Problem with OpenStack Getting Started Guide

Steven Dake sdake at
Fri Jan 6 19:10:36 UTC 2012

On 01/03/2012 02:02 PM, Mark McLoughlin wrote:
> On Tue, 2012-01-03 at 18:35 +0000, Daniel P. Berrange wrote:
>> On Tue, Jan 03, 2012 at 11:29:40AM -0700, Steven Dake wrote:
>>> On 01/03/2012 05:32 AM, Mark McLoughlin wrote:
>>>> On Fri, 2011-12-23 at 13:16 -0700, Steven Dake wrote:
>>>>> Killing the first VM that was started (which has a MAC address equal to
>>>>> the br0) will cause deletion of vnet0 and cause the bridge driver to
>>>>> flush the arp table and choose a new bridge interface.  This results in
>>>>> disconnection of the remaining VM for 30-60 seconds.  
>>>> What exactly is happening during this time? The guest's routing table is
>>>> configured with the host as its gateway and it has a stale ARP cache
>>>> entry for the host?
>>>> Cheers,
>>>> Mark.
>>> br0 adopts the mac address of the first interface added to it.  If the
>>> first interface added to it is removed, br0 finds a new mac address from
>>> the "next" interface in the bridge.  When the mac address is removed,
>>> the arp table is flushed for 30-60 seconds.
> You mean the host kernel arp table is empty for 30-60 seconds? or ...?

yes WRT the bridge vnet interfaces

> A stale arp cache in the guest, I can understand. Anything else smells
> like a bug.

not sure

>> Aside from the connectivity blackout, this mac address also causes
>> pain for recent Windows guests, which will think they have been moved
>> to a new physical network everytime the MAC addr changes, causing them
>> to popup annoying dialog boxes on every login
> Yep, I understood that from the libvirt commit message - makes perfect
> sense. I'm just curious what exactly is going on in this example.
> Cheers,
> Mark.

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