resolution virtual networks

 we have to add the vnet or should be added as the resolution network for the private DNS zone.

In order for virtual machines in other networks to resolve virtual machines  in the DNS zone, the network must first be defined as the resolution network for the private DNS zone.

To publish a private DNS zone to your virtual network, you specify the list of virtual networks that are allowed to resolve records within the zone.

These are called resolution virtual networks.

You may also specify a virtual network for which Azure DNS maintains hostname records  whenever a VM is created, changes IP or is deleted. This is called a registration virtual network.

reference:

https://docs.microsoft.com/en-us/azure/dns/private-dns-overview