NIS2 requires essential and important entities to prove demonstrable segmentation between IT and OT environments. Energy, transport, and manufacturing operators face a specific technical question. How do you connect monitoring tools to sensitive control systems? The connection must not open a return path for attackers. Firewalls rely on software rules. Those rules can be misconfigured or bypassed. A data diode solves this differently. Hardware physically enforces one-way data flow. There is no reverse path for ransomware, remote command injection, or human error to exploit. Regulators increasingly expect this kind of provable separation, not just a policy document.

This guide compares six vendors offering hardware-enforced unidirectional data transfer for NIS2-covered critical infrastructure. It covers throughput, certifications, and deployment models. Use it to match the right diode to your network, your compliance timeline, and your audit requirements.

Data Diode Vendors at a Glance

Vendor	Key Feature / Strength	Max Throughput
Network Critical	Standalone module or integrated within SmartNA-PortPlus and SmartNA-XL	Not disclosed
Owl Cyber Defense	Common Criteria EAL4+ protocol filtering diodes	Up to 100 Gbps
Waterfall Security Solutions	WF-600 self-contained unidirectional gateway	Up to 10 Gbps
Advenica	SecuriCDS diodes rated to Top Secret classification	Up to 10 Gbps
Garland Technology	SPAN-compatible hardware data diode for OT networks	Up to 1 Gbps
Forcepoint	Integrates with Forcepoint Cross Domain Solutions	Not disclosed

Network Critical

Network Critical offers a data diode as a standalone hardware module. It is also available as an integrated option inside the SmartNA-PortPlus and SmartNA-XL platforms. This lets an operator add unidirectional enforcement to an existing deployment. There is no need to rack a separate appliance. The diode enforces one-way communication at the hardware level. Downstream firewalls and access control lists cannot be misconfigured into allowing a return path. The physical path simply does not exist.

The hybrid TAP and packet broker architecture combines passive access, traffic aggregation, and enforced unidirectional flow. All three sit in a single chassis. This matters most in space-constrained OT environments such as substations and remote drilling platforms. A combined device reduces both rack space and deployment risk in those settings. Drag-n-Vu gives network admins a single graphical interface. It configures TAP, broker, and diode functions together. This removes the specialist-engineer dependency that some competing platforms still require.

Network Critical's perpetual licensing model avoids per-port subscription fees. Those fees drive up three-year TCO for larger incumbent vendors. For OT operators managing long infrastructure lifecycles, predictable CapEx matters as much as the technical separation itself. Budget owners can plan multi-year OT refresh cycles without an annual licensing surprise.

Proven results:

• BP: Centralized monitoring across refinery buildings using fail-safe passive optical TAPs that need no power at remote sites
• Airbus: Achieved complete packet capture across mission-critical test rig traffic with zero impact on live testing
• Vodafone: Achieved 100 percent accurate traffic visibility across a multi-generation network spanning multiple countries

Owl Cyber Defense

Owl Cyber Defense builds Protocol Filtering Diodes for government, defense, and critical infrastructure customers. The Owl Talon platform enforces hardware-based one-way transfer with FPGA protocol filtering. The flagship line scales to 100 Gbps for high-throughput environments such as plant historians. Owl's diodes carry Common Criteria EAL4+ evaluation. They align with NIST RMF and NERC CIP-relevant practices.

The compact Owl Talon One delivers up to 1 Gbps through a single PCIe card. It lets agencies turn commercial off-the-shelf servers into diode appliances without extra rack hardware. The OPDS-1000 targets demanding industrial control applications. It offers three throughput tiers, from 26 Mbps up to 1,000 Mbps, in a 1U rack-mountable chassis.

Owl's positioning skews heavily toward US government and defense buyers. The company has a track record in ISR feeds and continuous SOC monitoring. European critical infrastructure operators evaluating Owl typically work through regional integration partners rather than direct sale.

Waterfall Security Solutions

Waterfall Security Solutions pioneered the unidirectional gateway category. It remains one of the most widely deployed names in OT security. The flagship WF-600 gateway offers 1 Gbps or 10 Gbps throughput options. Standard high-availability configurations are included. It ships as a self-contained platform, so no external software runs on industrial or enterprise computers.

