The defined network and security demarcation point between an organization's information technology systems and operational technology systems, positioned according to a reference architecture such as the Purdue Model and enforced through network segmentation controls.

Key Points

Historically maintained through simple physical isolation — OT networks had no connection to IT networks or the internet at all — an assumption that has eroded as remote monitoring, predictive maintenance, and IoT integration have driven deliberate IT-OT connectivity
The Purdue Model provides the classic reference architecture defining layered zones between enterprise IT and plant-floor OT, with the boundary typically positioned between specific defined levels
Now maintained primarily through active network segmentation — firewalls, demilitarized zones, one-way data diodes — rather than physical absence of any connection
A poorly defined or inconsistently enforced boundary is a primary vector by which a compromise originating in conventional IT systems (phishing, ransomware) can reach safety-critical OT systems
Boundary definition directly shapes what remote access into OT is possible at all — a well-architected boundary can permit controlled, monitored remote access without fully collapsing the separation OT security depends on

Concept

Where OT environments once assumed inherent security through physical isolation from any external network, the IT-OT boundary today is an actively engineered and maintained control point — typically involving firewalls, demilitarized zones, and carefully scoped data flows — that permits necessary IT-OT data exchange (production data to enterprise systems, remote diagnostics into OT) while preventing a compromise on either side from freely reaching the other.

Explainer

The security stakes of IT-OT boundary design are asymmetric in a way that shapes how it's typically architected: IT compromises are common and relatively well-tolerated in isolation (a phishing-compromised laptop is a routine, containable incident), while an OT compromise carries physical safety and process disruption consequences that make even a low-probability boundary failure unacceptable, which is why boundary controls are typically designed to fail toward isolation rather than toward connectivity when something goes wrong. This asymmetry is also why boundary architecture increasingly favors mechanisms like data diodes — allowing data to flow only outward from OT to IT, never the reverse — for the most safety-critical OT zones, accepting reduced IT-to-OT visibility in exchange for a boundary that cannot be crossed inbound at all, even by a sophisticated attacker. For CE verticals, IT-OT boundary architecture is the single most consequential OT security design decision most organizations make, since nearly every other OT security control — remote access policy, network segmentation, monitoring — is defined relative to where and how that boundary is drawn and enforced.

Cite this entry

IT-OT Boundary. ConnectedEarth Knowledge Base. https://connectedearth.space/knowledge-base/it-ot-boundary/ (updated 13 September 2026).