Unable to create Isolated Network for VDC in vCloud director

Question

When I try to post XML to vcloud director api for adding isolated net work i am getting the following error from api.

Request XML

<?xml version="1.0" encoding="UTF-8"?>
<OrgVdcNetwork name="Isolated"  xmlns="http://www.vmware.com/vcloud/v1.5">
   <Description>Isolated Organization VDC Network</Description>
   <Configuration>
  <IpScopes> 
     <IpScope>
        <IsInherited>true</IsInherited>
        <Gateway>192.168.1.1</Gateway>
        <Netmask>255.255.255.0</Netmask>                 
     </IpScope>
  </IpScopes>
  <FenceMode>isolated</FenceMode>

Response

Gateway address and subnet mask have to be provided when creating routed/isolated org VDC network.

Any help in this is highly appreciated.