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

[Shirley Ma]

Jason Gunthorpe <jgunthorpe at obsidianresearch.com> wrote on 03/06/2007
02:17:40 PM:

> On Tue, Mar 06, 2007 at 12:52:27PM -0800, Shirley Ma wrote:
>
> > The IPv6 stack will generate ND and router solicitation messages
> > when sending packet. The duplicated address can be detected
> > anytime. Am I right? So if the multicast join completion later, the
> > duplication address will be detect later.
>
> No, this isn't right.
>
> When a new address is assigned to the interface it starts out in the
> tentative state. This triggers DAD which will move the address out of
> the tentative state and makes it usable. The DAD procedure is on a
> timer since it is probing with ND packets to find a duplicate. I don't
> think DAD will activate again once the initial probing is done.
>
> RS is in two parts. First when the interface first comes up the kernel
> sends out RS packets to get a router to respond faster. This is also
> on a timer. Second, the routers send out RS packets on their own from
> time to time and the kernel will act on them.
>
> All of this needs the right multicast groups to be active before the
> sequences are started. DAD needs full membership in the solicited node
> multicast group and RS needs memberships in the all-hosts and
> all-routers groups.
> > My point is IPoIB should behave as other networking device drivers.
>
> IPoIB is not like other networking fabrics. IB has multicast that
> requires synchronization with the SM. Ethernet has no such thing.
>
> Jason

So we could have same IPv6 addresses even without IPoIB if the NS doesn't
respond on time for any reason, right?
Then DAD is broken in current code already. In IPoIB case, we allow
duplicated IPv6 addresses after the interface up and running but not before
if any reason the multicast join successfully much later, probably after
several tries? That doesn't make any sense to me.

Thanks
Shirley Ma
IBM Linux Technology Center
15300 SW Koll Parkway
Beaverton, OR 97006-6063
Phone(Fax): (503) 578-7638
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