[openib-general] Re: IB Address Translation service

[Michael S. Tsirkin]

Quoting r. Hal Rosenstock <halr at voltaire.com>:
> Subject: Re: IB Address Translation service
> 
> 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
> 

Some DHCP servers (dhcpd) let you configure a fixed IP per hardware address.
It seems to me that making this work requires an invariant QP, right?

-- 
MST - Michael S. Tsirkin