def add_server(self, name, prefer=False):
        """Add or update an NTP server entry to the node config

        Args:
            name (string): The IP address or FQDN of the NTP server.
            prefer (bool): Sets the NTP server entry as preferred if True.

        Returns:
            True if the operation succeeds, otherwise False.
        """
        if not name or re.match(r'^[\s]+$', name):
            raise ValueError('ntp server name must be specified')
        if prefer:
            name = '%s prefer' % name
        cmd = self.command_builder('ntp server', value=name)
        return self.configure(cmd)