Top 7 Data Diodes for Secure Log and File Transfer to SIEM in 2026

Getting logs out of an isolated network is straightforward. Doing it without opening a path back in is the hard part. A firewall rule can be misconfigured or exploited. A data diode removes that risk at the hardware level, physically permitting traffic in one direction only. Teams feeding a Security Information and Event Management (SIEM) platform from an OT, ICS, or classified network need this guarantee. It matters more than throughput or price. Regulatory drivers including NERC CIP, IEC 62443, and NIS2 increasingly expect this provable separation. A documented firewall policy is no longer enough. This guide compares seven vendors offering hardware-enforced one-way transfer. Each is suited to secure log, telemetry, and file delivery into a SIEM.

Comparing Data Diodes for Secure SIEM Log Transfer

Vendor	Key Feature / Strength	Max Throughput
Network Critical	Data diode capability built into existing hybrid TAP and packet broker chassis	—
Owl Cyber Defense	FPGA-based protocol filtering diodes for defence and intelligence missions	Up to 100G
Waterfall Security Solutions	Largest native OT and SCADA connector library on the market	Up to 10G
Advenica	Common Criteria EAL4+ certified, no-configuration hardware diode	Up to 1G
OPSWAT	Preconfigured optical diode with EAL4+ and C1D2 certification	Up to 1G
BAE Systems	Raise the Bar-compliant diode for classified defence networks	Up to 10G
Garland Technology	Data diode TAPs integrated into a broader OT visibility portfolio	Up to 10G

1. Network Critical

Network Critical has added a data diode solution to its existing OT visibility range. Rather than sourcing a standalone box for every unidirectional requirement, the company offers a standalone hardware data diode module. Diode-configured options are also available on the SmartNA-PortPlus and SmartNA-XL platforms. This matters most in space-constrained OT sites. A site already running SmartNA-XL for traffic visibility can configure unidirectional flow on the same chassis.

The diode enforces guaranteed one-way transmission for logs, metrics, and files. Data moves from secure or classified networks to lower-trust environments only. It is protocol-agnostic across IP-based traffic, removing the configuration overhead that protocol-specific diodes can introduce. Network Critical states sub-millisecond latency and 99% reliability in high-throughput environments. Drag-n-Vu software gives network admins a single graphical interface for configuring TAP, broker, and diode functions together. This avoids the multi-vendor console sprawl common in OT deployments.

Proven results:

BP: Centralised monitoring across refinery buildings using fail-safe passive optical TAPs needing no power at remote sites
HSBC: Achieved zero latency on monitoring technologies supporting real-time financial systems
Darktrace: API integration with SmartNA-PortPlus automated traffic filtering and mapping for continuous SOC monitoring

2. Owl Cyber Defense

Owl Cyber Defense builds Protocol Filtering Diodes (PFDs) for high-assurance defence and intelligence missions. The Owl Talon One delivers up to 1 Gbps of hardware-enforced one-way transfer from a single PCIe card. Owl Talon Torrent scales further, reaching 100 Gbps for backbone-level data movement. Both combine FPGA-based protocol filtering with physical separation, so only well-formed, policy-approved data crosses the boundary.

Owl's diodes have completed US Government PFD evaluation. They align with Raise the Bar and Zero Trust guidance. Use cases include intelligence, surveillance, and reconnaissance feeds, command-and-control telemetry, and continuous SOC and SIEM monitoring. No inbound path into the protected network is exposed. Owl also offers an Incident Response Device. It extends one-way protection to forensic transfer from potentially compromised endpoints, without exposing clean analysis environments. This gives buyers a single platform across multiple mission profiles, avoiding the need to mix diode vendors by use case.

3. 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. The flagship WF-600 gateway offers 1 Gbps or 10 Gbps throughput. It ships with standard high-availability configurations and a self-contained software platform, needing no external hosts on either network.

