zone and conduit

In the context of industrial cybersecurity, especially IEC 62443, zone and conduit refers to a structured way of segmenting operational technology (OT) environments and controlling communication between those segments.

Zones

A zone is a logical or physical group of assets that share similar cybersecurity requirements, such as security level, trust level, or functional role. A zone can include:

• Control systems and controllers (PLCs, DCS nodes)
• SCADA servers, HMIs, engineering workstations
• Network equipment associated with those systems
• In some cases, supporting IT systems that have aligned risk and protection needs

Zones are usually defined during risk assessment and architecture design. Each zone typically has:

• Clear boundaries
• Documented assets
• Assigned security level targets or comparable cybersecurity objectives

A zone does not have to be a single VLAN, room, or cabinet, although it may map to these. It is primarily a grouping concept based on security requirements, not just topology.

Conduits

A conduit is a defined communication path that connects two or more zones. It represents:

• The logical communication flow between zones
• The controls that protect that flow, such as firewalls, data diodes, VPNs, or protocol break devices
• The policies applied to that traffic, such as allowed protocols, ports, and directions

Conduits are designed to enforce the required cybersecurity posture between zones. In many architectures, critical functions such as remote access, cross-site replication, or MES/ERP integration are modeled as conduits between a control zone and a higher-level business or DMZ zone.

Operational use in industrial environments

In regulated manufacturing and other industrial operations, defining zones and conduits is a common step in:

• Cybersecurity risk assessments for OT and industrial control systems
• Network segmentation and defense-in-depth architecture design
• Documenting how MES, historians, and ERP systems connect to plant-floor equipment
• Supporting security procedures for remote support, vendor access, and data exchange

Zones and conduits are usually captured in network and security architecture diagrams, and referenced in site standards, operating procedures, and change control documentation.

Relation to IEC 62443

IEC 62443 introduces the concepts of zones and conduits as core elements of secure industrial automation and control system architecture. The standard uses them to:

• Structure the allocation of cybersecurity requirements to groups of assets
• Define where security controls should be applied to communication paths
• Support risk-based segmentation between systems with different security levels

While implementations vary, using zones and conduits aligns with IEC 62443-style approaches to designing and documenting OT cybersecurity controls.

Common confusion

• Zone vs. VLAN or subnet: A zone may be implemented with one or more VLANs or subnets, but it is defined by common cybersecurity requirements, not only by IP addressing.
• Conduit vs. physical link: A conduit is about the logical and controlled communication path, which may traverse multiple physical links, switches, or service providers.
• Zone and conduit vs. safety zones: Process safety zones or functional safety partitions are different concepts, although they may influence how cybersecurity zones are defined.

Link to the source context

In the context of IEC 62443 guidance for asset owners, zoning and conduits are typically introduced when applying parts such as IEC 62443-3-2, where sites identify industrial control system assets, group them into zones with defined security levels, and specify conduits that manage and protect communications between those zones.