A CISO's Guide: Using Edge Products to Enforce Zero Trust in OT

For a CISO, the Operational Technology (OT) network is a terrifying blind spot. Legacy PLCs and machines typically lack the native features (like authentication or encryption) required to implement a modern security strategy. This guide explains how industrial edge products act as the "Zero Trust Proxy" for these dumb devices. We explore how using secure edge products allows you to implement micro-segmentation, enforce identity-based access (ZTNA), and stop lateral movement, effectively wrapping your legacy infrastructure in a modern security layer without replacing a single machine.

As a CISO, your mandate is clear: "Never trust, always verify." You have successfully rolled out Zero Trust across your IT enterprise—laptops, servers, and cloud apps. But then you look at the factory floor (OT), and your strategy hits a brick wall.

Your production lines run on PLCs that were designed in the 1990s. They have hardcoded passwords (or none at all). They communicate in clear text. They cannot run antivirus, and they certainly cannot run a Zero Trust agent.

How do you enforce "Zero Trust" on a device that trusts everyone?

The answer is not to replace the billions of dollars of legacy equipment. The answer is to wrap them in a protective layer. Industrial edge products—specifically secure routers and gateways—are the missing link. They act as the Zero Trust Proxy, providing the security brains that your legacy hardware lacks.

In the IT world, security is software-defined. In the OT world, security was traditionally physical (air gaps). Now that IT/OT convergence has bridged that gap, your OT network is exposed.

The fundamental problem is that legacy OT devices are "insecure by design."

• No Authentication: If you can ping a PLC, you can often reprogram it.
• Flat Networks: To make things "easy," many factories run flat Layer 2 networks. If a hacker breaches one HMI, they can move laterally to every machine in the plant.
• No Logs: Most legacy devices don't keep audit logs of who accessed them.

You cannot fix the device. You must fix the access to the device. This is the role of modern industrial edge products.

In NIST's Zero Trust architecture, there is a concept called the Policy Enforcement Point (PEP). The PEP sits in front of a resource and enforces the rules set by the Policy Administrator.

Your PLCs are the "Resource." Your secure edge products are the PEP.

By placing an industrial edge product (like a Robustel gateway) between the OT network and the rest of the world, you create a chokepoint where Zero Trust policies can be applied.

The first step in Zero Trust is assuming a breach will occur. Your goal is to contain it.

• The Old Way: A firewall at the plant perimeter. Once inside, it's a free-for-all.
• The Zero Trust Way: You deploy industrial edge products at the machine or cell level. Each edge product creates a "Micro-Segment"—a network of one.
• The Result: If Ransomware hits Line A, it hits the edge product's internal firewall on Line B and stops. The edge products prevent lateral movement, turning a catastrophic site-wide outage into a minor, contained incident.

VPNs are the enemy of Zero Trust because they grant network access, not application access. Once a user is on the VPN, they are "on the network."

• The Solution: Use your edge products combined with a management platform like Add One Product: RCMS to implement ZTNA.
• How it Works: When an engineer needs to fix a machine, they don't just "VPN into the plant." They request access to specific edge products. RCMS verifies their identity (MFA) and policy permissions. Only then does it create a temporary, encrypted tunnel to that specific edge product.
• The Benefit: The engineer never touches the wider network. They connect only to the asset they are authorized to touch, and the edge products enforce this isolation.

A Zero Trust architecture is only as strong as its weakest enforcement point. If your edge products can be compromised, the strategy fails.

As a CISO, you must demand that the industrial edge products themselves are trustworthy.

1. Secure Boot: The device must verify its own firmware signature at startup to ensure no rootkits have been installed.
2. Hardened OS: The OS (like RobustOS Pro) must be minimized and hardened against exploits.
3. Certified Process: This is non-negotiable. Demand IEC 62443-4-1 certification. This proves the vendor follows a secure development lifecycle. You cannot build a Zero Trust network on untrusted hardware.

Zero Trust requires continuous verification. You can't verify what you can't see. Legacy PLCs don't generate security logs. But your industrial edge products do.

• The Data: A modern edge product logs every connection attempt, every blocked packet, and every user login.
• The Insight: By feeding these logs from your edge products into your SIEM (Security Information and Event Management) system, you finally gain visibility into the OT environment. You can see who is trying to access the blast furnace controller—and stop them.

You cannot upgrade the past, but you can secure it. For the next decade of industrial operations, Zero Trust will not be installed on the machines; it will be installed in front of them.

Your fleet of industrial edge products is the most critical security asset you own. They are the enforcers, the segmenters, and the guardians of your legacy infrastructure. By selecting secure, certified edge products and managing them with a Zero Trust mindset, you can bring military-grade security to a 1990s factory floor.