Do we know that OPC, the interface between ICS and IT, is very common on OT sites?

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How widely is OPC used as the interface between ICS and IT on OT sites and what are the security measures?

In OT security, interfaces like OPC are very widely used to bridge data between Purdue L2 (Control Network) and Purdue L3 (Operations Network). This practice is common but comes with significant security considerations.

How Widely is OPC Used?

  • OPC Classic and OPC UA (Unified Architecture) are among the most common industrial protocols used for data exchange.

  • OPC interfaces serve as middleware that aggregates and forwards process data (like sensor readings, alarms, or setpoints) from control systems (DCS/PLC/SCADA) at L2 to higher-level systems such as MES (Manufacturing Execution Systems) or historian databases at L3.

  • This kind of data flow is critical for operations management, analytics, and business decision-making.

Why It's Common:

  • Most industrial systems are built on the Purdue Enterprise Reference Architecture, which defines strict segmentation between OT and IT.

  • Direct communication between L2 and L3 is not ideal, so OPC is often used as a controlled and standardized interface layer.

  • OPC UA, in particular, is favored because of its built-in security features like encryption and authentication (which are lacking in older OPC Classic).

Security Considerations:

  • Risk of lateral movement: If improperly secured, attackers can leverage OPC interfaces to move from IT into OT environments.

  • Protocol vulnerabilities: OPC Classic uses DCOM, which has many known vulnerabilities and is hard to firewall.

  • Need for segmentation: Even with OPC, data should ideally pass through a DMZ (Demilitarized Zone) using an OPC gateway or firewall.

  • Best practices include:

    • Using read-only interfaces whenever possible.

    • Employing secure OPC UA gateways.

    • Applying network segmentation and firewalls to enforce one-way data flows.

    • Monitoring and logging all OPC traffic for anomalies.


OPC (especially OPC UA) is widely adopted for process data exchange between L2 and L3.
Security must be carefully managed, ideally using a DMZ architecture and strong access controls.
OPC UA is preferred over OPC Classic due to modern security features.

Here's a detailed OT security checklist for implementing and managing interfaces like OPC between Purdue L2 and L3. This is structured to help with risk mitigation, secure architecture design, and ongoing operations.

OT Security Checklist for OPC Interfaces (L2 ↔ L3)

1. Architecture & Segmentation

  • Use a Demilitarized Zone (DMZ) between L2 and L3.

  • Disallow direct communication between L2 and L3.

  • Ensure that OPC servers/interfaces are hosted in the DMZ, not directly on L2 or L3 networks.

  • Deploy firewalls between all levels (L2 ↔ DMZ, DMZ ↔ L3).

  • Configure strict firewall rules, allowing only required ports and protocols.

2. Protocol & Interface Hardening

If Using OPC UA:

  • Enforce encryption (TLS) for all OPC UA connections.

  • Require certificate-based authentication for OPC UA clients and servers.

  • Limit access via application-level ACLs (Access Control Lists).

If Using OPC Classic (DCOM):

  • Use tunneling software to encapsulate OPC Classic in a secure protocol (e.g., OPC UA or HTTPS).

  • Harden DCOM settings (minimize permissions, disable anonymous access).

  • Limit DCOM-related ports and monitor for abnormal behavior.

3. Application Security

  • Keep OPC software up to date with vendor patches.

  • Run OPC services with least privilege (e.g., non-admin accounts).

  • Disable unused features/protocols in OPC servers and clients.

  • Use read-only access where applicable — especially from L3 to L2.

4. Monitoring & Logging

  • Enable detailed logging of OPC connections and data flows.

  • Use SIEM integration to detect anomalies or unauthorized access.

  • Monitor for unusual traffic patterns, especially outside normal hours.

  • Correlate OPC activity with user authentication logs.

5. Access Control

  • Apply multi-factor authentication (MFA) for remote access to OPC systems.

  • Define and enforce role-based access controls (RBAC) for all OPC users.

  • Regularly audit user accounts, privileges, and access logs.

  • Isolate vendor access using jump servers or remote access gateways.

6. Network Security Measures

  • Implement intrusion detection systems (IDS) in the DMZ.

  • Use deep packet inspection (DPI) for OPC traffic if supported.

  • Ensure all systems are backed up regularly and tested for restoration.

  • Use firewalls or unidirectional gateways if only one-way communication is needed.

7. Testing & Validation

  • Perform regular vulnerability scans on OPC systems (especially in the DMZ).

  • Conduct penetration tests focused on OT/IT interfaces.

  • Validate fail-safe behavior: if OPC fails, critical OT operations must continue safely.

  • Include OPC paths in disaster recovery and incident response plans.

8. Governance & Compliance

  • Maintain asset inventory of all OPC servers, clients, and connections.

  • Document data flows and update diagrams periodically.

  • Align with NIST SP 800-82, ISA/IEC 62443, or your industry-specific standard.

  • Provide OT cybersecurity training for engineers and operators.



#CPS #OT #XIoT #IoT #IIoT #IoMT #CPSSecurity #OTSecurity #IoTSecurity #CPS보안 #OT보안 #IoT보안



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