Bug#268631: force preference of IPv4 over IPv6
> Yes, let's deploy IPv6, but also make sure that nobody use it!
If I understand what you're saying correctly, in essence, you feel sad
inside when two IPv6-enabled hosts communicate using IPv4.
That is not a technical argument.
For the next few years at least, when both are available, IPv4 will
typically be faster and more reliable than IPv6. That is the world we
are living in.
Imagine that you're Joe Network Admin. Which of the following two
scenarios would make you more likely to deploy IPv6?
(a) If you deploy IPv6 your users will (mainly in the future) be able
to access more hosts, and have better connectivity. And
*nothing* will break or slow down, so you won't get any
complaints, only (mainly in the future) kudos.
(b) If you deploy IPv6 your users will (mainly in the future) be able
to access more hosts, and have better connectivity. However
connectivity to some hosts may be dramatically degraded or
disrupted, so you may get a bunch of immediate complaints, and
addressing these will in all likelihood be impossible without
It is up to us to choose whether option (a) or (b) holds, because
these are controlled by client preference of IPv4 or IPv6 when both
are available. Option (a) is "clients prefer IPv4". Option (b) is
"clients prefer IPv6".
If we go with option (a), we might actually be able to transition to
IPv6 pretty soon. With option (b), the Internet will stay a ratty
NATed IPv4 monster for much longer, possibly forever, because admins
would have to be IPv6-loving masochists to enable IPv6, and most
network admins just want their users to be happy and don't care about
helping to hasten widespread deployment of IPv6, especially if doing
so would make their users unhappy. Since I want to see IPv6 enjoy
widespread deployment, I think option (a) would be a wise decision.