Best Practices for Segmenting OT Networks and Securing Industrial Zones

In today’s fast-changing industrial landscape, industrial cybersecurity is critical, not just for compliance, but for business continuity, safety, and trust. The convergence of IT and OT systems, combined with the explosion of IoT devices, has created vast new threat surfaces. And while many organizations focus on detection and response, prevention remains one of the most powerful tools in your arsenal.

For plant managers, OT engineers, and CISOs, segmenting OT networks and properly zoning industrial systems is essential. Done right, it stops lateral movement, isolates critical assets, and drastically reduces the blast radius of any attack.

In this article, we’ll break down the threats, explain the value of segmentation and zoning, and give you practical steps to build a robust critical-infrastructure defense. Whether you’re overseeing a single facility or a global operation, this guide will help you build safer, smarter OT environments, with Shieldworkz as your strategic partner.

The New Threat Landscape in OT Security

OT networks were once isolated and air gapped. Not anymore. As industrial operations embrace digitization, connectivity is now a double-edged sword.

Today’s Key Threats Include:

Ransomware Attacks: These have migrated from IT into OT. Production halts can cost millions.

Supply Chain Attacks: Compromised third-party software or devices can open backdoors into your environment.

IoT Device Exploits: Insecure or misconfigured IoT sensors and controllers can provide attackers a foothold.

Insider Threats: Employees or contractors can accidentally or intentionally create pathways between zones.

Nation-State and APT Actors: These adversaries are patient, well-funded, and focused on long-term disruption.

“Over 60% of industrial organizations faced at least one cyber incident impacting OT system in 2024.”

That’s why proactive security measures like network segmentation are crucial. They don’t rely on identifying every threat, they stop attackers from spreading if they get in.

Understanding OT Network Segmentation & Zoning

What Is OT Network Segmentation?

Segmentation divides your network into smaller, controlled sections. Think of it as building firewalls within your digital environment. If one zone is compromised, others remain unaffected.

What Are Industrial Zones?

Zones are logical groupings of systems based on function, risk, and control level. The IEC 62443 standard defines zones and conduits:

• Zones: Groups of assets with similar security requirements

• Conduits: Controlled communication paths between zones

For example, you may have:

• A Corporate IT Zone for office systems

• A DMZ for shared services like historians

• A Supervisory Zone for SCADA systems

• A Control Zone for PLCs and actuators

Benefits of Segmentation for Industrial Cybersecurity

• Limits Attack Spread: Prevents lateral movement between systems

• Protects Legacy Assets: Older devices can be isolated without upgrades

• Simplifies Incident Response: Breaches are easier to contain and investigate

• Supports Compliance: Meets NERC CIP, IEC 62443, and other frameworks

• Improves Visibility: Network maps help monitor critical zones

When combined with zoning, segmentation gives you both structure and control, two pillars of resilient OT security.

Step-by-Step Guide to Segmentation Best Practices

Let’s break down how you can apply segmentation and zoning effectively.

1. Discover and Inventory All Assets

Before segmenting, know what you have:

• Passive network discovery tools (avoid disrupting operations)

• Identify all assets: PLCs, RTUs, HMIs, IoT sensors

• Tag each with metadata: location, function, vendor, OS

A clean asset inventory enables smart decisions.

2. Map Traffic Flows and Data Paths

Understand how systems communicate:

• Who talks to whom?

• What protocols are used (Modbus, OPC UA, etc.)?

• Which flows are essential, and which are risky?

Use tools like flow analyzers or tap mirroring to gain visibility.

3. Define Zones Based on Risk and Function

Break the network into zones such as:

• IT Zone

• OT DMZ

• Operations/SCADA Zone

• Engineering Workstations Zone

• Safety Instrumented Systems (SIS) Zone

Each zone should have clearly defined security levels.

4. Create Conduits Between Zones

Use firewalls, gateways, or proxies to manage traffic:

• Allow only approved protocols

• Inspect content where feasible

• Log all interactions

Avoid direct communication across zones without inspection.

