Defense-in-Depth Architecture
A single security control is easy to bypass in operational technology, which quickly becomes a single point of failure.
OT environments are different from IT by design. They support physical processes, safety systems, and equipment that run continuously. A misstep is not just a security issue. It can affect production schedules, worker safety, environmental compliance, and restart timelines that stretch into days rather than minutes. Relying on perimeter firewalls alone is no longer enough to protect these environments.
Industrial networks rarely fail because of one dramatic breach. More often, problems develop quietly inside the environment — moving through systems that were trusted, shared credentials that were never revisited, or connections that grew over time without clear boundaries.
Defense-in-Depth is built around this reality. Instead of assuming every issue can be stopped at the perimeter, it focuses on limiting how far a problem can travel once it appears.
At Arista Cyber, Defense-in-Depth architecture is treated as an engineering design exercise for industrial control systems. Physical safeguards, segmentation, access control, endpoint protections, and monitoring are planned together so weaknesses are contained early and do not cascade into operational incidents.
These designs follow IEC 62443, NIST SP 800-82, and the Purdue Model, which helps ensure resilience is part of the original structure of the environment — not something added later after issues surface.
LAYERED DEFENSES ARE NOT OPTIONAL THEY ARE OPERATIONAL TECHNOLOGY’S BACKBONE
Key Advantages
Layered security takes pressure off individual controls. When something does go wrong, operations have the space to contain the issue and continue running safely.
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1. Reduced attack surface
Segmentation limits exposure by separating systems based on function and risk. When an issue arises, it stays contained within defined zones instead of spreading across the environment. -
2. Restricted lateral movement
Multiple layers make it significantly harder for threats to move freely between systems or escalate privileges. Even if one control is bypassed, additional barriers slow or stop progression. -
3. Standards-driven design
Architectures are mapped to IEC 62443, NIST CSF, and recognised industrial best practices from the outset, supporting compliance and long-term governance. -
4. Operational continuity protected
Controls are selected and positioned with uptime in mind. Security improvements are introduced in a way that avoids disruption to production and safety processes. -
5. Consistent visibility and control
Oversight is maintained from field devices through to supervisory systems and enterprise boundaries, supporting both operations and incident response.
In OT environments, layered defenses are not optional. They form the foundation of secure and resilient operations.
Why Defense-in-Depth Works in OT
Defense-in-Depth mirrors how industrial systems are already designed. Redundancy, fail-safes, and isolation are standard engineering principles in OT. Security architecture should follow the same logic.
Instead of assuming every threat can be blocked at the perimeter, DiD accepts that incidents may occur and focuses on limiting impact. Containment, early detection, and controlled recovery matter just as much as prevention. This approach aligns far better with the realities of industrial operations, where availability and safety are always the top priorities.
Deliverables
Each engagement results in practical, implementation-ready artefacts that your teams can use immediately.
1.Custom Defense-in-Depth blueprint
A DiD architecture tailored to your OT environment, operational constraints, and risk profile.
2.Purdue Model–aligned segmentation
Clearly defined zones, conduits, and trust boundaries that reflect how systems actually interact, not how diagrams assume they should.
3.Integrated security control stack
A coordinated design covering each DiD layer:
Physical → Network → Endpoint → Identity → Application → Monitoring
4.Integration guidance
Clear direction for deploying firewalls, DMZs, industrial intrusion detection, and access control systems so technologies work together rather than in isolation.
These deliverables support both hands-on engineering execution and governance review.
Our Approach
We start by building an accurate model of your OT environment. The work starts with understanding how your environment is actually put together. Zones, conduits, trust boundaries, and control components are mapped based on how operations run day to day, not how diagrams suggest they should look. That visibility matters before any controls are introduced.
From there, a zero-trust mindset is applied in a practical way. The goal is not to shut things down or over-restrict communication, but to be intentional about what needs to be talked about, when it should be done so, and what level of trust is appropriate.
Design choices are shaped by real plant conditions. Segmentation, access paths, intrusion detection, and device hardening are planned as a set, so controls support each other and fit naturally into existing workflows instead of working against them.
Throughout the process, operational safety remains central. Recommendations are evaluated not just for security effectiveness but for their impact on availability, maintenance workflows, and incident response procedures.
All guidance is aligned with recognised standards and delivered in a form that teams can implement without guesswork. The result is a security architecture that strengthens protection while respecting performance, safety, and operational realities.
Who This Architecture Is For
Defense-in-Depth architecture is particularly valuable for organisations that operate:
- 1.Critical production lines
- 2.Safety-instrumented systems
- 3.Distributed industrial environments
- 4.Legacy control systems alongside modern platforms
- 5.Regulated infrastructure is subject to audits and inspections
In these environments, knowing that a single failure will not cascade into a larger incident provides confidence to both technical teams and leadership.
Shows Compliance Without Slowing Operations
Because the architecture aligns directly with IEC 62443, NIST SP 800-82, and the Purdue Model, it supports compliance naturally rather than forcing it later. Documentation, segmentation rationale, and control placement all tie back to recognised frameworks, making audits more predictable and far less disruptive.
Ready to Strengthen Your OT Architecture?
Security in OT is not about adding more tools. It is about making deliberate design decisions that reduce risk while keeping operations stable.
If you are reviewing your current architecture or planning changes to your OT environment, now is the right time to ensure layered defenses are built in from the start.
Talk to Arista Cyber about designing a Defense-in-Depth architecture that supports safety, availability, and long-term resilience.
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