zones and conduits

In industrial and OT cybersecurity, zones and conduits commonly refer to a structured way of segmenting systems and controlling communications between those segments. The concept is widely associated with IEC 62443 and similar standards for securing industrial automation and control systems.

Definition

Zones are groupings of assets (such as controllers, servers, workstations, sensors, and applications) that share similar security requirements and risk profiles. A zone typically:

• Represents a logical or physical segment of the system (for example, a plant floor control network, a DMZ, or an engineering workstation group)
• Is defined by common security policies, such as required authentication, allowed services, or target security level
• Can map to network segments, functional areas, or combinations of both

Conduits are the controlled communication paths that connect zones. A conduit typically:

• Represents the data flows between zones (for example, between a control network and a historian, or between OT and IT networks)
• Implements security controls for those flows, such as firewalls, VPNs, demilitarized zones (DMZs), or data diodes
• Defines which protocols, ports, and directions of traffic are permitted between zones

How zones and conduits are used operationally

In industrial environments, zones and conduits are used to:

• Model the architecture of industrial automation and control systems at a security level
• Support risk assessments by showing where critical assets reside and how they are interconnected
• Guide design and configuration of network segmentation, access control lists, and security gateways
• Document intended communication paths for change management, compliance reviews, and incident response

For example, a manufacturing site might define separate zones for field I/O, control systems, safety systems, a site operations network, and enterprise IT. Conduits would then describe and restrict traffic between these zones, such as historian data flows from OT to IT or remote maintenance connections into control networks.

Relationship to IEC 62443

IEC 62443 commonly uses zones and conduits as core concepts for designing and documenting a secure industrial control system architecture. The standard encourages grouping assets into zones with defined target security levels and controlling inter-zone communication through conduits with appropriate technical and procedural safeguards. This approach supports lifecycle activities such as design, implementation, and ongoing verification of security controls in OT environments.

Common confusion

• Zones vs. VLANs or subnets: A zone is a security and risk construct, not strictly a network construct. A single zone can span multiple subnets, and one subnet can contain multiple zones if they have different security requirements.
• Conduits vs. network devices: A conduit is the secured communication path and its policies, not just the physical device. A firewall, router, or gateway may implement part of a conduit, but the conduit includes the defined rules, monitoring, and documentation for that traffic.
• Zones vs. physical areas: Physical plant areas (for example, a packaging line) and zones are not always the same. Zones are defined primarily by security needs and logical interactions, even though they often align with physical layouts.

Manufacturing-relevant examples

• A “Safety Instrumented System” zone separated from a “Basic Process Control System” zone, with a tightly controlled conduit allowing only specific diagnostic data.
• A “Site Operations” zone containing MES and historian servers, connected via conduits to both control system zones (for process data) and the enterprise IT zone (for reporting and planning).
• A remote access conduit that permits vendor maintenance connections to a specific control zone through a gateway with strong authentication and logging.

Use in documentation and governance

Zones and conduits are often documented in architecture diagrams, security plans, and procedures. They support coordination between OT, IT, engineering, and quality teams by providing a clear model of where critical functions reside and how information moves across the manufacturing environment.