Privacy settings
We use cookies and similar technologies that are necessary to run the website. Additional cookies are only used with your consent. You can consent to our use of cookies by clicking on Agree. For more information on which data is collected and how it is shared with our partners please read our privacy and cookie policy: Cookie policy, Privacy policy
We use cookies to access, analyse and store information such as the characteristics of your device as well as certain personal data (IP addresses, navigation usage, geolocation data or unique identifiers). The processing of your data serves various purposes: Analytics cookies allow us to analyse our performance to offer you a better online experience and evaluate the efficiency of our campaigns. Personalisation cookies give you access to a customised experience of our website with usage-based offers and support. Finally, Advertising cookies are placed by third-party companies processing your data to create audiences lists to deliver targeted ads on social media and the internet. You may freely give, refuse or withdraw your consent at any time using the link provided at the bottom of each page.
Thank you! Your submission has been received!
Oops! Something went wrong while submitting the form.

RADIUS (Remote Authentication Dial-In User Service) protocol

A typical password and an SSID were the most popular way for joining users to corporate networks for quite a while. At that point, maintaining this while offering ad-hoc VPN accessibility to individuals who required it proved to be more work than most organizations had anticipated. This made greater sense when the bulk of staff were physically present in the workplace daily, but even then, it was still difficult to manage.

In addition to being time-consuming and unreliable, this approach leaves networks vulnerable to attack. Fortunately, the RADIUS protocol makes the process easier for consumers to get into networks and reduces the amount of work that IT has to do managing network connections. In-depth explanations of RADIUS's features, functions, benefits, and drawbacks are provided in this article.

RADIUS (Remote Authentication Dial-In User Service) protocol

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

RADIUS is an agreement or protocol – a set of guidelines that govern how something interacts with the outside world or functions. Through it, users can be authorized and validated before using an external web. It takes care of authenticating, validating, and doing bookkeeping services in order to link workstations. 

Since RADIUS can stop unauthorized users—and intruders—from accessing your system, it is a crucial tool for web access management.

The RADIUS authentication server and NAS (both are explained below in the article) are needed for the verification agreement. It accomplishes a number of identical tasks as a LDAP and offers local identification facilities by keeping a current database of login information for users. TCP cannot compete with it in terms of security. RADIUS functions diligently on ports 1813 and 1812.

The 3 main components of RADIUS

  1. NAS

The connecting point between an individual and a networked device is known as a network access server (NAS).

  1. Client/Supplicant

The machine or person requesting network connectivity.

  1. RADIUS Server

A verification server that makes sure that the individual has the proper authorization levels for entering the network. Additionally, this server can offer bookkeeping services for billing, timekeeping, and connection/device information.

radius architecture


One of the first established dial-up server configurations for businesses was the Livingston Portmaster, which debuted in 1991 and ushered in the RADIUS server age. In order to interact with it and offer centralized validation, permission, and administrative services for dialing up clients, Livingston Enterprises, Inc. came up the Automated Identification Dial-In Customer Service Guidelines.

RFC 2138, published in 1995 by the IETF, formalized the RADIUS protocol. ISPs and manufacturers of network hardware have ever since largely embraced the RADIUS standard.

The provisioning of AAA support for a variety of products and devices is made possible by RADIUS servers, a crucial component of many technology-based solutions at present. For example, they can serve as portals for wireless networks, VPN server facilities, and VoIP solutions.


UDP-based software that works in background is often used by servers executing the RADIUS protocol on Windows or UNIX terminals. Before replying, the client or NAS—an apparatus or system like an access point for wireless communication or a VPN—waits for the webserver to issue a request.

The RADIUS server gathers every user's login data for identification reasons. It responds to the client's message after receiving this information. This is how RADIUS ports get requests for interconnections from clients, validate every user's credentials, and then give the right setup data back to the server so that it may provide someone with the service they need.

Clients can gain from the server featuring an extensible system that is simple to adapt to different security protocols while keeping your interactions and safety operations separate.

How does RADIUS work?

RADIUS uses a client/server framework to function. NAS, which is a RADIUS client, receives user login credentials. The NAS then uses the RADIUS verification network to verify the user's information. Further details like an IP, user/login name, and an encrypted password could be included in the connection metadata.

In physically complex or scattered systems, a RADIUS gateway client can be utilized for forwarding authentication requirements to other RADIUS servers.

Various types of servers verify universal connectivity, including:

  • Users can submit queries to encrypted virtual private network servers, enabling secure links to encrypted networks.
  • Wireless access points connect to a system by accepting queries from mobile clients.
  • Switches for controlled networks that use the 802.1x verify entrance protocol.

The web server that controls RADIUS is the component that inspects an individual's extent of approval after evaluation. This guarantees that authorized people can only view information belonging to an organization. RADIUS may be utilized to locate customers and provide details about the tools employed during a particular session for the sake of invoicing.

Competent resource management benefits licensed vendors of services. Upon accepting a login request, the site's computer typically checks the individual's genuine identity against an encrypted customer registry or transfers the details to a separate identity contributor.

The server side checks the user's presented login credentials and delivers an Access-Accept signal to the NAS if the setup functions as intended. An Access-Reject response is given to the user if a link cannot be created.

Following the exchange, the NAS sends financial information to the platform's RADIUS server facilitating the long-term preservation or shipment of operational data and serving as a repository for product trading.

How does RADIUS work?

