Comment 23 for bug 1633479

This does *not* appear to resolve a closely related problem where the link-local address has not yet been assigned. See LP: 1718568

In brief, the loop

        case " $out " in
            *\ dadfailed\ *)
                error "$dev: ipv6 dad failed."
                return 1;;
            *\ tentative\ *) :;;
            *) return 0;;
        esac

exits with 'return 0' with the lack of a link-local address as " " ($out empty) matches the default pattern as would a valid, link-local address.

One possible solution is to add "the missing case" that matches $out being empty that performs the "wait and try again" action.