added reverse DNS support

Author: rohinkoul

articles/virtual-network/virtual-networks-name-resolution-for-vms-and-role-instances.md

@@ -10,7 +10,7 @@ ms.devlang: na
 ms.topic: article
 ms.tgt_pltfrm: na
 ms.workload: infrastructure-services
-ms.date: 3/25/2019
+ms.date: 3/2/2020
 ms.author: rohink
 ---
 
@@ -20,16 +20,20 @@ Depending on how you use Azure to host IaaS, PaaS, and hybrid solutions, you mig
 
 When resources deployed in virtual networks need to resolve domain names to internal IP addresses, they can use one of two methods:
 
+* [Azure DNS private zones](../dns/private-dns-overview.md)
 * [Azure-provided name resolution](#azure-provided-name-resolution)
 * [Name resolution that uses your own DNS server](#name-resolution-that-uses-your-own-dns-server) (which might forward queries to the Azure-provided DNS servers)
 
 The type of name resolution you use depends on how your resources need to communicate with each other. The following table illustrates scenarios and corresponding name resolution solutions:
 
 > [!NOTE]
-> Depending on your scenario, you might want to use Azure DNS private zones. For more information, see [Using Azure DNS for private domains](../dns/private-dns-overview.md).
->
+> Azure DNS private zones is the preferred solution and gives you flexibility in managing your DNS zones and records. For more information, see [Using Azure DNS for private domains](../dns/private-dns-overview.md).
+
+> [!NOTE]
+> If you use Azure Provided DNS then appropriate DNS suffix will be automatically applied to your virtual machines. 
+> For all other options you must either use Fully Qualified Domain Names (FQDN) or manually apply appropriate DNS suffix to your virtual machines.
 
-| **Scenario** | **Solution** | **Suffix** |
+| **Scenario** | **Solution** | **DNS Suffix** |
 | --- | --- | --- |
 | Name resolution between VMs located in the same virtual network, or Azure Cloud Services role instances in the same cloud service. | [Azure DNS private zones](../dns/private-dns-overview.md) or [Azure-provided name resolution](#azure-provided-name-resolution) |Hostname or FQDN |
 | Name resolution between VMs in different virtual networks or role instances in different cloud services. |[Azure DNS private zones](../dns/private-dns-overview.md) or, Customer-managed DNS servers forwarding queries between virtual networks for resolution by Azure (DNS proxy). See [Name resolution using your own DNS server](#name-resolution-that-uses-your-own-dns-server). |FQDN only |
@@ -38,17 +42,18 @@ The type of name resolution you use depends on how your resources need to commun
 | Name resolution from App Service Web Apps in one virtual network to VMs in a different virtual network. |Customer-managed DNS servers forwarding queries between virtual networks for resolution by Azure (DNS proxy). See [Name resolution using your own DNS server](#name-resolution-that-uses-your-own-dns-server). |FQDN only |
 | Resolution of on-premises computer and service names from VMs or role instances in Azure. |Customer-managed DNS servers (on-premises domain controller, local read-only domain controller, or a DNS secondary synced using zone transfers, for example). See [Name resolution using your own DNS server](#name-resolution-that-uses-your-own-dns-server). |FQDN only |
 | Resolution of Azure hostnames from on-premises computers. |Forward queries to a customer-managed DNS proxy server in the corresponding virtual network, the proxy server forwards queries to Azure for resolution. See [Name resolution using your own DNS server](#name-resolution-that-uses-your-own-dns-server). |FQDN only |
-| Reverse DNS for internal IPs. |[Name resolution using your own DNS server](#name-resolution-that-uses-your-own-dns-server). |Not applicable |
+| Reverse DNS for internal IPs. |[Azure DNS private zones](../dns/private-dns-overview.md) or [Azure-provided name resolution](#azure-provided-name-resolution) or [Name resolution using your own DNS server](#name-resolution-that-uses-your-own-dns-server). |Not applicable |
 | Name resolution between VMs or role instances located in different cloud services, not in a virtual network. |Not applicable. Connectivity between VMs and role instances in different cloud services is not supported outside a virtual network. |Not applicable|
 
