ephemeral-port-range
When the server accepts passive FTP data connections, it uses the system's
standard method of picking a random port number for the remote client to
connect to. For some primitive firewalls, you may want to restrict the
range of these random port numbers. Odds are you don't need this
feature. In addition, it isn't guaranteed to work 100% of the time anyway.
Examples:
ephemeral-port-range=4900-4999
#ephemeral-port-range= (commented out)
Recommendation:
#ephemeral-port-range= (commented out)