OT Segmentation 101: How to Secure Industrial Networks Against Modern Threats

Operational technology (OT) networks weren’t built for modern cyber threats. The typical OT environment contains hundreds of unmanaged devices from vendors dating back decades. OT networks are hard to monitor, hard to control, and incredibly costly to disrupt – properly securing them is exceedingly difficult, even as it grows increasingly urgent.  

Ransomware groups targeting OT rose 60% last year, but only 19% of organizations felt they were completely prepared to handle OT security issues during the same period. To combat rising OT security threats and boost overall security posture, organizations need robust OT network segmentation – that doesn’t introduce new complexity.  

We’ll explore what OT segmentation is, why it’s key for modernizing security strategies, and share tips for unifying segmentation in an era of converged IT/OT networks.  

What Is OT Network Segmentation?  

Operational technology (OT) network segmentation is the process of isolating industrial control systems (ICS), sensors, programmable logic controllers (PLCs), and other OT infrastructure from broader IT networks and from each other.  

Segmented zones are defined based on factors like function, asset type, criticality, or risk level, and are protected by access control policies that determine what traffic can move between them. 

OT segmentation reduces the attack surface and limits lateral movement between systems, protecting industrial organizations from the costly risk of downtime. In other words, OT segmentation is about containment: if one area is compromised, segmentation helps ensure the damage doesn’t spread. 

OT Network Segmentation vs. OT Microsegmentation  

OT network segmentation isolates the network into secure zones. OT microsegmentation further secures the infrastructure by controlling traffic between individual assets within those zones. 

While traditional network segmentation relies on boundaries like VLANs or subnets, microsegmentation operates at the asset level, enabling precise traffic control and reducing the risk of lateral movement, even in flat or legacy OT environments. 

Why Is OT Network Segmentation Important for Security?  

A flat network is an attacker’s playground. With no meaningful internal boundaries, once they breach an endpoint – whether via phishing, a remote access service, or a vulnerable legacy system – they can move laterally to sabotage production, hold critical systems hostage, and disrupt supply chains.  

A closer look at today’s biggest OT security trends reveals why segmentation is so vital.  

Accelerating OT/IT Convergence 

The days of air-gapped industrial networks are gone. Cloud adoption, IoT, remote operations, and Industry 4.0-driven pressures around efficiency and uptime mean OT systems are increasingly intertwined with enterprise IT infrastructure.  

Seventy percent of OT systems are projected to connect to IT networks in the next year – a 20% increase year-over-year.  

While this convergence modernizes operations and improves efficiency, it also broadens the attack surface and exposes OT to risks it was never designed to handle. Segmentation helps security teams regain control, enforcing boundaries where traditional perimeter-based security falls short. 

Ransomware Attacks Targeting OT Start in IT  

While ransomware attacks remain a top cybersecurity concern for nearly every organization, no industry is hit harder and more consistently by ransomware than the industrial sector.  

Ransomware attacks spiked 87% YoY in 2024 across industrial organizations, making this industry the top ransomware target for four consecutive years. More specifically, 2024 saw a 60% uptick in ransomware groups impacting OT/ICS. 

As ransomware threats rise and OT/IT networks converge, security teams can’t afford to ignore the fact that 75% of attacks on OT systems start with an IT breach.  Vulnerabilities in the corporate environment – like VPNs, web apps, or compromised credentials – give hackers an initial foothold. From there, they move laterally, often undetected until they reach OT systems.  

Because of this, security teams must start rethinking OT segmentation to focus security strategies on a converged IT/OT environment. 

Insecure Remote Access and Legacy Tech Risks  

Sixty-five percent of OT environments featured insecure remote access conditions in 2024 and nearly half of organizations with OT-heavy environments have SSH communicating to publicly routable addresses. Meanwhile, one in every four penetration tests finds default credentials in industrial environments and the industry’s ongoing reliance on legacy tech is hardly secret among cybercriminals.  

In other words, it’s not hard for sophisticated hackers to find their way in. To protect mission-critical assets, industrial organizations need robust network segmentation across IT and OT/ICS environments.  

Real-World Example: How Ransomware Bypasses Traditional Defenses  

In examining a recent ransomware attack example, we see how easily cyber adversaries slip past solutions like EDR.  

The Akira ransomware gang gained initial access by exploiting exposed remote access solutions; while the attack was initially blocked by the defenders’ EDR solution, Akira pivoted, identifying an unsecured webcam via a network scan as an opportunity to bypass EDR systems.  

This attack highlights how easily attackers can reach vulnerable OT assets after leveraging IT insecurities to gain initial access, and emphasizes the importance of network segmentation, as outlined by MITRE’s post-breach guidance.  

