On Fri, 2006-05-12 at 13:10, Jason Gunthorpe wrote: > On Fri, May 12, 2006 at 08:11:17AM -0400, Hal Rosenstock wrote: > > > > To allow what Roland is talking about you need an unambiguous > > > mechanism where the SA can signal to the client that the path > > > needs a GRH. > > > > Ah, you are referring to the SA path record response not the request. > > Yes.. Though I think we are still talking about different things in a > few places ;> > > How about this, how do you see this scenario: > > 1) Client gets a DGID from 'someplace' > 2) Client sends a SA query to resolve the DGID to a Path Record > 3) Client configures a QP based on the Path Record > > Now, the question I'm interested in is this: > During step #3 what test should the client apply to determine if a > GRH should be used with the QP. > > Other issues around the GRH like management MAD responses use and > multicast I feel are well specified and don't need more consideration.
Thanks for clarifying. > > > Think of it the other way, HopLimit < 2 means it _can't_ be forwarded > > > off subnet, so that result from the SA should _always_ cause the > > > requesting client to not use a GRH for that path. > > > > Not always true in terms of local subnet (multicast and management MAD > > response exceptions). > > Yes, but these are well specified. Multicast must always have a GRH. > MAD requests are covered under my scenario above and MAD responses > to MAD requests with GRH's are specified to use the GRH and set the > HopLimit = 0xFF. Where does the spec say HopLmt needs to be 0xFF for multicast ? > Also, I would assume when building a router that multicast packets > with a hop limit of 0 are non-forwardable based on the rules in IBA. 0 or 1 hop limit for both unicast and multicast > > Are you saying HopLimit is supplied to the SA in the request ? It could > > be but it's optional in general. In the router case, an off subnet DGID > > should be sufficient. I would think the HopLimit (as well as the other > > GRH fields) would need to be returned by the SA to the client. > > Talking about a request for a Path to the SA from a client now: > I would suggest that if the client wishes to restrict itself to paths > that are only on-link then it could send a SA request with the > path record HopLimit=0. Yes (or HopLimit=1). > A SA request with HopLimit=* (masked out > of component mask) should let the SA return routed paths. Yes. > I also think that the SA response should have a HopLimit of 0 for > local paths 1 would also be valid here too. > and a HopLimit >= 2 for routed paths. Yes. > However, I can't find any wording in IBA that would require this > behavior. In terms of the SA responses to Path/MultiPathRecord requests, the HopLimit is required to be filled in in the response. Is that what you are asking ? It's up to the SA to determine this and for the client to use the values returned subsequently just as it does for DLIDs, SLs, etc. > > Not sure exactly what you mean by full control over the routing header > > (GRH). The SA supplies the info for the headers to the client and the > > client is responsible for putting the correct info in the headers. Do > > you mean supplies sufficient info for the client to do this correctly ? > > If so, I agree. > > As far as I can see IBA includes all header information for the GRH > and LRH in the PathRecord response. It does not define a how to > determine if the path described by a PathRecord response requires > a GRH or not. I think the rules are there: Multicasts always have GRH. Unicasts off subnet have GRH and on subnet they are optional. Off subnet is either determined by the prefix comparison or HopLimit >=2 in the response from the SA. The latter is implied by C8-16 on p. 229. -- Hal > Thanks, > Jason _______________________________________________ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general