Network Segmentation

To meet the network segmentation requirement, you must separate clinical systems, medical devices, and PHI repositories from general corporate traffic using enforceable technical boundaries (VLANs/VRFs, firewalls/ACLs, and tightly controlled pathways). Your goal is to reduce lateral movement by default, document the segmentation design, and continuously prove that only approved flows exist ¹.

Key takeaways:

• Segment by function and risk: clinical/PHI/device networks must not share flat connectivity with user and guest networks ¹.
• “Segmentation” means enforced controls plus validated allow-lists, not a diagram or a naming convention.
• Evidence matters: auditors expect configs, network flow justifications, and ongoing verification records, not intent statements.

Network segmentation is one of the fastest ways to reduce blast radius after a compromise, especially in environments where legacy clinical systems and medical devices cannot be patched quickly. HICP Practice 5.1 requires that you isolate clinical systems, medical devices, and PHI repositories from general network traffic ¹. For a CCO, GRC lead, or security compliance owner, the practical challenge is turning that sentence into boundaries that an auditor can test and an operator can maintain.

Operationalizing segmentation means you define “zones,” decide which systems belong in each zone, and implement enforced controls between zones with explicit, documented allow-lists for required clinical workflows. You also need a repeatable method to prove the segmentation remains intact over time, despite network changes, mergers, and third-party connectivity.

This page gives requirement-level guidance: what the requirement means in plain English, who it applies to, exactly what to build, what evidence to retain, where audits get stuck, and a practical execution plan you can run with your network and security teams.

Regulatory text

Requirement (HICP Practice 5.1): “Implement network segmentation to isolate clinical systems, medical devices, and PHI repositories from general network traffic.” ¹

Operator interpretation:
You must build and enforce technical separation so that:

• End-user, guest, and general corporate devices cannot directly reach clinical systems, medical devices, or PHI data stores.
• Connectivity into sensitive zones exists only through controlled choke points (firewalls, ACLs, microsegmentation policy engines) with documented, least-privilege rules.
• Segmentation is maintained as the environment changes, and you can demonstrate the control works ¹.

Plain-English requirement interpretation (what “counts”)

Segmentation “counts” when an independent tester (internal audit, assessor, or security engineer) can verify that:

• Assets in a clinical/PHI/device zone cannot initiate or receive arbitrary connections from the general network.
• Only approved protocols, ports, and source/destination pairs are permitted, and each allowed path has a business/clinical justification.
• Administrative access is controlled and ideally routed through hardened management paths (jump hosts, management VLANs, or dedicated admin tooling).

A segmentation diagram is necessary, but not sufficient. Auditors and incident responders care about enforceable boundaries and proof.

Who it applies to

Entity types: Healthcare organizations and Health IT vendors ¹.

Operational contexts where this becomes urgent:

• Hospitals and clinics with mixed IT/OT and shared switching infrastructure.
• Environments with medical devices that require broad network reachability by default.
• EHR and ancillary systems (lab, radiology, pharmacy) with multiple inbound/outbound integrations.
• Hosted platforms where PHI repositories exist in cloud VPCs/VNETs and need separation from general workloads and developer networks.
• Third-party connections (billing, telehealth, device manufacturers) that terminate “somewhere” on your network and often become accidental bridges.

What you actually need to do (step-by-step)

1) Define the segmentation objective and scope

Start with a written statement that maps directly to HICP 5.1: isolate clinical systems, medical devices, and PHI repositories from general traffic ¹.
Then define what “general network” means for your organization (typical buckets: user LAN, guest Wi‑Fi, shared services, printing, building management, dev/test).

2) Build an asset-to-zone inventory (minimum viable)

You cannot segment what you cannot place.

• Identify systems that store/process/transmit PHI (databases, file shares, EHR app tiers, imaging archives).
• Identify clinical systems (EHR front ends, clinical workstations, nurse station endpoints, lab systems).
• Identify medical devices (infusion pumps, imaging devices, patient monitoring, lab analyzers).
• Tag each asset with an owner, location, IP range, and required dependencies.

Practical shortcut: if inventory is incomplete, start with IP ranges and switch ports for known clinical/device areas, then refine.

