private function isReserved(string $host): bool
    {
        $hosts = [$host];
        if (!\preg_match('/^([0-9]{1,3}\.){3}[0-9]{1,3}$/', $host)) {
            $tmp = \gethostbynamel($host);
            $hosts = $tmp !== false ? $tmp : [];
        }

        $res = true;
        $flags = FILTER_FLAG_IPV4 | FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE;
        foreach ($hosts as $host) {
            if (\filter_var($host, FILTER_VALIDATE_IP, ['flags' => $flags]) !== false) {
                $res = false;
                break;
            }
        }

        return $res;
    }