 ## Azure-provided name resolution
 
-Along with resolution of public DNS names, Azure provides internal name resolution for VMs and role instances that reside within the same virtual network or cloud service. VMs and instances in a cloud service share the same DNS suffix, so the host name alone is sufficient. But in virtual networks deployed using the classic deployment model, different cloud services have different DNS suffixes. In this situation, you need the FQDN to resolve names between different cloud services. In virtual networks deployed using the Azure Resource Manager deployment model, the DNS suffix is consistent across the virtual network, so the FQDN is not needed. DNS names can be assigned to both VMs and network interfaces. Although Azure-provided name resolution does not require any configuration, it is not the appropriate choice for all deployment scenarios, as detailed in the previous table.
+Azure provided name resolution provides only basic authoritative DNS capabilities. If you use this option the DNS zone names and records will be automatically managed by Azure and you will not be able to control the DNS zone names or the life cycle of DNS records. If you need a fully featured DNS solution for your virtual networks you must use [Azure DNS private zones](../dns/private-dns-overview.md) or [Customer-managed DNS servers](#name-resolution-that-uses-your-own-dns-server).
+
+Along with resolution of public DNS names, Azure provides internal name resolution for VMs and role instances that reside within the same virtual network or cloud service. VMs and instances in a cloud service share the same DNS suffix, so the host name alone is sufficient. But in virtual networks deployed using the classic deployment model, different cloud services have different DNS suffixes. In this situation, you need the FQDN to resolve names between different cloud services. In virtual networks deployed using the Azure Resource Manager deployment model, the DNS suffix is consistent across the all virtual machines within a virtual network, so the FQDN is not needed. DNS names can be assigned to both VMs and network interfaces. Although Azure-provided name resolution does not require any configuration, it is not the appropriate choice for all deployment scenarios, as detailed in the previous table.
 
 > [!NOTE]
 > When using cloud services web and worker roles, you can also access the internal IP addresses of role instances using the Azure Service Management REST API. For more information, see the [Service Management REST API Reference](https://msdn.microsoft.com/library/azure/ee460799.aspx). The address is based on the role name and instance number. 
 >
->
 
 ### Features
 
@@ -64,13 +69,26 @@ Azure-provided name resolution includes the following features:
 
 Points to consider when you are using Azure-provided name resolution:
 * The Azure-created DNS suffix cannot be modified.
+* DNS lookup is scoped to a virtual network. DNS names created for one virtual networks can't be resolved from other virtual networks.
 * You cannot manually register your own records.
 * WINS and NetBIOS are not supported. You cannot see your VMs in Windows Explorer.
 * Host names must be DNS-compatible. Names must use only 0-9, a-z, and '-', and cannot start or end with a '-'.
 * DNS query traffic is throttled for each VM. Throttling shouldn't impact most applications. If request throttling is observed, ensure that client-side caching is enabled. For more information, see [DNS client configuration](#dns-client-configuration).
 * Only VMs in the first 180 cloud services are registered for each virtual network in a classic deployment model. This limit does not apply to virtual networks in Azure Resource Manager.
 * The Azure DNS IP address is 168.63.129.16. This is a static IP address and will not change.
 
+### Reverse DNS Considerations
+Reverse DNS is supported in all ARM based virtual networks. You can issue reverse DNS queries (PTR queries) to map IP addresses of virtual machines to FQDNs of virtual machines.
+* All PTR queries for IP addresses of virtual machines will return FQDNs of form \[vmname\].internal.cloudapp.net
+* Forward lookup on FQDNs of form \[vmname\].internal.cloudapp.net will resolve to IP address assigned to the virtual machine.
+* If the virtual network is linked to an [Azure DNS private zones](../dns/private-dns-overview.md) as a registration virtual network, the reverse DNS queries will return two records. One record will the of the form \[vmname\].[priatednszonename] and other would be of the form \[vmname\].internal.cloudapp.net
+* Reverse DNS lookup is scoped to a given virtual network even if it is peered to other virtual networks. Reverse DNS queries (PTR queries) for IP addresses of virtual machines located in peered virtual networks will return NXDOMAIN.
+
+> [!NOTE]
+> If you want reverse DNS lookup to span across virtual network you can create a reverse lookup zone (in-addr.arpa) [Azure DNS private zones](../dns/private-dns-overview.md) and links it to multiple virtual networks. You'll however have to manually manage the reverse DNS records for the virtual machines.
+>
+
+
 ## DNS client configuration
 
 This section covers client-side caching and client-side retries.