3) Design zones and trust boundaries

Create zones that match how traffic should (and should not) flow. Common starting zones:

• User/Corporate zone: laptops, general desktops, standard collaboration tools.
• Clinical workstation zone: endpoints used for patient care workflows.
• Medical device zone: IoMT/medical devices, often high risk due to patch constraints.
• PHI data zone: databases, storage, EHR back-end, imaging archives.
• Management zone: admin interfaces, hypervisor mgmt, network device mgmt.
• Third-party access zone (optional but common): vendor VPN termination, partner links, B2B integrations.

Document for each zone:

• Allowed inbound/outbound dependencies (e.g., device → device management server; clinical app → database).
• Prohibited paths (e.g., guest Wi‑Fi → PHI zone).

4) Implement enforced controls between zones

Pick controls that your environment can support, but insist on enforcement:

• Network segmentation: VLAN/VRF separation plus firewalling between segments.
• Security boundaries: next-gen firewall policy, internal segmentation firewalls, ACLs on L3 switches.
• Cloud segmentation: separate VPCs/VNETs, security groups/NSGs, route tables, private endpoints.
• Microsegmentation (optional): host-based policy for east-west control where network redesign is hard.

Minimum expectation for auditors: there is a policy enforcement point between general network traffic and the clinical/device/PHI zones, with explicit rules.

5) Convert workflows into allow-lists (and kill implicit access)

This is where most segmentation efforts stall.

• Gather required flows from app owners and clinical engineering (source, destination, protocol/port, direction, purpose).
• Implement rules as deny-by-default between zones, then add only what’s justified.
• Treat “any/any inside the hospital” as a finding, even if “temporary.”

If you lack flow visibility, deploy passive monitoring (NetFlow/sFlow, firewall logs) to observe traffic before tightening.

6) Add controls for remote access and third-party connectivity

Third-party access often bypasses segmentation if VPN users land in a broad subnet.

• Terminate third-party VPNs into a restricted zone.
• Require jump-host access into sensitive zones rather than direct RDP/SSH from the VPN pool.
• Restrict third-party routes to named systems and ports only.
• Ensure device manufacturer access cannot pivot into PHI repositories.

7) Validate segmentation (prove it works)

Validation must be testable and repeatable:

• Attempt connections from corporate/user networks into clinical/device/PHI subnets and confirm blocks.
• Confirm only documented allow-list flows succeed.
• Run periodic internal scans that verify segmentation boundaries (scope carefully around medical devices).

Capture results and remediation actions. This is often the difference between “designed” and “implemented.”

8) Operationalize change control

Segmentation breaks through exceptions.

• Require tickets for new firewall rules with business justification, owner approval, and expiration/review criteria.
• Keep diagrams and IPAM updated as part of network change procedures.
• Review “temporary” rules on a schedule and remove them.

Tooling note: teams often use systems like Daydream to centralize evidence collection (diagrams, rule reviews, approvals, test results) so audits do not turn into a scavenger hunt.

Required evidence and artifacts to retain

Auditors typically want objective proof across design, implementation, and operation:

• Network segmentation architecture diagram(s) showing zones and enforcement points.
• IP range/VLAN/VRF mapping per zone and asset category (clinical, device, PHI, general).
• Firewall/ACL policy exports (or screenshots plus change identifiers) that show deny/allow logic between zones.
• Allow-list register: for each permitted path, include source, destination, port/protocol, purpose, data sensitivity, system owner approval.
• Third-party access documentation: VPN termination design, permitted routes, jump host requirements, access reviews.
• Validation/test records: segmentation tests, attempted access results, issues opened/closed.
• Change control records: tickets/approvals for rule changes, exception justifications, reviews of temporary rules.

Common exam/audit questions and hangups

Expect these questions, and prepare evidence ahead of time:

1. “Show me how PHI repositories are isolated from general traffic.”
   They will want to see enforcement, not intent: firewall rules, routing, and proof of denied access.

2. “How do you classify ‘clinical systems’ and ‘medical devices’?”
   If definitions are fuzzy, you will struggle to demonstrate coverage. Maintain a category list and ownership.

