Roland,
Thanks for your quick response.
Even SM supports 1000 MCGs, it's still not sufficitent for 250 nodes
cluster, each node have 4 links for IPv6 without any scope/global IPv6
address configured.(250*4+ a few default MCGs) There will be a MCG overflow
problem anyway in IPv6oIB.
Thanks
Shirley Ma
IBM Linux Technology Center
15300 SW Koll Parkway
Beaverton, OR 97006-6063
Phone(Fax): (503) 578-7638
Roland Dreier
<[EMAIL PROTECTED]
m> To
Shirley Ma/Beaverton/[EMAIL PROTECTED]
02/16/2007 09:00 cc
AM "Michael S. Tsirkin"
<[EMAIL PROTECTED]>,
openib-general@openib.org
Subject
Re: IPv6oIB neighbour discover
broken when MCGs overflow
> We have a customer issue regarding IPv6oIB. In the subnet, there are
> limited number of MCGs supported. So when there are multiple IPv6
addresses
> are assigned to one interface, each IPv6 address will have one unique
> solicited-node address (depends on their groupID). Then in a large
subnet,
> we will have tons of MCGs. If IPv6 solicited node addresses exceed the
> number of MDGs in this subnet, then IPv6 neighbour discovery will be
> broken, this won't happen in Ethernet since sendonly doesn't require
sender
> to be joined any MCG.
> I have done an initial patch to addresss MCG overflow problem and
redirect
> the solicited-node address to all hosts node address, thus IPv6
neighbour
> discovery will work no matter how many IPv6 addresses in this subnet.
This
> patch is only triggered with IPv6 enabled and MGC overflows, so there is
> almost no performance penalty.
I really don't like this approach, since it can break things in very
subtle ways (eg suppose one node fails to join its solicited node
group, but then a later node wants to talk to it and succeeds in
joining the solicited node group as a send-only member -- since the
first node is not a member then it will never see the ND messages).
I much prefer to fix the SM not to impose too-low limits on the number
of MCGs. Supporting O(# nodes) MCGs is really not a very onerous
requirement on the SM.
- R.
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