Single Client Access Name (SCAN) is a single name assigned to the cluster. Instead of connecting directly to individual node listeners, clients can connect to a database instance via a SCAN listener using a SCAN VIP. The SCAN listener is responsible for routing connections to your cluster nodes ensuring load balancing. It simplifies drastically your network setup when the number of cluster nodes is important. Typically there are 1 to 3 SCAN listeners per cluster, regardless of the number of nodes. In addition, SCAN VIP addresses can failover between nodes. The Oracle RAC listener is a process that listens for incoming client connection requests and manages the traffic to the database instance. Listeners use node VIP addresses tied to specific nodes to receive connections to that node.
Each database listener registers with the SCAN listener and updates it with the current load metric. The SCAN listener receives requests and routes the requests to the Local listener on the least loaded node. The local listener is using a virtual IP (VIP) address. A VIP is an IP address that is not bound to a specific network interface card. It can be moved between nodes in the cluster and is a resource managed by Oracle Clusterware. VIPs are used to provide faster connection failover and avoid TCP/IP timeout issues when a node fails.
Each node will have a public IP address assigned to the network interface for that particular node.