The ActivePort property property array is used to change
the range of local port numbers used for active mode file transfers.
The property array index specifies the port that should be changed,
and may be one of the following values:
| Value |
Description |
| ftpActivePortLow |
Change or return information for the low port number. |
| ftpActivePortHigh |
Change or return information for the high port number. |
The localport value specifies the new port number to be
used. Valid port numbers are in the range of 1025 through 65535.
This property array is used to modify the range of local port
numbers used for active mode file transfers. When using active mode,
the client listens for an inbound connection from the server rather
than establishing an outbound connection for the data transfer. In
most cases, passive mode transfers are preferred because they
mitigate potential compatibility issues with firewalls and NAT
routers.
If active mode transfers are required, the default port range used
when listening for the server connection is between 1024 and 5000.
This is the standard range of ephemeral ports used by the Windows
operating system. However, under some circumstances that range of
ports may be too small, or a firewall may be configured to deny
inbound connections on ephemeral ports. In that case, the
ActivePort property can be used to specify a different range
of port numbers.
While it is technically permissible to assign the low and high
port numbers to the same value, effectively specifying a single
active port number, this is not recommended as it can cause the
transfer to fail unexpectedly if multiple file transfers are
performed. A minimum range of at least 1000 ports is recommended. For
example, if you specify a low port value of 40000 then it is
recommended that the high port value be at least 41000. The maximum
port value is 65535.