How to Implement OT Network Segmentation 

In environments where uptime is non-negotiable, segmentation can feel daunting. But with the right approach, it’s achievable – and it doesn’t have to spell complexity. Here’s a simplified breakdown of how to implement OT network segmentation:  

Gain Visibility into Network Assets and Behavior  

You can’t protect what you can’t see, and few organizations have a complete inventory of their OT devices, much less an understanding of how they communicate.  

The first step is creating a real-time inventory of OT (and ideally, IT assets for a comprehensive approach), mapping their behaviors, and understanding their communication patterns. Automation can help here – learning traffic baselines to easily identify unauthorized or risky flows. 

Tag and Group Assets  

Once assets are discovered, group them logically based on function, location, criticality, or communication needs. This makes it easier to define segmentation policies without disrupting necessary workflows. 

Define and Enforce Policies  

Use the observed behaviors and groupings to write least-privilege access policies: only allow traffic that is explicitly required and deny everything else by default. These policies should be enforced through device-level firewalls, switches, or security appliances that support fine-grained rule application. 

Modern OT Segmentation: What to Look For  

Not all segmentation solutions are created equal. In dynamic environments, manual strategies don’t scale – and traditional tools often fall short. Look for modern capabilities like: 

Automated Learning and Policy Creation  

Manual configuration, tagging, grouping, and policy creation and management are error-prone and unsustainable. A solution that automatically learns behavior and suggests segmentation policies accelerates deployment, streamlines ongoing management, and improves accuracy. 

Continuous Monitoring and Just-in-Time Access Controls  

Threats evolve. Networks change. Effective segmentation should be as dynamic as the environments it secures. Look for solutions that monitor network behavior in real time and enforce just-in-time MFA for privileged ports and sensitive systems, ensuring users can only access what they need, and only when they need it. 

Agentless Architecture  

Rather than installing agents on endpoints, prioritize a solution that leverages native OS controls like host-based firewalls and access control lists (ACLs) to secure legacy and fragile OT systems without risking disruptions. 

Unified Coverage Across Environments  

Modern security requires seamless, consistent policy enforcement across both IT and OT assets. A patchwork of solutions creates gaps hackers know how to exploit. Look for platforms that unify segmentation across converged environments.  

How Unified IT/OT Segmentation Works  

A comprehensive and unified approach to OT segmentation, like Zero Networks, makes it easy to granularly segment IT and OT networks for uncompromising security in an era of sophisticated cyber threats.  

Centrally Managed Rules and Policies  

After learning all network connections, Zero’s unified OT/IT microsegmentation solution creates corresponding rules and highly accurate least-privilege policies for IT and OT networks, which are centrally applied using automation to the host-based firewalls of managed IT devices and to ACLs of the switches connecting the unmanaged OT devices. 

Secure Privileged Ports with MFA  

Admin protocols like RDP, SSH, RPC, WMI, and SMB are some of attackers’ favorite exploits. To ensure no hidden vulnerabilities are left for hackers, just-in-time network layer MFA adds another dimension of security, allowing only necessary traffic without disrupting normal operations.  

Apply Fine-Grained Policies Everywhere  

By relying on native OS controls like host firewalls and ACLs, security teams can finally secure all network traffic to truly protect OT systems:  

	(to) IT Devices	(to) OT Networks
(from) IT Devices	Least-privilege permissions applied to all device firewalls (clients and servers), effectively preventing lateral movement.  Privileged ports are protected with Just-In-Time MFA, enabling IT teams to perform remote maintenance operations when needed while blocking all other traffic at the network level.	Unless automated learning has indicated a need to keep a specific connection open, all outbound connection requests from IT to OT are blocked.   When access to an OT device is required, users must authenticate with MFA to gain temporary access. This outbound block and MFA effectively prevent attackers from moving laterally into the OT network after compromising the IT network.
(from) OT Devices	All connection requests from OT to IT are blocked, unless the learning process has indicated that a certain connection needs to remain open. This prevents an attacker who has compromised an OT asset from moving laterally into the IT network.	The automation engine creates a granular, least-privilege policy and applies it via ACL to all OT routers and switches. These rules allow or block traffic through the ACL to the OT devices, preventing an attacker who has compromised an OT asset from moving laterally within the OT network.

How Zero Networks Simplifies Converged IT and OT Microsegmentation  

From data centers and OT to legacy systems and beyond, Zero Networks delivers a single platform – with a single set of rules – for microsegmenting diverse and dynamic landscapes.  

As IT network vulnerabilities leave OT systems at risk in converged modern networks, take a self-guided product tour to see how Zero Networks makes powerful segmentation effortless.