The WF-600 is managed through a single web interface. That interface covers configuration, monitoring, and troubleshooting. A broad connector library supports industrial control systems, SCADA platforms, and most OT data products. This removes the need for custom integration work in most deployments. Waterfall also offers the BlackBox. This is a tamper-proof log repository, designed to survive an attack that compromises the rest of the network.

Waterfall's installed base spans thousands of critical infrastructure and manufacturing sites. This gives it strong reference depth for NIS2 conversations in energy and water. The tradeoff is a narrower throughput ceiling. Vendors built for defense-grade or hyperscale environments generally scale further.

Advenica

Advenica is a Swedish vendor whose SecuriCDS diode range serves government and critical infrastructure customers. Its products are rated up to Top Secret classification. The DD1000A and DD1000i models are approved by the Swedish Armed Forces at component assurance level N3. The newer DD1G Gen 2 carries Common Criteria EAL4+ certification.

The DD1G Gen 2 is a hardware-only diode with full Gigabit throughput. It has no configuration options, which removes the risk of misconfiguration entirely. It supports Power over Ethernet for simplified cabling at remote or space-constrained sites. For 10 Gbps environments, Advenica's DDSFX-10G ships in an SFP form factor. Customers needing bidirectional application support can pair any hardware diode with the Advenica Data Diode Engine.

Advenica's certification depth suits operators in defense-adjacent critical infrastructure across the European Union. Its field presence outside Europe is limited compared with US-based competitors. Buyers outside the EU should confirm local support arrangements before committing to the platform.

Garland Technology

Garland Technology offers a Hardware Data Diode built around SPAN port connections. This differs from inline TAP access used by most other vendors here. The device regenerates a SPAN port to multiple out-of-band monitoring tools. It physically blocks any return path, at 10/100/1000M network speeds.

Garland positions the diode for utility substations, manufacturing facilities, and metro locations. A straightforward SPAN-based deployment is often preferable to a full TAP rebuild in these settings. The device requires no configuration. Garland's broader OT security partner ecosystem, including Nozomi Networks and Radiflow, gives buyers pre-built integration paths for downstream security tools. Garland's no-subscription pricing model mirrors the CapEx-only structure that OT buyers increasingly prefer over annual licensing.

Garland's diode throughput tops out at 1 Gbps. This suits substation and lower-speed industrial links well. It is not built for high-throughput data center or telecom environments. Buyers needing 10 Gbps or above should look elsewhere in this list.

Forcepoint

Forcepoint sells a data diode designed to work alongside its broader Cross Domain Solutions portfolio. The product provides optical isolation for one-way data transfer. It is built to meet Raise the Bar guidelines and GDPR-driven hardware separation requirements.

Forcepoint's diode integrates with existing CDS deployments. This suits organizations already standardized on Forcepoint for cross-domain data movement. Public throughput specifications are not available for the current product line. The company's recent product messaging has shifted toward AI-driven data security. Hardware diode innovation appears to be a lower current priority. Buyers should request a current data sheet directly. Much of Forcepoint's public diode documentation still dates from its original 2020 launch.

For NIS2-covered entities without an existing Forcepoint estate, this narrower recent focus is worth weighing carefully. Vendors with more current, diode-specific engineering investment may offer clearer specification support during procurement.

How to Choose the Right Data Diode for NIS2 Compliance

Throughput and Protocol Support

Match diode throughput to the link you are protecting, not to a vendor's headline figure. A 1 Gbps diode is fine for a substation SCADA feed. It will bottleneck a 100 Gbps data center interconnect. Confirm whether the diode is protocol-aware or a pure hardware pass-through. Protocol filtering adds inspection, at the cost of some latency. Ask for a real-world latency figure under expected traffic load. A headline throughput number will not tell you how the diode performs once protocol filtering and inspection are switched on.

Certification and Assurance Level

Government and defense buyers typically need NCDSMO or Raise the Bar compliance. Critical infrastructure operators covered by NIS2 should look for Common Criteria EAL4+ as a baseline. IEC 62443 alignment matters for ICS-specific deployments. Ask any vendor for their actual certification scope, not just a general security claim.

