Ubuntu12.04 libvirt virbr0 network bridge setup

Offical Ubuntu website provides a very good and thorough guide for installing Xen in Ubuntu.

But, I personally prefer libvirt for managing network bridges, not changing network configuration as stated in the official website. So, I install libvirt:

sudo apt-get install libvirt0

Then type

virsh net-list --all

It shows nothing!!? That is because on Ubuntu. You need to add user to libvirtd

adduser `id -un` libvirtd

Don't use "adduser $user libvirtd". I tried this one first but it did not work.


Then, load default bridge setting by

sudo virsh net-define /var/lib/libvirt/network/default.xml

Note: the path is not the same as /usr/share/libvirt/networks/default.xml, which is demonstrated on libvirt wiki.

Next, start bridging and make it auto start:

virsh net-autostart default
virsh net-start default

This Ubuntu is running Xen inside Virtual Box. So, sub-network  is a problem. You may see

error: internal error Network is already in use by interface eth0

Then, if you type "virsh net-list --all" to show again, it indicates the device is inactive.

That is because 192.168.122.xxx is the default. But, the host machine is already using 192.168.122.xxx. So, the bridge can not be setup.
Solution:

I change the subnet to 192.168.1.xxx. in /var/lib/libvirt/network/default.xml

Now, type "ifconfig" and you should see virbr0 is there.

References
http://ubuntuforums.org/showthread.php?t=1789126
http://wiki.libvirt.org/page/Networking

Ending picture today:
Capital hill and its Christmas tree [courtesy of my dear wife - Claire Huang]