public function validateHost($host = null)
    {
        if ($host === null) {
            $host = $this->_host;
        }

        // If the host is empty, then it is considered invalid
        if (strlen($host) === 0) {
            return false;
        }

        // Check the host against the allowed values; delegated to Zend_Filter.
        $validate = new Zend_Validate_Hostname(Zend_Validate_Hostname::ALLOW_ALL);

        return $validate->isValid($host);
    }