Network Segmentation and Air Gaps
Dividing a network into isolated zones limits how far an intruder can move, and an air gap is the strongest form of that isolation.
Segmentation
A flat network lets any compromised device talk to any other, so a single foothold can spread everywhere. Segmentation partitions the network into zones with controlled boundaries, so that traffic between zones is filtered, inspected, and limited to what is genuinely required. The goal is to contain a breach: an attacker who lands in the office zone should not be able to reach a magnet controller.
Techniques
- VLANs and subnetting to separate broadcast domains
- Firewalls and access control lists at zone boundaries
- Micro-segmentation down to individual workloads
- Demilitarized zones (DMZs) that mediate between trust levels
Air Gaps
An air gap is physical isolation: the protected network has no wired or wireless connection to less trusted networks. It is the strongest boundary because there is no path for network traffic to cross at all. True air gaps are used for the most safety- and security-critical systems.
The Limits of Air Gaps
Air gaps are rarely absolute in practice. Data still needs to move for updates, configuration, and logs, and that movement happens via removable media or maintenance laptops, which become the crossing point. Malware has jumped air gaps through infected USB drives. An air gap reduces attack surface dramatically but does not eliminate the need for media controls, monitoring, and discipline.
Fusion Context
The safety instrumented system of a fusion plant is a natural candidate for the deepest isolation, so that its protective logic cannot be reached or altered over any network. Control networks for the Hyperion breeder and burner designs are specified with strict segmentation from business IT, controlled gateways for the data that must flow, and unidirectional links where telemetry needs to leave but no command should ever enter. See data diodes for how that one-way flow is enforced in hardware.