[openib-general] ib_gid_is_link_local

[Jason Gunthorpe]

On Thu, Jan 04, 2007 at 05:13:52PM -0500, Hal Rosenstock wrote:

> > The way I was hoping to start out is by putting this in the SA and the
> > routers, not in the end nodes.
> 
> We can start there but this is a very fundamental question. I have heard
> people weigh in on both sides...

Yes, but fortunately the two methods can co-exist and we can prototype
the expected router support in opensm and get some experience
there.

> > With this kind of model the IB path lookup would return a LID/SL/etc
> 
> Map S/DGID and perhaps TClass to LID/SL/MTU ?

Yeah, I think so.

> all known MLIDs on that subnet rather than all possible MLIDs ? It's
> really the MGIDs that are of interest rather than the MLIDs. The router
> needs to subscribe to traps 66/67 multicast groups in and out of
> existence. MLIDs on each side of the router may not be the same for a
> non link local MGID.

Yes, we can definately do that.

However, it might be smart to have opensm consider the routers to be a
send-only member for every MLID..

> By onlink, are you saying these wouldn't be forwarded ?

Not necessarily, the resulting MLID could still end up going to a
router.. 

A onlink line routing table just terminates the routing
lookup. 'unreachable' is another termination. A via line changes the
next hop GID and creates more lookups until an onlink is reached.

I honestly don't have a good idea how routed multicast can work on IB
without alot of ugly overhead. What do you do if you route between 4
1000 node clusters with IPv6? How can you avoid registering 4000
multicast groups with each SM and still have IPv6 SNM work correctly?

> Are you referring to running a spanning tree for multicast ? In any
> case, I think it will be a while before the routing protocols come into
> the picture and whether the SM is involved or not is another piece of
> some of the fundamental routing questions/devisions to be made.

Yes, but in this case I don't think multicast routing can be pushed to
the host. It is either the router or some combination of the router
and the SM.

Jason