VM will not run and fail with below error if we create VM without configuring Network attachment definition(NAD) 

failed to create virtual machine pod: admission webhook "ipam-claims.k8s.cni.cncf.io" denied the request: failed to extract CNI configuration from NAD: unexpected end of JSON input

so before creating VM to connect to servicemesh we need to create Network attachment definition(NAD) in the target namespace. The target namespace needs to be configured for the Istio sidecar to be injected and working properly. 

Always reproducible. We have to create NAD in the namespace where the vm is created. When Multus is installed a NAD called istio-cni must be created in each namespace where Istio sidecar containers are to be used.

apiVersion: "k8s.cni.cncf.io/v1"
kind: NetworkAttachmentDefinition
metadata:
  name: istio-cni

We need to add spec of the NAD to the istio-cni for the vm to be up and running

    1.We have to add the NAD(Network attachment definition) config in the cni created inside the namespace when multus is installed like mentioned below

apiVersion: k8s.cni.cncf.io/v1
kind: NetworkAttachmentDefinition
metadata:
  labels:
    maistra.io/member-of: istio-system
  name: istio-cni
  namespace: vm-project
spec:
  config: |
    {
      "cniVersion": "0.3.1",
      "type": "bridge",
      "bridge": "br1",
      "ipam": {
        "type": "host-local",
        "subnet": "192.168.1.0/24"
      }
    }

Getting below error when we tried creating vm without NAD(Network Attachment Definition) like below:

failed to create virtual machine pod: admission webhook "ipam-claims.k8s.cni.cncf.io" denied the request: failed to extract CNI configuration from NAD: unexpected end of JSON input

VM should be up and running