# What is a Data Diode or Unidirectional Gateway?

> A data diode is a boundary device designed to permit data transfer in only one physical direction.

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## Content

A unidirectional gateway is the wider solution built around that one-way property, often using paired proxies or replication software so applications can move approved information across the boundary without creating a return network path.

These controls are used where preventing inbound communication is more important than ordinary two-way connectivity — for example, exporting operational data from a high-consequence environment. The architecture must still address protocol behavior, delivery assurance, monitoring, maintenance, fail-safe operation, and the sensitivity of information allowed to leave.

### Key points

- **Primary security property:** The protected direction is enforced by hardware rather than only a configurable software rule.
- **Common uses:** Replicating historian data, files, logs, video, or selected database content from a higher-consequence zone.
- **Design trade-off:** Protocols that expect acknowledgments or interactive sessions require proxying, replication, or a different workflow.
- **Operational caution:** Some processes require trusted feedback or emergency control; forcing them through a one-way design can harm availability or safety.
- **Important limitation:** A diode is not an air gap, does not make the endpoints trustworthy, and does not prevent unauthorized data from leaving in the permitted direction.

### Related terms

[Operational technology (OT) security](<https://yellowcube.eu/glossary/operational-technology-security/>) · [Network segmentation](<https://yellowcube.eu/glossary/network-segmentation/>) · [Industrial control system (ICS)](<https://yellowcube.eu/glossary/industrial-control-system/>) · [Supervisory control and data acquisition (SCADA)](<https://yellowcube.eu/glossary/supervisory-control-and-data-acquisition/>) · [Industrial demilitarized zone (IDMZ)](<https://yellowcube.eu/glossary/industrial-demilitarized-zone/>)

### Sources

[NIST glossary: Data Diode](https://csrc.nist.gov/glossary/term/data_diode) · [NIST SP 800-82r3: Guide to Operational Technology Security](https://csrc.nist.gov/pubs/sp/800/82/r3/final)

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