A typical connect attempt from a database client to an Oracle RAC database instance can be summarized, as follows:

The database client connects to SCAN (which includes a SCAN VIP on a public network), 

providing the SCAN listener with a valid service name.

The SCAN listener then determines which database instance hosts this service and routes 

the client to the local or node listener on the respective node.

The node listener, listening on a node VIP and a given port, retrieves the connection 

request and connects the client to the an instance on the local node.