Comment 23 for bug 1447715

for NetworkManager, this is fixed starting in wily (see comment 13) and so should work in xenial/yakkety; and in trusty, dhclient still works (per description stating dhclient works in isc-dhcp-client 4.2.4-7ubuntu14). I'm not sure if NetworkManager using dhcpv6 works in precise (but who is using precise with NetworkManager?). It would be useful if anyone could test NetworkManager on precise using dhcpv6.

for ifupdown/dhclient, as scott said in bug 1633479 comment 13, in older trusty/precise dhclient, it actually retries and so the bug doesn't exist there. In yakkety, this is already fixed in ifupdown (via fix included in debian ifupdown pulled into yakkety). So this bug only is possibly applicable in xenial; and I just confirmed that by updating only isc-dhcp-client to version 4.3.3-5ubuntu12.4, it does succeed in getting a dhcpv6 address.

So no, it doesn't seem that this patch to ifupdown is needed in xenial, and if applied I don't think there would be any noticable difference. So it should be fine to mark this Won't Fix for xenial, as it was fixed in isc-dhcp-client via bug 1633479.