# What is an Air Gap?

> An air gap physically or logically isolates a system or network from untrusted networks — no shared cabling, wireless, or routine data path to the outside.

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## Content

Air gaps protect systems where compromise would be catastrophic: industrial control networks, classified systems, backup vaults, and signing or key-management infrastructure. Data crosses the gap only through controlled means — scanned removable media, one-way transfer devices, or scheduled physical processes.

### Key points

- **Whole-boundary design:** Account for maintenance laptops, vendor remote access, USB devices, firmware updates, telemetry paths, and administrative jump hosts — the gap fails at its convenience exceptions.
- **Enforced one-way transfer:** Data diodes and scheduled, scanned media exchanges preserve isolation better than ad hoc file copies.
- **Important limitation:** Air gaps raise cost and reduce monitoring, patching, and response capability — isolated systems can drift unpatched and unaudited. They have also been bridged historically via removable media and maintenance paths, so an air gap reduces exposure; it does not eliminate it.

### Related terms

[Network segmentation](<https://yellowcube.eu/glossary/network-segmentation/>) · [Data diode / unidirectional gateway](<https://yellowcube.eu/glossary/data-diode-unidirectional-gateway/>) · [Industrial demilitarized zone (IDMZ)](<https://yellowcube.eu/glossary/industrial-demilitarized-zone/>) · [Operational technology (OT) security](<https://yellowcube.eu/glossary/operational-technology-security/>) · [Immutable backup](<https://yellowcube.eu/glossary/immutable-backup/>)

### Sources

[NIST SP 800-82 Rev. 3, Guide to Operational Technology Security](https://csrc.nist.gov/pubs/sp/800/82/r3/final) · [CISA, Recommended Cybersecurity Practices for Industrial Control Systems](https://www.cisa.gov/resources-tools/resources/recommended-cybersecurity-practices-industrial-control-systems)

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