nova/doc/api_samples/os-attach-interfaces/attach-interfaces-create-net_id-req.json

{
    "interfaceAttachment": {
        "fixed_ips": [
            {
                "ip_address": "192.168.1.3"
            }
        ],
        "net_id": "3cb9bc59-5699-4588-a4b1-b87f96708bc6"
    }
}