5. Apply Least Privilege Access Control

Limit who and what can cross zone boundaries:

• Enforce role-based access control

• Require MFA for sensitive access

• Implement user and device authentication per zone

6. Deploy OT-Aware Firewalls

Standard IT firewalls often fail in OT. Use firewalls built for:

• ICS protocols

• Low latency and deterministic traffic

• Industrial DPI (deep packet inspection)

They enable protocol whitelisting and anomaly detection.

7. Secure Remote Access

Vendors and remote engineers need access, but it must be secure:

• Use VPNs with session control 

• Add jump hosts and record sessions

• Restrict access by time, role, and endpoint

8. Segment Legacy and Vendor-Locked Systems

Some systems can’t be patched or updated:

• Place them in tightly controlled zones

• Restrict their communication to known conduits

• Use unidirectional gateways if needed

9. Monitor and Alert on Cross-Zone Traffic

Use network intrusion detection systems (NIDS) with:

• Protocol-specific detection (Modbus, DNP3)

• Behavioral baselining

• OT-optimized anomaly alerts

This allows early detection of misbehavior or breaches.

10. Continuously Update Your Architecture

Networks evolve. So should your segmentation:

• Regularly review asset inventories and data flows

• Update zoning models during changes

• Audit rulesets and test failover conditions

Industrial Zones in Action: Real-World Scenarios

Scenario 1: Manufacturing Plant with Mixed Vendors

You’ve got Siemens PLCs, Rockwell drives, and legacy HMIs. With segmentation:

• Place HMIs in their own engineering zone

• Create conduits only to authorized PLCs

• Use firewalls to block rogue traffic from new devices

Result: A single compromised HMI doesn’t cascade through the line.

Scenario 2: Remote Wind Farms Managed Centrally

Your turbines are in remote locations, but engineers access them from HQ. Use:

• VPNs into a dedicated remote management zone

• Access brokers with MFA and session logging

• Local monitoring zones isolated from the internet

Result: Secure access without exposing turbines directly.

Scenario 3: Water Utility with IoT Sensors

IoT sensors are collecting pressure and flow data. With segmentation:

• Create a dedicated IoT zone

• Only allow data to flow to historian zone

• Block any commands from IoT zone to control systems

Result: Malicious sensor tampering can’t alter critical operations.

How Shieldworkz Strengthens OT Segmentation

At Shieldworkz, we don’t just recommend segmentation, we help you build it securely and sustainably.

Our Core Capabilities Include:

Asset Discovery and Network Mapping

• Passive discovery tools for OT

• Zone identification and traffic visualization

IEC 62443 Zoning Framework

• Apply global standards to your operations

• Define zones and conduits with precision

OT-Specific Firewalls and NIDS

• Detect, block, and alert on abnormal activity

• Deep packet inspection for ICS protocols

Secure Remote Access

• Role-based access control with logging

• Managed access for third parties

Compliance Support

• Templates and assessments for IEC 62443, NERC CIP, and more

• Audit-ready documentation and change logs

Legacy System Protection

• Segmentation strategies for unpatchable systems

• Air gaps, firewalls, and unidirectional gateways

We speak your language, PLC to policy. Whether you're running legacy equipment or deploying greenfield sites, we tailor solutions that work for you.

Conclusion: Build a Safer, Smarter OT Network

As the threats to OT and cyber-physical systems grow more advanced, so must our defenses. Segmenting your OT networks and properly zoning your industrial assets is one of the most impactful steps you can take.

Here’s your quick recap:

• Inventory assets and map your data flows

• Define zones based on function and risk

• Control conduits with firewalls and rules

• Restrict access with least privilege and MFA

• Monitor traffic and audit configurations

• Partner with experts like Shieldworkz to do it right

This isn’t just about security, it’s about protecting uptime, safety, and reputation.

Ready to take the next step?

Download our OT, ICS & IOT Threat Landscape report or Request a Free Consultation to see how Shieldworkz can strengthen your OT security posture.

Together, let’s engineer security that’s resilient, compliant, and built for the future.