From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: KVM doesn't send an arp announce after live migrating a domain
Date: Wed, 25 Aug 2010 11:38:12 +0300
Message-ID: <20100825083812.GG10499@redhat.com>
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To: Nils Cant <nils.cant@kangaroot.net>
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On Wed, Aug 25, 2010 at 09:52:16AM +0200, Nils Cant wrote:
> Hey guys,
> 
> not sure if this is a bug or a feature request. It's just something
> we've noticed and are having problems with.
> 
> We're using the qemu-kvm lenny-backports package on Debian 5.0.5.
> 
> When doing a live migration from the virsh shell, the server in
> question becomes unreachable because the ARP cache on our switches
> still thinks the server is on another port.
> 
> As soon as the server sends out some traffic, such as a ping, the
> ARP cache get's updated as expected. If it does nothing, the server
> remains unreachable until the ARP cache expires on the switches. (in
> our case 4 hours)
> 
> We would like to be able to do live migration for customer machines
> on which we have no access, so we really need KVM to send out an ARP
> announcement/gratuitous ARP when doing a live migration.
> 
> Could anyone tell me if this is a bug in KVM, libvirt, or the debian
> qemu-kvm package? (or if I'm doing something wrong? :-) )
> 
qemu sends gratuitous ARP after migration. Check forward delay setting on your
bridge interface. It should be set to zero.
  
> I've been tcpdumping the bridged network interfaces on the hosts
> while doing the migrate, and couldn't see any ARP broadcasts.
> 
> Debian 5.0.5
> Kernel: 2.6.32-bpo.3-amd64
> qemu-kvm                      0.12.4+dfsg-1~bpo50+2
> libvirt0                      0.7.6-1~bpo50+1
> 
> migrate --live testserver qemu+ssh://192.168.1.3/system
> 
> Thanks in advance,
> 
> Nils
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--
			Gleb.