Fwd: Re: [openib-general] static LID computation with TS_HOST_DRIVER

[Michael Krause]

At 08:49 AM 9/29/2004, David M. Brean wrote:
>The subnet management state is protected by an M_Key (see section 
>14.2.4).  The M_Key is managed by the SM.  The M_Key is not exposed via 
>the Verbs or through SA queries [the exception being the trusted entity, 
>but that entity is another SA or higher layer management application - so 
>let's ignore for this situation.]   An endnode implementation should not 
>allow any back-door mechanism that enables changing the subnet management 
>state without the M_Key if the port is protected.  Note, the M_Key and 
>protection bits can be in persistent storage and preserved across port 
>power cycles to eliminate the power-up exposure.  So, without making 
>subnet assumptions/restrictions, there is no reliable way for an IB 
>client, like the local MAD layer, to specify the LID.
>
>LID assignment is SM policy and the SM may choose to preserve a port's 
>LID, however, I don't think IB clients should depend on this behavior.

It has been the clear intent of the IBTA that LID assignment be strictly 
done by the SM as centralized management is the operating paradigm 
defined.  It has also been clear from the start that LID values are, by 
definition, dynamic and should never be preserved or relied upon by 
endnodes.  There is no requirement or policy that a SM should attempt to 
preserve LID assignment.  Given I authored addressing and other sections of 
the IB specs and chaired the workgroup responsible for the link wire 
protocols, I'm fairly confident that this is the intent of the IBTA.

Mike


>-David
>
>Roland Dreier wrote:
>
>>    David> Ok.  How does the port inform the SM that it has a
>>    David> "preferred" LID?
>>
>>The port will already have a LID assigned when the SM discovers it.
>>My understanding is that the SM is "encouraged" to preserve a port's
>>LID if it doesn't conflict with any other LIDs, and this is what we're
>>relying on.
>>
>>- Roland
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