[ewg] Multiple IP subnets in a single partition

[richard Croucher]

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 <Richard.croucher at informatix-sol.com> 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.
> 
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