code: def _expired(self):
          
          LOG.info('Negotiated hold time %s expired.', self._holdtime)
          code = BGP_ERROR_HOLD_TIMER_EXPIRED
          subcode = BGP_ERROR_SUB_HOLD_TIMER_EXPIRED
          self.send_notification(code, subcode)
          self.connection_lost('Negotiated hold time %s expired.' %
                               self._holdtime)
          self.stop()
docs: Hold timer expired event handler.