What Is a RADIUS Server and How Does It Work?

A RADIUS server is technology that enables remote user validation or the ability to access a server remotely. A report from the Pew Research Center in 2023 estimates that about 14 percent of Americans work from home all the time, making the total number about 22 million [1].

With more employees working from home and businesses needing to secure remote access, network security is increasingly important. A remote authentication dial-in user service, commonly called a RADIUS server or an AAA server, can provide remote user validation. 

First developed in 1991 to authenticate, authorize, and account for networked devices, RADIUS servers remain a security essential today. Explore what a RADIUS server is, its pros and cons, and when you might want to use RADIUS server authentication.

What is a RADIUS server?

A remote authentication dial-in user service (RADIUS) server is a method of validating users’ security information and accounting for what devices access your network. The RADIUS server works on the client side to secure your environment while enabling remote access. With RADIUS, the user enjoys a seamless and transparent authentication process. They seek access to the server from their remote device, and authentication, authorization, and accounting happen behind the scenes.

You may also see a RADIUS server called an AAA server. This name reflects the protocol’s authentication, authorization, and accounting focus.

The RADIUS or AAA server helps heighten security by efficiently verifying users without compromising privacy for the user or the system. This protocol dictates who can access your network but can also control services accessed and bandwidth. You may also note the “dial-in” in the full RADIUS name. Why? That refers to the server enabling remote authentication via phone or other connection.

Read more: What Does a Network Security Engineer Do?

Types of RADIUS servers  

RADIUS wireless security has two modes: synchronous authentication mode and asynchronous authentication mode.

• Synchronous authentication mode: The user logs in using a passcode, token card, or other authentication method. The client machine notifies the RADIUS server, which sends the data to an authentication server to validate the credentials. The RADIUS server then either accepts or rejects the login. 

• Asynchronous authentication mode: Also known as challenge-response mode. However, after RADIUS validates the credentials, the authentication server sends out a challenge (e.g., entering a random code) to the user. The user responds, and RADIUS sends that data for authentication, and then, using the Accept or Reject information from that server, RADIUS responds to the user’s request.

How does RADIUS authentication work?

RADIUS authentication is frictionless for the user. On your side, you’ll need a RADIUS server, a reference directory of users and approved devices, and a RADIUS client (or network access server).

A remote device tries to connect to the RADIUS client, and the client notifies the RADIUS server. The server then:

• Checks the directory for the user’s security information

• Acts as a middleman between the authentication server and the client

• Logs data such as when the user logged on, how often, and the network session duration

A shared secret is key in this protocol. Whether it’s a password or something else, this model relies on the servers and clients knowing something an attacker couldn’t know.

Pros and cons of RADIUS servers 

Cybersecurity is a constantly shifting field requiring you to keep up with the latest advancements and learn authentication protocols if you want to work in IT. Attackers are highly motivated to find new ways to access your networks and leverage any vulnerabilities. When deciding which type of authentication to use, weigh both the benefits and potential pitfalls of RADIUS servers.

Pros

Understanding RADIUS advantages can help you determine if this is the right server for you. RADIUS has several benefits, such as:

• Enables authentication across multiple databases using a range of methods 

• Offers role-based access control 

• Supports a zero-trust network architecture (ZTNA) to minimize risk

• Centralizes security to simplify password management for users and authentication

• Allows for the deauthorization of a single user or device to prevent access

Cons

RADIUS can have drawbacks as well. These include:

• Installing and managing the necessary on-premises hardware can prove complicated.

• New security vulnerabilities are possible if you don’t implement RADIUS correctly.

• You have many configuration options and compatibility concerns to consider. 

How to learn more about RADIUS servers

If you’re working, or want to work in, network administration or IT support, you could gain from learning more about RADIUS authentication servers. According to Glassdoor, the estimated total pay for computer network support specialists in the US is 83,041 per year [2]. This figure includes an average base salary of $69,433 and $13,608 in additional pay. Additional pay may represent profit-sharing, commissions, or bonuses.

Explore coursework and certifications that could help your career path below.

Read more: 10 Entry-Level IT Jobs and What You Need to Get Started

Degree

Begin your career in IT with an associate or bachelor’s degree in computer science, information technology, or a related field. Generally, you don’t need an advanced degree to start, but having one in a relevant area can help you stand out. 

Certifications

You have several certification options available to enhance your knowledge of IT and network administration. You might consider:

• ISACA Certified in Risk and Information Systems Control (CRISC)

• ISC2 Certified Information Systems Security Professional (CISSP)

• ISACA Certified Information Security Manager (CISM)

• Cisco Certified Network Associate (CCNA)

• Cisco Certified Network Professional (CCNP) Enterprise

• CompTIA Network+

• Microsoft Certified: Azure Administrator Associate

Read more: 10 Essential IT Certifications

Learn more about RADIUS servers with Coursera

RADIUS servers create an easy-to-use client-server architecture for remote users to access data on an organization’s server from a reference of user authentication credentials and approved devices. A RADIUS server is just one part of network security. Discover more about securing digital technologies with Google’s IT Support Professional Certificate on Coursera. This program covers technical support fundamentals, computer networking, system administration, and more. Upon completion, gain exclusive access to career resources like resume review, interview prep, and career support.