ecs和oss通过内网通信失败，何解？！

用discuz 3.2搭建的，用的dz官方插件。测试时图片根本无法上传到oss。何解？
我的配置如下。
$_config['extend']['storage']['curstorage'] = 'aliyun';
$_config['extend']['storage']['aliyun']['access_id'] = 'xxxx';
$_config['extend']['storage']['aliyun']['access_key'] = 'xxsss';
$_config['extend']['storage']['aliyun']['access_host'] = NULL;
$_config['extend']['storage']['aliyun']['bucket'] = 'Bucket名称';
$_config['extend']['storage']['aliyun']['attachurl'] = 'http://Bucket名称.oss-cn-qingdao-internal.aliyuncs.com';