Comment 2 for bug 908809

Are you using dhcp on eth0? I have seen inconsistencies where nova moves the address from eth0 to br100 and then dhcp adds it back. If so, try switching to a static ip. Also, I have had to set promisc mode on br100 before to get things to work. That said, you may have more luck using HA network mode. When you create the network set the --multi_host flag to true. Then you can run nova-network on all of the hosts and each instance will route out through its own host.