I had a openvz node. I tried to install KVM with the multivirt support. When I start virtnetwork, openvz nodes loose their network connection sometime later, around 5 minutes or so. I had several openvz vz in that node. I didn't reboot the server after installing multivirt. Although within that 5 minutes, if I setup a KVM node, all works fine. Is there anyone with similar problem?
Solved this. Here is the thing I did for future reference:
Edit your /etc/vz/vz.conf file and comment out the following:
VE_ROUTE_SRC_DEV="viifbr0"
make sure to replace eth0 with viifbr0. Once done, run service vz restart to restart each of your VZ and take the new bridge device as source IP. I was suggested simply restarting vz should work, although, I resolved the issue with the above process and didn't want to restart all the containers once again to check if that works. If you are facing the problem first time, you might just want to try restarting 'vz' without doing any edit and see for result.
I also noticed, this problem arrives if you are trying to install KVM over OpenVZ. It doesn't happen for KVM 'first' nodes.