Waterfall's connector library covers most industrial control system, SCADA, and OT data products on the market. This simplifies integration compared with diodes that demand custom proxy development for every protocol. The company positions the WF-600 as a direct replacement for one firewall layer at the IT and OT boundary. It argues that hardware-enforced separation removes entire classes of remote attack. Waterfall's BlackBox product offers a tamper-proof log repository designed to survive an attack. It preserves evidence of how an intrusion occurred, even if the source network is compromised. Customers span power generation, oil and gas, and manufacturing, across more than 1,000 sites.

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 DD1G Gen 2 is a hardware-only diode offering full Gigabit throughput with no configuration options. This removes the risk of misconfiguration entirely. It supports Power over Ethernet for simplified cabling at space-constrained or remote sites, and carries Common Criteria EAL4+ certification.

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. This standalone proxy software layer manages file transfer and sensor data export. It does so without compromising the underlying one-way hardware guarantee. Advenica's customer base leans heavily toward European national authorities and operators of essential infrastructure, including electricity and water utilities.

5. OPSWAT

OPSWAT offers the MetaDefender Optical Diode, a preconfigured device built for secure OT and IT data and file transfers. The base platform supports 100 Mbps with a field upgrade path to 1 Gbps. This suits sites where bandwidth needs are modest but certification requirements are strict. MetaDefender Optical Diode is certified to Common Criteria EAL4+. The DIN rail model also holds Class 1 Division 2 certification for hazardous sites, including oil, gas, and chemical plants.

The wider MetaDefender NetWall family scales from 100 Mbps to 10 Gbps. It offers N+1 redundancy and active-active clustering options. OPSWAT documents deployments protecting refinery control networks from corporate IT, supporting compliance with TSA cybersecurity directives. The product is listed in the NATO Information Assurance Product Catalogue and supports on-diode protocol conversion. This reduces the need for separate proxy infrastructure in straightforward OT-to-IT replication use cases.

6. BAE Systems

BAE Systems supplies the XTS Diode, a Raise the Bar-compliant one-way transfer device. It is validated by the National Cross Domain Strategy Management Office and the National Security Agency. The manufacturer's own specification lists throughput of up to 10 Gbps. The footprint is compact and rugged, suited to tactical and mobile deployments. It runs on BAE's STOP high-assurance operating system or Red Hat Enterprise Linux. Forward error correction is built in to recover messages after one-way transmission.

XTS Diode integrates with BAE's XTS Guard cross-domain solution. It supports UDP and TCP-based file sharing and streaming. The product's primary market is defence, the intelligence community, and coalition partners requiring NCDSMO compliance documentation. A separate Data Diode Solution offers Common Criteria EAL7+ certification for the highest-assurance government use cases. This gives buyers a path to scale assurance level without changing vendor.

7. Garland Technology

Garland Technology is a TAP specialist. It has built a dedicated hardware data diode line into its broader OT visibility portfolio. Its Hardware Data Diode enforces one-way traffic from SPAN or TAP outputs to monitoring destinations at 1 Gbps. The Portable-Configurable Data Diode TAP extends coverage to 1G and 10G fibre links. Five configurable modes are set by physical DIP switches.

The AggregatorTAP: Data Diode variant consolidates multiple network segments into a single monitoring feed. It protects the source of each data stream between segments with different security requirements. Garland positions data diodes alongside its existing TAP, bypass, and packet broker lines. Customers already using Garland for visibility get a single vendor relationship for both monitoring and unidirectional segmentation. The company maintains a dense OT security partner ecosystem, including Nozomi Networks, TXOne, Dispel, EmberOT, and Radiflow.

How to Choose a Data Diode for SIEM Log Transfer

Throughput and Data Volume

Match the diode's rated throughput to your actual data volume, not your network's overall link speed. Most OT-to-IT diode traffic consists of logs, historian data, and telemetry rather than full-rate production traffic. A 1 Gbps diode often covers requirements that a 10 Gbps network link would suggest you need more. Oversizing wastes budget; undersizing forces you to queue or drop data at the boundary.

