The PORT instruction tells the remote server to connect to our specified IP address. The string may be a plain IP address, a host name, a network interface name (under Unix) or just a '-' symbol to let the library use your system's default IP address. Default FTP operations are passive, and thus won't use PORT.
The address can be followed by a ':' to specify a port, optionally followed by
a '-' to specify a port range. If the port specified is 0, the operating
system will pick a free port. If a range is provided and all ports in the
range are not available, libcurl will report
#CURLE_FTP_PORT_FAILED for the
handle. Invalid port/range settings are ignored. IPv6 addresses followed by
a port or portrange have to be in brackets. IPv6 addresses without port/range
specifier can be in brackets.
Examples with specified ports:
.nf eth0:0 192.168.1.2:32000-33000 curl.se:32123 [::1]:1234-4567 .fi
You disable PORT again and go back to using the passive version by setting
this option to