The Passive property enables or disables passive FTP file
transfers between the local and remote host. In passive transfer
mode, the client is responsible for establishing the data
connection between the remote server and the local system. By
default, the Passive property is set to True, with the
client establishing the data connection with the server.
The majority of FTP servers support passive mode transfers, and
in most cases, passive mode is required when attempting to upload
or download files when the client is behind a firewall or a router
that performs Network Address Translation (NAT). However, if the
Passive property is set to True and the server does not
support passive mode, an error will be returned the next time a
file transfer or directory listing is attempted. In this case, set
the Passive property to False and attempt the transfer
again.
Note that setting this property has no effect when uploading or
downloading a file using the Hypertext Transfer Protocol
(HTTP).