How to Configure Radius TLS for Secure Authentication

The logs point to TLS. The Radius server is running, the network is fine, but clients cannot connect. This is where correct Radius TLS configuration matters.

Radius uses TLS for secure communication between the client and the authentication server. Without proper configuration, you get handshake errors, certificate rejections, or silent timeouts. The setup requires alignment between server certificates, CA trust stores, and the TLS policy in the Radius configuration file.

Start with the certificates. Generate a server certificate signed by a trusted CA. Store it in the /etc/raddb/certs directory or your equivalent path. The certificate must match the server’s hostname exactly, or TLS will fail. The private key must be readable only by the Radius process.

Edit the radiusd.conf or mods-enabled/eap module config to include the following:

tls {
 cert_file = /etc/raddb/certs/server.pem
 private_key_file = /etc/raddb/certs/server.key
 ca_file = /etc/raddb/certs/ca.pem
 dh_file = /etc/raddb/certs/dh
 cipher_list = "HIGH"
}

Keep cipher_list strict and avoid weak protocols. Always use a strong DH param file.

On the client side, configure the TLS trust store to include the same CA that signed the server certificate. If you are using EAP-TLS, verify both sides accept mutual certificate authentication. Debug with radiusd -X to see exact TLS errors during handshake.

Test your Radius TLS configuration with OpenSSL:

openssl s_client -connect your-radius-server:2083 -CAfile /etc/raddb/certs/ca.pem

If the output shows certificate chain verified and no protocol mismatches, the TLS channel is ready.

Good Radius TLS configuration removes uncertainty. It ensures every login, every packet is encrypted and authenticated. Missteps here lead to unstable infrastructure and wasted hours.

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