Xen users - Aug 2006 - changing MAC address makes VM unreachable

I''m using 3.0.2-3 and have gotten a matching user report from someone
using
3.0.1.  

After powering off a VM, changing its MAC address and rebooting, it becomes
unreachable.  

I made sure all ARP caches expired first before trying to contact the VM.
Looking at the network traffic shows the ARP who-has query hanging
indefinitely.  "brctl showmacs xenbr0" also shows the old, working
entry has
gone before the problem occurs.  I tried arping -A variations from within the
VM with no success.

Before I investigate further, does anyone know why this is happening and/or any
workarounds?

Thanks,
Tim 

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On Mon, 31 Jul 2006 23:24:52 -0500
Tim Freeman <tfreeman@mcs.anl.gov> wrote:
> I''m using 3.0.2-3 and have gotten a matching user report from
someone using
> 3.0.1.  
> 
> After powering off a VM, changing its MAC address and rebooting, it becomes
> unreachable.  
Solved this, the random MACs being generated (by non-Xen software) in the
non-working case were not unicast.

As outlined here: 

http://wiki.xensource.com/xenwiki/XenNetworking

"Ensure you choose a unicast address.  That is, one with the low bit of the
first octet set to zero. For example, an address starting aa: is OK but ab: is
not. It is best to keep to the range of addresses declared to be "locally
assigned" (rather than allocated globally to hardware vendors). These have
the
second lowest bit set to one in the first octet. For example, aa: is OK, a8:
isn''t."

Tim 

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