Active Directory Migration: A Step-by-Step Guide from Windows Server 2016 to Windows Server 2025

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Active Directory Migration: A Step-by-Step Guide from Windows Server 2016 to Windows Server 2025

Introduction

Upgrading your Active Directory infrastructure is an important part of maintaining a secure, supported, and high-performing IT environment. Migrating from Windows Server 2016 to Windows Server 2025 provides improved security, better performance, enhanced management capabilities, and long-term Microsoft support.

This guide walks through a practical Active Directory migration process that System Administrators can use in production environments while minimizing downtime and ensuring a smooth transition.

Why Upgrade Your Domain Controllers?

Migrating to Windows Server 2025 provides several benefits:

·       Improved security features

·       Better Active Directory performance

·       Enhanced virtualization support

·       Improved Windows Admin Center integration

·       Modern PowerShell management

·       Better compatibility with current Microsoft technologies

·       Extended product support lifecycle

Prerequisites

Before beginning the migration, ensure you have:

·       Windows Server 2025 installed on the new server

·       Static IP address configured

·       Latest Windows Updates installed

·       Correct server hostname

·       Domain Administrator credentials

·       Recent System State backup

·       Verified Active Directory health

·       Healthy DNS replication

Step 1 – Check Active Directory Health

Run these commands on the existing Domain Controller.

Check Domain Controller health:

dcdiag /v

Check replication:

repadmin /replsummary

Verify detailed replication:

repadmin /showrepl

Resolve any errors before continuing.

Step 2 – Verify FSMO Roles

Confirm the current FSMO role holders.

netdom query fsmo

Document the results before making changes.

Step 3 – Verify DNS Health

Test internal DNS resolution.

nslookup yourdomain.local

Verify:

·       Forward Lookup Zone

·       Reverse Lookup Zone

·       SRV Records

·       DNS Forwarders

Healthy DNS is essential for a successful migration.

Step 4 – Join the New Server to the Domain

Configure:

·       Static IP

·       Preferred DNS pointing to the existing Domain Controller

·       Correct hostname

Join the server to the domain and restart it.

Step 5 – Install Active Directory Domain Services

Install the AD DS role:

Install-WindowsFeature AD-Domain-Services -IncludeManagementTools

After installation, promote the server as an Additional Domain Controller.

During promotion:

·       Select Add a domain controller to an existing domain

·       Install DNS Server

·       Configure the Global Catalog

·       Specify the Directory Services Restore Mode (DSRM) password

Step 6 – Verify Replication

After promotion completes:

repadmin /syncall /AdeP

Then verify:

repadmin /replsummary

Confirm that:

·       SYSVOL is replicated

·       NETLOGON share exists

·       DNS zones are synchronized

Step 7 – Transfer FSMO Roles

Move FSMO roles to the new server:

Move-ADDirectoryServerOperationMasterRole `
-Identity "NEW-DC" `
-OperationMasterRole 0,1,2,3,4

Verify:

netdom query fsmo

Ensure all five roles now reside on the new Domain Controller.

Step 8 – Update DNS Settings

Update clients and servers to use the new Domain Controller as their preferred DNS server.

Recommended configuration:

Preferred DNS

New Domain Controller

Alternate DNS

Secondary Domain Controller

Verify name resolution from multiple client computers.

Step 9 – Validate Active Directory Services

Test the following:

·       User logon

·       Computer authentication

·       Group Policy processing

·       DNS resolution

·       File share access

·       Active Directory Users and Computers

·       DHCP authorization (if applicable)

Run:

gpupdate /force

Verify expected policies are applied.

Step 10 – Monitor the New Domain Controller

For several days after migration, monitor:

·       Event Viewer

·       DNS logs

·       Replication status

·       Authentication events

·       CPU usage

·       Memory utilization

·       Disk space

·       Backup jobs

Address any warnings before decommissioning the old server.

Step 11 – Demote the Old Domain Controller

Only demote the old Domain Controller after confirming:

·       No FSMO roles remain

·       Replication is healthy

·       DNS is functioning correctly

·       Clients authenticate successfully

·       Backups are complete

Remove Active Directory Domain Services using Server Manager or PowerShell and allow the demotion process to complete.

Common Migration Problems

Problem

Possible Cause

Recommended Solution

Replication errors

DNS or network issues

Verify DNS configuration and run repadmin diagnostics

Missing SYSVOL or NETLOGON

Replication incomplete

Check DFS Replication service and event logs

Clients cannot log in

Incorrect DNS settings

Ensure clients use internal DNS servers

FSMO transfer fails

Replication or permissions issue

Resolve replication problems before retrying

Group Policy not applying

DNS or SYSVOL issue

Verify replication and run gpresult on affected clients

Migration Checklist

Use this checklist during your migration:

·       ✔ Back up the existing Domain Controller

·       ✔ Verify Active Directory health

·       ✔ Check DNS functionality

·       ✔ Install Windows Server 2025 updates

·       ✔ Promote the new Domain Controller

·       ✔ Verify replication

·       ✔ Transfer FSMO roles

·       ✔ Update DNS configuration

·       ✔ Test user authentication

·       ✔ Monitor the environment before decommissioning the old server

Best Practices

·       Always perform a full backup before migration.

·       Use a staged migration rather than replacing the Domain Controller immediately.

·       Maintain at least two Domain Controllers for redundancy.

·       Verify Active Directory health before transferring FSMO roles.

·       Test authentication and Group Policy after every major change.

·       Keep detailed migration documentation for future audits and disaster recovery.

Conclusion

Migrating Active Directory from Windows Server 2016 to Windows Server 2025 is a critical project that strengthens security, improves performance, and prepares your infrastructure for future growth. By validating Active Directory health, ensuring reliable DNS, transferring FSMO roles carefully, and thoroughly testing authentication before retiring the old server, you can complete the migration with minimal risk and downtime.

Following a structured migration process helps maintain business continuity while ensuring a modern, reliable Active Directory environment.

Meta Description

Learn how to migrate Active Directory from Windows Server 2016 to Windows Server 2025 with this step-by-step guide. Covers AD health checks, DNS, replication, FSMO role transfer, validation, and best practices.

Tags

·       Active Directory

·       Windows Server 2025

·       Domain Controller

·       FSMO

·       System Administrator

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