Which domain controller should be online to meet the technical requirements for DC4?

The technical requirement is to deploy a new domain controller, DC4, into the west.contoso.com domain. The Active Directory Domain Services (AD DS) installation process requires communication with an existing domain controller within the target domain. This existing controller serves as a replication partner and provides access to the domain-wide Flexible Single Master Operation (FSMO) roles. In this scenario, DC3 is the domain controller in west.contoso.com and holds the essential domain-specific FSMO roles, such as the RID Master (which allocates a new RID pool to DC4) and the PDC Emulator. Therefore, DC3 must be online for the promotion of DC4 to succeed.

A. DC1 is in the root domain (contoso.com), not the target domain. While it holds forest-level roles, it is not the primary requirement for adding a DC to a child domain.

B. DC2 is in an entirely different child domain (east.contoso.com) and is not involved in the process of adding a domain controller to the west.contoso.com domain.

1. Microsoft Learn

"Active Directory FSMO roles in Windows": Under the "Domain-wide operations master roles" section

it describes the RID master's function: "The RID master is responsible for processing RID Pool requests from all domain controllers in a particular domain." This is a mandatory step when a new domain controller is promoted. The new DC (DC4) must contact the RID master in its domain (west.contoso.com)

which is DC3.

2. Microsoft Learn

"Troubleshooting Domain Controller Deployment": This document details common promotion failures. Under the "Domain Controller Promotion and Demotion" section

it lists errors such as "The wizard cannot contact the RID master

" which confirms that the availability of the RID master in the target domain is a critical prerequisite for successful promotion.

3. Microsoft Learn

"Install a Replica Domain Controller in an Existing Domain (Level 200)": In the "Prerequisites" section

it is implicitly required to have network connectivity to an existing domain controller in the domain where the replica is being installed. The wizard itself requires specifying the target domain

and it will then locate a DC within that domain to proceed. In this case

DC3 is the only DC in the target west.contoso.com domain.