How Does RADIUS Work?

As organizations move toward cloud-based, hybrid, and remote environments, managing secure network access has become more complex. At the core of this challenge is RADIUS (Remote Authentication Dial-In User Service), a protocol that has quietly enabled secure authentication and policy enforcement for decades.

In this article, we’ll explain how RADIUS works, what makes it indispensable for modern access control, and how cloud-native platforms like Portnox Cloud are redefining its capabilities for the zero trust era.

Portnox, a recognized leader in cloud-native NAC, RADIUS, and ZTNA, helps enterprises simplify authentication, automate device posture enforcement, and unify access control across all environments.

What Is RADIUS?

RADIUS is a network protocol responsible for authentication, authorization, and accounting (AAA), which is the foundation of access control in enterprise environments. It ensures that only verified users and devices can connect to the network, defines what resources they can access, and tracks their activity for auditing and compliance.

It plays a central role in securing wired, wireless, and VPN access, acting as the policy enforcer that validates identity and applies permissions before a session begins.

RADIUS and 802.1X Authentication

RADIUS operates closely with the 802.1X standard, which governs secure network access for Ethernet and Wi-Fi. Through 802.1X, RADIUS confirms user or device identity before granting access, a key principle in zero trust Network Access (ZTNA) architectures.

Common Authentication Methods

RADIUS supports several Extensible Authentication Protocol (EAP) methods, such as:

• EAP-TLS (Transport Layer Security): Uses digital certificates on both the client and server to enable mutual authentication and eliminate password reliance.
• PEAP (Protected EAP): Establishes a TLS tunnel before validating credentials like usernames and passwords.

Both methods strengthen authentication and reduce the risks of credential theft, man-in-the-middle attacks, and unauthorized access.

Centralized Access Control

RADIUS centralizes authentication and policy management, ensuring consistent security enforcement across all network entry points. It integrates with existing directory services and identity providers (IdPs), reducing administrative overhead while maintaining compliance visibility.

How RADIUS Works

At a high level, RADIUS sits between the user or device requesting access and the network infrastructure granting it. The process is policy-driven, ensuring that every connection aligns with organizational security standards.

1. Authentication Request

When a user or device connects to the network via a switch, wireless controller, or VPN, the Network Access Server (NAS) sends an authentication request to the RADIUS server. This request includes credentials or certificate data, depending on the authentication method in use.

The RADIUS server then validates the request against a centralized identity source such as Google Workspace, Microsoft Entra ID, or Okta, confirming that the user is who they claim to be.

2. Authorization and Policy Enforcement

Once the identity is verified, the RADIUS server applies predefined authorization policies that determine network permissions. These policies may assign users to specific VLANs, restrict access to sensitive systems, or enforce compliance checks such as device posture validation.

By managing these rules centrally, organizations can enforce least-privilege access consistently across all network segments.

3. Accounting and Auditing

RADIUS also handles accounting, which records session details like connection time, data usage, and device identity. These logs provide valuable insights for auditing, compliance, and forensic analysis.

This feature allows IT and security teams to maintain visibility into every network connection, supporting both operational oversight and regulatory reporting.

4. Certificate-Based Authentication for Passwordless Access

Modern RADIUS implementations, particularly those using EAP-TLS, enable certificate-based authentication that replaces traditional passwords with digital certificates. This approach not only prevents credential theft but also simplifies user onboarding and access management, aligning with zero trust principles of continuous verification.

RADIUS Components

A functioning RADIUS environment relies on three primary components that work together to deliver authentication and policy enforcement:

• RADIUS Client (NAS): The device, such as a switch or wireless access point, that forwards access requests to the RADIUS server.
• RADIUS Server: The core system that processes requests, applies access policies, and logs session details.
• User Directory or Identity Database: A repository (often Okta, Google Workspace, or Entra ID) that stores user credentials, certificates, and group information.

Communication between the client and server typically occurs via UDP ports 1812 (authentication) and 1813 (accounting), with encrypted data to prevent interception. 

Enterprise-grade RADIUS setups include redundancy and high availability to maintain continuous authentication. Cloud-native solutions like Portnox Cloud also offer scalability and elasticity, automatically adjusting to meet fluctuating authentication demands without additional infrastructure.

Why Enterprises Use RADIUS

RADIUS continues to serve as the backbone of enterprise network security due to its combination of security, control, and scalability.

Enhanced Security and Compliance

By consolidating authentication under one protocol, RADIUS reduces password reuse, centralizes credential management, and enforces consistent access controls.

It integrates seamlessly with multi-factor authentication (MFA) and certificate-based access, supporting phishing-resistant authentication that aligns with zero trust objectives.

The detailed accounting logs generated by RADIUS simplify compliance reporting under standards such as HIPAA, PCI DSS, ISO 27001, and NIST 800-53, providing auditable proof of access control across the enterprise.

Operational Efficiency

Centralized RADIUS management allows IT teams to apply or update policies once, with immediate effect across all access points, devices, and users. This reduces manual configuration, minimizes errors, and improves scalability for large or distributed networks.

With cloud-delivered RADIUS, deployment takes minutes instead of weeks, removing the need for on-premises hardware, VPN tunnels, or software agents. 

Portnox’s agentless model significantly lowers maintenance costs while extending secure access to BYOD and IoT environments, where unmanaged devices must still adhere to corporate security policies.

RADIUS Compared to Other Authentication Protocols

Although RADIUS is a cornerstone of network authentication, it often coexists with other AAA and directory protocols, each serving a specific purpose.

RADIUS vs. TACACS+

Both RADIUS and TACACS+ provide AAA functions, but they differ in scope and structure. 

TACACS+ separates authentication, authorization, and accounting into distinct processes, making it ideal for network device administration. RADIUS, by contrast, combines these functions to control end-user access to network resources.

While TACACS+ offers granular administrative control, RADIUS provides a unified framework for enforcing user and device authentication across wireless, wired, and VPN connections.

RADIUS and Directory Services (LDAP / Active Directory)

LDAP and Active Directory manage user identities and credentials, while RADIUS serves as the enforcement layer that verifies those credentials during network access attempts. Together, they form a complementary system; LDAP provides the “who,” and RADIUS determines the “how” and “when” of network access.

This integration ensures that access control policies are enforced consistently, regardless of location or device type.

Legacy Appliances vs. Cloud-Native RADIUS

Traditional RADIUS implementations such as Cisco ISE, Aruba ClearPass, and Forescout deliver powerful functionality but rely on hardware appliances, complex configurations, and extensive IT expertise.

These systems often require constant patching and high ongoing costs to maintain performance and security.

Portnox Cloud RADIUS modernizes this experience through a cloud-native, agentless model. It delivers the same AAA functionality but without the operational burden.

Organizations benefit from faster deployment, automatic updates, and elastic scalability, all while maintaining compliance and Zero Trust enforcement across distributed workforces.

Conclusion

RADIUS remains a cornerstone of secure access control. It authenticates users and devices, applies least-privilege policies, and provides the visibility needed for compliance and zero trust readiness.

By reengineering RADIUS for the cloud era, Portnox Cloud delivers the same reliability and rigor through a simple, scalable SaaS model. It allows enterprises to enforce access control, integrate seamlessly with identity providers, and maintain secure access across hybrid networks — without the complexity of traditional deployments.

Explore how Portnox brings RADIUS, NAC, and ZTNA together in one unified platform.

Request a Demo to see how Portnox Cloud simplifies authentication, authorization, and compliance across every network connection.