OSDOCS-6962_RN:adding release note

release_notes/ocp-4-18-release-notes.adoc

@@ -419,6 +419,12 @@ For more information, see xref:../nodes/clusters/nodes-cluster-enabling-features
 [id="ocp-release-notes-installation-and-update_{context}"]
 === Installation and update
 
+[id="ocp-4.18-installation-and-update-ovn-kubernetes-join-subnet_{context}"]
+==== Install-time configuration for the `ovn-kubernetes` join subnet feature is enabled
+With this release, you can configure the IPv4 join subnet that is used internally by `ovn-kubernetes` when installing a cluster. You can set the `internalJoinSubnet` parameter in the `install-config.yaml` file and deploy the cluster into an existing Virtual Private Cloud (VPC).
+
+For more information, see xref:../installing/installing_aws/installation-config-parameters-aws.adoc#installation-configuration-parameters-network_installation-config-parameters-aws[Network configuration parameters].
+
 [id="ocp-release-notes-olm_{context}"]
 === Operator lifecycle