What is a private Azure DNS zone
Azure Private DNS provides a reliable, secure DNS service to manage and resolve domain names in a virtual network without the need to add a custom DNS solution. By using private DNS zones, you can use your own custom domain names rather than the Azure-provided names available today.
The records contained in a private DNS zone aren't resolvable from the Internet. DNS resolution against a private DNS zone works only from virtual networks that are linked to it.
You can link a private DNS zone to one or more virtual networks by creating virtual network links. You can also enable the autoregistration feature to automatically manage the life cycle of the DNS records for the virtual machines that get deployed in a virtual network.
To understand how many private DNS zones you can create in a subscription and how many record sets are supported in a private DNS zone, see Azure DNS limits
Single-label private DNS zones aren't supported. Your private DNS zone must have two or more labels. For example, contoso.com has two labels separated by a dot. A private DNS zone can have a maximum of 34 labels.
You can't create zone delegations (NS records) in a private DNS zone. If you intend to use a child domain, you can directly create the domain as a private DNS zone. Then you can link it to the virtual network without setting up a nameserver delegation from the parent zone.
The following list of reserved zone names are blocked from creation to prevent disruption of services:
Public Azure Government Microsoft Azure operated by 21Vianet azclient.ms azclient.us azclient.cn azure.com azure.us azure.cn cloudapp.net usgovcloudapp.net chinacloudapp.cn core.windows.net core.usgovcloudapi.net core.chinacloudapi.cn microsoft.com microsoft.us microsoft.cn msidentity.com msidentity.us msidentity.cn trafficmanager.net usgovtrafficmanager.net trafficmanager.cn windows.net usgovcloudapi.net chinacloudapi.cn