What is a RADIUS Server?
If you’ve ever connected to Wi-Fi at work, logged in with your company username and password, or used a VPN, there’s a good chance you’ve already interacted with a RADIUS server—even if you didn’t know it.
RADIUS stands for Remote Authentication Dial-In User Service. Despite the old-fashioned name (it was created back in the 1990s), RADIUS is still widely used today as a way to manage who can connect to a network and what they can do once connected.
A Real-World Analogy: The Security Guard at the Door
Think of a RADIUS server like a security guard standing at the entrance of a building:
- When you arrive, you show your ID badge (your username and password).
- The guard checks your badge against the company’s list of employees (authentication).
- If you’re allowed in, the guard tells you where you can go—maybe just the lobby, or maybe you get access to the executive floor too (authorization).
- Meanwhile, the guard also writes down what time you came in and when you left (accounting).
The guard doesn’t make up the rules—they just enforce the policies set by the company. In the same way, a RADIUS server doesn’t decide your permissions; it checks against a central database like Active Directory or LDAP to verify who you are and what you’re allowed to access.
What a RADIUS Server Does
Behind the scenes, a RADIUS server handles three main tasks:
- Authentication – Proves you are who you say you are.
- Authorization – Grants you the correct level of access.
- Accounting – Keeps records of when and how you used the network.
Everyday Example
Let’s say you connect to your office Wi-Fi:
- You type in your work username and password.
- The Wi-Fi access point asks the RADIUS server, “Is this person allowed in?”
- The RADIUS server checks your credentials against the company’s employee database.
- If you’re valid, you’re in. If not, access is denied.
All of this happens in seconds, but it ensures that only the right people get onto the network.
Why Companies Use RADIUS
Organizations rely on RADIUS because it provides one central checkpoint for network access. Instead of having to manage usernames and passwords on every Wi-Fi router, VPN server, or firewall, everything points back to the RADIUS server. This gives IT teams:
- Simpler management
- Stronger, consistent security policies
- Better tracking of who used the network and when
Modern Uses of RADIUS
Even though “dial-in” is in the name, RADIUS is still very much alive. It’s commonly used for:
- Office Wi-Fi authentication
- VPN logins
- Network device administration (like routers and switches)
- Guest Wi-Fi portals
In short: A RADIUS server is like a digital security guard for your network. It checks IDs, decides what areas each person can access, and keeps a log of who came and went—all to keep the network safe and organized.
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