OPC UA Server Client Gateway: How to Run Both Modes Simultaneously

Why an OPC UA Server Client Gateway Changes Everything in Industrial Integration

In modern industrial environments, data flows in multiple directions at once. An OPC UA server client gateway is the architectural solution that allows a single device or software instance to simultaneously act as both a data consumer and a data provider — bridging the gap between field-level equipment and upper-tier enterprise systems without requiring separate hardware or complex middleware. Whether you are connecting a Siemens S7-1500 PLC to a SCADA platform, feeding real-time data to an MES, or enabling cloud integration, understanding how dual-mode OPC UA operation works is essential for any Industry 4.0 initiative.

This article explains the technical architecture behind running OPC UA in server and client mode simultaneously, the industrial use cases that benefit most from this approach, and how platforms like vNode Automation make this deployment straightforward without any programming required.

Understanding OPC UA: A Quick Technical Primer

OPC UA (OPC Unified Architecture) is the leading machine-to-machine communication protocol for industrial automation. Defined by the OPC Foundation, it provides a platform-independent, service-oriented architecture that supports secure, reliable data exchange between industrial devices and systems. Unlike its predecessor OPC DA, OPC UA does not rely on DCOM and works seamlessly across Windows, Linux, and embedded platforms.

At its core, OPC UA operates on a client-server model. An OPC UA Server exposes data — such as PLC tags, sensor readings, or process variables — through a structured address space. An OPC UA Client connects to one or more servers to read, write, or subscribe to that data. Most traditional implementations keep these roles separate. The real innovation comes when a single gateway instance performs both roles simultaneously.

The Architecture of a Dual-Mode OPC UA Server Client Gateway

A dual-mode OPC UA server client gateway essentially sits in the middle of your data pipeline, collecting data from multiple sources while simultaneously making that aggregated data available to multiple consumers. Here is how the layers work in practice:

• Client side (southbound): The gateway acts as an OPC UA Client, connecting to OPC UA Servers embedded in PLCs, DCS systems, drives, or other industrial devices. It subscribes to tags, reads process variables, and collects alarms and events.
• Server side (northbound): The same gateway instance acts as an OPC UA Server, exposing a unified, consolidated address space to SCADA systems, historians, MES platforms, cloud connectors, and any other OPC UA Client application that needs the data.
• Internal data brokering: The gateway manages the internal mapping between what it collects as a client and what it publishes as a server, applying filtering, scaling, unit conversion, and aggregation in the middle layer.

This architecture eliminates the need for direct point-to-point connections between each PLC and each enterprise application — a topology that quickly becomes unmanageable as the number of devices and consumers grows. Instead, the OPC UA server client gateway acts as a single integration hub.

Real-World Use Cases with Siemens, Rockwell, and Schneider Equipment

Siemens S7 PLCs and SCADA Integration

A typical scenario involves a production line equipped with Siemens S7-1200 and S7-1500 PLCs, each running an OPC UA Server natively (supported from TIA Portal V14 onwards). An OPC UA server client gateway connects to all these PLCs as an OPC UA Client, subscribing to hundreds or thousands of tags — temperatures, pressures, cycle counts, motor states — and then re-exposes the consolidated data through its own OPC UA Server interface. The plant’s SCADA system (such as Siemens WinCC or a third-party platform) connects to this single OPC UA Server endpoint instead of managing individual connections to each PLC. This dramatically simplifies SCADA configuration and improves maintainability.

Rockwell Automation Allen-Bradley Systems

Rockwell Automation’s Allen-Bradley PLCs — including the ControlLogix and CompactLogix families — are widely deployed in North American and global manufacturing facilities. While Allen-Bradley natively uses EtherNet/IP, many integrators add OPC UA connectivity through Rockwell’s FactoryTalk suite or third-party servers. In a mixed environment, an OPC UA server client gateway can connect to these OPC UA endpoints on the Rockwell side while simultaneously serving data to analytics platforms, MES systems like SAP ME, or cloud-based ML/AI engines. The gateway abstracts the underlying Rockwell-specific address space into a standardized OPC UA namespace that any consumer can read.

Schneider Electric EcoStruxure and Power Monitoring

Schneider Electric’s EcoStruxure platform supports OPC UA natively across its Modicon PLCs and power monitoring devices. In energy management and building automation projects, a gateway configured as an OPC UA server client gateway can simultaneously pull data from Schneider power meters and Modicon M340/M580 PLCs while publishing aggregated energy KPIs to a BI platform or a cloud dashboard. This dual-mode operation is particularly valuable in environments where the same data needs to reach multiple consumers — a local historian, a remote SCADA, and a cloud analytics tool — without creating multiple separate polling connections to the source devices.

ABB DCS and Drives Integration

ABB’s AC 800M DCS and drive systems are common in process industries such as oil and gas, chemicals, and pulp and paper. An OPC UA server client gateway deployed at the plant edge can connect to ABB’s OPC UA interfaces, collecting process data from control loops, and then serve this data upstream to both an on-premise OSIsoft PI Historian and an Azure IoT Hub simultaneously. This multi-destination delivery from a single gateway client session reduces load on the source systems and ensures data consistency across all consumers.

