@Balaguru Krishnamoorthy Thank you for reaching out to Microsoft Q&A. I understand that you want to NAT traffic on both sides of the VPN i.e. on Azure as well as On-premise sides. Azure VPN Gateway supports only 1:1 NAT rules. It does not support Port Address Translation or PAT. If you want to implement PAT on Azure side, I would suggest you to go with a 3rd party VPN solution on Azure Marketplace such as VNS3. Hope this helps.
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