[libvirt] KVM doesn't send an arp announce after live migrating a domain

[Daniel P. Berrange]

On Wed, Aug 25, 2010 at 01:40:19PM +0300, Avi Kivity wrote:
>  On 08/25/2010 12:21 PM, Nils Cant wrote:
> >On 08/25/2010 10:38 AM, Gleb Natapov wrote:
> >>qemu sends gratuitous ARP after migration. Check forward delay 
> >>setting on your
> >>bridge interface. It should be set to zero.
> >>
> >
> >Aha! That fixed it. Turns out that debian bridge-utils sets the 
> >default to 15 for bridges.
> >Manually setting it to 0 with 'brctl setfd br0 0' or setting the 
> >'bridge_fd' parameter to 0 in /etc/network/interfaces solves the issue.
> >
> 
> I think libvirt is doing something about this, copying list for further 
> info.

libvirt doesn't set a policy for this. It provides an API for 
configuring host networking, but we don't override the kernel's
forward delay policy, since we don't presume that all bridges 
are going to have VMs attached. In any case the API isn't available
for Debian yet, since no one has ported netcf to Debian, so I 
assume the OP set bridging up manually. The '15' second default is
actually a kernel level default IIRC. 

The two main host network configs recommended for use with libvirt+KVM
(either NAT or bridging) are documented here:

  http://wiki.libvirt.org/page/Networking

Regards,
Daniel
-- 
|: Red Hat, Engineering, London    -o-   http://people.redhat.com/berrange/ :|
|: http://libvirt.org -o- http://virt-manager.org -o- http://deltacloud.org :|
|: http://autobuild.org        -o-         http://search.cpan.org/~danberr/ :|
|: GnuPG: 7D3B9505  -o-   F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|