Stickiness applies to the following subscriber RADIUS accounting sessions: start, interim, and stop. By default, the subscriber sticks with the server that served its last accounting message. For example, if server 1 served the subscriber an accounting start message, then the subsequent interim messages and stop message from the same subscriber is sent to server 1. If server 1 is out of service, server 2 is used for the subsequent interim and stop messages. When server 1 recovers, the interim and stop messages sticks with server 2. The RADIUS accounting messages are always be forwarded to the server that serviced the subscriber’s last accounting message.
Typically, when using the direct access algorithm, the primary server (lowest configured server index) serves all RADIUS request messages. The other RADIUS servers are used for backup purposes only and may be using a lighter-weight processor. Therefore, it is best to revert to the primary server as soon as it is restored. This can be accomplished by disabling stickiness in direct mode; the RADIUS accounting messages are forwarded to the primary server after it is restored.
In a round-robin algorithm, while each subscriber session is assigned to a different server in round-robin order, a particular subscriber sticks with a server for the entire accounting session. Disabling stickiness sends a subscriber’s RADIUS accounting messages to the list of configured RADIUS servers in a round-robin order.