In the Windows Server hybrid administration guidance for DNS, Microsoft describes that DNS zones stored in Active Directory can use application directory partitions to customize replication scope beyond the default domain- or forest-wide options. The study materials state that "custom application directory partitions allow DNS data to replicate only to the DNS servers that are explicitly enlisted in that partition." They further emphasize that while DNS Manager lets you pick among built-in scopes or select an existing application partition, "creating a new application directory partition is performed with command-line tools (dnscmd) or Windows PowerShell." The documented procedure is: "Use dnscmd /CreateDirectoryPartition <FQDN-of-partition> to create the custom partition, then dnscmd /EnlistDirectoryPartition on each DNS server that should host and replicate the data." Because you must have the partition replicate to only four of the domain controllers, you first create the partition, and then enlist only those four DNS servers. Tools such as Active Directory Sites and Services or Active Directory Administrative Center do not create DNS application directory partitions, and DNS Manager cannot create a new custom partition; it can only use an existing one. Therefore, the correct tool to meet the requirement is dnscmd.exe, after which you enlist just the selected four DNS servers into that partition.