Top 6 Data Diodes for Air-Gapped Network Monitoring in 2026

Air-gapped and segmented operational technology (OT) networks still need to share data with the outside world. Plant historians feed enterprise analytics. Sensor telemetry reaches a security operations center (SOC). Software updates need to reach isolated control systems. A data diode makes this possible without opening a return path an attacker could exploit. Unlike a firewall, which enforces separation through configurable rules, a data diode enforces it in hardware. There is no policy to misconfigure and no software interface to bypass. Regulatory frameworks including NERC CIP, NIS2, and IEC 62443 increasingly point buyers toward this kind of physical segmentation. This guide compares six vendors offering hardware-enforced, one-way data transfer for OT, ICS, and classified network environments.

At a Glance: Data Diodes for Air-Gapped Network Monitoring

Vendor	Key Strength	Max Throughput
Network Critical	Data diode integrated into existing hybrid TAP and packet broker hardware	N/A
Waterfall Security Solutions	Pioneered the unidirectional gateway category, largest deployed base	Up to 10 Gbps
Owl Cyber Defense	Protocol-aware filtering diodes at defense-grade assurance levels	Up to 100 Gbps
Advenica	Hardware-only design with no configuration to exploit	Up to 1 Gbps
BAE Systems	Common Criteria EAL 7+ evaluated diode for classified networks	N/A
Garland Technology	SPAN-based data diode TAP for existing OT visibility fabrics	Up to 1 Gbps

1. Network Critical

Network Critical brings data diode capability into the same hardware family that handles network TAP and packet broker duties. Teams can add unidirectional enforcement to infrastructure they may already operate. There is no need to deploy a standalone appliance as the only option. The data diode function operates with sub-millisecond latency. It is engineered for 99 percent reliability, even in high-throughput, high-risk environments. It is also protocol agnostic across IP-based traffic. This removes the configuration overhead that protocol-specific diodes can introduce elsewhere.

Deployment options include a standalone hardware module. Teams can also configure the diode within the SmartNA-PortPlus packet broker, or directly on the SmartNA-XL hybrid TAP. This hybrid approach combines passive access, traffic management, and enforced one-way flow in a single chassis. For teams running Network Critical TAP or packet broker hardware, this avoids the complexity a separate diode appliance introduces. Drag-n-Vu software manages the surrounding configuration without requiring specialist diode engineering knowledge.

Proven results:

BP: Passive fiber TAPs enabled centralized monitoring of IT and OT systems across refinery buildings without impacting live production traffic
State of Maryland: SmartNA-XL delivered comprehensive traffic visibility while helping the Department of Information Technology meet regulatory compliance and audit requirements
Airbus: Network TAPs captured mission-critical test rig data with failsafe technology, later extending to the military A400M aircraft programme

2. Waterfall Security Solutions

Waterfall Security Solutions pioneered the unidirectional gateway category. It remains one of the most widely deployed names in OT and ICS security. Its flagship WF-600 Unidirectional Security Gateway combines a hardware diode layer with replication software. It supports 1 Gbps or 10 Gbps throughput options and high availability configurations. The company positions its gateways as a direct replacement for one layer of firewalls at the IT and OT boundary.

Waterfall's SEC-OT methodology is widely referenced in industrial cybersecurity literature. The company reports deployments across more than 1,000 sites spanning power generation, oil and gas, and manufacturing. Its DiodeCore platform serves smaller sites that need unidirectional enforcement without the full WF-600 footprint. Waterfall also offers a long-standing DIN rail option for space-constrained installations. The company argues that hardware-enforced separation removes entire classes of remote attack that firewall misconfiguration can expose.

3. Owl Cyber Defense

Owl Cyber Defense has developed data diode technology for over 25 years. It holds a strong position in defense and intelligence community deployments. Its Owl Talon One appliance delivers up to 1 Gbps of one-way transfer with FPGA-based filtering in a single device. The higher-throughput Owl Talon Torrent scales to 100 Gbps. It combines the same protocol-aware filtering with the bandwidth needed for backbone-level OT and analytics data movement.

