Rather than pick addresses totally at random, this changes the
preference to be private IP4 > public IP4 > DNS. (Ordering is not
guaranteed, but in many cases there will only be one of each type of IP
anyways.) All three of these are preferred over IP6, which also goes
public > private.
This seems likely to match the common case where you're getting into a
machine on the private side from the public side. It's harder to know if
DNS is private or not, so IPs are preferred in this case.
Jeff Mitchell