Explanation/Reference:
Oracle Clusterware requires a cluster interconnect configured for inter-node communication.
Note:
* The Oracle Clusterware interconnect is a non-traditional interconnect and should be considered, in shared global cache applications, such as Oracle RAC, to be an I/O subsystem for inter-node global cache buffer transfers with the latency and bandwidth requirements of high performance cluster computing.
* The interconnect network is a private network using a switch (or multiple switches) that only the nodes in the cluster can access.
And
Oracle Clusterware requires that you connect the nodes in the cluster to a private network by way of a private interconnect. The private interconnect is a separate network that you configure between cluster nodes. The interconnect used by Oracle RAC is the same interconnect that Oracle Clusterware uses. This interconnect should be a private interconnect, meaning it is not accessible to nodes that are not members of the cluster.
Reference: Oracle Real Application Clusters (RAC) and Oracle Clusterware Interconnect Virtual Local Area Networks (VLANs) Deployment Considerations