code: def _enable_l1_keepalives(self, command):
          
  
          env = os.environ.copy()
          if "IOURC" not in os.environ:
              env["IOURC"] = self.iourc_path
          try:
              output = yield from gns3server.utils.asyncio.subprocess_check_output(self._path, "-h", cwd=self.working_dir, env=env, stderr=True)
              if re.search("-l\s+Enable Layer 1 keepalive messages", output):
                  command.extend(["-l"])
              else:
                  raise IOUError("layer 1 keepalive messages are not supported by {}".format(os.path.basename(self._path)))
          except (OSError, subprocess.SubprocessError) as e:
              log.warning("could not determine if layer 1 keepalive messages are supported by {}: {}".format(os.path.basename(self._path), e))
docs: Enables L1 keepalive messages if supported.
  
          :param command: command line