Re: [Xen-devel] using a different MAC in netfront than the onegiven by netback

[David Edmondson <dme@xxxxxxx>]

On Mon, Aug 18, 2008 at 06:02:03PM +1000, James Harper wrote:
> > On Mon, Aug 18, 2008 at 01:42:28PM +1000, James Harper wrote:
> > > Is there any problem if netfront (or Windows in my case) uses a
> > > different MAC address than the one given to it by netback? NLB
> (Network
> > > Load Balancing) appears to need to assign a Locally Administered
> Address
> > > to the network interface.
> > >
> > > The only issue I can think of is if iptables added rules on a MAC
> > > address basis, which it doesn't at least in 3.2.x...
> > 
> > This will break on Solaris dom0, where there's an implicit filter for
> > the MAC address assigned by the dom0 tools.
> > 
> > It might be useful to allow the guest to extend the set of unicast
> > addresses it receives in a manner similar to the multicast stuff (that
> > no-one else implements :-/).
> > 
> 
> Windows NLB isn't going to work with the GPLPV drivers on a Solaris Dom0
> then,

With any software that uses a MAC address other than that assigned,
irrespective of the drivers, in fact.

I recall that the RTL8139 code in qemu-dm also filters, but perhaps
that gets disabled if the guest sets promiscuous mode.

Does the driver in question (your GPLPV driver in this case) get
notified when Windows wants to use an extra unicast address? Perhaps
it just pushes the device into promiscuous mode?

> unless the filter can be lifted on a case by case basis?

There are some knobs in the driver stack that should make this
possible. I'll look into it.

> Or maybe the multicast mode of NLB will work around that problem...

Multicast should "just work".

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