1. Understanding Zero Trust
1.1 What Is Zero Trust?
Zero Trust is a security model based on one core idea:
Never trust, always verify—regardless of network location.
Traditional perimeter-based security assumed that anything inside the corporate network was trusted. Zero Trust rejects this assumption entirely. Every user, device, workload, and application must continuously prove its legitimacy before accessing resources.
Zero Trust is not a product. It is a framework that spans identity, endpoints, networks, applications, and data.
1.2 Core Principles of Zero Trust
Most Zero Trust frameworks (NIST SP 800-207, Google BeyondCorp, etc.) converge on these principles:
- Explicit verification: Authenticate and authorize based on identity, device posture, location, and behavior.
- Least-privilege access: Grant only the minimum access required, scoped by time, role, and context.
- Assume breach: Design controls as if attackers are already inside the environment.
- Continuous assessment: Trust is not static. Access decisions are reevaluated continuously.
1.3 Zero Trust Network Access (ZTNA)
Zero Trust Network Access (ZTNA) is a common entry point into Zero Trust adoption. Instead of exposing networks via VPNs, ZTNA provides:
- Identity-based access to specific applications
- Continuous posture assessment
- Reduced attack surface
ZTNA is one component of Zero Trust—not the entire model.
1.4 Common Misconceptions About Zero Trust
- Misconception 1: Zero Trust replaces NAC
Reality: Zero Trust defines what must be verified; NAC helps enforce how access is granted at the network edge. For a more fundamental look, see our article on What Zero Trust Really Means. - Misconception 2: Zero Trust means no network security
Reality: Networks still matter—but they are no longer the trust boundary. - Misconception 3: Buying a ZTNA product = Zero Trust
Reality: Zero Trust requires coordinated controls across identity, endpoints, policy enforcement, and monitoring.
2. Understanding Network Access Control (NAC)
2.1 What Is NAC?
Network Access Control (NAC) is a security approach that enforces policies on devices attempting to connect to a network.
At its core, NAC answers four questions:
- Who is the user?
- What is the device?
- Is the device compliant?
- What level of access should be granted?
2.2 How NAC Works
A typical NAC deployment includes:
- Authentication (802.1X, MAC auth, captive portals)
- Authorization (role-based or identity-based access)
- Policy enforcement via switches, wireless controllers, and VPN gateways
Platforms like Aruba ClearPass centralize these functions with granular policy engines.
2.3 Key NAC Capabilities
Modern NAC solutions—especially Aruba NAC—offer:
- Identity-based access control: Ties users and devices to roles rather than IP addresses.
- Device posture assessment: Checks OS version, antivirus status, certificates, and compliance.
- IoT onboarding: Automatically profiles and segments unmanaged and headless devices.
- Guest access management: Secure self-registration, sponsorship, and time-bound access.
- Policy enforcement: Dynamic VLANs, ACLs, and segmentation based on real-time context.
2.4 Where NAC Excels
- Controlling access at the network edge
- Managing BYOD and IoT sprawl
- Enforcing compliance before granting connectivity
- Providing visibility into who and what is on the network
2.5 Limitations of NAC
Despite its strengths, NAC has boundaries:
- Enforcement typically stops after initial network access
- Limited visibility into application-layer behavior
- Cannot replace identity providers or application-level authorization
- Complex NAC deployment if network infrastructure is inconsistent
3. Zero Trust vs NAC: A Clear Comparison
3.1 Conceptual Difference
| Aspect | Zero Trust | NAC |
|---|---|---|
| Nature | Security philosophy | Security control |
| Scope | End-to-end architecture | Network access layer |
| Trust Model | Continuous verification | Pre/post-admission checks |
| Focus | Identity, device, app, data | Devices connecting to network |
3.2 Operational Difference
Zero Trust defines security outcomes. NAC provides policy enforcement mechanisms. Think of Zero Trust as the strategy and NAC as one of the tactical tools.
3.3 Where They Overlap
- Identity-based access
- Device posture evaluation
- Policy-driven enforcement
3.4 Where They Complement Each Other
NAC strengthens Zero Trust by:
- Enforcing least privilege before network access
- Segmenting devices dynamically
- Supporting ZTNA by validating device trust
4. Real-World Use Cases
4.1 Enterprise Campus Network
Challenge: Thousands of users, contractors, and IoT devices.
Solution:
- NAC deployment using Aruba ClearPass
- Role-based access and IoT onboarding
- Zero Trust principles applied via least privilege and segmentation
4.2 Hybrid Workforce
Challenge: Employees working from home, office, and public networks.
Solution:
- ZTNA for application access
- NAC for on-prem and VPN entry points
- Unified policy enforcement across environments
4.3 Healthcare or Manufacturing IoT
Challenge: Legacy, unmanaged devices with no agents.
Solution:
- NAC device profiling
- Microsegmentation
- Zero Trust assumption of breach applied at the network layer
5. Deployment Considerations: NAC in a Zero Trust Strategy
5.1 Step-by-Step NAC Deployment (Practical)
Step 1: Visibility First
- Discover all devices (users, endpoints, IoT)
- Classify device types and risk levels
Step 2: Start with Monitor Mode
- Deploy NAC in visibility-only mode
- Avoid disrupting production traffic
Step 3: Define Policy Models
- Identity-based access
- Device posture requirements
- Guest access workflows
Step 4: Gradual Enforcement
- Enforce policies by role, not VLAN sprawl
- Introduce segmentation incrementally
Step 5: Integrate with Identity & Security Stack
- Directory services
- MDM/UEM
- SIEM and SOC workflows
5.2 Zero Trust Alignment Checklist
- Are access decisions identity-driven?
- Is device posture validated continuously?
- Are policies centrally defined and enforced?
- Is segmentation dynamic and context-aware?
6. Risks and Challenges
6.1 Common Pitfalls
- Treating NAC as a “set and forget” tool
- Over-enforcing policies too quickly
- Ignoring unmanaged and IoT devices
- Confusing Zero Trust marketing with actual architecture
6.2 Organizational Challenges
- Skill gaps in NAC deployment
- Resistance from network teams
- Poor documentation of access requirements
7. Best Practices
- Adopt Zero Trust incrementally, not as a big-bang project
- Use NAC as a policy enforcement engine, not just an access gate
- Prioritize identity-based access over network location
- Design policies around business roles, not infrastructure limitations
- Continuously audit and refine policies
Final Recommendation
Zero Trust and NAC are not rivals—they are interdependent.
If Zero Trust defines who should access what, under which conditions, NAC enforces those decisions at one of the most critical control points: the network edge. Aruba NAC solutions such as Aruba ClearPass demonstrate how modern NAC can support Zero Trust outcomes through identity-based access, posture assessment, IoT onboarding, and dynamic policy enforcement.
For enterprises serious about Zero Trust, NAC is not optional—it is foundational.
Key Takeaway: Zero Trust is the destination. NAC is one of the most reliable vehicles to get there—when deployed thoughtfully and aligned with identity-driven security principles.