OSDOCS-4083: Added OVN-Kubernetes as the default networking plug-in

Author: bergerhoffer

migrating_from_ocp_3_to_4/planning-migration-3-4.adoc

@@ -148,6 +148,13 @@ If your {product-title} 3.11 cluster used the `ovs-subnet` or `ovs-multitenant`
 
 For more information, see xref:../networking/network_policy/about-network-policy.adoc#about-network-policy[About network policy].
 
+[discrete]
+==== OVN-Kubernetes as the default networking plug-in in Red Hat OpenShift Networking
+
+In {product-title} 3.11, OpenShift SDN was the the default networking plug-in in Red Hat OpenShift Networking. In {product-title} {product-version}, OVN-Kubernetes is now the default networking plug-in.
+
+For information on migrating to OVN-Kubernetes from OpenShift SDN, see xref:../networking/ovn_kubernetes_network_provider/migrate-from-openshift-sdn.adoc#migrate-from-openshift-sdn[Migrating from the OpenShift SDN network plug-in].
+
 [id="migration-preparing-logging"]
 === Logging considerations