SCNET · Enterprise IT · Ankara, Türkiye
Passive discovery builds an asset inventory by listening to network traffic; it sends nothing to the devices. Active scanning, unremarkable on an IT network, can push an industrial controller into a state where it stops responding.
Short answer: in OT, discovery starts by listening. The active step follows only once its scope and window are written down.
Most industrial controllers were never designed to answer a request they did not expect. A port scan that is harmless on the IT side can disturb a device's cycle on the plant floor. The risk comes from limited response capacity, not from malice.
Traffic taken from a mirror port or a network tap reveals the devices and the conversations between them: which address speaks which protocol to whom, and which connection was never expected. Most of the inventory emerges without sending a single packet.
Listening only finds what speaks. A standby unit sitting idle, a line that is down, or a sensor that reports rarely will be missing from a passive inventory. That gap is accepted and recorded; closing it takes a separate decision.
Active querying is not forbidden outright; it is conditional. Once scope, time window, stop conditions and the plant owner's approval are written down, it is tried against a limited set of assets. Production safety comes first in every case.
It depends on how the network speaks. A line with a daily cycle may need a few days; a plant with shift or seasonal variation needs longer observation. The measure is how many assets remain missing.
A network tap or a separate switch configuration is assessed. Either option goes through change management, with confirmation up front that production will not be affected.
No. Passive discovery produces an inventory and a communication map; vulnerability assessment is separate work and, on the OT side, follows its own authorization and window rules.
Let us pick the line to start with and plan the listening point and the observation period together.
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