Having recently dual-booted my main desktop system with Ubuntu 10.10 64-bit, I decided to setup virt-manager to handle KVM virtual machines. While I don’t have a current use for VMs other than to play around with things as I run into them, I wanted them to be able to talk to other physical machines on my network w/o adding another hop into my internal network.
Therefore, I needed bridging such that virtual machines were assigned IPs (statically or dynamically) in the same subnet as my main desktop. To do this, I followed steps 2.1 and 2.2 from KVM Networking – Community Ubuntu Documentation guide.
Once I did this, everything seemed happy. However, I noticed that the default bridged network of 192.168.1.x and the default bridge interface virbr0 were still being created, even after restarting libvirtd. Additionally, this was causing dnsmasq to be started on the system. With the bridging method I’m using, there’s no need for that since the virtual machines can reach the name server on my network. A little more research showed that essentially both problems here were the result of the symlink /etc/libvirt/qemu/networks/autostart/default.xml . Once I removed that, libvirtd was no longer using them, but it hadn’t shut them down. A little brctl and kill love and all was well again in the universe. :)