def t_network_record_type_ip6(val):
    """
    Convert/validate: Network record type.

    :param any val: Value to be converted/validated
    :return: network record type.
    :rtype: str
    :raises ValueError: if the value is not valid network record type
    """
    if str(val) == 'ipv6':
        return str(val)
    raise ValueError("Invalid type '{:s}' for network record".format(val))
