NSE 7 – OT Security 6.4 — Question 18

As an OT administrator, it is important to understand how industrial protocols work in an OT network.
Which communication method is used by the Modbus protocol?

Answer options

• A. It uses OSI Layer 2 and the primary device sends data based on request from secondary device.
• B. It uses OSI Layer 2 and both the primary/secondary devices always send data during the communication.
• C. It uses OSI Layer 2 and both the primary/secondary devices send data based on a matching token ring.
• D. It uses OSI Layer 2 and the secondary device sends data based on request from primary device.

Correct answer: D

Explanation

The correct answer is D because the Modbus protocol follows a master-slave configuration, where the primary (master) device requests data and the secondary (slave) device responds. Options A, B, and C misrepresent the roles of the devices in the Modbus communication process, incorrectly suggesting that the primary device does not request data or that both devices send data simultaneously.