Difference between RAC public IP, private IP and Virtual VIP

 In Oracle RAC clusters, we see three types of IP addresses:

1. Public IP:  The public IP address is for the server.  This is the same as any server IP address, a unique address which exists in /etc/hosts.
   
   
2. Private IP: Oracle RCA requires "private IP" addresses to manage the CRS, the clusterware heartbeat process and the cache fusion layer. Oracle Clusterware uses the interfaces you identify as private for the cluster interconnect. If you identify multiple interfaces during information for the private network, then Oracle Clusterware configures them with Redundant Interconnect Usage. Any interface that you identify as private must be on a subnet that connects to every node of the cluster. Oracle Clusterware uses all the interfaces you identify for use as private interfaces.
   
   
3. Virtual IP:  Oracle uses a Virtual IP (VIP) for database access.  The VIP must be on the same subnet as the public IP address.  The VIP is used for RAC failover (TAF).
   
   
   The virtual IP (VIP) address is registered in the grid naming service (GNS), the DNS, or in a hosts file.Select an address for your VIP that meets the following requirements:The IP address and host name are currently unused (it can be registered in a DNS, but should not be accessible by a ping command).