OPC UA modern architecture in SCADA systems - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding OPC UA Client-Server Model

In OPC UA architecture, what is the primary role of the server?

A To store data permanently without sharing

B To request data from multiple clients simultaneously

C To act as a passive listener without responding

D To provide data and services to clients upon request

💡 Hint

Think about who holds the data and who asks for it.

The OPC UA server hosts data and services. Clients connect to servers to read or write data.

💻 Command Output

intermediate

OPC UA Secure Channel Establishment Output

What output indicates a successful secure channel creation in an OPC UA client log?

SCADA systems

opcua-client --connect opc.tcp://localhost:4840
[INFO] Secure channel established with server at opc.tcp://localhost:4840

A [INFO] Secure channel established with server at opc.tcp://localhost:4840

B [ERROR] Connection refused by server

C [WARNING] Certificate rejected by server

D [DEBUG] Attempting to reconnect to server

💡 Hint

Look for confirmation messages about secure channel status.

A successful secure channel is confirmed by an info log stating it was established.

❓ Configuration

advanced

Configuring OPC UA Server Endpoint

Which configuration snippet correctly sets an OPC UA server endpoint to listen on port 4840 with no security?

A endpoint = opc.tcp://0.0.0.0:4840; securityPolicy=Basic256; messageSecurityMode=Sign

B endpoint = http://0.0.0.0:4840; securityPolicy=None; messageSecurityMode=None

C endpoint = opc.tcp://0.0.0.0:4840; securityPolicy=None; messageSecurityMode=None

D endpoint = opc.tcp://localhost:4840; securityPolicy=None; messageSecurityMode=SignAndEncrypt

💡 Hint

Check protocol, IP binding, port, and security settings.

Option C uses the correct OPC UA TCP protocol, binds to all interfaces, port 4840, and disables security.

❓ Troubleshoot

advanced

Diagnosing OPC UA Client Connection Failure

An OPC UA client fails to connect to the server and logs the error: 'BadCertificateUntrusted'. What is the most likely cause?

A The server endpoint URL is incorrect

B The client certificate is not trusted by the server

C The client is using an unsupported protocol version

D The server is offline and unreachable

💡 Hint

Focus on certificate trust issues in secure connections.

'BadCertificateUntrusted' means the server rejected the client's certificate because it is not in the trusted list.

🔀 Workflow

expert

OPC UA Data Subscription Workflow

Arrange the steps in the correct order for an OPC UA client to subscribe to data changes from a server.

A 1,2,3,4

B 2,1,3,4

C 1,3,2,4

D 3,2,1,4

💡 Hint

Think about establishing connection before monitoring data.

The client must first create a session, then a subscription, add items to monitor, and finally receive updates.