Technical Considerations When Running OPC UA in Dual Mode

Running an OPC UA server client gateway in dual mode introduces specific technical considerations that engineers must address during design and deployment:

• Session management: The gateway must maintain stable OPC UA client sessions with all source devices while simultaneously managing multiple server sessions from consumers. Session timeouts, keep-alive intervals, and subscription parameters must be tuned carefully for each source.
• Address space design: The OPC UA Server address space exposed by the gateway should be logically organized — typically by plant area, machine, or process unit — rather than simply mirroring the raw PLC structure. This makes it easier for SCADA and MES applications to navigate and subscribe.
• Security configuration: OPC UA supports certificate-based authentication and encrypted communications. In dual mode, the gateway must manage its own certificates as a server, and validate certificates from the source servers it connects to as a client. OPC UA security specifications define the message security modes (None, Sign, Sign & Encrypt) that must be configured appropriately for each connection.
• Redundancy and failover: In critical applications, the gateway itself should be redundant. A Primary and Backup node configuration ensures that if the primary gateway fails, the backup takes over without data loss — maintaining both the client connections to source devices and the server connections to consumers.
• Store & Forward capability: Network interruptions between the gateway and upstream consumers are inevitable. A robust OPC UA server client gateway implementation should buffer data locally during outages and forward it once connectivity is restored, ensuring zero data loss.
• Tag volume scalability: Industrial plants can have tens of thousands of tags. The gateway must handle high tag counts without performance degradation. Tag-based licensing models used by some vendors create cost barriers at scale — a critical selection criterion when evaluating solutions.

Benefits of the Dual-Mode Architecture for IT/OT Convergence

The OPC UA server client gateway architecture is particularly well-suited for the IT/OT convergence challenges that Industry 4.0 demands. On the OT side, it speaks the native language of PLCs, DCS systems, and field devices. On the IT side, it presents a clean, standardized, secure data interface that enterprise applications and cloud platforms can consume without needing to understand industrial protocols.

Key business benefits include:

• Reduced integration complexity: One gateway replaces a web of point-to-point connections, reducing configuration effort and the risk of inconsistent data.
• Faster time to value: New applications — a new analytics tool, a new cloud platform — simply connect to the existing OPC UA Server endpoint rather than requiring new PLC-level configuration.
• Improved data governance: Centralizing data collection in a single gateway makes it easier to apply consistent naming conventions, engineering unit conversions, and access control policies.
• Scalability: Adding new source devices (new PLCs, new sensors) means adding a new client connection to the gateway, not reconfiguring every consumer application.

For a deeper understanding of how OPC UA compares to other IIoT protocols, Wikipedia’s OPC UA article provides a comprehensive overview of the protocol’s history and capabilities.

How vNode Solves This

vNode Automation was designed from the ground up to operate as a true OPC UA server client gateway — simultaneously running as an OPC UA Client to collect data from any source device and as an OPC UA Server to deliver consolidated data to any consumer application, all within a single software instance.

Here is specifically how vNode addresses every challenge discussed in this article:

• True dual-mode OPC UA: vNode’s OPC UA Module acts as both OPC UA Client and OPC UA Server at the same time, with no additional configuration complexity. Engineers configure source connections and server namespace mappings through a web-based interface — no programming required.
• Unlimited tags, no licensing barriers: Unlike competitors that charge per tag, vNode supports unlimited tags. This means a plant with 50,000 tags from Siemens, Rockwell, and Schneider devices pays the same as a plant with 5,000 tags — eliminating the cost barrier to full data visibility.
• Store & Forward built-in: vNode’s Store & Forward capability ensures that if the upstream OPC UA consumer or cloud platform becomes unavailable, data is buffered locally and delivered without loss once the connection is restored.
• Built-in redundancy: vNode’s Redundancy Module provides Primary + Backup node automatic failover, ensuring the OPC UA server client gateway remains available even if the primary node fails. SCADA, MES, ERP, and BI systems maintain uninterrupted data access.
• Multiplatform deployment: vNode runs on Windows, Linux, and ARM embedded systems, making it deployable on industrial PCs, edge computers, or embedded gateways already present in the plant — no new specialized hardware required.
• Multi-protocol southbound connectivity: Beyond OPC UA, vNode connects natively to Siemens S7 (300/400/1200/1500), Modbus TCP/RTU, EtherNet/IP (for Rockwell Allen-Bradley), BACnet, ABB proprietary protocols, and many more — meaning it can serve as an OPC UA server client gateway even for devices that do not natively support OPC UA, translating their proprietary protocols into a standardized OPC UA address space.
• Multi-destination data delivery: In addition to its OPC UA Server output, vNode can simultaneously deliver data to MQTT brokers, SQL databases, MongoDB, OSIsoft PI, AWS IoT, Azure IoT, Google Cloud, and more — making it a true integration hub for the entire plant data architecture.

Whether you are integrating a new Siemens TIA Portal line, migrating a Rockwell FactoryTalk environment, or building an energy monitoring solution around Schneider EcoStruxure devices, vNode provides a plug-and-play path to dual-mode OPC UA operation with enterprise-grade reliability.

Ready to deploy a production-ready OPC UA server client gateway in your facility? Contact the vNode team to discuss your architecture, or explore the vNode User Manual for detailed technical documentation on OPC UA configuration, address space design, and security setup.