Exam CAS-004 topic 1 question 307 discussion

Check Gemini's (partial) response: Modbus protocol: Modbus is a lightweight protocol that traditionally doesn't implement strong authentication or encryption mechanisms. Port usage: Modbus typically uses port 502 for communication. However, due to limitations in the protocol itself, relying solely on port restrictions for security isn't ideal.

Even if you don't know those port numbers, you could still narrow it down to A or D because the OPC traffic is the only traffic inbound to the server.

The security engineer should recommend **D. Restrict inbound traffic so that only the OPC server is permitted to reach the Modbus server on port 502**. Modbus is a communication protocol used for transmitting information over serial lines between electronic devices. The standard Modbus TCP/IP protocol uses port 502 for communication. Therefore, to allow the OPC server to communicate with the Modbus server while limiting operational disruptions, the inbound traffic to the Modbus server on port 502 should be restricted so that only the OPC server can reach it.

Modbus communicates over TCP port 502.