TP-Link TL-R600VPN Configuration Manual page 176

Configuring Authentication
Authentication
Type
Primary RADIUS
Server
Secondary
RADIUS Server
Authentication
Port
Authorized Share
Key
Retry Times
Timeout Interval
Authentication
Method
Choose the authentication type as RADIUS Authentication.
Enter the IP address of the primary RADIUS server.
Optional. Enter the IP address of the secondary RADIUS server. If the primary
server is down, the secondary server will be effective.
Enter the service port for RADIUS authentication. By default, it is 1812.
Specify the authorized share key. This key should be the same configured in the
RADIUS server.
Specify the number of times the router will retry sending authentication requests
after the authentication failed.
Specify the timeout interval that the client can wait before the RADIUS server
replies.
Specify the authentication protocol as PAP or CHAP.
RADIUS Authentication Configuration
Configuration Guide 168