这就是所谓的被动模式，或者叫做PASV，当客户端通知服务器它处于被动模式时才启用。
This was known as passive mode, or PASV, after the command used by the client to tell the server it is in passive mode.
如很多公司在向国外厂商订货之后，往往是被动地等待，特别是等货到达港口后好几天才得到货代或承运人的到货通知。
Like many companies in order to foreign manufacturers, is often after passively wait for, especially of goods at ports such as after several days to get forwarder or carrier's arrival notice.
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