Network Architect / Engineer — IT/OT & Network Integration

Mission Overview:

Keystone Solutions is looking for a Network Architect / Engineer for one of its clients. Our client, a large international organisation operating critical infrastructure across multiple countries, is currently undergoing a major network transformation programme. Following a strategic acquisition and the growing need for stronger cybersecurity and operational resilience, they are looking for a senior Network Architect to help shape the future of their IT and Operational Technology (OT) environments. 

Consultancy Model at Keystone Solutions:

As a Keystone Solutions consultant, you will work on site and in hybrid settings alongside client stakeholders, driving outcomes while benefiting from Keystone's community of experts. You will apply your expertise within the client's environment, bringing best practices, rigorous documentation, and pragmatic execution. This consultancy mission provides the opportunity to contribute to diverse challenges while Keystone Solutions supports your professional development and exposure to multiple engagements over time.

About the Role:

We are looking for a hands-on Lead Network Architect to drive the technical convergence of two major corporate networks (the client and an acquired company) and build a resilient, future-proof IT/OT infrastructure. This is not a theoretical or project management position: we need a pragmatic, deeply knowledgeable engineer-architect who designs concrete solutions, engineers complex fixes, and authors actionable implementation roadmaps. In this role, you will be the driving force behind two critical group-level challenges:

• Leading the Corporate Network Integration: the client and the acquired company currently operate overlapping IPv4 address spaces and disparate infrastructure. You will own the strategy and execution plan to resolve IP conflicts, design robust interconnection and routing topologies, and deliver seamless, secure integration across the group.
• Building the IT/OT Zero Trust Architecture from scratch: To meet the stringent resilience requirements of the NIS2 Directive (Essential Entity level), a legacy perimeter/VLAN approach will not suffice. The target IT/OT segmentation model does not exist yet. Working in close synergy with the client's Security Architect, you will co-author a group-wide model from a blank canvas, embedding Zero Trust principles and IEC 62443 zones and conduits directly into the fabric of IT and operational parking systems.

You will not inherit someone else's pre-packaged design. You will tackle real-world brownfield complexity (overlapping subnets, multi-country footprint, legacy OT hardware) while architecting a modern, greenfield segmentation standard. If you thrive on deep IP/routing challenges, understand operational technology constraints, and want end-to-end technical ownership of a large-scale European infrastructure merger, this role was built for you. Reporting directly to both the client's CISO and the Head of Infrastructure, you will operate at the intersection of core operations and governance. You will work in close, daily collaboration with the client's Security Architect (defining IEC 62443 zones, conduits, and Zero Trust enforcement) and the Enterprise Architects to ensure network designs align seamlessly with the broader group target architecture. These responsibilities will be performed as a Keystone Solutions consultant embedded with the client.

Key Responsibilities:

• Resolve the IP address overlap between the client and the acquired company: assess the scope and extent of the conflict between the two networks, and design a recommended resolution path (re-addressing, NAT, or identity-based access abstraction).
• Co-author a Zero-Trust-based IT/OT segmentation model: this is a from-scratch deliverable, not an existing artifact — define zones and conduits using the IEC 62443 structure, with Zero Trust principles (continuous verification, least privilege, assume breach) as the architectural cornerstone, in close collaboration with the client's Security Architect, who owns final approval of target security levels.
• Confirm SD-WAN alignment: as a secondary check — confirm the SD-WAN transport project does not undermine the Zero Trust segmentation design, escalating only if a conflict is found; SD-WAN is supporting infrastructure here, not the architectural driver.
• Deliver a validated pilot design: a working, documented reference design for a representative group of sites, ready for wider rollout.
• Document for handover: ensure the design and its reasoning are fully usable by the client's permanent teams once this engagement ends.

All responsibilities above will be executed within the Keystone Solutions consultancy framework, working closely with client stakeholders.

What We're Looking For (Must-Have Skills & Experience):

• Real, hands-on Zero Trust Architecture design experience: NIST SP 800-207 principles applied to network segmentation — not just Zero Trust Network Access for remote users, but continuous verification and least-privilege enforcement between network zones themselves. This is the architectural cornerstone of the role.
• Extremely strong, hands-on IPv4 expertise: addressing, subnetting, route summarization, and real-world experience resolving IP address-space conflicts between two merging corporate networks — essential for the integration work specifically.
• Proven network segmentation design experience: ideally across converged IT/OT environments, not IT alone.
• Working knowledge of IEC 62443 zone/conduit methodology (or an equivalent segmentation framework), with the ability to define a model from first principles rather than apply an existing one.
• Practical, enterprise-scale experience with VLANs, VRFs, routing, and firewall policy design.
• Comfortable working across both classic IT infrastructure and OT/industrial network environments.
• Strong documentation discipline: this design needs to outlive your assignment and be usable by others.

Nice-to-Have:

• Familiarity with Zero Trust platforms (e.g., Palo Alto Prisma Access, Zscaler, Illumio) — even if your prior experience is user/application access rather than site/OT segmentation.
• Familiarity with NetBox, runZero, Armis, or similar IPAM/asset-discovery tooling.
• Prior experience supporting network integration following a merger or acquisition.
• Familiarity with ServiceNow CMDB.
• Exposure to SD-WAN or MPLS-to-SD-WAN transitions — useful context, but secondary to the Zero Trust segmentation work above.

Why This Client Engagement Is Unique:

• Shape, from a blank page, how a 2,200+ site pan-European operator segments and secures its network for the next decade.
• Play a direct, hands-on role in a live M&A network integration — not a theoretical exercise.
• Work closely with the client's CISO and Security Architect on a programme with genuine executive visibility.
• A focused, well-scoped engagement: clear deliverables, a defined end date, and real impact within it.

Consultancy Advantages with Keystone Solutions:

• Consultancy Nature of Work: Operate as a Keystone Solutions consultant embedded with the client, combining on-site presence with hybrid flexibility to drive measurable outcomes in complex environments.
• Dynamic Projects: Build a portfolio of impactful missions across industries and technologies over time, applying your expertise to diverse integration and IT/OT segmentation challenges.
• Turbo-Charged Learning and Development: Benefit from knowledge sharing and professional growth supported by Keystone Solutions, enhancing your capabilities while delivering at the client.
• Ambition Skyrocketing within a Consultancy Framework: Accelerate your career through varied, high-visibility engagements, taking ownership of end-to-end designs and pilots that shape enterprise architectures.

Keystone Solutions' Values in Action:

As a Keystone Solutions consultant (a K-Stone), you bring our consultancy ethos to every engagement — partnering closely with client teams, delivering pragmatic, secure-by-design architectures, and documenting solutions that stand the test of time. You will exemplify our commitment to quality execution, collaboration, and continuous improvement throughout this mission.

Location and Engagement Details:

• Engagement: Initial 6-month consultancy mission with strong potential for extension, delivered by Keystone Solutions at the client.
• Primary Location: Brussels headquarters preferred, with occasional travel to key sites; hybrid options considered case by case.
• Collaboration: Daily interaction with client stakeholders, including the CISO, Head of Infrastructure, Security Architect, and Enterprise Architects.

Who Succeeds in This Role:

• Engineers who relish deep IP and routing challenges in brownfield environments.
• Architects who can define Zero Trust and IEC 62443 segmentation models from first principles.
• Consultants who document rigorously and hand over solutions that are immediately actionable by client teams.

Application:

If you are ready to tackle technical and strategic challenges in a dynamic consultancy environment, apply today at Keystone Solutions Career Portal.