How to Add an Additional Domain Controller to an Existing Domain
Applies to: Windows Server 2019, 2022 and 2025.
A second controller improves directory and DNS availability when promotion begins from healthy replication and correct DNS.
Active Directory changes affect authentication across the environment. Use tested backups, separate privileged accounts and a maintenance plan. See networkmanager.info for managed Windows VPS services.
Prerequisites
- Join the server to the domain.
- Use only AD-integrated DNS resolvers.
- Run dcdiag and repadmin on existing controllers.
- Choose the correct AD site.
Procedure
Step 1: Verify domain health
Check secure channel and service records.
Test-ComputerSecureChannel -Verbose
Resolve-DnsName -Type SRV _ldap._tcp.dc._msdcs.corp.exampleStep 2: Install AD DS
Add the role.
Install-WindowsFeature AD-Domain-Services -IncludeManagementToolsStep 3: Promote
Prompt for authorized credentials.
$cred=Get-Credential 'CORP\DomainAdmin'
Install-ADDSDomainController -DomainName 'corp.example' -Credential $cred -InstallDNSStep 4: Check replication
After restart, validate all partners.
Verification
The new controller should be discoverable without persistent failures.
Get-ADDomainController -Filter *
repadmin /replsummary
dcdiag /test:dnsRollback and recovery
If promotion completed, demote cleanly. Do not remove the computer account as a substitute.
Operational notes
Add monitoring and system-state backup immediately after acceptance.
Official references
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