[ofa-general] Re: [openib-general] Fw: [PATCH] enable IPoIB only if broadcast join finish

[Roland Dreier]

 > I believe even IPv6 with ethernet, the interface will be UP and RUNNING
 > even they have a duplicated IPv6 address so IPv4 can work. I don't know why
 > we do thing differently here.

That's not the point.  The point is that if we bring the interface up
before the multicast groups are joined, then IPv6 DAD has a chance of
incorrectly not detecting duplicate addresses (think about it -- if
IPv6 autoconf/DAD starts before all the multicast groups are ready,
then the IPv6 stack will generate ND and router solicitation messages,
but they will just be queued up pending multicast join completion, and
if that doesn't happen before the timeouts occur, then the IPv6 stack
will incorrectly conclude that a duplicate address doesn't exist, even
if it does)

The real question is what tradeoff do we want to make for broken
fabrics where some multicast groups can never be joined.  Is it worth
the (small) risk of breaking IPv6 autoconf on good fabrics in order to
behave more gracefully on broken fabrics?

 - R.