:return: all knows subnets

def get_subnets():
        """
        :return: all knows subnets
        """
        LOGGER.debug("SubnetService.get_subnets")
        args = {'http_operation': 'GET', 'operation_path': ''}
        response = SubnetService.requester.call(args)
        ret = None
        if response.rc == 0:
            ret = []
            for subnet in response.response_content['subnets']:
                ret.append(Subnet.json_2_subnet(subnet))
        elif response.rc != 404:
            err_msg = 'SubnetService.get_subnets - Problem while getting subnets. ' \
                      '. Reason: ' + str(response.response_content) + '-' + str(response.error_message) + \
                      " (" + str(response.rc) + ")"
            LOGGER.warning(err_msg)
        return ret