Given how Debian and Ubuntu nowadays enable IPv6 support by default, the routing table includes some IPv6 entries by standard. However, this has the unpleasant side-effect that lib C tries to connect to public IPv6 addresses, even in a case when the only IPv6 entries are for loopback and local link. Apparently, libc incorrectly assumes that the mere presence of any IPv6 means that there is a usable default IPv6 route. This results in, among other things, APT failing at fetching packages from the Debian repository if the DNS rotation returned the IPv6 address for the server first. I was thus wondering whether libc6 could be made to reject public IPv6 addresses, in cases when the host has no IPv6 gateway in its routing table? Or would there be a smarter way to prevent applications from failing at contacting IPv6 addresses whenever there is no IPv6 connection to the outside world?
