I agree with Hal. If you look for Path Record to ANOTHER subnet you should provide the GRH in the sent packet address ...
Eitan Zahavi Design Technology Director Mellanox Technologies LTD Tel:+972-4-9097208 Fax:+972-4-9593245 P.O. Box 586 Yokneam 20692 ISRAEL > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:openib-general- > [EMAIL PROTECTED] On Behalf Of Hal Rosenstock > Sent: Thursday, May 11, 2006 2:20 PM > To: Jason Gunthorpe > Cc: Roland Dreier; [email protected] > Subject: Re: [openib-general] question regarding GRH flag in ib_ah_attr > > On Thu, 2006-05-11 at 01:48, Jason Gunthorpe wrote: > > On Wed, May 10, 2006 at 09:56:58PM -0700, Roland Dreier wrote: > > > Hal> Huh ? In this case, aren't the subnet prefixes are required > > > Hal> to be different ? > > > > > > It's kind of a crazy thing to do but I don't see anything in the IB > > > spec that forbids two subnets with the same subnet prefix, or any > > > reason why a router couldn't route between them. The SMs would just > > > have to be smart enough to return the LID of the router for paths to > > > ports on the other subnet, and the routers would have to have explicit > > > routes rather than forwarding based on just GID prefix. > > > > Hmm, this is an interesting point, you can do this in IP land using > > host routes. > > > > How about this - the Path record (and related) SA responses include > > the Hop Limit fields and the spec says: > > > > 8.3.6 Hop Limit: [..] Setting this value to 0 or 1 will ensure that > > the packet will not be forwarded beyond the local subnet. > > > > So, it is within the spec to use HopLmt >= 2 as the GRH required flag. > > That would be a simpler check but HopLimit is not a required component > of PathRecord but I think this may not be sufficient as just because a > HopLimit >= 2 doesn't mean that a packet would be forwarded off subnet. > > > I'd propose that the combination of a non-link-local prefix and a >= 2 > > Hop Limit should force a GRH. SM's that do not support routers should > > always fill in 0 for HopLmt. > > Why is a request with just a non link local prefix (with HopLimit > wildcarded) not sufficient ? > > -- Hal > > > Jason > > _______________________________________________ > openib-general mailing list > [email protected] > http://openib.org/mailman/listinfo/openib-general > > To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general _______________________________________________ openib-general mailing list [email protected] http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