Certification and Compliance Fit

Check which standards your sector or contract actually requires before comparing vendors. Government and defence buyers typically need NCDSMO or Raise the Bar compliance. Critical infrastructure operators look for Common Criteria EAL4+ as a baseline and IEC 62443 alignment for ICS-specific deployments. Some unidirectional gateways also support NERC CIP and NIS2 documentation requirements directly.

Deployment Footprint and Integration

Consider whether you are deploying into a data centre 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. If you already run network TAPs or a network packet broker, check whether unidirectional flow can run on it. Key questions to weigh:

Does the site have spare rack units, or does space constrain you to a standalone module?
Is mains power available, or do you need Power over Ethernet or DIN rail options?
Will the diode sit alone, or integrate with a hybrid TAP and packet broker platform already on site?

Protocol and Application Support

A pure hardware diode requires unidirectional protocols such as UDP. If your applications rely on TCP handshakes or other acknowledgement-based protocols, you need a proxy layer on each side. Some vendors bundle this proxy software directly. Others require you to build or source it separately, which changes total deployment effort.

Total Cost of Ownership

Factor in the licensing model, not just the hardware cost. Perpetual hardware licensing with predictable support fees avoids the OpEx volatility of subscription platforms over a multi-year deployment. For sites already running visibility hardware, an OT network monitoring platform that also handles unidirectional flow can cut fleet costs.

Frequently Asked Questions

What Is a Data Diode?

A data diode is a hardware device that physically enforces one-way data flow. It works between two networks of different trust levels. Unlike a firewall, it has no return path to exploit. The hardware itself, not software rules, prevents reverse traffic. This makes data diodes a common choice for connecting OT and ICS networks to enterprise IT and SIEM platforms.

How Is a Data Diode Different From a Firewall?

A data diode enforces unidirectional flow at the hardware level. A firewall relies on software rules that can be misconfigured or bypassed. A true data diode cannot pass return traffic under any configuration. Organisations often deploy both. A firewall handles general segmentation; a diode secures the highest-assurance one-way boundaries feeding a SIEM.

Can a Data Diode Feed Logs Directly Into a SIEM?

Yes. Most OT-to-IT diode deployments exist specifically to move logs, telemetry, and file exports to a SIEM. They do this without exposing a path back into the source network. A network packet broker or TAP typically sits upstream of the diode. It filters and aggregates traffic before the data crosses the one-way boundary, keeping SIEM ingestion volumes manageable.

How Much Does a Data Diode Cost?

Data diode pricing varies widely by throughput, certification level, and deployment model. Costs range from a few thousand pounds for a basic Gigabit diode. High-assurance, Common Criteria-certified systems cost significantly more. Diode capability built into existing visibility hardware can lower total deployment cost, by avoiding a dedicated appliance for every link.

Do I Need a Data Diode for IEC 62443 or NIS2 Compliance?

Many OT and ICS compliance frameworks specify physical segmentation between control systems and external networks. IEC 62443, NERC CIP, and NIS2 are examples. Data diodes are a recognised way to satisfy these requirements. Whether one is mandatory depends on your specific regulatory scope, so check your framework's exact wording before committing budget.

Can a Data Diode Work Alongside a Network TAP or Packet Broker?

Yes, and many OT deployments combine the two. A network TAP gives you visibility into traffic on the link. A data diode controls the direction that data is allowed to travel. Pairing them on shared hardware, where supported, reduces rack space. It also simplifies management compared with running separate appliances for each function.

Build Your One-Way Data Architecture With Network Critical

Choosing a data diode for SIEM log transfer means balancing certification, throughput, and deployment footprint. It also means deciding how many separate boxes your team wants to rack and manage. Network Critical folds unidirectional flow into the same SmartNA-PortPlus and SmartNA-XL hardware already handling TAP and broker duties. This cuts deployment complexity in space-constrained OT environments.

That approach pairs with perpetual hardware licensing rather than a subscription model. OT teams get predictable costs across a multi-year deployment. Combined with Drag-n-Vu configuration, network admins manage TAP, broker, and diode functions from one interface. There is no need to juggle separate vendor consoles. If you are weighing a standalone diode against an integrated approach, speak to the Network Critical team about your build.