def _is_hostmask(self, ip_str):
        """Test if the IP string is a hostmask (rather than a netmask).

        Args:
            ip_str: A string, the potential hostmask.

        Returns:
            A boolean, True if the IP string is a hostmask.

        """
        bits = ip_str.split('.')
        try:
            parts = [x for x in map(int, bits) if x in self._valid_mask_octets]
        except __HOLE__:
            return False
        if len(parts) != len(bits):
            return False
        if parts[0] < parts[-1]:
            return True
        return False
dataset/ETHPy150Open Exa-Networks/exabgp/lib/exabgp/dep/ipaddress.py/_BaseV4._is_hostmask