Use ADLB from the Windows Server 2003 Branch Office Guide to Rebalance Connections Between Writeable Domain Controllers in the Hub

Updated: June 3, 2009

Applies To: Windows Server 2008

The Windows Server 2003 Active Directory Branch Office Guide provides guidelines for detecting and resolving inbound and outbound replication overload conditions on bridgehead servers that run Windows Server 2003. It also provides guidelines for using the Windows 2000 Active Directory replication compression algorithm on slow wide area network (WAN) links. For convenience, the guidelines from the Windows Server 2003 Active Directory Branch Office Guide are reproduced in the following sections. You can follow the same guidelines for preventing bridgehead servers from becoming overloaded while you replace your existing bridgehead servers that run Windows Server 2003 with bridgehead servers that run Windows Server 2008.

You can use the Active Directory Load Balancing (ADLB) tool (Adlb.exe) from the Windows Server 2003 Active Directory Branch Office Guide to load-balance connections between writeable domain controllers, including domain controllers that run Windows Server 2008. Adlb.exe does not attempt to load-balance connections between read-only domain controllers (RODCs) and writeable domain controllers. However, because RODCs automatically redistribute connections among bridgehead servers that run Windows Server 2008, you can focus your monitoring efforts on the connections between the bridgehead servers and the Windows Server 2003 domain controllers that remain in the branch offices.

For example, consider a topology in which one hub site has four bridgehead servers that run Windows Server 2003. The hub site is connected to 100 branch office sites, and each site has a domain controller that runs Windows Server 2003. After you run Adlb.exe, each bridgehead server has replication connections to 25 domain controllers, as shown in the following illustration.

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In this situation, if you upgrade any Windows Server 2003 domain controllers, they maintain their existing connection objects after the upgrade. Upgrade is preferred because if you replace any Windows Server 2003 domain controllers by demoting them and promoting writeable Windows Server 2008 domain controllers in their place, you must re-create any manual connection objects that existed on the original Windows Server 2003 domain controllers.

If you run the ADLB tool, these additional connection objects from RODCs will be ignored and the bridgehead server will end up with the same load as other bridgehead servers that are generated from writeable branch domain controllers, in addition to the load that is generated from the RODCs. It will also be a single point of failure even if other Windows Server 2003 domain controllers are available at the hub. As a consequence, the higher the percentage of Windows Server 2008 bridgehead servers you have in the hub, the better the load will be distributed across them.

The following topics explain how you can help prevent hub site domain controllers from becoming overloaded by replication operations during the transition period in which you still have writeable domain controllers in branch offices:

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