IEC 62443 and the Purdue model for plant managers.

Industrial networks have different priorities from office networks: safety and availability come first. Two reference ideas help organise their security.

The Purdue model

A layered view of an industrial site:

• Level 0: sensors, actuators and the physical process.
• Level 1: controllers such as PLCs.
• Level 2: supervision, HMIs and local control.
• Level 3: site operations, such as historians and manufacturing systems.
• Level 4 and 5: business and enterprise IT.

Traffic between levels should be limited, deliberate and monitored. A demilitarised zone sits between plant and enterprise.

IEC 62443

A family of standards for industrial automation and control system security. Key ideas:

• Zones: groups of assets with similar security needs.
• Conduits: the controlled paths between zones.
• Security levels: the strength of protection needed against different attackers.
• Roles: responsibilities of asset owners, integrators and product suppliers.

Designs and procedures can be aligned to the standard, even where a formal assessment is not part of the project.

Practical consequences

• Segment the network by function and risk.
• Place industrial firewalls at conduits.
• Control remote vendor access through a recorded jump host.
• Patch carefully, testing before deployment and keeping backups of controllers.
• Monitor passively to avoid disturbing the process.

Start small

Map assets and flows, define zones, then add controls zone by zone during planned shutdowns.