Owl's Protocol Filtering Diode (PFD) approach inspects and filters each packet at the hardware layer using field-programmable gate arrays (FPGAs). This differs from software rules alone. Its diodes align with NSA and National Cross Domain Strategy and Management Office (NCDSMO) expectations. Common Criteria evaluations support its defense and intelligence assurance claims. The pocket-sized Owl Incident Response Diode (IRD) serves forensics teams. It allows one-way USB transfer from compromised endpoints without exposing clean analysis environments.

4. Advenica

Advenica is a Swedish high-assurance vendor. Its SecuriCDS data diode range serves government and critical infrastructure customers up to Top Secret classification. The SecuriCDS DD1000A is designed in hardware only, with no software installed and no configuration to make. Advenica states the device cannot be misconfigured because there is nothing to configure. It delivers full Gigabit throughput in a compact 1U form factor.

The companion SecuriCDS DD1000i adds built-in proxy servers for application-specific data handling. It keeps the unidirectional function isolated in a separate hardware component. Both models carry Swedish Armed Forces approval at component assurance level N3, covering data up to SECRET classification. Non-public approvals exist in other European countries too. Advenica's positioning centers on Nordic and European government and defense buyers. These buyers prioritize sovereign, independently evaluated hardware over raw throughput figures.

5. BAE Systems

BAE Systems brings defense-grade credibility to the data diode space. It was built for U.S. Department of Defense (DoD) and intelligence community (IC) needs before expanding into critical infrastructure. Its Data Diode Solution supports unidirectional transfer of files, streaming data, and email. It converts information into sequenced UDP packets for transfer, then reconverts it on the receiving side. The XTS Diode extends this with a Raise the Bar (RTB) compliant, one-way transfer design.

BAE Systems holds the first Common Criteria EAL 7+ evaluated product of its kind in the United States. This assurance level is rarely seen outside classified government procurement. The company's FPGA-based hardware options exceed standard RTB requirements for demanding access and filtering needs. Its footprint spans North America, Europe, Asia Pacific, the Middle East, and Africa. It serves defense, intelligence, space, and critical infrastructure customers, where classification-level integrity outweighs raw bandwidth.

6. Garland Technology

Garland Technology approaches the data diode problem from its existing TAP and packet broker product line. It is not a dedicated diode specialist. Its Hardware Data Diode, including the P1GCCAS-Custom model, accepts a SPAN input and outputs two unidirectional copies of that traffic. There is no physical connection between the monitoring ports and the live network ports. This eliminates any possible intrusion path back through the monitoring destination.

This SPAN-based approach suits organizations that already run Garland TAPs or packet brokers. They can add unidirectional enforcement to an existing out-of-band monitoring fabric rather than deploy a new dedicated appliance. Garland markets the product specifically for industrial, manufacturing, utility, and military environments. Its OT security partner ecosystem, including a Nozomi Networks integration, extends the data diode line into existing threat workflows.

How to Choose a Data Diode for Air-Gapped Network Monitoring

Production Safety and Fail-Safe Enforcement

Any risk to production traffic is an automatic disqualification in most OT evaluations. Confirm that unidirectional enforcement happens at the hardware level. It should never rely on a software rule that could be misconfigured or bypassed. A true hardware data diode has no return path to exploit. That is the entire point of choosing one over a firewall at an OT boundary.

Change Management and Deployment Complexity

OT teams rarely get more than a brief maintenance window to deploy new hardware. Look for solutions that avoid reconfiguring SCADA systems or programmable logic controllers (PLCs) during installation. Devices that integrate into your existing TAP or network packet broker fabric typically need less change management. A standalone appliance usually needs its own rack space, power run, and cabling plan.

