bug#17976: 24.3; url-retrieve-synchronously doesn't fallback to IPv4

[Juliusz Chroboczek]

>> This is independent of IPv6.  A hostname could also resolve to multiple
>> IPv4 addresses where only one of them is (currently) reachable.

Please hear this man.

> But how does this work in practice?  How are we doing name resolution?
> Do we have access to all the IP addresses?  Do we have access to the
> IPv6 addresses without...  doing stuff?  :-)

If we don't, it's a bug that must be fixed.  The multihoming techniques
that are being developed at IETF right now rely on giving multiple
addresses to a single host (and implementing a routing infrastructure to
match), we really need to be trying them all.

-- Juliusz