Up to five RADIUS servers can be configured. They can be selected to authenticate user requests in two ways, using either the direct method or the round-robin method. The default method is direct.
In direct mode, the first server, as defined by the server-index command, is the primary server. This server is always used first when authenticating a request.
In round-robin mode, the server used to authenticate a request is the next server in the list, following the last authentication request. For example, if server 1 is used to authenticate the first request, server 2 is used to authenticate the second request, and so on.