code: def _check_vbox_port_forwarding(self):
          
  
          result = yield from self._execute("showvminfo", [self._vmname, "--machinereadable"])
          for info in result.splitlines():
              if '=' in info:
                  name, value = info.split('=', 1)
                  if name.startswith("Forwarding") and value.strip('"').startswith("GNS3VM"):
                      return True
          return False
docs: Checks if the NAT port forwarding rule exists.
  
          :returns: boolean