Throughput and Protocol Requirements

Match the diode's throughput to the actual link you are monitoring, not to the fastest option a vendor offers. A plant historian feed rarely needs more than 1 Gbps. Backbone-level ISR or analytics traffic may need 10 Gbps or higher. Consider whether you need:

Protocol-aware filtering at the hardware layer, useful for defense and intelligence use cases
Simple, protocol-agnostic pass-through for straightforward OT telemetry export
Support for specific industrial protocols such as Modbus or DNP3 further downstream

Compliance and Certification Requirements

Regulatory frameworks vary in how prescriptive they are about diode certification. IEC 62443 and NIS2 generally require documented segmentation and audit-ready evidence. They do not always name a specific certification. Government and defense procurement often specifies Common Criteria Evaluation Assurance Level (EAL) ratings or national accreditation. Confirm which standard your auditor or program office actually requires before narrowing your vendor list.

Vendor Viability and Support Model

Critical infrastructure and defense buyers should weigh a vendor's track record alongside its specification sheet. Consider years in operation and named references in comparable sectors. Check whether the vendor can support your deployment geography directly, rather than through a distributor. For buyers already invested in a TAP or packet broker platform, extending that vendor can simplify long-term support.

Frequently Asked Questions

What Is a Data Diode?

A data diode is a hardware device that physically enforces one-way data flow between networks of differing trust levels. It maintains secure communication from a protected network outward without allowing any traffic back in. A firewall relies on configurable software rules. A data diode's separation is built into the hardware itself.

How Is a Data Diode Different From a Firewall?

A data diode enforces one-way communication at the hardware level. A firewall enforces separation through software rules and access control lists. Firewalls can be misconfigured or exploited through a vulnerability in their rule set. A properly implemented data diode has no software interface on the return path. This removes that entire category of risk.

Do I Need a Data Diode for an Air-Gapped OT Environment?

Yes, if you need to export data from an air-gapped environment while keeping it fully isolated from inbound traffic. Data diodes are commonly used in OT and ICS environments for secure segmentation. They separate critical systems from less-trusted networks. They let you send telemetry, logs, or files outward without creating any path back into the protected network.

What Is the Difference Between a Data Diode and a Unidirectional Gateway?

The National Institute of Standards and Technology (NIST) SP 800-82 defines the underlying hardware primitive as a data diode. It is the physical component that enforces one-way flow. A unidirectional gateway combines that hardware with protocol connectors, server replication, and a management layer. The diode is the physical foundation. The gateway software makes that foundation operationally useful for industrial systems.

Does a Data Diode Support Compliance Frameworks Like IEC 62443 or NERC CIP?

Yes, data diodes support compliance with frameworks including IEC 62443, NERC CIP, and NIS2. They provide provable, hardware-enforced network segmentation. Auditors generally look for documented evidence of separation between OT and IT zones. A data diode gives you a physical control to point to, rather than a policy that could drift over time.

Will a Data Diode Add Latency to My Network?

A well-engineered data diode adds minimal latency, often well under a few milliseconds. The exact figure depends on the vendor and throughput tier. High-assurance products are engineered for continuous operation in high-throughput environments without becoming a bottleneck. Confirm latency figures against your specific throughput requirement. Higher-throughput models generally introduce more processing overhead than simple pass-through designs.

Build Your Air-Gapped Visibility Architecture With Network Critical

Choosing a data diode means choosing infrastructure your compliance program will depend on for years. The right vendor should match your throughput needs and certification requirements. It also needs to fit the realities of deploying inside a production OT environment without downtime.

Network Critical's data diode capability extends the same hybrid TAP and packet broker architecture used across energy, aerospace, and finance. Unidirectional enforcement can run on hardware you may already operate, rather than adding a separate appliance to your rack. Perpetual licensing avoids the subscription costs common among enterprise platform vendors. To discuss your air-gapped monitoring requirements and receive a free network audit, speak to the Network Critical team.