Glossary · Networking

RADIUS (Remote Authentication Dial-In User Service)

RADIUS is a protocol that centralizes authentication, authorization and accounting for network access such as Wi-Fi, VPN and switch ports.

Updated October 6, 2026

RADIUS (Remote Authentication Dial-In User Service) is a client-server protocol that centralizes authentication, authorization and accounting (AAA) for people connecting to a network. A network access device, such as a Wi-Fi controller, VPN gateway or switch, forwards the login to a RADIUS server and enforces the answer it gets back.

Why it matters

Instead of storing a password on every device, you keep identities in one place, often a directory reached over LDAP. RADIUS can return attributes with its approval, such as which VLAN to place the user in or a session time limit, and it logs start and stop records for auditing. It usually runs over UDP, ports 1812 for authentication and 1813 for accounting, and is the back end for 802.1X enterprise Wi-Fi.

Example

A laptop connects to the staff SSID. The access point sends an Access-Request to the RADIUS server. The server checks the credentials and replies Access-Accept with Tunnel-Private-Group-Id = 20, so the laptop lands in VLAN 20. A wrong password gets Access-Reject.

Common mistakes

  • Using a weak or shared secret between device and server; it protects the traffic between them.
  • Running a single RADIUS server, so a failure locks everyone out.
  • Assuming RADIUS encrypts the whole exchange; only the password field is obscured in the classic protocol.

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Keep reading

Glossary · Networking802.1X (Port-Based Network Access Control)802.1X is an IEEE standard that blocks a network port until the connecting device authenticates, commonly with a RADIUS server.Glossary · NetworkingAccess Point (Wireless AP)A wireless access point is a device that connects Wi-Fi clients to a wired network, acting as the bridge between radio and Ethernet.Glossary · NetworkingAnycast RoutingAnycast announces the same IP address from many locations, so network routing sends each user to a nearby site and absorbs traffic floods.

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