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--- title: Azure Firewall policy DNS settings description: You can configure Azure Firewall policies with DNS server and DNS proxy settings. services: firewall-manager author: duau ms.service: azure-firewall-manager ms.custom: devx-track-azurepowershell ms.topic: how-to ms.date: 06/21/2024 ms.author: duau --- # Azure Firewall policy DNS settings You can configure a custom DNS server and enable DNS proxy for Azure Firewall. Configure these settings when you deploy the firewall, or configure them later from the **DNS settings** page. By default, Azure Firewall uses Azure DNS and DNS Proxy is disabled. ## DNS servers A DNS server maintains and resolves domain names to IP addresses. By default, Azure Firewall uses Azure DNS for name resolution. The **DNS server** setting lets you configure your own DNS servers for Azure Firewall name resolution. You can configure a single server or multiple servers. If you configure multiple DNS servers, the server used is chosen randomly. You can configure a maximum of 15 DNS servers in **Custom DNS**. > [!NOTE] > For instances of Azure Firewall that are managed by using Azure Firewall Manager, the DNS settings are configured in the associated Azure Firewall policy. ### Configure custom DNS servers #### [Portal](#tab/browser) 1. Under Azure Firewall **Settings**, select **DNS Settings**. 2. Under **DNS servers**, you can type or add existing DNS servers that were previously specified in your virtual network. 3. Select **Apply**. The firewall now directs DNS traffic to the specified DNS servers for name resolution. #### [CLI](#tab/azure-devops-cli) The following example updates Azure Firewall with custom DNS servers by using the Azure CLI. ```azurecli-interactive az network firewall update \ --name fwName \ --resource-group fwRG \ --dns-servers 10.1.0.4 10.1.0.5 ``` > [!IMPORTANT] > The command `az network firewall` requires the Azure CLI extension `azure-firewall` to be installed. You can install it by using the command `az extension add --name azure-firewall`. #### [PowerShell](#tab/powershell) The following example updates Azure Firewall with custom DNS servers by using Azure PowerShell. ```azurepowershell $dnsServers = @("10.1.0.4", "10.1.0.5") $azFw = Get-AzFirewall -Name "fwName" -ResourceGroupName "fwRG" $azFw.DNSServer = $dnsServers $azFw | Set-AzFirewall ``` --- ## DNS proxy You can configure Azure Firewall to act as a DNS proxy. A DNS proxy is an intermediary for DNS requests from client virtual machines to a DNS server. If you want to enable FQDN (fully qualified domain name) filtering in network rules, enable DNS proxy and update the virtual machine configuration to use the firewall as a DNS proxy. :::image type="content" source="../firewall/media/dns-settings/dns-proxy-2.png" alt-text="Diagram showing DNS proxy configuration using a custom DNS server."::: If you enable FQDN filtering in network rules, and you don't configure client virtual machines to use the firewall as a DNS proxy, then DNS requests from these clients might travel to a DNS server at a different time or return a different response compared to that of the firewall. It’s recommended to configure client virtual machines to use the Azure Firewall as their DNS proxy. This puts Azure Firewall in the path of the client requests to avoid inconsistency. When Azure Firewall is a DNS proxy, two caching function types are possible: - **Positive cache**: DNS resolution is successful. The firewall caches these responses according to the TTL (time to live) in the response up to a maximum of 1 hour. - **Negative cache**: DNS resolution results in no response or no resolution. The firewall caches these responses according to the TTL in the response, up to a max of 30 minutes. The DNS proxy stores all resolved IP addresses from FQDNs in network rules. As a best practice, use FQDNs that resolve to one IP address. ### Policy inheritance Policy DNS settings applied to a standalone firewall override the standalone firewall’s DNS settings. A child policy inherits all parent policy DNS settings, but it can override the parent policy. For example, to use FQDNs in network rule, DNS proxy should be enabled. But if a parent policy does **not** have DNS proxy enabled, the child policy won't support FQDNs in network rules unless you locally override this setting. ### DNS proxy configuration DNS proxy configuration requires three steps: 1. Enable the DNS proxy in Azure Firewall DNS settings. 2. Optionally, configure your custom DNS server or use the provided default. 3. Configure the Azure Firewall private IP address as a custom DNS address in your virtual network DNS server settings. This setting ensures DNS traffic is directed to Azure Firewall. #### [Portal](#tab/browser) To configure DNS proxy, you must configure your virtual network DNS servers setting to use the firewall private IP address. Then enable the DNS proxy in the Azure Firewall **DNS settings**. ##### Configure virtual network DNS servers 1. Select the virtual network where the DNS traffic is routed through the Azure Firewall instance. 2. Under **Settings**, select **DNS servers**. 3. Under **DNS servers**, select **Custom**. 4. Enter the firewall's private IP address. 5. Select **Save**. 6. Restart the VMs that are connected to the virtual network so they're assigned the new DNS server settings. VMs continue to use their current DNS settings until they're restarted. ##### Enable DNS proxy 1. Select your Azure Firewall instance. 2. Under **Settings**, select **DNS settings**. 3. By default, **DNS Proxy** is disabled. When this setting is enabled, the firewall listens on port 53 and forwards DNS requests to the configured DNS servers. 4. Review the **DNS servers** configuration to make sure that the settings are appropriate for your environment. 5. Select **Save**. #### [CLI](#tab/azure-devops-cli) You can use the Azure CLI to configure DNS proxy settings in Azure Firewall. You can also use it to update virtual networks to use Azure Firewall as the DNS server. ##### Configure virtual network DNS servers The following example configures the virtual network to use Azure Firewall as the DNS server. ```azurecli-interactive az network vnet update \ --name VNetName \ --resource-group VNetRG \ --dns-servers <firewall-private-IP> ``` ##### Enable DNS proxy The following example enables the DNS proxy feature in Azure Firewall. ```azurecli-interactive az network firewall update \ --name fwName \ --resource-group fwRG \ --enable-dns-proxy true ``` #### [PowerShell](#tab/powershell) You can use Azure PowerShell to configure DNS proxy settings in Azure Firewall. You can also use it to update virtual networks to use Azure Firewall as the DNS server. ##### Configure virtual network DNS servers The following example configures the virtual network to use Azure Firewall as a DNS server. ```azurepowershell $dnsServers = @("<firewall-private-IP>") $VNet = Get-AzVirtualNetwork -Name "VNetName" -ResourceGroupName "VNetRG" $VNet.DhcpOptions.DnsServers = $dnsServers $VNet | Set-AzVirtualNetwork ``` ##### Enable DNS proxy The following example enables the DNS proxy feature in Azure Firewall. ```azurepowershell $azFw = Get-AzFirewall -Name "fwName" -ResourceGroupName "fwRG" $azFw.DNSEnableProxy = $true $azFw | Set-AzFirewall ``` --- ### High availability failover DNS proxy has a failover mechanism that stops using a detected unhealthy server and uses another DNS server that is available. If all DNS servers are unavailable, there's no fallback to another DNS server. ### Health checks DNS proxy performs five-second health check loops for as long as the upstream servers report as unhealthy. The health checks are a recursive DNS query to the root name server. Once an upstream server is considered healthy, the firewall stops health checks until the next error. When a healthy proxy returns an error, the firewall selects another DNS server in the list. ## Next steps - [Azure Firewall DNS Proxy details](../firewall/dns-details.md) - [FQDN filtering in network rules](fqdn-filtering-network-rules.md)