The OpenShift Container Platform cluster uses a virtualized network for pod and service networks. The OVN-Kubernetes Container Network Interface (CNI) plug-in is a network provider for the default cluster network. OVN-Kubernetes, which is based on the Open Virtual Network (OVN), provides an overlay-based networking implementation.
A cluster that uses the OVN-Kubernetes network provider also runs Open vSwitch (OVS) on each node. OVN configures OVS on each node to implement the declared network configuration.
In order to create clusters using OVN you must install the preview extension. Existing clusters cannot be migrated to OVN.
See the documentation for more details: Configure OVN-Kubernetes network provider fo Azure Red Hat OpenShift clusters