Any one knows when cdc-ecm device get IP address?

I am working on USB CDC-ECM device. CDC class code was created in CUBE. I modified device descriptor as described in ECM specification add to project LwIP stack. After connecting device(STM32F205) to host it detects as Ethernet interface with described MAC, but it uses IPv6. Any body knows when device should send its IP address? This must be done by LwIP or during initialization process? Has any one good example?