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

[Sean Hefty]

>>The active side clearly cannot learn what the SLID of the passive
>>side's router should be.
>>
>>We don't want to have the routers snoop and alter CM GMPs.
>>
>>The passive side cannot use information from the LRH to get the router
>>LID since the LRH may not be reversible.
>>
>>The only option seems to be to have the passive side do a path record
>>query on a SGID in the CM REQ...
>>
>>This is a spec problem unfortunately.
> 
> 
> Yes and I would expect that this would be changed.

Looking at the problem more, I think that the issue extends to the remote port 
LID as well.  My expectation with a local path record query is that the SLID is 
the local port, and the DLID is the local router.  This should be sufficient for 
one-way UD traffic, but for connected traffic we still need to discover the 
remote router and remote port LIDs.

I think that we need a way for the local node to query the remote SA to obtain 
this information.  Or we need a new path record for routable paths that includes 
this information.

- Sean