What Is Remote Authentication Dial In User Service(RADIUS)?

In the realm of network security, Remote Authentication Dial-In User Service (RADIUS) stands as a powerful protocol that enables organizations to centrally manage user access and authentication across diverse network devices and services. Let's learn about the inner workings of RADIUS and explore how it streamlines the authentication process while ensuring robust security measures.

What Is RADIUS?

The Remote Authentication Dial-In User Service (RADIUS) is an information exchange protocol designed for distributed environments, employing a client/server model. Its primary objective is to safeguard networks against unauthorized access, particularly on networks that prioritize security and allow remote user access. RADIUS is a universally supported standard protocol across mainstream devices and stands as the most widely utilized AAA protocol within operational networks. It utilizes the User Datagram Protocol (UDP) for transmission, ensuring efficient real-time performance. Furthermore, RADIUS incorporates reliable features such as retransmission and backup server mechanisms, guaranteeing a high level of dependability. Implementing RADIUS is straightforward, and it facilitates multithreading on servers to authenticate a large volume of users.

How Does RADIUS Work?

Client and Server Model

The RADIUS protocol functions on a model of client and server interaction. Normally, a Network Access Server (NAS) serves as the RADIUS client, while the RADIUS server operates as a daemon process on a UNIX or Windows NT machine. The client transmits user information to designated RADIUS servers and acts based on the response received. User connection requests are received by RADIUS servers, which authenticate the user and provide the necessary configuration information for the client to offer services. Additionally, a RADIUS server can act as a proxy client to other RADIUS servers or different types of authentication servers.

• 1. The user initiates PPP authentication to the NAS.

• 2. The NAS prompts the user for a username and password (in the case of Password Authentication Protocol [PAP]) or a challenge (in the case of Challenge Handshake Authentication Protocol [CHAP]).

• 3. The user provides the requested information.

• 4. The RADIUS client (NAS) sends the username and encrypted password to the RADIUS server.

• 5. The RADIUS server responds with an Accept, Reject, or Challenge message.

• 6. The RADIUS client (NAS) takes appropriate action based on the services and service parameters bundled with the Accept or Reject message.

The following diagram illustrates the interaction between a dial-in user, the RADIUS client, and the server.

Authentication and Authorization

The RADIUS server has the capability to support various authentication methods for user verification. It can handle PPP, PAP, CHAP, UNIX logins, and other authentication mechanisms when provided with the user's username and original password.

The typical user login process involves a query (Access-Request) sent from the NAS to the RADIUS server, followed by a corresponding response (Access-Accept or Access-Reject) from the server. The Access-Request packet contains the username, encrypted password, NAS IP address, and port. Initially, RADIUS used UDP port number 1645, which conflicted with the "data metrics" service. To resolve this conflict, RFC 2865 officially assigned port number 1812 for RADIUS. The request format also provides information about the type of session the user wishes to initiate. For instance, if the query is in character mode, it implies that the Service-Type is Exec-User. However, if the request is in PPP packet mode, the inference is that the Service-Type is Framed User and Framed Type is PPP.

Upon receiving the Access-Request from the NAS, the RADIUS server searches its database for the corresponding username. If the username is not found, either a default profile is loaded, or the RADIUS server promptly sends an Access-Reject message. This rejection message can be accompanied by a text message stating the reason for refusal.

In RADIUS, authentication and authorization are intertwined. If the username is found and the password is correct, the RADIUS server responds with an Access-Accept message, which includes a list of attribute-value pairs defining the parameters for the session. These parameters typically include service type (shell or framed), protocol type, IP address assignment (static or dynamic), applied access list, or a static route to be installed in the NAS routing table. The configuration information in the RADIUS server determines what can be installed on the NAS. The following figure illustrates the sequence of RADIUS authentication and authorization.

Accounting

The accounting capabilities of the RADIUS protocol can be utilized separately from RADIUS authentication or authorization processes. It provides the collection and logging of information such as network traffic, connection time, data transfer volume, and more. The RADIUS server receives these messages and logs the relevant information for billing, auditing, and network management purposes. Through RADIUS Accounting, administrators can gain detailed insights into network user behavior and resource consumption, enabling better network resource management and control.

The Characteristics of RADIUS

• Distributed environment for authentication and authorization.

• Support for multiple authentication methods.

• Real-time performance and quick response.

• Flexible configuration of session parameters.

• Integration of authentication and authorization.

• Reliability and fault tolerance.

• Wide support and standardization.

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Summary

In conclusion, Remote Authentication Dial-In User Service (RADIUS) is a powerful protocol that makes user authentication and authorization in network environments. Its centralized and secure approach offers organizations improved access control, streamlined user management, and enhanced network security.

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