What is the "Passive Mode" option in WS_FTP Pro?
Answer/Solution: You can find the "Passive
Mode" option in the Connection window, Advanced tab.
In version 7.5 the passive mode option can be found by
clicking once on your site profile within the "connect to remote
host" window, then click "edit" to the right.
In the FTP protocol two ports are normally used, 20 and 21.
Port 21 is the control channel in which requests such as PUT, GET, and PWD
are sent to the server.
Port 20 is the data channel in which actual files, folders and directory
listings are sent.
Normally, when you connect to an FTP site, the site establishes the data
connection to your PC (the client) on Port 20. However, if the site allows
passive transfers, you can have your PC establish the data connection. We
recommend that you use passive mode for most transfers.
Definition from RFC 959:
This command requests the server to "listen" on a data port (which is not its default data port) and to wait for a connection rather than initiate one upon receipt of a transfer command. The response to this command includes the host and port address this server is listening on.
Certain ftp servers support both active and passive transfers while other
ftp servers only allow active transfers.
In some cases passive mode may be required for users who are behind some
types of router-based firewalls or behind a gateway requiring passive transfers.
If the transfer method in which you are using is rejected by the server, the
result is usually a "Blocking Call Cancelled" error message.
For more information
WS_FTP - Receive error: blocking call cancelled
WS_FTP Pro 8.0 User's Guide -