They should prioritise the model that matches the estate they actually run. Agent-based tools can be strong on managed servers, but agentless coverage is often more realistic for OT, IoT, and other unmanaged assets. The right sequence is usually coverage first, then deeper optimisation where agents are viable.
How the better segmentation model depends on the estate you actually run
Microsegmentation is an enforcement problem as much as a design problem. The better approach is the one that can cover the assets you need to control without creating blind spots, operational drag, or rollout failure. In practice, that means assessing where agents can be deployed, where they cannot, and whether your segmentation model can still express policy consistently across both populations.
Agent-based coverage is usually strongest where you control the endpoint stack and can tolerate software deployment, upgrade, and health management. Agentless coverage is often the only practical path for unmanaged or hard-to-touch assets, including many OT and IoT environments, where installing software is unrealistic or unsafe.
Why coverage should come before optimisation
The first decision is not which model is more elegant, but which one closes the largest exposure surface fastest. If a segmentation design only works on part of the estate, it may look precise while leaving critical traffic paths unsegmented. A broader but lighter-weight enforcement model can therefore be the safer starting point, even if it is less granular.
That trade-off matters because segmentation failures are often driven by deployment friction, inconsistent policy scope, or operational exceptions that quietly expand over time. A mixed estate usually benefits from a phased strategy: establish broad coverage where the environment is least controllable, then deepen enforcement where agents, telemetry, and host-level controls are viable.
What changes when you combine both models
Most mature programmes end up hybrid. Agentless controls help you establish baseline containment across legacy, third-party, embedded, and otherwise unmanaged assets, while agent-based controls add richer context, stronger host visibility, and more precise workload-level policy on systems you own. The goal is not to pick a side, but to avoid forcing a single control model onto incompatible asset classes.
Used together, the two approaches can also reduce migration risk. Agentless segmentation can provide immediate boundary control while teams validate where agent deployment is safe, where it creates acceptable overhead, and where identity or workload awareness materially improves policy quality.
Risk and Threat Considerations
Choosing the wrong primary model can leave unmanaged assets exposed, create false confidence in policy coverage, or encourage exceptions that weaken segmentation over time. In adversarial terms, gaps in enforcement create the easiest lateral-movement paths, especially where legacy systems, shared services, or operational technology sit outside the agent deployment footprint.
Failure mechanism: The control fails when the chosen architecture cannot be applied consistently across the real asset mix, so policy exists on paper but not on the traffic paths that matter most.
Impact: Attackers or misconfigurations can exploit unsegmented east-west movement, and operators may not notice until they discover that critical systems were never actually under the intended control boundary.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
NIST Zero Trust (SP 800-207) and CIS Controls v8 set the technical controls, while ISO/IEC 27001:2022 defines the regulatory obligations.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST Zero Trust (SP 800-207) | default — Zero Trust Architecture | Microsegmentation is a zero trust segmentation pattern for mixed estates. |
| Recommendation — Apply zero trust principles to segment unmanaged and managed assets by verified policy. | ||
| CIS Controls v8 | CIS-12 — Network Infrastructure Management | Segmentation choice affects network boundaries and enforceable traffic controls. |
| Recommendation — Define and maintain segmentation boundaries that match the assets and traffic paths in scope. | ||
| ISO/IEC 27001:2022 | A.8.20 — Networks Security | Segmentation is a core network security control for reducing lateral movement exposure. |
| Recommendation — Implement network segregation controls that enforce least-access between trust zones. | ||
Practitioner Guidance
What to prioritise: Start with the assets that are hardest to instrument, because they usually define the minimum viable segmentation model. If OT, IoT, or other unmanaged systems are in scope, agentless coverage often becomes the baseline, not an optional complement.
What to verify: Confirm that the chosen model can enforce the same policy intent across managed and unmanaged zones, and that exceptions are tracked rather than absorbed into permanent waiver lists. If a control cannot be deployed without custom exceptions on day one, treat that as a design signal, not just an implementation inconvenience.
Practitioner takeaway: Prioritise the model that delivers real coverage for the assets you have today, then use agent-based depth to refine control where you can actually operate it safely and at scale.
Related resources from NHI Mgmt Group
- When should teams prioritise agentless coverage over agent-based rollouts?
- Should organisations prioritise agentless CSPM over agent-based deployment for cloud posture?
- Should organisations choose agentless DSPM over agent-based models?
- When should organisations combine agent-based, agentless, host-based, and identity-based microsegmentation?