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When the client wants to use a passive data connection, the server should provide the port to use. By default, FTPServer will choose any available port. However this can be overridden using the configuration parameter config.listeners.default.data-connection.passive.ports (if using the default Listener. The allowed passive ports can then be specified as a single port (e.g. 20020), multiple ports (e.g. 20020, 20030, 20040) or a range of ports (e.g. 20020-20030). Ranges can be closed (e.g. 20020-20030) or open ended (e.g. 60000-). Open ended ranges start at 1 and end at 65535, that is, the range 60000- will allow all ports between 60000 and 65535. Any combination of specified values or ranges can be used.

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