What is the Zones and Conduits Model?
The Zone and Conduit model is a concept within industrial Cybersecurity used to logically divide networks and control communication between them.
It is part of the IEC 62443 standard and is a core principle for designing secure automation systems in, for example, factories, water treatment plants, power stations or other operational technology (OT) environments.
🧱 Key terms
| Term | Description |
|---|---|
| Zone | A logical group of systems or devices with the same security requirements. Examples: PLC Zone, MES Zone, ERP Zone. |
| Conduit | The communication channel between Zones. Data traffic flows through it. A Conduit must be secured and managed (e.g. with Firewall, VPN, Monitoring). |
🧠 Why zones and conduits?
- Network segmentation prevents an incident from spreading uncontrollably.
- Security policy can be tailored to risks and functions per Zone.
- Control over data flows prevents unwanted access or data leaks.
🔄 Relationship with the Purdue Model
The Zone and Conduit model complements the Purdue Model:
- The Purdue Model describes the functional layers (from Sensor to ERP).
- The Zone and Conduit model describes how to lay out and let those layers communicate logically and securely.
🧠 Example: Levels 1 and 2 of the Purdue Model (PLCs and SCADA) can fall into a single OT Zone. Communication with Level 3 (MES) runs through a secured Conduit (e.g. with Firewall and Logging).
🏭 Example of zones
| Zone | Type of security |
|---|---|
| PLC Zone (Level 1) | Local traffic only, physically segregated |
| SCADA/HMI Zone (Level 2) | Authentication and network security |
| MES Zone (Level 3) | Logging, network access via Firewall |
| ERP Zone (Level 4) | IT security, user authentication |
🔐 Security measures per conduit
Every Conduit between Zones must be assessed for risks. Commonly used measures:
- Firewall or data diodes
- Encryption (VPN, TLS)
- Authentication and authorisation
- Monitoring and Logging
- Unidirectional communication where required
📌 In summary
The Zone and Conduit model is a strategy for logically dividing and protecting industrial networks. By isolating Zones and controlling Conduits, the risk of cyber attacks or disruption is greatly reduced — and the architecture aligns with international standards such as IEC 62443.