Re: [Xen-devel] vif tx drops

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

One option is to have the backend interfaces pick their MAC addresses
from a well-known range: e.g., AA:00:FF:00:00:00 + <vif id>.
These wouldn't need to be unique -- they'd never be seen 'on the
wire'.

The random MAC allocator would never pick a MAC in that range, and
xend could ensure that manually-selected MACs never fall in that
range and print an error if they did.

It's a shame that the backend needs a MAC different from the frontend
-- but if it doesn't then the bridge code complains. :-(

 -- Keir

> I temporarilly solved this by converting the IP to hexidecimal and
> setting the first 2 bytes of the mac to DE:AD. Unfortunately xen
> increments the 3rd if you set the mac. We need a way to set the mac on
> both ends of the vif device. 
> 
> Maybe we can have things this way. options...
> a: set the mac on one end and have a standard "increment" bit somewhere
> higher up(say first byte).
> b: set the macs on both ends
> c: set a specific range of macs to use
> 
> Either way xen really should test (not certain how exactly) to see if
> it's already in existence prior to using a mac that is dynamicly set.
> Not testing is playing russian roulette IMHO (as some including myself
> have found out already).
> 
> Opinions?
> 
> On Wed, 2004-10-13 at 15:17, Keir Fraser wrote:
> > > 
> > > " This is *definitely* worth checking
> > > " out at this point, and can be fixed by picking your own MAC addresses.
> > > 
> > > Yep.  How big a space do you randomize for mac addrs?
> > > 
> > > # grep -i AA:00:00:24:22:F3 a
> > > batch009 (172.16.12.19) at AA:00:00:24:22:F3 [ether] on eth0
> > > batch075 (172.16.12.85) at AA:00:00:24:22:F3 [ether] on eth0
> > > 
> > 
> > I think AA:00:00:00:00:00 - AA:00:00:7F:FF:FF (i.e., 8 million
> > addresses). But the random-number generator is crap.
> > 
> > You're definitely best off generating your own if creating any decent
> > number of VMs.
> > 
> >  -- Keir
> > 
> > 
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