As discussed in Understanding Application Directory Partitions in Active Directory, an application directory partition is a partition that contains Active Directory objects, is part of the forest DNS namespace, and is replicated among domain controllers (DCs) in a forest. Application directory partitions can be created by Active Directory-aware applications or manually.
DNS is a built-in component of Windows that utilizes application directory partitions. By default, when the DNS Server role is installed on the first DC in a forest root domain named domain.com, two partitions are created, named DomainDnsZones.domain.com and ForestDnsZones.domain.com. As their names imply, these partitions have different replication scopes: the DomainDnsZones partition is replicated to every DNS server within a domain, while the ForestDnsZones partition is replicated to every DNS server in a forest. If any child domains are subsequently created, each will have its own DomainDnsZones partition, but there is only one ForestDnsZones partition per forest.
These two partitions are represented inside the corresponding domain's forward lookup zone in the DNS Management console, as shown below:
The function of these application directory partitions is to control the replication scopes of Active-Directory integrated DNS zones. When a zone is created, its replication scope can be set to one of the following options:
All DNS servers running on domain controllers in the domain: This option stores the zone in the DomainDnsZones partition.
All DNS servers running on domain controllers in the forest: This option stores the zone in the ForestDnsZones partition.
All domain controllers in the domain: This option stores the zone in the domain partition rather than an application directory partition.
All domain controllers in the scope of a custom directory partition: This stores the zone in the specified application directory partition.
The replication scope of a DNS zone can also be set after its creation via the zones properties window
For more information, see Understanding DNS Zone Replication in Active Directory Domain Services.
The DomainDnsZones and ForestDnsZones partitions should not be deleted. If this occurs, however, they can be recreated. For information on recreating them, see How to Recreate the Default DNS Application Partitions in Active Directory.
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