The private IP address of an Azure Firewall cannot be manually modified after it has been assigned. When an Azure Firewall is created, it automatically receives a private IP address from the IP range of the virtual network's subnet where it is deployed. Manual changes to this IP address are not supported. For example, if your Vnet has an address space of 10.0.0.0/16 and you have created the AzureFirewallSubnet as 10.0.2.0/24, then the first available IP of that subnet i.e. 10.0.2.4 will be automatically assigned as the private IP address of your Azure Firewall while creation.
If you need an IP address from a specific address range for your firewall, you must ensure that your AzureFirewallSubnet includes that address before creating the firewall.
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