As the line between IT and OT continues to blur, industrial environments are facing a growing cybersecurity dilemma—legacy network designs that weren’t built to withstand today’s threats. Among the most critical vulnerabilities in operational technology (OT) infrastructure is flat network architecture—a design choice that, while once practical, now represents a significant security gap.

Cyberattacks targeting OT environments like manufacturing floors, utilities, and energy systems are no longer hypothetical. From ransomware that halts production to nation-state threats targeting critical infrastructure, the stakes have never been higher. And if your industrial systems still rely on a flat, unsegmented network, your exposure may be greater than you think.

What Is a Flat Network in OT?

In simple terms, a flat network is a network topology where all devices are on the same broadcast domain, meaning they can all “see” each other and communicate freely. In OT environments, this often includes PLCs, SCADA systems, HMIs, sensors, engineering workstations, and sometimes even business applications.

Historically, flat networks were embraced in industrial settings for their simplicity, ease of troubleshooting, and performance efficiency. But what worked in a pre-connected world now poses a serious risk.

Why Flat Networks Pose a Cybersecurity Threat to Industrial Environments

1. Lateral Movement Is Too Easy

If a malicious actor compromises a single device—say, through phishing or a remote access vulnerability—they can often move sideways across the entire OT network. There are no internal barriers, which means they can reach critical control systems with little resistance.

2. Lack of Visibility and Control

Flat networks offer minimal visibility into device behavior or communications. Security teams struggle to identify anomalous activity, unauthorized devices, or policy violations—especially when OT and IT environments are managed separately.

3. Legacy Systems Amplify the Risk

Many OT systems weren’t designed with cybersecurity in mind. They often run outdated operating systems, lack encryption, and can’t be easily patched. Once inside a flat network, attackers can exploit these vulnerabilities with ease.

4. High Impact of Incidents

A security breach in OT doesn’t just affect data—it affects physical operations. Think downtime, production loss, equipment damage, or even safety risks for employees and customers. A single breach in a flat network can ripple across an entire plant or facility.

The Misconception of Air-Gapped Security in OT

Many organizations assume their OT environments are “safe” because they’re air-gapped, or separated from the internet. In reality, most OT systems today are at least partially connected to corporate IT networks or external vendors—for cloud analytics, remote monitoring, or third-party support.

This IT/OT convergence introduces new attack vectors. Remote access tools, USB devices, and weak segmentation make it possible for attackers to reach OT networks without needing direct physical access.

How to Address Flat Network Vulnerabilities in OT Cybersecurity

Mitigating the risks of flat OT networks starts with modernizing your architecture and aligning security best practices with operational needs. Here’s where to begin:

1. Implement Network Segmentation

Use industrial demilitarized zones (IDMZs), VLANs, and firewalls to isolate OT zones from IT systems and from each other. Segmentation limits the blast radius of a breach and makes lateral movement far more difficult.

2. Gain Full Asset Visibility

You can’t protect what you don’t know about. Use OT-aware monitoring tools to create a real-time inventory of every device, system, and communication pathway on your network.

3. Apply Zero Trust Principles

Adopt least-privilege access controls in your OT environment. Even within trusted zones, users and devices should authenticate and only access what’s necessary for their function.

4. Monitor for Anomalies

Leverage security tools that are purpose-built for OT environments. These platforms understand industrial protocols (like Modbus, DNP3, BACnet) and can alert you to suspicious behavior that would go undetected by traditional IT security tools.

5. Bridge the Gap Between IT and OT Teams

Security is a shared responsibility. IT and OT stakeholders must collaborate on risk assessments, incident response plans, and technology investments to create a cohesive cybersecurity strategy.

From Legacy to Resilient: The Future of OT Cybersecurity

Operational technology is no longer isolated. As it continues to integrate with cloud platforms, edge devices, and enterprise networks, cybersecurity in OT must evolve. Flat networks may have served a purpose in the past, but today, they’re a liability. Modern threats require modern defenses—and that starts with segmentation, visibility, and a culture of security across both IT and OT domains.

Found this interesting?

We dive deeper into this topic—along with real-world OT security challenges and strategies—in our recent podcast episode:
Flat Networks, Big Risks: The Cybersecurity Gap in OT

Tune in to hear insights from experts who are helping organizations modernize their industrial security posture every day