Security glossary
Key takeawaysKey takeaways are generated with AI assistance. Because automated summaries can occasionally contain errors or miss important context, always refer to the full blog post for complete information.RADIUS (Remote Authentication Dial-In User Service) is a network protocol that centralizes authentication, authorization, and accounting for users and devices accessing enterprise networks through Wi-Fi, wired 802.1X, and VPN gateways. A network access server acts as the RADIUS client, forwarding user credentials to a central RADIUS server, which returns an access decision and authorization attributes such as VLAN assignments or session timeouts. Organizations depend on RADIUS to enforce consistent access policies across multiple network devices from different vendors, but must manage server redundancy, shared secret security, and potential configuration issues like certificate failures or port mismatches to ensure reliable authentication and prevent login failures or data exposure.
RADIUS works between a network access server, which acts as the RADIUS client, and a central RADIUS server. The client never checks credentials itself; it forwards them and enforces the answer.
RADIUS runs over UDP, so deployments usually configure timeouts, retries, and backup servers. Only the password attribute is obscured with the shared secret, so RADIUS traffic should be carried over protected links, or over TLS where supported.
A firewall rule, routing change, or wrong source address can stop requests from reaching the server. Switches and controllers then time out and may fall back to a guest VLAN, local account, or no access, depending on configuration.
Users authenticate successfully but land in the wrong VLAN or role because the server returns an attribute the device does not honor, or none at all. Vendor-specific attribute names and values often differ between device makers.
With only one RADIUS server configured, a failure or maintenance window blocks new logins and reauthentication. Configure at least two servers on each client and test failover behavior before an outage does it for you.
In 802.1X deployments using certificate-based EAP methods, an expired server certificate or a client that does not trust its issuer causes authentication to fail for many devices at once. The cause is usually the certificate, not the user accounts.
Article Refers to a family of protocols that mediate network access.
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Article A subnetwork that contains and exposes an organization’s external-facing services to an untrusted, usually larger, network such as the internet.
Article It aims to ensure a certain level of operational performance or uptime for a system.
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