[openib-general] Problem is routing CM REQ was: Use a GRH when appropriate for unicast packets

[Hal Rosenstock]

On Thu, 2007-02-08 at 14:54, Sean Hefty wrote:
> >Hum, you mean to meet the LID validation rules of 9.6.1.5? That is a
> >huge PITA..
> >
> >[IMHO, 9.6.1.5 C9-54 is a mistake, if there is a GRH then the LRH.SLID
> > should not be validated against the QP context since it makes it
> > extra hard for multipath routing and QoS to work...]
> 
> Yes - this gets messy.
> 
> >Here is one thought on how to do this:
> >To meet this rule each side of the CM must take the SLID from
> >the incoming LRH as the DLID for the connection. This SLID will be
> >one of the SLIDs for the local router. The other side doesn't need to
> >know what it is. The passive side will get the router SLID from the
> >REQ and the active side gets it from the ACK.
> >
> >The passive side is easy, it just path record queries the DGID and
> >requests the DLID == the incoming LRH.SLID.
> 
> This requires that the passive side be able to issue path record queries, but I
> think that it could work for static routes.  A point was made to me that the
> remote side could be a TCA without query capabilities.

Are you referring to SA query capabilities ? Would such a device just be
expected to work without change in an IB routed environment anyway ?

-- Hal

> 
> There's still the issue of what value is carried in the remote port LID in the
> CM REQ (12.7.21), and I haven't even gotten to APM yet...
> 
> >The nasty problem is with the active side - CMA will select a router
> >lid it uses as the DLID and the router may select a different LID for
> >it to use as the SLID when it processes the ACK. By C9-54 they have to
> >be the same :< So the active side might have to do another path record
> >query to move its DLID and SL to match the routers choosen
> >SLID. Double suck :P
> 
> As long as the SA and local routers are in sync, we may be okay here without a
> second path record query.
> 
> - Sean
> 
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