Comment 2 for bug 1764478

this is also related to bug 1447715 in which i added the DAD wait to ifupdown. however, since bug 1633479 fixed the issue in dhclient instead of ifupdown, at around the same time, i marked bug 1447715 as wontfix, since that ifupdown change was no longer required to get dhclient working.

But, now with this bug, the side-effect of changing dhclient to do its 'PREINIT6' (as mentioned in last comment) seems to be prohibitive and it probably is much easier to simply re-open bug 1447715 and push that ifupdown fix into xenial.

That approach does mean that manual running of dhclient -6 -S will always fail with an interface that's down (or was brought up immediately before running dhclient -S, which is what ifupdown does). However, while manually running dhclient -6 on a currently down interface in order to both bring it up and get a dhcpv6 address does make sense, running dhclient -6 -S on a down interface does not really make sense, since doing that will only get the 'other' network info like DNS server, and won't actually set up an address on the interface. So I think I have to agree with the conclusion in bug 1633562, to mark waiting for dad when manually running dhclient -6 -S as invalid.

So, I'll mark this bug as a dup of that original bug, and I'll re-open bug 1447715 to push that ifupdown fix into xenial.