Re: Comments on draft-ietf-ipoib-link-multicast-04.txt

> > For interoperatibilty.  The requirement is the host and router must 
agree
> > on using a common mechanism for exchanging the IP multicast packet.
> > Implementations are free to choose a mechanism as long as all other
> > implementations with which they communicate also choose to implement 
the
> > same mechanism.  I don't think this is an area where we can or should 
punt
> > - a minimal, common approach needs to be mandated such that all IPoIB
> > nodes implement that mechanism so that any two IPoIB nodes will
> > interoperate.
> 
> Roy,
> 
> Yes, I agree that a common method must be described for 
interoperability.
> Though, in this case, even with the flexibility
> interoperability is maintained - the onus being on the router :
> 
> The packet may be sent to the routers on broadcast-GID or the
> all-router GID. The router itself will listen on both -
> broadcast-GID since it is required by IPoIB and all-routers as a
> result of other specs (IPv6 & IGMP). Therefore the packet will be
> received by the router irrespective of the MGID used as long as
> the router accepts any multicast packets on these MGIDs. I have
> described the need for this in my previous reply.
> 
> 
> We could do one of three things when the relevant MGID does not
> exist:
> 
> 1. The host must always forward on broadcast MGID
>    and the router must always accept IP multicast packets on the
>    broadcast GID.
> 
> 2. The host must always forward on all-router MGID and the router
>    must always accept IP multicast packets on the all-router
>    MGID
> 
> 3. The host must always forward on broadcast GID or all-router
>    MGID. The router must accept IP multicast packets on both the
>    broadcast MGID and all-router MGID.
> 
> 
> We have chosen case 3 . Is there a strong feeling that one of the
> other cases is preferable?
> 
> It appears that the method chosen(case 3) needs to be
> explicitly stated in the draft.

My preference is for case 2, as sending to the all-router MGID reduces the 
amount of multicast traffic an IPoIB host must filter as oppposed to 
sending to the broadcast GID.  I can live with case 3, but if it is chosen 
would prefer the text to state that the all-router MGID SHOULD be used, 
but the broadcast GID MAY be used.
 
Roy