[openib-general] IB Address Translation service

[David M. Brean]

Your case #3 is an application where the limitations of RARP on IB 
appear.  I can't think of any other interesting configurations beyond 1-3.

-David

Hal Rosenstock wrote:

>Reviving an old thread...
>
>On Sat, 2005-03-05 at 10:22, David M. Brean wrote: 
>  
>
>>There is an I-D for DHCP on IB.  IPoIB defines a "broadcast" address and 
>>DHCP (and ARP) on IB use it.  Could make RARP work using this mechanism, 
>>but as someone else pointed out, the IB hardware address contains a 
>>QPN.  The I-D for IPoIB says something like:
>>
>>    The link-layer address for IPoIB includes the QPN which might not be
>>    constant across reboots or even across network interface resets.
>>    Cached QPN entries, such as in static ARP entries or in RARP servers
>>    will only work if the implementation(s) using these options ensure
>>    that the QPN associated with an interface is invariant across
>>    reboots/network resets.
>>
>>So, there are requirements on the IPoIB implementation to make RARP 
>>work.  Folks in the IPoIB work group decided not to go much further than 
>>these statements for RARP support since most folks felt that DHCP is (de 
>>facto) replacement.
>>    
>>
>
>There are 3 cases I can envision:
>
>1. A single IPoIB interface per HCA port. In this case, the RARP server
>can just match on the hardware address (port GID) without the QPN.
>
>2. In the case of VLANs, I think we are likely OK as well. In that case,
>there is a separate IP subnet (per PKey) so the port GID is unique per
>IP subnet (the port GID is unique on that partition (IP subnet)). I
>think there is a different QPN per VLAN.
>
>So I don't think that the above 2 cases require an invariant QPN.
>
>3. The third case is multihomed interfaces on the same IPoIB subnet. I
>don't think this is currently supported by IPoIB (but may someday). That
>would either not be supported by RARP or some way to have invariant QPNs
>would be needed. I'm not sure how important this case is.
>
>Is the above correct ? Are there other cases ? 
>
>-- Hal
>
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