Using neutron flat dhcp. I built ten vms and then deleted. And then built ten vms, found that ten of the ip and some in front of the same, The new ten of which there is a vm network barrier, just before the construction of the vms also have this ip. If you enter the vm and ping the gateway, the network immediately better.

I deleted the back, and built 10 vms, there are several and the same as the previous ip, found that there are several ip unreasonable

If I quickly delete and build the host this situation is more obvious. But one night, today in the point of view, and found all pass.

How to solve this problem, I do not want to go every time to ping gateway