def tap_stop(self):
        """
        Stop a TAP driver.
        """
        if not self.tap_running():
            return
        LOGGER.info('%s: stopping tap driver.' % self.fullname)
        reply, _ = self.parent.transport.katcprequest(
            name='tap-stop', request_timeout=-1,
            require_ok=True, request_args=(self.name, ))
        if reply.arguments[0] != 'ok':
            raise RuntimeError('%s: failure stopping tap '
                               'device.' % self.fullname)