rate-limited techniques to identify exposed services, ICS protocol endpoints, and devices that may respond to unauthorized read/write commands. The intent is not simply to find vulnerabilities, but to understand how exploitation could impact real-world processes, and how segmentation, monitoring, and compensating controls can prevent such scenarios.