Azure Firewall provides automatic SNAT for all outbound traffic to public IP addresses. Azure Firewall doesn’t SNAT when the destination IP address is a private IP address range per IANA RFC 1918. This logic works perfectly when you egress directly to the Internet. However, with forced tunneling enabled, Internet-bound traffic is SNATed to one of the firewall private IP addresses in the AzureFirewallSubnet. This hides the source address from your on-premises firewall. You can configure Azure Firewall to not SNAT regardless of the destination IP address by adding *0.0.0.0/0* as your private IP address range. With this configuration, Azure Firewall can never egress directly to the Internet. For more information, see [Azure Firewall SNAT private IP address ranges](snat-private-range.md).
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