KVM host network restart breaks client's networking

[^rooker]

[PROBLEM]
I had to change the IP of a KVM virtual machine host running Debian 7 (wheezy). I did a "ifdown" and "ifup" of the "br0" interface and didn't expect anymore to do.

I was wrong:

Restarting the KVM host's network breaks the network connectivity for its clients
Maybe because the client was still running. I don't know.

I found others who had the same problem. A thread on ubuntuforums called "8.04 KVM Restarting Networking in Host Breaks Networking In Guests" or a post on serverfault.com titled "KVM guests lose connectivity after networking restart" described my problem - but didn't really contain working solutions.

Rebooting the clients also didn't work.


[SOLUTION]
IDEA: Restart the virtualization services

First, shutdown all client machines. Just to make sure.

Maybe restarting only "libvirtd", but I also restarted the clients:

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$ /etc/init.d/libvirt-guests stop
$/etc/init.d/libvirt-bin stop

Now there should be no services running containing the name "virt". The output of the following command should be rather empty:

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ps aux | grep virt

Restart the services:

Code: Select all

$ /etc/init.d/libvirt-bin start
$ /etc/init.d/libvirt-guests start

You should see "vnet" network interfaces now again. While the problem persisted, they were not there.

If everything went fine, your clients should be able to boot happily with their network interfaces being connected again!