Network Segmentation: Reducing Lateral Movement Risks in OT/ICS Environments
In today’s hyper-connected industrial landscape, operational technology (OT) networks that control critical infrastructure, manufacturing lines, and utilities face unprecedented cybersecurity risks. The convergence of IT and OT environments, while boosting operational efficiency, also opens industrial control systems (ICS) and Internet of Things (IoT) devices to cyber adversaries with increasing sophistication. Network segmentation is no longer just a recommended practice-it is a cybersecurity imperative to reduce lateral movement risks and contain breaches before they escalate into costly operational disruptions.
This blog explores the vital role of network segmentation in defending OT/ICS networks against modern cyber threats, why traditional flat network architectures are dangerous liabilities, and how industrial organizations can strategically segment their networks to minimize risk while maintaining availability and operational continuity.
Understanding OT Network Segmentation
What is Network Segmentation in OT/ICS?
Network segmentation is the practice of dividing a larger network into smaller, isolated zones or segments with controlled communication gates between them. In OT and ICS environments, this means isolating critical assets such as programmable logic controllers (PLCs), supervisory control and data acquisition (SCADA) systems, human-machine interfaces (HMIs), and sensors into distinct security zones based on purpose, criticality, or risk.
Rather than allowing free communication across a flat industrial network, segmentation enforces strict traffic controls, limiting unnecessary connections and reducing the attack surface. If an attacker compromises one segment, network segmentation prevents them from freely moving laterally to other critical systems, containing the impact and protecting operational integrity.
OT Network Segmentation vs. IT Network Segmentation
Though seemingly similar in concept, OT segmentation involves specialized requirements compared to IT network segmentation. OT environments prioritize safety, real-time performance, and continuous availability, often running legacy industrial devices that cannot tolerate downtime or intrusive security measures. Industrial protocols and ruggedized hardware necessitate fit-for-purpose segmentation strategies tailored to complex, heterogeneous OT systems, unlike the largely software-defined approach in IT.
Why Network Segmentation is Critical for Reducing Lateral Movement Risks
The Risks of Flat OT Networks
Many legacy OT environments were designed in isolation with an implicit trust model, assuming network air-gaps and limited external access. Today, that assumption no longer holds. As OT merges with IT for digital transformation and remote management, flat networks without segmentation provide intruders with free rein once they gain initial entry, often through compromised IT endpoints or third-party vendor access.
Without segmentation boundaries, attackers can traverse across the OT network laterally, escalating privileges, sabotaging production, deploying ransomware, or shutting down critical infrastructure. The consequences are dire-including operational downtime, physical damage, safety incidents, and regulatory penalties.
Rising Cyber Threats Targeting OT
Ransomware targeting OT systems surged 60% year-over-year in 2024, with attackers increasingly initiating intrusions through IT network breaches. Studies show approximately 75% of OT system attacks start as IT environment compromises. Thus, segmenting OT from IT and within OT zones is essential to block adversaries from moving silently from corporate networks into control systems.
Types of Network Segmentation in OT/ICS
Understanding different segmentation approaches can help organizations implement layered defenses effectively:
- IT/OT Separation: The foundational division that isolates IT corporate networks from OT industrial environments, minimizing exposure paths for threats originating in the IT domain.
- Functional Segmentation: Zoning OT assets based on function (e.g., production cells, safety systems, process control) to restrict access between unrelated operational segments.
- Geographic Segmentation: Physically separating networks by location or facility to prevent network-wide breaches spreading across distributed sites.
- Microsegmentation: Finer-grained isolation within zones, controlling traffic between individual devices or applications to contain breaches even within segments.
Implementing Effective OT Network Segmentation
Adopting a Layered Segmentation Model
A multi-layered defense incorporating segmentation reduces the blast radius of attacks and improves operational control. A widely referenced framework is the Purdue Model, which organizes networks into zones and levels based on process control functions and business systems. Modern adaptations extend this model by incorporating microsegmentation and zero-trust principles tailored for OT environments.
Purpose-Built ICS Segmentation Appliances
Instead of using generic IT firewalls, industrial security requires dedicated ICS security appliances to enforce segmentation at each control zone. These devices can monitor traffic, block unauthorized connections, alert on anomalies, and maintain strict whitelist policies without disrupting the real-time demands of control networks. This approach allows operators to authorize only necessary communication-such as an HMI talking to its specific PLC-while preventing unauthorized lateral movement.
Defining Access Policies and Monitoring
Clear segmentation boundaries must be enforced with well-defined access control policies specifying which devices, users, and protocols are permitted between zones. Continuous monitoring for anomalous traffic patterns, leveraging AI-powered anomaly detection, further strengthens the segmentation’s efficacy.
Challenges and Best Practices
Addressing Legacy OT Systems
Many ICS devices are legacy systems lacking native security features, making them vulnerable and difficult to segment without causing operational issues. Improving segmentation requires careful assessment, layered protection, and sometimes isolating legacy devices into protected subnets while planning phased upgrades.
Minimizing Operational Disruptions
Industrial operations prioritize uptime and reliability, so segmentation projects must balance security with availability carefully. Implementing segmentation gradually, using bump-in-the-wire appliances and validating policies in controlled environments help avoid unintended downtime.
Segmentation is recognized as a best practice in key OT security standards including NERC CIP (power sector) and IEC 62443 (industrial automation). Following these guidelines supports compliance and enhances resilience.
Compliance and Industry Standards
Future Trends in OT Network Segmentation
- Dynamic and Adaptive Segmentation: Using AI and machine learning for real-time anomaly detection and automatic policy adjustments to respond rapidly to evolving threats.
- Increased Microsegmentation: Asset-level traffic control reduces attack surfaces in complex, converged IT/OT environments.
- Integration with Zero Trust Architecture: Segmenting networks with strict identity and device verification, ensuring no implicit trust even inside segments.
- Cloud and Edge-aware Segmentation: Expanding controls to cloud-connected OT resources and edge computing devices for comprehensive protection.
Conclusion
Network segmentation is a foundational pillar of modern OT and ICS cybersecurity, crucial for reducing lateral movement risks and protecting critical industrial infrastructure from increasingly sophisticated cyberattacks. By strategically dividing networks into controlled zones, implementing purpose-built industrial segmentation appliances, and maintaining vigilance through monitoring and policies, organizations can secure their operational environments without compromising availability.
With cyber threats accelerating and IT/OT convergence deepening, effective network segmentation is no longer optional-it’s a strategic necessity for resilient industrial operations in 2025 and beyond.
This expert insight into OT network segmentation offers actionable guidance and the latest best practices to strengthen your industrial cybersecurity posture, contributing to safer, more secure, and continuously operational critical infrastructure.