RADIUS Server: installation guide

A RADIUS server allows you to centralize authentication and authorization of network access, for example for WLAN, VPN or switches. When setting it up, several elements are essential: the choice of a suitable environment, the implementation of secure authentication methods, rigorous user management as well as a stable network configuration.

A RADIUS server is a central service intended forauthentication, authorization and access logging (accounting). To install a RADIUS server, you can use software solutions like FreeRADIUS, which you configure on your own system. Network devices, such as access points or VPN gateways, poll the server each time they connect to see if access is authorized.

Technical prerequisites:

• A Linux or Windows server with an IP address
• RADIUS-compatible network equipment (e.g. access points, routers, switches)
• Access to firewall and network configurations

A RADIUS server must operate reliably, efficiently and stably. When installing the RADIUS server, the choice of hosting environment influences performance, but also scalability, costs and maintenance. Among the most common solutions are VPS and dedicated servers:

• Virtual Private Server (VPS): suitable for small to medium environments, such as an enterprise WLAN, VPN accesses or test environments. A VPS is generally sufficient as long as the authentication volume remains moderate and no high availability is required.
• Dedicated server: Recommended for many concurrent requests, high security requirements, or when high availability and redundancy are required. In sensitive environments or those subject to regulatory obligations, a dedicated server is often the best option for configuring a RADIUS server reliably.

In the following example, we start from a classic Linux environment like Ubuntu or Debian. The basic steps remain similar on other systems.

Step 1: Install a RADIUS Server

Firstly, you must install suitable server software. This provides RADIUS functionality and then processes requests from network equipment. The widely used FreeRADIUS software is particularly popular. It supports common authentication methods as well as connections to directory services like LDAP or Active Directory.

In a Linux environment, for example under Debian or Ubuntu, FreeRADIUS can be installed directly via the package manager:

sudo apt update
sudo apt install freeradius freeradius-utils

After installation, the service is automatically configured and started. The RADIUS service is therefore already active in the background, but it is not yet ready for production use, as essential configurations remain to be defined.

Step 2: Configure the RADIUS server base

After installation, the RADIUS server is started, but it does not yet define which users are allowed, which devices are allowed to send requests or how they should be verified. These elements are defined during basic configuration. With FreeRADIUS, most settings are in text files, editable with an editor like nano, vim or Notepad++. Here are the main points to configure:

• Define customers: network devices authorized to authenticate with the RADIUS server are registered with their IP address and a shared secret.
• Define authentication types: depending on the use case, different mechanisms can be used, for example simple passwords or encrypted methods for WLAN or VPN access.
• Link users or a directory: For testing, users can be created locally. In production, the server is generally connected to a central directory such as LDAP or Active Directory.

Step 3: Configure network devices as RADIUS clients

The devices that should use the RADIUS server are then configured. In most cases these are WLAN access points, switches or VPN gateways.

The following information must be provided:

• RADIUS server IP address: it indicates under which address the server can be reached. Network devices use this address to send authentication requests.
• Port : it defines the network port used for communication with the RADIUS server. By default, UDP 1812 is used for authentication and UDP port 1813 for accounting. Other ports can be configured depending on the environment.
• Shared secret: it is a common secret, configured identically on the RADIUS server and on the network equipment. It helps secure communication and ensures that only authorized devices can send requests.

Step 4: Perform a functional test

Before going into production, a test must be carried out. Here are the most common checks:

• Login with a test account: allows you to verify that the RADIUS server is accessible, that the authentication data is correctly processed and that access is authorized when the identifiers are valid.
• Log analysis: allows you to identify errors or refusals, check the origin of requests and understand why a connection was accepted or refused.
• Test with incorrect identifiers: helps ensure that unauthorized access is properly blocked and that no unexpected behavior occurs.
• Test with different terminals or authentication methods: helps ensure that the RADIUS server operates reliably in different scenarios.

Step 5: Put into production and secure the RADIUS server

After a conclusive test, the RADIUS server can be used in production. The following measures must then be implemented:

• Firewall rules for security: the RADIUS server should not be freely accessible from all networks. Firewall rules define which devices and networks are allowed to communicate with it.
• Encrypted communication: RADIUS uses a shared secret by default, but does not encrypt all exchanges. In production, it is recommended to use encrypted authentication mechanisms, for example EAP variants with TLS.
• Regular system updates: They fix known security vulnerabilities, improve stability, and ensure compatibility with current clients and recent encryption methods.
• Backing up configuration files: Regular backups allow the server to be quickly restored in the event of a breakdown, misconfiguration or system change.

What should you consider when installing a RADIUS server?

A RADIUS server plays a central role in access control. It is therefore essential to plan well and apply fundamental principles from the start.

Define clear authentication and authorization rules

Define precisely who is allowed to log in and what rights are assigned to them. This can range from simple access to a WLAN to differentiated authorizations depending on user groups. The clearer these rules are, the simpler the operation will be to manage and evolve.

Ensure security

Communication between the RADIUS server and network equipment must be secure. Use robust shared secrets and favor modern, encrypted authentication methods. Regular updates to the operating system and RADIUS software are essential to fix known security vulnerabilities.

Manage users

In small environments, local user accounts may be sufficient. In larger infrastructures, it is recommended to connect the server to a central directory such as LDAP or Active Directory. This avoids duplicates and facilitates the management of arrivals and departures.

Enable logging and analysis

Logging and analysis should be enabled from the start. Log files show who logged in, when, and whether there were any failed login attempts. This information is useful for fault diagnosis, but also for security analyzes and compliance requirements.

Guarantee availability

If the RADIUS server goes down, connections may be interrupted. It is therefore important to anticipate redundancy needs, for example with a second RADIUS server or regular backups of the configuration. This improves fault tolerance and facilitates recovery in the event of an incident.