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CURLOPT_LOCALPORT - set local port number to use for socket #include <curl/curl.h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_LOCALPORT, long port); Pass a long. This sets the local port number of the socket used for the connection. This can be used in combination with CURLOPT_INTERFACE(3) and you are recommended to use CURLOPT_LOCALPORTRANGE(3) as well when this option is set. Valid port numbers are 1 - 65535. 0, disabled - use whatever the system thinks is fine All

CURL *curl = curl_easy_init();
if(curl) {
 curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/foo.bin");
 curl_easy_setopt(curl, CURLOPT_LOCALPORT, 49152L);
 /* and try 20 more ports following that */
 curl_easy_setopt(curl, CURLOPT_LOCALPORTRANGE, 20L);
 ret = curl_easy_perform(curl);
 curl_easy_cleanup(curl);
}

Added in 7.15.2 Returns CURLE_OK CURLOPT_LOCALPORTRANGE "(3), " CURLOPT_INTERFACE "(3), "