security zone

A security zone is a deliberately defined segment of a network, system, or facility that groups assets with similar security requirements, access rules, and risk profiles. In industrial and manufacturing environments, security zones are commonly used to separate control systems, production networks, business IT networks, and external connections so that risks and protections can be managed in a structured way.

Security zones are typically defined based on factors such as criticality of the process, data sensitivity, allowable connectivity, and required trust level. Each zone has documented boundaries, allowed communication paths, and security controls such as authentication, authorization, monitoring, and change management.

How security zones are used in industrial environments

In regulated industrial operations, security zones commonly appear as:

• Control system zones that contain PLCs, DCS, safety instrumented systems, and other OT controllers.
• Production or MES zones that host manufacturing execution systems, historians, and quality systems.
• Corporate IT zones for ERP, email, office networks, and business applications.
• DMZ or perimeter zones that sit between internal networks and external partners, vendors, or the internet.

Traffic between security zones is usually restricted and monitored. For example, a defined conduit or segmented connection may be the only permitted path between an OT control zone and an enterprise IT zone, with rules specifying which protocols, ports, and data flows are allowed.

What a security zone includes and excludes

A security zone typically includes:

• Systems and devices with similar security requirements and risk tolerance.
• Defined logical and/or physical network segments.
• Documented security controls and access policies for that group.

It does not, by itself, specify individual network devices (such as a specific firewall), communication sessions, or specific user accounts. These are mechanisms and actors that enforce or operate within zones, not the zone definition itself.

Common confusion

• Security zone vs. network segment: A network segment is a technical subdivision of a network. A security zone may contain one or more segments and is defined by security policy and risk, not just topology.
• Security zone vs. conduit or connection: A security zone is the area or domain being protected. A conduit or controlled connection is the managed communication path between zones.
• Security zone vs. VLAN: VLANs are one possible technical implementation. A security zone is a higher-level concept and may be realized using VLANs, firewalls, routing rules, or combinations of these.

Link to the conduit context

In many industrial cybersecurity reference models, security zones are the defined areas that need protection, while conduits are the controlled and documented paths that allow traffic between those zones. When designing or validating a conduit, the source and destination security zones, as well as the policies that govern their interaction, must be clearly identified.