Deployment Complexity

Consider whether you are deploying into a data center rack, a remote substation, or a space-constrained drilling platform. DIN rail and Power over Ethernet options reduce cabling and power overhead at remote sites. A hybrid TAP and packet broker architecture folds diode enforcement into existing visibility hardware. This avoids adding a separate appliance and its own rack footprint. It also cuts the number of vendor support contracts your team has to manage across a distributed OT estate.

Integration with Existing OT Tools

If you already operate network TAPs or packet brokers, check whether unidirectional enforcement can run on that existing hardware. This can avoid the cost and cabling of a standalone diode appliance.

• Confirm compatibility with your OT security platform, such as Dragos, Claroty, or Nozomi Networks
• Check whether the vendor publishes verified integration documentation, rather than a generic compatibility claim
• Ask how the diode's management interface handles day-to-day configuration changes

Total Cost of Ownership

Perpetual hardware licensing with no per-port subscription fees keeps CapEx predictable. This matters across a long OT infrastructure lifecycle. Factor in support costs, spares, and whether the vendor charges separately for firmware updates. A lower sticker price on the appliance itself can still produce a higher three-year total, once support contracts are included.

Compliance Documentation

NIS2 auditors expect evidence, not just a vendor claim of unidirectional enforcement. Ask for independent test reports, Common Criteria certificates, or national accreditation letters. Vendors with published, dated compliance mappings to NIS2, NERC CIP, or IEC 62443 make audit preparation considerably faster. Keep copies of every certificate on file. Auditors increasingly ask for the underlying documents rather than a vendor's summary claim.

Frequently Asked Questions

What Is a Data Diode?

A data diode is a hardware device that physically enforces one-way data flow between two networks. It uses optical or electronic components that only allow signals to travel in a single direction. Unlike a firewall, there is no software rule to misconfigure or bypass. The reverse path simply does not exist at the hardware level.

Does NIS2 Require a Data Diode?

NIS2 does not name data diodes specifically. It requires essential and important entities to demonstrate proportionate technical measures for network segmentation. For high-risk IT/OT boundaries in energy, transport, and manufacturing, a hardware data diode is often the most defensible option. It proves that separation with physical evidence rather than a policy claim.

What Is the Difference Between a Data Diode and a Network TAP?

A network TAP passively copies traffic for monitoring, without enforcing direction. A data diode goes further. It physically blocks any return path, so it protects the source network rather than simply observing it. Many OT deployments use both together. A TAP feeds monitoring tools while a diode protects the sensitive side of the boundary.

How Much Does a Data Diode Cost?

Data diode pricing ranges from a few thousand dollars for a basic SPAN-based unit. It can reach tens of thousands for a certified, protocol-aware appliance with support contracts. Government and defense-grade diodes with Common Criteria evaluation typically sit at the higher end. Integrated options that add diode functionality to existing TAP or packet broker hardware can reduce total spend.

Can a Data Diode Replace a Firewall?

A data diode does not replace a firewall in a bidirectional network segment, since it only supports one-way traffic. It is best suited to boundaries where data genuinely only needs to move in one direction. An example is OT telemetry feeding an IT historian. Most NIS2-covered operators use diodes for these specific one-way paths, alongside firewalls elsewhere in the architecture.

Do I Need a Data Diode for Every OT Boundary?

No single control fits every boundary in an OT network. Data diodes suit strictly one-way flows, such as telemetry export or historian replication. Bidirectional control traffic still needs a firewall or an industrial DMZ. A unidirectional gateway with a controlled return channel can also handle specific protocols where some limited feedback is genuinely required.

Build Your NIS2 Compliance Architecture With Network Critical

Choosing the wrong data diode creates a compliance gap. It can also force a costly rebuild once your network scales past its throughput ceiling. Network Critical's data diode deploys as a standalone module. It is also available as an integrated option inside the SmartNA-PortPlus and SmartNA-XL platforms. You are not left managing a separate appliance on top of your existing visibility hardware. Perpetual licensing keeps three-year costs 40 to 60 percent lower than subscription-based incumbents. Drag-n-Vu lets your own team configure TAP, broker, and diode functions from one interface.

For operators facing an NIS2 audit on IT/OT segmentation, that combination matters. Hardware assurance and predictable cost carry as much weight as the certification paperwork itself. Speak to the Network Critical team to review your architecture. Together you can identify where unidirectional enforcement fits your compliance timeline.