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

Hi Margaret,

> (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.

I think it may actually be safe to assume that the IB GUID in question is
__always__ globally unique (regardless of the value in its "u" bit). The IB
spec says: 

"The manufacturer assigns an EUI-64 __with_global_scope_set__"

The IPv6 IID can therefore be based on this manufacturer assigned GUID which
is __required__ by the IB spec to be one with global scope. The mechanism
for building the IPv6 IID could then be as simple as taking the IB mfg
assigned GUID and set (if it was not already so) its "u" bit (i.e. ignore
the interpretation that the vendor may have given to the IB spec).

To close the loop, the IBTA would have to explicitly forbid the use of the
same 63 bit combination with two different values for the u bit as two valid
globally unique GUIDs. I can't speak for the entire IBTA but it looks to me
that this would be acceptable. Furthermore, it is my understanding that the
definition of locally unique IB GUIDs would then be irrelevant to the ipoib
spec.

Does it make sense?

Thanks,

Diego