[CentOS-virt] KVM integrated network (user mode) dying after inactivity

[George Dunlap]

On Wed, Jun 4, 2014 at 7:40 PM, Timo Schöler <timo at riscworks.net> wrote:
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> Hi list,
>
> I searched the web for bug reports regarding this phenomenon I see on
> *multiple* machines of a customer, however, I didn't find an exact
> fit. So, I'd like to ask here whether anyone else has run into this.
>
> I have multiple CentOS 6 machines running using KVM to virtualize a
> bunch of machines on them (LVM-based).
>
> Software releases as following:
>
> [root at fe00 ~]# rpm -qa|egrep '(virt|kvm)'
> virt-viewer-0.5.6-8.el6_5.3.x86_64
> libvirt-python-0.10.2-29.el6_5.7.x86_64
> libvirt-client-0.10.2-29.el6_5.7.x86_64
> qemu-kvm-0.12.1.2-2.415.el6_5.8.x86_64
> libvirt-0.10.2-29.el6_5.7.x86_64
> python-virtinst-0.600.0-18.el6.noarch
>
> [root at fe00 ~]# uname -r
> 2.6.32-431.17.1.el6.x86_64
>
> The VMs (here: two) have the "default" connection provided by KVM
> (heading to the internet) as well as a bridged interface to connect to
> a high performance backbone, where sensitive data is kept and
> bandwidth is an issue (or better, not :), on a second interface within
> the VMs:
>
> [root at fe00 ~]# brctl show
> bridge name     bridge id               STP enabled     interfaces
> br1             8000.001b21xxxxxx       yes             eth1
>                                                         vnet1
>                                                         vnet3
> virbr0          8000.525400xxxxxx       yes             virbr0-nic
>                                                         vnet0
>                                                         vnet2
>
> br1 is the interface connected to the backbone, virbr0 KVM's user mode
> network.
>
> After some time of inactivity on the virbr0 interface, from *within*
> the VMs connection is *lost*. The interface(s) lose their IP; running
> dhclient(8) is not of any use.
>
> To get the machine back onto track, ``service libvirtd restart'' has
> to be issued: Vanished iptables rules show up again. (This, in
> contrast to an Ubuntu document [0], fixes it without shutting the
> VM(s) down.) Starting dhclient(8) within the VMs gets connectivity back.

Have you verified that the iptables rules disappear?  That is:
* Initially, the NAT rule is present
* After inactivity, the NAT rule disappears
* After restarting libvirtd, the NAT rule re-appears?

 -George