CompTIA CASP+ (CAS-004) — Question 608

A security consultant has been asked to recommend a secure network design that would:

• Permit an existing OPC server to communicate with a new Modbus server that is controlling electrical relays.
• Limit operational disruptions.

Due to the limitations within the Modbus protocol, which of the following configurations should the security engineer recommend as part of the solution?

Answer options

• A. Restrict inbound traffic so that only the OPC server is permitted to reach the Modbus server on port 135.
• B. Restrict outbound traffic so that only the OPC server is permitted to reach the Modbus server on port 102.
• C. Restrict outbound traffic so that only the OPC server is permitted to reach the Modbus server on port 5000.
• D. Restrict inbound traffic so that only the OPC server is permitted to reach the Modbus server on port 502.

Correct answer: D

Explanation

The correct answer is D because Modbus typically operates over TCP on port 502, and restricting inbound traffic ensures that only the OPC server can communicate with the Modbus server without exposing it to other potential threats. Options A, B, and C are incorrect as they either use the wrong port or restrict the wrong type of traffic, which would not effectively secure the communication between the servers.