As modern networks scale to support an ever-growing number of users, devices, and services, the need for robust and reliable RADIUS servers becomes critical. From ISPs and enterprise Wi-Fi providers to corporate VPNs and cloud services, RADIUS servers underpin essential authentication, authorization, and accounting (AAA) infrastructure. To ensure these servers meet high standards of performance and reliability, rigorous testing is non-negotiable. That's where Penzzer shines.

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Introduction to RADIUS Protocols and Their Importance

Remote Authentication Dial-In User Service (RADIUS) is a client-server protocol that provides centralized authentication, authorization, and accounting (AAA) management for users who connect to and use network services. The protocol is detailed in several RFCs that define its specifications, behaviors, and extensibility mechanisms.

RADIUS operates over UDP and uses port 1812 for authentication and authorization, and port 1813 for accounting. Its design is lightweight yet powerful, making it ideal for environments with high authentication request rates. RADIUS is employed across many applications, including ISP access services, Wi-Fi authentication, VPNs, and enterprise-level remote access solutions.

The protocol's behavior and expectations are standardized across multiple documents:

• RFC 2865: Defines the base RADIUS protocol.
• RFC 2989: Establishes the criteria for evaluating AAA protocols and systems.
• RFC 3579: Specifies the usage of EAP (Extensible Authentication Protocol) with RADIUS.
• RFC 5176: Describes the Dynamic Authorization Extensions including CoA (Change of Authorization) and Disconnect Messages.

Understanding these RFCs is essential for anyone looking to implement or test RADIUS servers, especially when validating security, scalability, and compliance requirements.

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Using Penzzer as a RADIUS Test Client

Penzzer is an advanced RADIUS test client designed to simulate, debug, and monitor RADIUS and NAS interactions. Its flexible configuration and powerful scripting capabilities allow users to:

• Generate RADIUS Access-Request, Accounting-Request, CoA-Request, and Disconnect-Request messages.
• Customize packet attributes for authentication, authorization, and accounting.
• Simulate high-throughput environments with millions of virtual clients.
• Monitor server responses and analyze timing, response codes, and attribute handling.

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Authentication Testing (RFC 2865)

Penzzer can validate a server's compliance with RFC 2865 by generating Access-Request packets with various combinations of required attributes, including:

• User-Name
• User-Password (encrypted using shared secret and MD5 as per RFC 2865)
• NAS-IP-Address
• NAS-Port
• Service-Type

For each request, the server must respond with one of:

• Access-Accept
• Access-Reject
• Access-Challenge

Penzzer supports response validation and can automate sequences to test authentication retries, incorrect password handling, and attribute-based access controls.

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Example Test Case: Credential Variance

You can use Penzzer to send Access-Requests with different username/password combinations to test how the RADIUS server manages common attack patterns such as:

• Username enumeration
• Weak password detection
• Lockout policies

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Authorization Scenarios

Authorization decisions in RADIUS are often policy-driven, based on attributes included in Access-Request or returned in Access-Accept packets. Penzzer allows detailed customization of both request and response attribute sets to test scenarios such as:

• VLAN assignment via Tunnel-Type, Tunnel-Medium-Type, and Tunnel-Private-Group-ID.
• QoS settings through Vendor-Specific Attributes (VSAs).
• Role-based access control through Filter-Id and Class attributes.

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Advanced Use Case: Multi-Role Mapping

By scripting multiple roles and attributes for different simulated users, Penzzer allows for testing access controls for scenarios like guest access vs employee access vs contractor access.

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Accounting Validation (RFC 2866)

Accounting operations are validated using the Accounting-Request packet type, with Acct-Status-Type indicating the accounting stage:

• Start
• Stop
• Interim-Update

Penzzer can track session identifiers, counters (e.g., Acct-Input-Octets, Acct-Output-Octets), and simulate usage over time. This is essential for testing billing systems and usage logs.

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Simulated Time Progression

By simulating long session durations with increasing usage counters, engineers can test rollover behaviors, database truncation, and large-volume traffic accounting.

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EAP Testing (RFC 3579)

When EAP is encapsulated in RADIUS, it allows for flexible and secure authentication mechanisms, including:

• EAP-TLS: Client certificate-based authentication
• EAP-TTLS/PEAP: Tunnelled authentication supporting legacy credential types

Penzzer can craft RADIUS packets with EAP-Message attributes, simulate handshake stages, and validate server-side processing logic and error handling.

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EAP Handshake Debugging

Advanced users can inspect per-stage EAP exchanges, test timeout handling, simulate corrupted EAP messages, and validate server fallbacks for incomplete handshakes.

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Dynamic Authorization (RFC 5176)

Dynamic Authorization allows real-time control over user sessions. Penzzer can send:

• CoA-Request: To change session parameters like VLAN or bandwidth.
• Disconnect-Request: To forcefully terminate a user session.

These messages test the server's ability to map sessions and enforce changes without breaking active connections.

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Simulated Policy Shift

Using Penzzer's dynamic session table, you can simulate a scenario where a user exceeds a data cap and receives a CoA that moves them to a throttled profile.

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Load Testing and Performance Benchmarking

Scalability is a core requirement for AAA systems. RFC 2989 emphasizes the ability to handle thousands of concurrent requests and millions of users. Penzzer's session engine can generate such load scenarios, simulating various NAS behaviors with configurable delays, jitter, and parallel execution.

Metrics collected during these tests include:

• Request rate (requests per second)
• Response latency (min/avg/max)
• Error rate (timeouts, rejects)
• Server CPU and memory utilization (when integrated with monitoring tools)

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Stateful Session Management

One of Penzzer's differentiators is its ability to maintain state across sessions. This allows for:

• Proper sequencing of authentication, authorization, accounting, and dynamic authorization.
• Simulation of session expiration, idle timeouts, and re-authentication cycles.
• Verification of session identifiers and correlation between different RADIUS request types.

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Fuzzing and Protocol Robustness

Penzzer also supports fuzzing techniques to test protocol robustness:

• Inject malformed attributes (e.g., incorrect lengths, unknown types)
• Randomize attribute order
• Send unexpected combinations of mandatory and optional attributes

This uncovers edge-case bugs, security flaws, and protocol handling issues not visible during standard testing.

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Real-World Testing Scenarios

Penzzer enables replication of real-world conditions, such as:

• Simultaneous multi-user logins from various NAS IPs
• Failover testing by simulating primary/secondary RADIUS server behavior
• Policy update simulation during active sessions

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Disaster Recovery and High Availability

Engineers can test failover to secondary RADIUS servers and validate session continuation, accounting resumption, and policy enforcement during outages.

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Integration with CI/CD Pipelines

For DevOps and continuous delivery environments, Penzzer can be integrated into CI/CD pipelines. This ensures:

• Regression testing after RADIUS server updates
• Continuous validation of authentication policy logic
• Automated security checks for new configurations

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Monitoring and Debugging

Penzzer provides detailed logs and packet traces for every request/response interaction. These are essential for:

• Analyzing server behavior
• Correlating RADIUS events with logs from NAS devices
• Debugging authentication failures and accounting mismatches

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Vendor-Specific Extensions and Compatibility Testing

Many RADIUS implementations include Vendor-Specific Attributes (VSAs). Penzzer supports:

• Dynamic attribute dictionaries
• VSA injection and parsing
• Compatibility checks against devices from Cisco, Juniper, Aruba, etc.

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