Subject: RE: [Ipoverib] Interoperability

From: "Culley, Paul" <[email-masked]>
Date: Fri, 18 Jan 2002 13:54:22 -0600

These are key questions, and a source of some of the confusion on this
reflector.  One or two members seem to think that an endnode can choose
LID and SL values in some fashion without going to the SA (or having the
information derived from the SA).  While this can certainly be made to
work, if a vendor provides both the SA and the endnodes, it will not
work across every possible implementation of the SM/SA.

The only interface architected by IB that is guaranteed to return paths
suitable to get the data across, is the PathRecord query.  Between that
and requirements on SM that any given SLID/SL/DLID set work in both
directions, you have just about got all the useful defined mechanisms
that an endnode can use.

As has been pointed out, any device can give any single other device the
information it has on a path between them, but that information must
include all three elements SLID/SL/DLID, one way or the other.  Changing
any one element risks that the packets will be dropped either going or
returning with the inverted SLID/DLID.

As it stands now, using an SGID and DGID, with TClass=0 and FlowLabel=0
will also provide an interoperable query for PathRecord within the
subnet.

It is the goal of most of the IB members to make IB routing work with
the same interfaces, and the same way, although that work is far from
done.  If we pull this off, then endnodes designed before IB routers
become available will still work across subnets.  To this end I am
warning about practices that won't work, like getting LIDs from the body
of the packet, where they are not valid if they cross an IB subnet
boundary, in the hope that IPoIB stuff will work when IB routers become
available.

I certainly hope it is the goal of the IPoIB group to enable
interoperability between endnode devices (supporting IPoIB) and SAs, IB
routers etc. that don't know about IP.  This means adding no new
constraints on the IB infrastructure, only to the endnodes or new IP
routers attached to the IB fabric.

Paul R. Culley
Compaq Sr. Fellow
281-514-5543

-----Original Message-----
From: Ashwin Kamath [mailto:[email-masked]]
Sent: Friday, January 18, 2002 1:04 PM
To: [email-masked]
Subject: [Ipoverib] Interoperability

 There are two major implementation camps, with SA and without SA. Is it
the
goal of the architecture to be complete enough to deal with
interoperability
between implementations? Is interop supposed to be gauranteed if two
distinct implementations adhere to the specs?
 In my opinion, it must be complete enough that two distinct
implementations, must interoperate if they adhere to IpoIB spec.
Comments...

-Ashwin.

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