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Usually, installing a new DC replicates every object from a replica domain controller. On a local area network (LAN) connection, this is generally not a problem. However, when there are slow or bandwidth-restricted links between the corporate office and a DC installed in the remote office location, replicating every object across the connection can impact the service of other business-critical applications used in the remote office.
Starting with Windows Server 2008 and 2008 R2, Microsoft's Ntdsutil has included a new way to create installation media for provisioning a new DC in your Active Directory environment. Using the IFM approach allows loading the Active Directory data from media instead of transferring every object across the network.
It also eliminates the need to perform replication to a domain controller on one network, disconnect the domain controller, ship the DC to the destination network, and then get the domain controller in sync again. A DC that becomes disconnected from the Active Directory replication topology can lead to issues.
Note that any changes that occurred since the IFM set was created require replication. However, the changes are minimal compared to replicating the entire Active Directory database across a slow WAN link connection.
Install secondary DC from media on Server 2019/2022 ^
In remote locations, installing a read-only domain controller (RODC) is the preferred option. It offers additional security and performance benefits, such as storing account credentials only of users who hit the RODC for authentication. When you use IFM to make the installation media for an RODC, it removes cached passwords. The installation media for an RODC can be created on either a writable domain controller or another RODC.
The SYSVOL folder can also be included in the installation media. However, DFS replication for SYSVOL must be used between DCs for the SYSVOL folder to be included in the IFM media.
The IFM media set works by first creating the IFM media to bring your secondary domain controller RODC or a writeable domain controller online. To create the IFM media, type the following commands at an administrator prompt:
ntdsutil activate instance ntds ifm help
Notice the options when viewing the help for the IFM ntdsutil command. We are interested in RODC-specific commands. You can create an RODC with the IFM media set without SYSVOL, or one with SYSVOL. Depending on your needs at the remote site, you can decide whether you need to include SYSVOL.
To create the IFM media, type the option you want and the path to the folder where the media set will be created. In the example below, we create an IFM set, including SYSVOL.
Create Sysvol RODC c:\ifm
With an RODC, you will see an Active Directory folder and a SYSVOL folder if you choose to include SYSVOL. If you are creating a full writeable domain controller, you will also see a registry folder included.
Now that you have the IFM media set created, the folder will be copied to your new RODC. It can be copied before provisioning at the secondary site or at the time of promotion.
Add the Active Directory Domain Services role ^
The first step in your RODC is to add the Active Directory Domain Services role. Below, the Add Roles and Features wizard is launched, and the server is selected.
Select the Active Directory Domain Services role.
Click the Add Features button to add the required features for ADDS.
There is nothing further to add on the following Features screen, so just click Next.
Click Next on the AD DS informational screen. On the confirmation screen, click Install. This installs the Active Directory Domain Services role, but it does not promote the server to a domain controller just yet.
Installation of the Active Directory Domain Services role is successful.
Promote the server to a domain controller ^
Click the informational flag in the top right-hand corner of Server Manager. Then, click Promote this server to a domain controller.
Since we are adding an RODC to an existing Active Directory environment, select Add a domain controller to an existing domain.
On the Domain Controller Options screen, select the domain controller capabilities and site information. Here, we select the Read only domain controller (RODC) option.
Configure the RODC options you want to set, including the accounts allowed to replicate passwords to the RODC.
On the Additional Options screen, select Install from media and set the path where the IFM media set is located. I have copied the media set to the same directory location on the RODC. You can verify the media set as well. Click Next.
Next, specify the locations of the AD DS database, log files, and SYSVOL.
Note the "directory information will be copied primarily from" information displayed on the Review Options screen. This indicates that we have used the install from media option for the RODC.
The prerequisite check is next. You will see a warning about Windows NT 4.0 compatibility. However, it should succeed. Click Install.
After the promotion of the RODC and install from media is complete, you will see your session about to log out. This indicates the installation is done, and the server is about to reboot.
Wrapping up ^
The IFM option allows companies to eliminate the bulk of replication traffic when bringing an additional domain controller online. It is a useful option in remote locations where WAN bandwidth may be limited.
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It allows installing AD objects as part of the domain controller promotion process instead of needing to replicate the directory in whole across the network. With RODC, you can copy both the directory and SYSVOL to bring your new RODC online.