Re: [Xen-devel] vif tx drops

[Brian Wolfe <brianw@xxxxxxxxxxxx>]

So the xen side of the vif isn't see on the wire except for a: the
backend driver domain( usually domain-0) and that vif's front and driver
domain eh? (I got the front and back end locations right yes?)

Interesting...

Either way it goes, how would one go about verifying that the MAC is
truly unique on it's visible lan? I'd be i very interested in this as a
safety precaution. Right now I can't think of how to do the uniqueness
test... 8-P if someone can give me an idea or two I could try to code it
since it's something that I want.(brain fried this morning)

On Thu, 2004-10-14 at 03:21, Keir Fraser wrote:
> 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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> 
> 
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