Remote Authentication Dial-In User Service (RADIUS) is a network protocol that provides centralized authentication, authorization, and accounting (AAA) for users accessing network services. RADIUS is widely used by Internet Service Providers (ISPs), large organizations, and academic institutions for managing access to network resources. In this article, we will focus on configuring and managing a RADIUS server on the CentOS operating system, which is a popular choice for many server applications due to its stability and extensive support.

Installation and Basic Configuration

First, it is necessary to install the RADIUS server. On CentOS, the most common choice is FreeRADIUS, which is open-source software providing full support for the RADIUS protocol. You can install FreeRADIUS using the following command in the terminal:

sudo yum install freeradius freeradius-utils

After installation, it is important to perform the basic configuration of the server. FreeRADIUS configuration files are located in the directory /etc/raddb/. The main configuration file is radiusd.conf, which contains basic server settings, including logging, modules, and security settings.

Client Configuration

To communicate with the RADIUS server, it is necessary to define clients, which are devices that will request user authentication and authorization. Information about clients is configured in the file /etc/raddb/clients.conf. Each client is defined by a block with the following parameters:

• client with the IP address or domain name of the client.
• secret with a secret key for securing communication.
• nas_type specifying the type of Network Access Server.

Configuration of Authentication and Authorization Modules

FreeRADIUS supports various authentication and authorization methods that can be configured according to the network's needs. Common modules include pam, LDAP, sql, and others. Configuration of these modules is done in files located in /etc/raddb/mods-enabled/.

For connecting to an LDAP server and using it for authentication and authorization, it is necessary to modify the ldap file in /etc/raddb/mods-available/ and then enable it by creating a symlink in /etc/raddb/mods-enabled/.

Accounting Configuration

Accounting is an important part of the RADIUS protocol, allowing tracking of users' usage of network services. Accounting configuration is done in the file /etc/raddb/sites-available/default and /etc/raddb/sites-available/inner-tunnel, where various accounting methods can be configured, including details of user session records.

Securing the RADIUS Server

Security is a crucial aspect of RADIUS server management. Due to the sensitivity of information processed by the RADIUS server, careful security settings are necessary. Basic security measures include strong encryption of communication, careful management of access rights, and regular software updates.

Encryption of Communication

To secure communication between the RADIUS server and clients, it is recommended to use the Transport Layer Security (TLS) protocol. TLS configuration requires the creation of certificates for both the server and clients. Certificates can be generated using openssl or obtained from an accredited Certification Authority. TLS settings are specified in the file /etc/raddb/mods-available/eap, where various EAP methods including PEAP and TTLS, utilizing TLS, can be configured.

Management of Access Rights

Access rights should be assigned on the principle of least privilege. User accounts used for managing the RADIUS server should have limited access only to necessary functions and files. This limitation can be implemented through Linux user roles and groups, as well as through careful configuration of network firewall rules to prevent unauthorized access to RADIUS services.

Regular Software Updates

Keeping software up to date is crucial for the security of any system. Regular updates include not only the FreeRADIUS package but also the CentOS operating system and all its dependencies. Updates may contain security patches addressing known vulnerabilities. Updates to CentOS and FreeRADIUS can be performed using the yum update command.

 

Managing a RADIUS server on CentOS requires attention to detail and a good understanding of network principles and security. With proper configuration and adherence to best practices, a RADIUS server can provide a robust solution for authentication, authorization, and accounting of network services. It is important to regularly monitor system logs, perform security audits, and test backup and restoration procedures to ensure service continuity and data protection.

In a world of constantly evolving cyber threats, it is also recommended to monitor security bulletins and community forums related to FreeRADIUS and CentOS to quickly respond to newly discovered vulnerabilities and threats.