Oracle Net Services provides the ability to distribute client connections across the instances in an Oracle RAC configuration. There are two types of load balancing that you can implement: client-side and server-side load balancing. Client-side load balancing distributes the connection requests across the listeners, independently at each client. With server-side load balancing, the SCAN listener directs a connection request to the best instance currently providing the service, based on the
-rlbgoal settings for the service.
In an Oracle RAC database, client connections should use both types of connection load balancing.
Oracle Database Net Services Administrator's Guide for detailed information about both types of load balancing