Zero Trust: Not a Product, but an Architecture of Processes and Behaviors

Zero Trust is a concept mentioned in almost every security presentation today. However, when we look at its implementation in the field, we often see it applied in the wrong place, with wrong expectations, and using the wrong tools. The main reason for this is that Zero Trust is positioned as a technology or a purchasable product. In reality, Zero Trust is not a licensed, boxed, or vendor-specific solution. It is an architectural perspective and, more importantly, a mindset.

The essence of Zero Trust is very clear: Never trust, always verify. Never grant default trust to any user, device, or connection. Trust must be continuously earned. This approach completely eliminates the traditional assumption of “inside is safe, outside is dangerous” because, in the modern IT world, the boundaries between inside and outside are no longer clear.

In summary:

  • Zero Trust is not a product but an architectural approach
  • It rejects the concept of default trust
  • Continuous verification is fundamental

Zero Trust initially became visible in practice through the visions of security vendors. As network security evolved with application awareness, user-based policies, and context awareness, the concept gained clarity. However, it is important to make a distinction: Zero Trust is not a concept “owned” by any vendor. While framed by analysts like Gartner, it cannot be represented by a single technology.

The reason is that Zero Trust requires multiple layers to work together consistently. If network, security, identity, user, device, and application layers operate independently, Zero Trust remains only a slogan with no architectural reality.

Key points of this section:

  • Zero Trust is not vendor-specific
  • It cannot be implemented with a single technology
  • Consistency across layers is required

In practice, Zero Trust architecture starts with a simple question:
“Should this user and this device really access the resource they are requesting right now?”

The first step to answer this meaningfully is verifying users and devices on the network. In offices, campuses, or factories, this verification is usually performed through identity systems. Active Directory, LDAP, or modern identity providers sit at the core of this process. In addition, what resources a user can access is determined not only by their identity but also by their role and risk level. Access is always limited based on need and security posture. But for Zero Trust, it’s not only about who the user is; the device’s status, whether it belongs to corporate inventory, and compliance with security policies also matter.

Even if the user is correct, if the device is not compliant, access is re-evaluated. This fundamentally changes the traditional “if the user is inside, it’s fine” approach.

Remember:

  • User verification alone is not enough
  • Device identity and status are also evaluated
  • Access decisions are context-aware

Zero Trust becomes even more important for users working remotely. Remote work is no longer an exception but the standard. However, many organizations still operate under the classic VPN model: the user connects to the VPN and instantly becomes part of the entire local network. This is not Zero Trust; it is only remote access.

Core Network Overview

In Zero Trust, remote access does not mean “access everywhere.” The user can only reach authorized applications or resources. SSL VPNs, client-based VPNs, or application-level access solutions come into play here. Some setups use micro-tunnels similar to personal VPNs that only allow access to specific resources. The goal is always the same: minimize access and maintain continuous control.

Key points:

  • VPN ≠ Zero Trust
  • Access should be resource-specific, not network-wide
  • Permissions are continuously verified

Another key difference between Zero Trust and traditional security is that verification is not a one-time event. A user may log in in the morning, but this does not mean they have unrestricted access all day. In Zero Trust, verification is continuous, and access is re-evaluated as user and device behavior changes. For example, if an anomaly is detected on a device, the user’s location changes, or suspicious activity is observed, the system may automatically request additional verification.

This is where Multi-Factor Authentication (MFA) comes into play. After username and password verification, additional layers such as SMS, mobile app notification, hardware tokens, or biometrics are used. Some organizations intentionally increase verification frequency, especially for critical systems like mail servers, financial systems, or ERPs, where users must re-authenticate periodically.

Summary:

  • Verification is continuous
  • MFA is a core component of Zero Trust
  • Periods are shortened for critical resources

The firewall layer plays a central role in Zero Trust architecture, but it is much more than a traditional “internet exit control” device. In Zero Trust, the firewall is a decision point aware of identity and context. Integration with identity systems, NAC solutions, and 802.1X is critical. Firewall rules should not be only IP or port-based. When user, group, and application-based rules can be applied, Zero Trust becomes practical. The value is knowing which user accesses which application under which conditions.

Summary of this layer:

  • Firewall is a policy decision point
  • Identity and application awareness is required
  • Port-based rules alone are insufficient

Zero Trust does not only apply at firewall or VPN layers. The architecture starts at the access layer. Initial verification in wired and wireless networks determines the security of the entire system. Traditionally, switch ports are assigned to static VLANs and multiple SSIDs are created. As the number of users and devices grows, this structure becomes unmanageable.

802.1X and NAC solutions control all switch ports and wireless access centrally. Users and devices are verified before connecting to the network, and based on this verification, VLANs or policies are dynamically applied. Verification and policy are applied not only at the port or SSID level but also at the user and application level. This ensures that different users on the same network infrastructure have different access rights and critical resources remain isolated.

Key points:

  • Zero Trust starts at the access layer
  • 802.1X provides central control
  • Static VLAN / SSID structures are not scalable

In modern Zero Trust, not only user devices but all endpoints are controlled. Printers, cameras, IP phones, card readers, and other devices are included in verification. Next-generation NAC solutions profile devices using multiple parameters such as DHCP fingerprint, CDP/LLDP, and vendor information. Device profiling is not limited to identity; device compliance, security status, and corporate standards are also evaluated. This prevents unauthorized or risky devices from connecting.

Key points:

  • Device profiling is critical
  • MAC address alone is insufficient
  • Inventory integration is required

Guest access is also controlled in Zero Trust. Through guest portals, visitors are verified and granted access only for limited times and permissions. Guests typically have internet-only access, and access to corporate resources is restricted. This physically enforces Zero Trust’s principle of “no one accesses everything.”

Key points:

  • Guest access is not unlimited
  • Time and permission-based control is applied
  • Trust is not assumed

Ultimately, Zero Trust is a layered architecture. Verification occurs at network entry, traffic and access are controlled via firewalls based on user and application, and additional layers like MFA are applied at the application level. When these layers work together, Zero Trust is truly realized. Success depends on consistent verification at all layers, not on a single point of control.

Key takeaways:

  • Zero Trust is layered
  • A single control point is insufficient
  • The process is continuous

Access and behaviors are monitored at every layer. If an abnormal or risky activity is detected, the system automatically restricts access or requests additional verification. This continuous observation is the most critical part of Zero Trust.

Conclusion

Zero Trust is not a product.
It cannot be established with a single device.
It cannot be implemented with a “set it and forget it” approach.

Zero Trust is a living architecture where firewalls, switches, and wireless infrastructure work together using centralized user and device information, and access is continuously re-evaluated at every stage. Therefore, Zero Trust should be seen not as a technology to purchase but as a capability to design and operate.

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This article was originally introduced on Substack in a shorter, narrative form. This version expands the architectural foundation for the series.

👉 Read the article on Substack: [Click Here](https://substack.com/home/post/p-183954997