Defending the OT Network: Segmentation and Passive Monitoring
You cannot harden a controller you cannot patch, so you harden the space around it. Two moves carry the defense. Segmentation carves the plant into small zones joined only by controlled conduits, with a demilitarized buffer that severs every unbroken path from the enterprise to the machinery. Passive, protocol-aware monitoring watches a mirrored copy of the traffic, understands industrial commands down to the register, and alarms on the illegal write hiding among legal reads. Neither touches the fragile gear. Together they shrink the blast radius and make an intruder visible. OT defense is architecture before it is any single product.
Knowledge check
Why must OT network monitoring be passive, and what capability makes a passive sensor effective rather than merely safe?
Show the answer
It must be passive because active probing can knock a deterministic controller off its scan cycle and trip the physical process. A passive sensor watches a mirrored copy of traffic and is effective because it parses industrial protocols down to the function code and register, letting it distinguish a routine read from a malicious write and alarm on illegal commands without ever transmitting onto the control bus.