An example of using RADIUS

When choosing an internet connection and trying to get signed in for the very first time, the username and password are filled in (it is later recollected, so you aren't required to input it on every attempt).

An access request is delivered to the NAS by the WAP, often known as a wireless access point or the back end. This data is moved from the NAS to the RADIUS-sanctioned server. RADIUS portals provide the option of maintaining individuals and passwords, or the server can check a web-based database or directory.

If the information you provided is precise, the RADIUS server informs the NAS of any limitations or constraints on what you may accomplish or function on the particular system and returns an Access-Accept response.

RADIUS mechanisms

Let's examine the RADIUS protocol's internal workings to determine how this is possible.

  1. Creating a Connection

PPP is the most commonly employed method for the scenarios most familiar to the company: validating an individual onto a network using their login credentials. A RADIUS server can support individuals via numerous procedures, including Telnet, rLogin, PPP, and SLIP. PPP, aka Point-to-Point Protocol, is a structure that allows a direct connection between two nodes, such as a supplicant and the NAS.

Every exchange involving interconnection between the NAS and the RADIUS server undergoes documentation using an agreed-upon secret. The synergetic secret is an identification code disseminated silently and without end-user knowledge between the RADIUS and NAS servers.

  1. Data Transmission

The client-server communication pattern includes something called a transport layer. Various pieces containing data are put together there. These communications include information such as login information and other request types. Both the UDP and TCP methods have the ability to facilitate transport. The acronym may be familiar to you since TCP/IP is one of the most widely used methods of communication on the internet. RADIUS, by nature, uses UDP, a distinct type of transport.

The differences between TCP and UDP are what led to UDP's selection. 

In simple terms, TCP periodically confirms that the information provided has actually been retrieved. If it happens, it is alerted. The administrative costs will increase as a result. Latency in systems, a big issue for the first few years of cheap-bandwidth systems, results from many moving components.

On the contrary, UDP offers a less noticeable connectivity expense. Additionally, it makes sure to transmit data swiftly – as soon as it receives it. However, it doesn’t guarantee to successful deliver the information/data packets.

In the scenario of RADIUS, it is the responsibility of the RADIUS server system, not the sender of the regulations, to guarantee that the communication is successful. In essence, whenever the end-user enters their data into their computer's network environments, a series of actions occur.

How does RADIUS authentication work?

This protocol checks the user's identity and examines network security policies applied to the individual during authorization. 

To put it simply, you must submit the required data as predetermined. If correct, you will obtain an Access-Accept signal from the RADIUS server (which signifies that the end-users equipment is able to enter the network's resources).

PAP and CHAP were two possible Point-to-Point Protocol-compatible technologies for RADIUS deployments from the late 1990s. The first verification methods need to be updated, but understanding how contemporary RADIUS operates properly requires knowledge.

  1. PAP

PAP operates in a way that is intuitive for us on every aspect of the consumer side. For instance: The user begins by entering their username and password. The customer provides the information to the client, then transmits it from the NAS to the RADIUS gateway.

Since PAP transmits both the username and password in simple text, it is vulnerable as anyone with the capacity to monitor messages between the NAS and RADIUS server might be competent to figure out the credentials swiftly.

  1. CHAP

CHAP, or the challenge-based Handshake Authentication Protocol, is a substitute for PAP. Despite the fact that it is easier to be more trustworthy than an evident-text password interaction, it is a far more protected authentication technique than PAP. Instead of transmitting credentials in plain text, CHAP encrypts the data being exchanged to hide it from prying eyes.

The way it works

Following the individual's password entry, the requester will pair the user's credentials with an obstacle, a randomly generated sequence of numerals obtained from the NAS. The MD5 hash algorithm is then applied to the username, password, and random string combo. The two are mixed up and rendered incoherent as a result. It is known as the reaction.

Pros and cons of the RADIUS


  • Encrypted VPN verification

When contrasting RADIUS and VPN, RADIUS verification allows for safe access to WiFi networks and supports VPNs. This adaptability makes it possible for anyone to effortlessly and securely interact with an internet connection.

  • Added safety advantages

As RADIUS enables users to create their login information, there is less risk of attackers breaking into a system (such as WiFi) because there isn't a single password that many users share.


  • Setting up a non-hosted RADIUS connection initially

Implementing and integrating this might be challenging for IT administrators, especially if the company currently offers outdated systems like Active Directory on-premises.  

  • Numerous configuration alternatives

Due to the wide variety of protocols and compatibility challenges, RADIUS servers' configuration and initial configuration can be difficult and complex. Even highly seasoned IT administrators must navigate challenging configuration procedures.

RADIUS Security

Since an individual is unable to establish a link if the credentials they provide are different from those in the RADIUS server's database structure, RADIUS can stop confidential data from being disclosed to unauthorized parties. 

RADIUS can be used in a wide range of connections, so it is an economical choice. Additionally, it can be redundant as more interactions are added. Additionally, it combines with the majority of safety protocols, such as PPP, UNIX login, and PAP.

RADIUS distinguishes the interaction and safety procedures. An organization gains from this since executives can modify the privacy mechanisms without altering the interaction channels.


If someone wants to verify people by employing the data in the controller's internal database structure, they must add those users' login credentials and passwords. If someone wants to implement a RADIUS server for user authorization, they must set the RADIUS server up on the physical controller.



RADIUS protocol - Github

Teaching Old Dogs New Tricks - Infosecurity Magazine

Subscribe for the latest news

February 26, 2024
Learning Objectives
Subscribe for
the latest news
Related Topics