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Re: [libvirt] [PATCH 9/9] add DHCP snooping support to nwfilter

On Wed, May 18, 2011 at 09:46:21AM +0100, Daniel P. Berrange wrote:
> On Wed, May 18, 2011 at 01:34:33AM -0700, David Stevens wrote:
> > Daniel Veillard <veillard redhat com> wrote on 05/17/2011 08:47:11 PM:
> >         There should be no reason why DHCP wouldn't work on a migrated
> > VM as well (the expectation being that the address, and therefore subnet
> > and DHCP server) would continue to work in the new location.
> Most migrations are on the same subnet, so the VMs existing acquired
> IP address will still be valid & thus DHCP requests won't be made
> after migration.

  Well it's worse than that, for a good live migration the guest should
not even notice something may have changed network wise, relying on
some DHCP traffic to rebuild the filtering tables is not acceptable IMHO

> We need to arrange for the auto-detected IP address on the source
> to be transfered to the destination during migration, either in
> the guest XML, or in the migration cookies we added to the v3
> migration protocol

  So NACK to making this the default until we have all the setup
in place to carry IP on migrations, and rebuilding the filtering rules
before the guest is restarted on the target.
  I'm fine with making this an option but not the default in the
meantime, though changing the default could be considered a behaviour
change and argued upon too.


Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/

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