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Merge pull request #267733 from greg-lindsay/dns-private-ptr
Add article on creating and managing reverse DNS in Azure Private DNS
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‎articles/dns/TOC.yml

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href: dns-protect-private-zones-recordsets.md
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- name: Import and export a DNS zone file
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href: private-dns-import-export.md
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- name: Create and manage reverse DNS zones
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href: private-reverse-dns.md
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- name: Use Azure Resource Graph Explorer
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href: private-dns-arg.md
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- name: Private Resolver

‎articles/dns/media/private-reverse-dns/add-virtual-network-link.png

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‎articles/dns/media/private-reverse-dns/create-private-record.png

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‎articles/dns/media/private-reverse-dns/create-private-zone.png

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‎articles/dns/media/private-reverse-dns/private-zone-and-record.png

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‎articles/dns/private-reverse-dns.md

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---
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title: Create and manage reverse DNS zones in Azure Private DNS
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description: Learn how to use Azure Private DNS to create reverse DNS lookup zones for your private IP address ranges.
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author: greg-lindsay
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ms.service: dns
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ms.topic: how-to
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ms.date: 03/22/2024
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ms.author: greglin
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---
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# Create and manage reverse DNS zones in Azure Private DNS
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In this article, you learn how to create a private reverse lookup DNS zone and add pointer (PTR) records to the zone using the Azure portal.
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## What is reverse DNS?
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Reverse DNS (as the name indicates) is the opposite process to forward DNS. Reverse enables you to resolve an IP address to a name (for example: 10.1.2.5 --> myvm.contoso.com), whereas forward DNS resolves a name to an IP address. Azure Private DNS supports both IPv6 and IPv4 reverse DNS.
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### IPv6 reverse DNS
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IPv6 reverse DNS zones use the special domain **ip6.arpa**. For more information about IPv6 reverse zones and records, see the IPv6 sections that describe [creating an IPv6 reverse zone](dns-reverse-dns-hosting.md#ipv6) and [adding an IPv6 reverse DNS record](dns-reverse-dns-hosting.md#ipv6-1) in the [Host reverse DNS lookup zones in Azure DNS](dns-reverse-dns-hosting.md) article for public DNS. Azure Private DNS also supports IPv6 reverse DNS zones under the [requirements and restrictions](#requirements-and-restrictions) described in this article.
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### IPv4 reverse DNS zones
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IPv4 reverse DNS zones contain pointer (PTR) records and use the reserved domain name: **in-addr.arpa**. These reverse DNS zones follow a hierarchical naming pattern. For example:
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- **10.in-addr.arpa** contains all PTR records for IPv4 addresses in the 10.0.0.0/8 address space.
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- **1.10.in-addr.arpa** contains all PTR records for IPv4 addresses in the 10.1.0.0/16 address space.
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- **2.1.10.in-addr.arpa** contains only PTR records for IPv4 addresses in the 10.1.2.0/24 address space.
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Private IPv4 reverse DNS zones are intended for use with private IP address space as defined in [RFC 1918](https://www.rfc-editor.org/info/rfc1918).
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### IPv4 reverse DNS records
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To create an IPv4 reverse DNS record in your zone, add the remaining IP address octets in reverse order into the appropriate in-addr.arpa zone and provide a fully qualified domain name value (also called a **ptrdname**). The number of remaining IP address octets depend on the scope of the reverse DNS zone. For example:
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* 10.1.2.5 in the 10.in-addr.arpa zone appears as: `5.2.1 IN PTR myvm.contoso.com.`
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* 10.1.2.5 in the 1.10.in-addr.arpa zone appears as:`5.2 IN PTR myvm.contoso.com.`
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* 10.1.2.5 in the 2.1.10.in-addr.arpa zone appears as:`5 IN PTR myvm.contoso.com.`
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> [!IMPORTANT]
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> A reverse DNS zone for address space with a longer prefix takes precendence. For example, if all three zones contain entries for the IPv4 address 10.1.2.5 as shown here, only the entry in the 2.1.10.in-addr.arpa zone will be used. If the longer prefix zone (2.1.10.in-addr.arpa) exists, then all reverse DNS entries for the corresponding /24 address space must be entered in this zone.
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## Requirements and restrictions
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- [Autoregistration](private-dns-autoregistration.md) isn't supported for reverse DNS.
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- A [virtual network link](private-dns-virtual-network-links.md) from the reverse zone is required to enable DNS resolution of PTR records. The process of [adding a virtual network link](#add-a-virtual-network-link) is demonstrated in this article. This is different from reverse DNS for public IP addresses, which don't require a virtual network link.
