Hello,
I would like to prepopulate the DNS cache with a IPv6 (preferred) and a
IPv4 address. When I try to do the same it works perfectly if the host
is dual stack, but not if it is IPv4 only. How was the usage for such a
scenario intended? I assumed that it would even try IPv4 if no IPv6 is
available.

Programm:
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <curl/curl.h>
#include <fcntl.h>

static CURLcode
prepoulate_dns_cache(CURL *curl)
{
        struct curl_slist *host = NULL;
        host = curl_slist_append(host, "gmvl.de:443:2a01:4f8:b0:2fff::2");
        host = curl_slist_append(host, "gmvl.de:443:88.198.249.254");
        return curl_easy_setopt(curl, CURLOPT_RESOLVE, host);
}

int
main(int argc, char **argv)
{
        CURL *curl = NULL;
        char *errbuf;

        errbuf = malloc(CURL_ERROR_SIZE);
        if (errbuf == NULL)
                exit(1);

        curl = curl_easy_init();
        if (! curl) {
                exit(1);
        }

        curl_easy_setopt(curl, CURLOPT_ERRORBUFFER, errbuf);
        curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
        prepoulate_dns_cache(curl);
        curl_easy_setopt(curl, CURLOPT_URL, "https://gmvl.de/");
        curl_easy_perform(curl);

        return 0;
}

C:\Users\carbon\Desktop>test
* Added gmvl.de:443:2a01:4f8:b0:2fff::2 to DNS cache
* Added gmvl.de:443:88.198.249.254 to DNS cache
* timeout on name lookup is not supported
* Hostname gmvl.de was found in DNS cache
* Trying 2a01:4f8:b0:2fff::2...
* connect to 2a01:4f8:b0:2fff::2 port 443 failed: Network unreachable
* Failed to connect to gmvl.de port 443: Network unreachable
* Closing connection 0

Cheers,
        Thomas
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Received on 2016-01-13