[stein][neutron] gratuitous arp

Hello, I have a problem on stein neutron. When a vm migrate from one node to another I cannot ping it for several minutes. If in the vm I put a script that ping the gateway continously, the live migration works fine and I can ping it. Why this happens ? I read something about gratuitous arp. Please, help me ? Any workaround , please ? Best Regards Ignazio