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- You can also forward DNS queries to a DNS resolver if the reverse zone is linked to the resolver's VNet.
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- Reverse zones must follow the naming guidelines described in this article and in [RFC 3172](https://www.rfc-editor.org/info/rfc3172).
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## Create a reverse lookup DNS zone
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1. Sign in to the [Azure portal](https://portal.azure.com).
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2. Select **Create a resource**, search for and select **Private DNS zones**, then select **+ Create**.
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3. On the **Create DNS zone** page, select, or enter the following settings:
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| Setting | Details |
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| --- | --- |
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| **Subscription** | Select your subscription.|
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| **Resource group** | Select or create a new resource group. |
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| **Name** | Enter a name for the DNS zone. In this example, the class C reverse DNS zone name **2.1.10.in-addr.arpa** is used. |
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| **Location** | Select the location for the resource group. The location is already be selected if you're using a previously created resource group. |
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See the following example:
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![Screenshot of creating a private reverse DNS zone.](./media/private-reverse-dns/create-private-zone.png)
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4. Select **Review create**, and then select **Create**.
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## Create a DNS PTR record
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1. Select **+ Record set** to open the **Add record set** pane.
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2. As described previously in this article, PTR records in a class C reverse DNS zone are single digit entries. In this example, enter the following:
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| Setting | Details |
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| --- | --- |
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| **Name** | Enter `5`.|
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| **Type** | Select `PTR - Pointer record type`. |
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| **TTL and TTL unit** | Use default values. |
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| **Domain name** | Enter `myvm.contoso.com`. |
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See the following example:
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<img src="./media/private-reverse-dns/create-private-record.png" alt="Screenshot of creating a private reverse DNS record." width="50%">
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3. Select **OK** to create the reverse DNS record.
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![Screenshot of a private zone with a reverse DNS record.](./media/private-reverse-dns/private-zone-and-record.png)
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## Add a virtual network link
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In order for resources to resolve the reverse DNS zone, you must add a virtual network link pointing to the VNet that contains those resources. You can add multiple virtual network links. In this example, a link is added to the VNet: **myeastvnet** that contains a virtual machine. The virtual machine is then used to verify reverse DNS resolution.
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1. Open the private zone overview, and then select **Virtual network links** under **Settings**.
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2. Select **+ Add**.
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3. Enter the following values on the **Add virtual network link** page:
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| Setting | Details |
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| --- | --- |
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| **Link name** | Enter a name for your link. For example: **myvlink**.|
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| **Subscription** | Select your subscription. |
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| **Virtual network** | Choose the virtual network that you wish to link to this private DNS zone. |
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| **Configuration** | Don't select the checkbox to enable auto registration. Selecting this setting prevents creation of the virtual network link. |
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See the following example:
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![Screenshot of adding a virtual network link.](./media/private-reverse-dns/add-virtual-network-link.png)
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4. Select **OK** and verify that the link is displayed on the Virtual network links page.
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## Test DNS resolution
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Using a VM in the linked virtual network: open a command line, type **nslookup 10.1.2.5** and press ENTER.
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If reverse DNS resolution is working, you see the *ptrdname* (FQDN value) that you entered into the reverse DNS zone:
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```PowerShell
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C:\>nslookup 10.1.2.5
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Server: UnKnown
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Address: 168.63.129.16
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Name: myvm.contoso.com
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Address: 10.1.2.5
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```
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## Next steps
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* For more information on reverse DNS, see [reverse DNS lookup on Wikipedia](https://en.wikipedia.org/wiki/Reverse_DNS_lookup).
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* Learn how to [manage reverse DNS records for your Azure services](dns-reverse-dns-for-azure-services.md).

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