OT Security Architecture Design
Retrofitting security into a running plant is far more expensive than designing it in. We design OT architecture compliant with IEC 62443 and the Purdue Model, so you get secure by design without a costly rebuild.
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What is OT Security Architecture Design?
OT Security Architecture Design means building security into a new factory or production line from day one — defining Purdue Model zones, IT/OT segmentation, Industrial DMZ, and secure remote access — so that production is protected without costly rework later. nFlo designs IEC 62443-compliant architecture in parallel with the OT network design phase, which is far cheaper than rebuilding a live plant, and delivers certification-ready documentation from the start.
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Discuss OT Security Architecture Design with your dedicated account manager.
Adding security later costs 10x more
Security built into architecture from day zero
Purdue Model
Proven layered architecture
Defense in Depth
Multi-layered protection
IEC 62443 Ready
Certification readiness
€12.5 Million Factory Without OT Security
New pharmaceutical factory. OT network architecture designed by integrator without security experience. After one year of production audit showed: flat network Level 0-3, no IT/OT segmentation, Industrial DMZ “shortcuts”, remote access via RDP without MFA. Retrofit cost: €2 million. Downtime for rebuild: 6 weeks. Plus IEC 62443 certification delay.
Without designing security from the start:
- Retrofit security costs 10x more than building in from the beginning
- Rework requires production downtime
- Delays in certifications and compliance
- Cyberattack risk from production day one
Security Built Into Factory DNA
We design OT security architecture in parallel with process architecture. Security is not an add-on - it’s the project foundation. Compliant with IEC 62443, Purdue Model, industrial best practices.
What you get:
- High-level OT architecture design with security by design
- Division into security zones by function and criticality
- IT/OT segmentation design per Purdue Model
- Industrial DMZ for secure data exchange
- Secure remote access architecture (VPN, jump hosts, MFA)
- OT monitoring and detection strategy
- Security technology selection (firewall, IDS/IPS, monitoring)
- Low-level design - detailed implementation project
- IEC 62443-3-3 compliance documentation
Who Is It For?
This service is for you if:
- You’re building new factory or production line from scratch
- You’re designing facility modernization and want to do it right
- You must meet IEC 62443 and want to be compliant from the start
- Integrators are designing your OT but don’t have security expertise
- You want to avoid costly security retrofit in a year
Purdue Model - Foundation of OT Architecture
Proven Architecture for Industry
Purdue Model is a reference model for industrial system hierarchy:
┌─────────────────────────────────────────┐
│ Level 4-5: Enterprise Network (IT) │
│ ERP, MES, Business systems │
├─────────────────────────────────────────┤
│ Level 3.5: Industrial DMZ │ ← Critical integration zone
│ Data historians, OPC servers │
├─────────────────────────────────────────┤
│ Level 3: Operations Management (OT) │
│ MES, SCADA servers │
├─────────────────────────────────────────┤
│ Level 2: Supervisory Control │
│ HMI, Engineering workstations │
├─────────────────────────────────────────┤
│ Level 1: Basic Control │
│ PLC, DCS, RTU, Safety systems │
├─────────────────────────────────────────┤
│ Level 0: Process │
│ Sensors, Actuators, Drives │
└─────────────────────────────────────────┘Security Zones
We divide OT network into zones by:
Function
- Production lines (different lines = different zones)
- Utilities (HVAC, compressed air, water treatment)
- Safety systems (Emergency shutdown, fire & gas)
Criticality
- Critical (safety systems, main production)
- High (key utilities)
- Medium (supporting systems)
Security Requirements (Security Level)
- SL 3 - safety critical systems
- SL 2 - production and key utilities
- SL 1 - supporting systems
Communication Channels (Conduits)
Controlled communication between zones:
Industrial Firewall
- Stateful inspection for OT protocols
- Deep packet inspection (Modbus, S7, DNP3)
- Application layer filtering
- Logging all traffic
Unidirectional Gateways
- Data diodes for critical systems
- Data flow in one direction only
- Physical impossibility of inbound connection
Jump Hosts / Bastion
- Controlled remote access point
- Session recording
- MFA requirement
- Time-limited access
How to design remote access for OT service technicians and vendors?
A system integrator or machine builder sometimes has to connect to an engineering workstation or an HMI panel. In an OT architecture design, that access does not bypass zones and conduits - it goes through a single privileged access management (PAM) gateway in the intermediate zone between IT and OT:
- Gateway in the Industrial DMZ - the technician connects to the gateway, not directly to the device; only the traffic allowed for the given task reaches the production zone.
- Task-bound access with approval - the process owner opens the service window, and access expires when it closes; vendors have no standing accounts.
- Session recording and supervision - a plant engineer can watch the session live and terminate it, and the recording remains for review after the shift.
- Credential vault - passwords to workstations and controllers are known to the gateway, not the technician, so they can be changed after every visit.
- Connection initiated from inside - when resources are published through a reverse proxy, the plant side initiates the tunnel, so the OT zone does not need inbound ports opened to the internet.
We will design how to fit such a gateway into the IEC 62443 zones and conduits as part of our PAM Implementation service; at nFlo we deploy it on platforms including Fudo Security.
PAM secures the technical side of remote access - it does not replace vendor contracts, risk analysis or the plant’s change management procedures.
Related Glossary Terms
Learn more about key concepts related to this service:
How we work
Our proven service delivery process.
Requirements
Process, security, compliance requirements
Zones & Conduits
Security zone division
Architecture Design
Detailed network and security design
Security Controls
Protection technology selection
Documentation
Implementation documentation
Benefits for your business
What you gain by choosing this service.
Cheaper Than Retrofit
No rebuild of a running plant
Secure From Day Zero
Protect production from first day
IEC 62443 Ready
Architecture ready for certification
Avoid Rework
No need to rebuild in a year
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Read more →Frequently Asked Questions
Common questions about OT Security Architecture Design.
At what stage of factory construction should we engage an OT security architect?
Ideally in parallel with the OT network design, before ordering equipment and configuration. Security built from the start costs up to 10x less than retrofit. If the integrator is already designing the OT network - the sooner the better.
How long does it take to design an OT security architecture?
The project takes 2-4 weeks. We deliver a high-level design (zones, segmentation, Purdue Model), low-level design (detailed implementation project) and IEC 62443-3-3 compliance documentation.
Does the architecture need to be IEC 62443 compliant if we don't plan certification?
Certification is optional, but IEC 62443 is the industry standard. Designing in compliance with the standard provides a proven architecture (Purdue Model, zones & conduits, defense in depth) and facilitates future certification without rework.
How do you handle secure remote access for OT vendors (Siemens, Schneider)?
We design a secure remote access architecture: VPN with MFA, jump hosts with session recording, time-limited access and granular permissions. The vendor only sees the systems relevant to their service, and every session is recorded.