3. “Where do third parties land on your network?”
   If the answer is “the same VPN pool as employees,” expect pushback.

4. “How do you ensure segmentation stays intact after changes?”
   Have a change process and periodic validation records.

5. “What exceptions exist, and who approved them?”
   Undocumented exceptions can become audit findings even when risk is understood operationally.

Frequent implementation mistakes (and how to avoid them)

• Mistake: VLANs without enforcement.
  VLAN separation alone often fails if routing permits broad inter-VLAN access. Put firewall/ACL policy between zones and test it.

• Mistake: Allow-lists built from guesses.
  Use actual flow logs and application owner sign-off. Otherwise you either break care delivery or allow too much.

• Mistake: “Temporary” any/any rules that never expire.
  Put expirations and periodic review on exception rules. Treat stale exceptions as high priority.

• Mistake: Medical device networks bridged to corporate for convenience.
  Provide controlled management access paths instead (management zone + jump host) so clinicians and biomedical teams can operate without flat connectivity.

• Mistake: Third-party connectivity designed outside governance.
  Force third-party network access through the same segmentation and approval process as internal access.

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this requirement, so this page does not list specific case examples. The risk logic behind HICP 5.1 is explicit: segmentation limits lateral movement if an endpoint, device, or server is compromised ¹. For healthcare environments, lateral movement risk is amplified by shared subnets, unmanaged devices, and legacy protocols common in clinical workflows.

A practical 30/60/90-day execution plan

First 30 days: establish scope, zones, and quick wins

• Confirm scope: identify PHI repositories, clinical system subnets, and known medical device ranges.
• Publish a zone model and a target network diagram with enforcement points.
• Implement immediate containment where feasible: block obvious risky paths (guest to anything sensitive; corporate to device VLANs unless required).
• Start collecting flow logs for clinical/device/PHI zones to inform allow-lists.
• Stand up an evidence folder structure (or Daydream workspace) for diagrams, configs, and approvals.

Days 31–60: enforce boundaries and document allow-lists

• Place firewall/ACL controls between general traffic and sensitive zones.
• Convert observed/required flows into documented allow-list entries with system owner approvals.
• Rework third-party VPN termination and routing so third parties reach only approved targets.
• Add a change process for new rules, including justification and review criteria.
• Run initial validation tests and log results with remediation tickets.

Days 61–90: validate, harden, and operationalize

• Tighten policies toward deny-by-default between zones, leaving only justified flows.
• Create recurring reviews for firewall rules and exceptions.
• Expand segmentation to management interfaces and admin paths.
• Perform a second validation cycle to confirm stability after changes.
• Prepare an audit-ready packet: diagrams, rule exports, allow-list register, test evidence, and exception log mapped to HICP 5.1 ¹.

Frequently Asked Questions

What is the minimum segmentation that will satisfy the network segmentation requirement?

You need enforceable separation between general network traffic and clinical systems, medical devices, and PHI repositories, with controlled pathways and documented allow-lists ¹. A diagram alone is not enough without policy enforcement and proof.

Do VLANs alone meet the network segmentation requirement?

VLANs help organize networks, but they do not automatically restrict traffic. Auditors typically expect firewall/ACL enforcement and validation that general traffic cannot freely reach clinical/device/PHI segments.

How do we handle medical devices that “need” broad network access?

Start by documenting required device communications, then enforce only those flows. Add a dedicated management path (management zone and jump host) so support teams can operate without opening general access.

How should third-party VPN access be segmented?

Terminate third-party access into a restricted zone and route only to approved systems and ports. Avoid placing third parties on the same broad network segments as employees or clinical endpoints.

How do we prove segmentation works to an auditor?

Retain firewall/ACL configs, routing evidence, an allow-list register with approvals, and validation test results showing blocked and permitted paths. Keep change tickets for rule changes and exception approvals.

We’re mid-merger with multiple sites. What’s a practical approach?

Use a zone model that applies across sites, then prioritize isolating PHI repositories and device networks at each location first. Document site-specific exceptions and put them under the same review and validation process.

Footnotes

1. HICP 2023 - 405(d) Health Industry Cybersecurity Practices