OSDOCS-6962:adding custom IPv4 support

modules/installation-configuration-parameters.adoc

@@ -407,6 +407,20 @@ endif::ibm-power-vs[]
 Set the `networking.machineNetwork` to match the CIDR that the preferred NIC resides in.
 ====
 
+|networking:
+  ovnKubernetesConfig:
+    ipv4:
+      internalJoinSubnet:
+|When you configure `networkType` to `OVNKubernetes`, `OVNKubernetesConfig` provides the configuration for ovn-kubernetes as the default pod network.
+
+You can use IPv4 to configure the IP settings for IPv4 connections. If you don’t configure IPv4, the default configuration is used. For more information about the default configuration values, see the individual IPv4 fields.
+
+`internalJoinSubnet` is a v4 subnet that is used internally by ovn-kubernetes in case the default one is already used by something else. `internalJoinSubnet` must not overlap with any other subnet that OpenShift is using or by the node network. The size of the subnet must be larger than the number of nodes. You cannot change the value after installation.
+
+|The default value is `100.64.0.0/16`.
+
+The subnet must be large enough to accommodate one IP per node in your cluster. The value must be in proper IPv4 CIDR format.
+
 |====
 
 [id="installation-configuration-parameters-optional_{context}"]