DC3 is a domain controller for the existing corp.fabrikam.com AD DS forest, deployed into Vnet1 in Azure. Domain controllers rely on AD-integrated DNS for locating other domain controllers, SRV records, and replication, so DC3 needs to host that zone itself, which requires installing the DNS Server role on DC3 and letting it host an AD-integrated copy of the corp.fabrikam.com zone. Azure ' s default virtual-network-provided DNS resolver has no awareness of AD DS records and cannot host or serve an AD-integrated zone, so every resource in Vnet1 that needs to locate the domain (including Azure VMs and DC3 ' s own replication partners) must be pointed at real DNS servers instead. That is accomplished by configuring the custom DNS Servers setting on Vnet1 to reference DC3 (and, once available, DC1 and DC2), which makes all Azure VMs in the virtual network resolve names through the AD-integrated DNS infrastructure rather than the platform resolver. An Azure DNS zone (public) or an Azure private DNS zone are separate, unrelated Azure-native DNS services that cannot host an AD-integrated zone and are not used for this scenario. Installing the DNS Server role on DC3 and pointing Vnet1 at it together satisfy the requirement.