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

[Jason Gunthorpe]

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