public function dn($dn = null)
    {
        if (false == is_null($dn)) {
            if (is_null($this->_dn) ) {
                $this->_dn = $dn;
            } else {
                $this->_newdn = $dn;
            }
            return true;
        }
        return (isset($this->_newdn) ? $this->_newdn : $this->currentDN());
    }