Re: [ewg] Multiple IP subnets in a single partition
On 10/12/2011 3:28 PM, richard Croucher wrote: I understand that's it not good practice however I'm seeking to understand whether actual problems have been observed. The only issues I can suggest will be because of ARP is in the shared broadcast domain.Is there any IPoIB state in the SM other than QoS? I can't think of any reason why there should be. Even though ARP requests will be seen by interfaces in a different subnet, they should not respond with it's GUID since they will not match the requested IP address. wrong, see http://lxr.linux.no/#linux+v3.0/Documentation/networking/ip-sysctl.txt#L926 I think this refers back to behaviour seen many years ago, when multihomed hosts were rare. There was a tendency for them to respond on all interfaces to ARP requests for their nodename and cause ARP resolution problems.. Is there a reproducable test case of this problem, since I certainly know of systems which are configured like this and appear to be working fine. Maybe, they've just been lucky, but so far I've seen numerous messages saying don't do it and none to say what actually goes wrong. For basic testing and/or PoC you can set net.ipv4.conf.*.arp_ignore to 1 or alike (2). For production, I wouldn't do that or at least do it after conducting a deeper study (I gave you the heads-up, so please share your findings...), Indeed, I know that in the iscsi multipathing world people use multi-homed NICs on the same IP subne, though. Or. ___ ewg mailing list ewg@lists.openfabrics.org http://lists.openfabrics.org/cgi-bin/mailman/listinfo/ewg
Re: [ewg] Multiple IP subnets in a single partition
I understand that's it not good practice however I'm seeking to understand whether actual problems have been observed. The only issues I can suggest will be because of ARP is in the shared broadcast domain.Is there any IPoIB state in the SM other than QoS? I can't think of any reason why there should be. Even though ARP requests will be seen by interfaces in a different subnet, they should not respond with it's GUID since they will not match the requested IP address. I think this refers back to behaviour seen many years ago, when multihomed hosts were rare. There was a tendency for them to respond on all interfaces to ARP requests for their nodename and cause ARP resolution problems.. Is there a reproducable test case of this problem, since I certainly know of systems which are configured like this and appear to be working fine. Maybe, they've just been lucky, but so far I've seen numerous messages saying don't do it and none to say what actually goes wrong. - Richard Croucher www.informatix-sol.com +44-7802-213901 On Wed, 2011-10-12 at 15:02 +0200, Or Gerlitz wrote: > richard Croucher wrote: > > [...] known issue that you should not configure multiple IP > subnets within a single partition. Is this problem still > current? Is this just following IP best practice or does it > cause real problems, e.g. with ARP requests [...] > > > > > simply put, you should not put two IP subnets on the same broadcast > domain, it has nothing to do with IB, talk to your IT team for f2f > explanation. > > Or. > ___ ewg mailing list ewg@lists.openfabrics.org http://lists.openfabrics.org/cgi-bin/mailman/listinfo/ewg
Re: [ewg] Multiple IP subnets in a single partition
richard Croucher wrote: > ** > [...] known issue that you should not configure multiple IP subnets within > a single partition. Is this problem still current? Is this just following > IP best practice or does it cause real problems, e.g. with ARP requests > [...] > > simply put, you should not put two IP subnets on the same broadcast domain, it has nothing to do with IB, talk to your IT team for f2f explanation. Or. ___ ewg mailing list ewg@lists.openfabrics.org http://lists.openfabrics.org/cgi-bin/mailman/listinfo/ewg
