RADIUS Server Explained | AAA Protocol

RADIUS stands for Remote Authentication Dial-In User Service. It helps an organization to centralize authentication for remote connections. It enables remote access servers (NAS) to communicate with a central server. It provides Authentication, Authorization, and Accounting (AAA) services for multiple access servers. Radius used port number 1812.

Basically, RADIUS works based on a client-server model runs in the application layer and used TCP or UDP protocol for sending requests. Here, requests are of two types: Access-Request and Accounting-Request. The first one manages authentication and authorization, while later, one takes care of accounting.

How RADIUS Works:

Here we will see how RADIUS works in a practical scenario. For understanding, you need to understand some terms:

User: It denotes the end-user who seeks authentication from RADIUS.

NAS: It stands for Network Access Server. The user first interacts with NAS for authentication and authorization.

RADIUS: This server validates the user against stored authentication data.

Now, we see steps in little detail:

Step 1: User initiates PPP authentication to the NAS (RADIUS client). PPP stands for Point-to-Point Protocol (PPP) and it is a data link layer (layer 2) communications protocol used to establish a direct connection between two nodes.

Step 2: NAS asked for credentials (e.g. username and password) for initial authentication.

Step 3: User provides credentials to NAS.

Step 4: NAS sends the username and encrypted password to the RADIUS server.

Step 5: RADIUS server responds with Accept, Reject, or Challenge based on input provided by NAS.

Step 6: The NAS acts accordingly and allows/reject authentication based on correctness of credentials.

Applications of RADIUS server

  • Many Internet Service Providers (ISP) use RADIUS for authentication of internal users.
  • Big organizations have more than one Network Access Servers (NAS) to manage employees. Those organizations use the RADIUS server to verify authentication, authorization and to track the accounting of users.

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Disclaimer: This tutorial is for educational purpose only. Individual is solely responsible for any illegal act.

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