1. 🛡️ Industrial Next-Generation Firewalls (NGFWs)
Industrial firewalls are the cornerstone of OT network segmentation.
Key Capabilities: These firewalls are designed to be ruggedized products and are specifically OT-Aware (OT-Aware) protocol-aware , such as Modbus, Profinet, or DNP3, unlike typical IT firewalls.
Applications with Legacy Devices: Use the firewall as a Policy Enforcement Point to create a "Firewall Bubble" around a group of legacy devices.
The firewall inspects and allows only the inbound/outbound traffic that is absolutely necessary according to the Least Privilege principle . The rest is blocked by default, which completely prevents lateral movement.
2. 🎛️ Agentless Microsegmentation Solutions
Since legacy devices cannot install agent software, modern microsegmentation solutions must be agentless.
Concept: These solutions work by using native OS controls, such as a firewall in the operating system or Access Control Lists (ACLs) at the network switch level, to enforce policies at the closest point to the asset.
Add-on technology:
Automated Asset Discovery & Tagging: Use tools to automatically discover all legacy OT devices on the network and tag them based on function or importance, enabling granular security policies to be created.
Machine Identity Providers: Technologies that continuously verify the identity of a machine ( e.g. Corsha) before allowing communication, which is crucial for machine-to-machine connectivity in OT.
3. 🌐 Software-Defined Perimeter (SDP) / ZTNA
Software-Defined Perimeter (SDP) , also known as Zero Trust Network Access (ZTNA), is an excellent approach to managing remote access for legacy OT devices.
Concept: SDP creates a "virtual security perimeter" that makes the infrastructure invisible to unauthorized users.
Applications with Legacy Devices:
Remote Access Control: Instead of using a traditional VPN that grants access to the entire network, SDP hides the control server (such as an HMI or SCADA) and only opens access to users who have passed Just-In-Time MFA authentication and have the correct context.
Attack Surface Limitation: Reduce vulnerabilities by hiding critical ports (e.g., RDP, SSH) from the external internet and even from unrelated internal networks, an effective compensatory strategy for older devices with unpatched vulnerabilities.
Deploying microsegmentation to legacy devices is therefore a process that focuses on using protection and control technologies outside of the device itself to achieve Zero Trust principles without disrupting system availability.
| Safety technology | Microsegmentation, Zero Trust (ZTA), Software-Defined Perimeter (SDP), ZTNA, Least Privilege, MFA, Policy Enforcement |
| Industrial Network | Legacy OT Devices, Industrial Firewalls (NGFWs), OT-Aware Protocol, ICS/SCADA, Automation, Asset Tagging |
| Tools & Strategies | Agentless Security, Compensating Controls, Lateral Movement, Point-to-Point Encryption, Automated Asset Discovery, Policy Enforcement Point, Just-In-Time Access |
| OT components | PLC, Modbus, Profinet, RDP/SSH Security, Machine Identity |
Concept: Image of several old OT machines surrounded by a "safety bubble" created by an Industrial Firewall, with protection icons displayed.
