RE: please read: Clarification on GUID's universal/loc al bit

Hi Diego,

At 5:56 PM -0700 5/23/04, Diego Crupnicoff wrote:
We know of deployed IB implementations where the "u" bit in the GUID 
is cleared.

The IBTA LWG has discussed this matter but no formal resolution has 
yet been voted. The LWG is looking for a way to solve the problem 
without affecting any existing implementation.

Given the above, I would suggest that IPoIB should define the way to 
derive an IPv6 interface identifier from an IB-port-GUID without 
making any assumptions on the value of its "u" bit.

Given the apparent ambiguity in the IB specification, there are only 
two things that I can think of to do in this situation:

(1) Ask the IBTA to clarify their specification, with the hope that 
vendors will  update their implementations to match the clarified 
value.  It seems unlikely, though, that this is a practical choice if 
vendors have already shipped hardware that has burned-in values with 
different interpretations of the "u" bit.

-or-

(2) Accept that we cannot tell, by looking at an IB GUID, whether it 
is of global or local scope.  In this case, the conservative choice 
would be to treat all IB GUIDs as if they are of local scope, always 
clearing the "u" bit in the IPv6 IID, regardless of how the bit is 
set in the IB GUID.

There is a potential downside to choice (2):  If we do come up with 
mechanisms that can take advantage of the fact that some IIDs are 
globally unique (to simplify routing, host identification, etc.), 
those mechanisms would not work on IB nodes.  However, I can't think 
of any other practical choice.

What do others think we should do here?

Margaret