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Application & OT Security · Intermediate

Passive OT Network Monitoring

Monitoring industrial networks by analyzing copies of traffic, without sending packets to fragile control devices.

Definition

Passive monitoring through SPAN ports or network taps builds OT asset inventories, baselines normal industrial protocol behavior and detects anomalies such as unexpected PLC program downloads. It is preferred because active scanning can crash or disrupt legacy OT devices.

Example

An OT monitoring sensor on a SPAN port alerts when a new host sends Modbus write commands to a PLC.

Exam tip

In OT, prefer passive discovery; active scans can disrupt controllers.

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