(kubernetes/GKE) How do I route traffic in istio based on client IP address?

Question

I am using GKE, with it's own set of istio mesh enabled. I do have a gateway and a virtual service, which is routing traffic just fine. But I wanted to direct traffic to diffrent paths based on source IPs. I do realise that we could use match / headers in virtual service as shown in this question, as below:

  - match:
- headers:
    x-forwarded-for:
      exact: 123.123.123.123

But it doesnt seem to work for me. Please suggest, thanks a lot.