OpenNebula

Hi,all!
I use opennebula3.2.1 in my environment. And the vnm is 802.1q.
Before you start the virtual machine, opennebula would do some pre network ready to work . Such as create a bridge like onebr1024...
But if my host reboot or restart or emergency power off, and so the host returned to normal after, my bridge disappeared.
Then if i create some virtual machines , all failed.
The log show :
Mon Feb 18 14:56:52 2013 [VMM][I]: Successfully execute network driver operation: pre.
Mon Feb 18 14:56:52 2013 [VMM][I]: Command execution fail: cat << EOT | /var/tmp/one/vmm/kvm/deploy /one_images/317/images/deployment.0 compute-57-10.local 317 compute-57-10.local
Mon Feb 18 14:56:52 2013 [VMM][I]: error: Failed to create domain from /one_images/317/images/deployment.0
Mon Feb 18 14:56:52 2013 [VMM][I]: error: Failed to add tap interface to bridge 'onebr1024': No such device
Mon Feb 18 14:56:52 2013 [VMM][E]: Could not create domain from /one_images/317/images/deployment.0

Because this host have no birdge.
Why openenbula show us pre network successful, but still no birdge created on this host?
对了，我的host都reboot过，难道reboot后主机网桥就不能使用了吗？？？