Agentless Zero Trust for every machine in your plant.
Most OT devices cannot run a security agent. Enforce access, segmentation and audit from the network instead. Nothing to install on machines, and the device never changes.
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Agentless Zero Trust puts the enforcement point on the network instead of the device. An overlay sits next to your OT network and brokers every session.
Before traffic reaches the PLC, HMI, or SCADA server, the overlay:
- checks who the user is
- checks what they are allowed to do
- records the session
The asset installs nothing and never changes. Trout Software's Access Gate works this way.
Enforcement blocks what monitoring only reports.
Most agentless OT security is passive. It watches traffic and flags anomalies. That helps, but a passive tool sees a malicious command only after it reaches the PLC. An industrial proxy in the access path works differently. It ends the session, checks the user and the exact command against policy, and forwards only what is allowed. It denies an attack in real time instead of reporting it later. Trout's Access Gate is this kind of enforcement point: it can deny the command, not only alert on it.
Passive monitoring
Detects anomalies after the fact and cannot block a command mid-session. It adds visibility but no control. On its own, it leaves the asset reachable.
Industrial proxy in the access path
Authenticates the user, authorizes the exact command, records the session, and denies anything outside policy in real time. Protocol-aware for OT (Modbus, DNP3, and more), not a generic reverse proxy.
Built for OT resilience. Industrial processes put uptime first. So the proxy runs with failover and a break-glass path. Operators always reach the asset in an emergency, and a single fault never stops the process.
Why can't OT devices run a security agent?
IT Zero Trust assumes each device can host an agent. The agent checks posture, enforces policy and reports telemetry. Most OT devices cannot host one. The real question is whether network-layer enforcement can do the agent's job.
Closed operating systems
Proprietary real-time OSes on PLCs and controllers do not allow third-party software to be installed.
Timing that cannot slip
Deterministic control loops cannot tolerate the jitter an agent introduces. A few milliseconds is a fault.
Warranties that void
OT vendor support and warranties typically void the moment endpoint software touches the device.
What replaces the agent in agentless OT security?
When the asset cannot host security software, the enforcement point moves to the boundary in front of it. Each capability below is what the agent would have done, delivered at the network layer instead.
Identity-bound access
MFA is enforced at the network boundary against your identity provider. Each session is tied to a named user, not a shared or service credential, and the asset never sees the identity directly.
Per-session authorization
Policy is per asset, per protocol, per session. A user can read a Modbus register on one PLC and be denied write on another, inside the same authenticated session.
Tamper-evident audit
Every session is logged with user, time, asset, protocol, and payload. Records are hash-chained and signed, so they stand up as audit evidence, not just alerts.
Microsegmentation
An overlay enforces per-asset boundaries on top of the existing network, aligned to IEC 62443 zones and conduits. The Layer 2 topology does not change, so safety and control assets can share a VLAN yet stay isolated.
Encryption for legacy protocols
Modbus, DNP3, OPC UA, and EtherNet/IP are wrapped in TLS at the boundary and forwarded natively to the asset. The device does not need to support TLS itself.
Just-in-time vendor access
Vendor and contractor sessions are scoped, time-bound, and revocable, and access closes automatically when the session ends. This is the controlled vendor remote access that NERC CIP-003-9 requires, with no standing access or shared credentials.
Access Gate adapts to your network
Pick your environment to see where the Access Gate sits, how much Zero-Trust coverage you get, and the migration path, from full coverage to partial coverage.
Questions about agentless Zero Trust for OT.
Move the enforcement point off the device and onto the network. An industrial proxy sits in the access path in front of the PLC, HMI or SCADA server. It authenticates the user, checks the exact command against policy and records the session. All of this happens before anything reaches the asset. Passive monitoring flags a malicious command only after it is sent. The proxy denies it in real time. It runs with failover and a break-glass path, so enforcement never costs uptime. Trout's Access Gate works this way and has been validated by a NATO navy for its most critical workloads.
Agentless Zero Trust enforces identity-based access, segmentation, and audit without installing software on the protected asset. Enforcement happens at a network boundary in front of the asset, not inside it. It is the practical posture for legacy OT, where most devices cannot host an agent.
Three reasons. Proprietary real-time operating systems on PLCs and industrial controllers do not allow third-party software. Deterministic control loops cannot tolerate the timing jitter an agent introduces. And OT vendor warranties typically void if endpoint software is installed.
No. Passive monitoring flags anomalies after the fact. It cannot block a malicious command in a live remote-access session before it is sent. Agentless Zero Trust adds enforcement at the network boundary. It can deny a session in real time, and log it too.
A firewall asks whether a port is allowed between two subnets. Agentless Zero Trust asks whether this specific user, in this specific session, may send this specific command to this specific asset, right now. The firewall enforces at Layer 4. Zero Trust enforces at the application layer, with identity binding, session attribution, and full payload logging.
Access Gate is an on-premise appliance that brokers access to OT assets. It connects beside your existing network, so production keeps running if it goes down. Every session ends at the appliance. Authentication, authorization and recording happen there, before traffic reaches the asset. The asset installs nothing and never sees the user identity directly.
The gate is the first service you run, not the last.
Secure your plants today. Control your digitalization tomorrow.
Access Gate puts compute on the wire, next to your assets. Once the gate is in, the same box hosts the services that pull OT in securely: remote access, protocol gateways, DNS and time, historian, update server. Accelerate your digitalization, in control.