[ofw] RE: [RFC] Remove path query from IPoIB

[Fab Tillier]

> Does Windows require the GRH (for some part of IPoIB) ? If so, that
> would cause an interop issue with implementations which don't send GRH
> (like Linux).

Yes, it requires the GRH to create the endpoint so that it can report the packet to NDIS, as well as to support sending a packet back.

Without an endpoint, the packet gets dropped.  The endpoint lookup can key by LID if there is no GRH, so as long as an endpoint exists by the time a packet without GRH is received all is well.

An ARP request (sent to the broadcast group) includes the GRH, so the endpoint can be created without problems.  The ARP response (unicast) doesn't need the GRH, as the code in IPoIB will create the endpoint based on the HW address in the ARP itself.  So if you go through ARP resolution all further unicast packets will be sent/received properly regardless of whether the GRH is present or not.

There is no code for IPv6 neighbor discovery, I don't know if there needs to be, I would suspect there should.  In any case, IPv6 has issues in large fabrics due to running out of MC groups for the solicited address groups, so there's work that needs to be done on the IPv6 front anyway.

-Fab