CURLcode curl_easy_setopt(CURL *handle, CURLOPT_FTP_USE_EPSV, long epsv);
DESCRIPTIONPass epsv as a long. If the value is 1, it tells curl to use the EPSV command when doing passive FTP downloads (which it does by default). Using EPSV means that it will first attempt to use EPSV before using PASV, but if you pass zero to this option, it will not try using EPSV, only plain PASV.
If the server is an IPv6 host, this option will have no effect as of 7.12.3.