def delete_os_dummy_rtr_nwk(self, rtr_id, net_id, subnet_id):
        """Delete the dummy interface to the router.  """
        subnet_lst = set()
        subnet_lst.add(subnet_id)
        ret = self.os_helper.delete_intf_router(None, None, rtr_id, subnet_lst)
        if not ret:
            return ret
        return self.os_helper.delete_network_all_subnets(net_id)