Problem with OpenStack Getting Started Guide

Mark McLoughlin markmc at redhat.com
Tue Jan 3 21:02:17 UTC 2012


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 ...?

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

> 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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