Set up and Configuration

Applies To: Windows Server 2003 with SP1

Q. Can NLB Clusters Be Configured and Managed From a Single Point?

A. A new tool in Windows Server 2003 called the Network Load Balancing Manager (NLB Manager) provides a single point of configuration and management of NLB clusters. Some key features of the NLB Manager:

  • Creating new NLB clusters and automatically propagating Cluster Parameters and Port Rules to all hosts in the cluster and propagating Host Parameters to specific hosts in the cluster.

  • Adding and removing hosts to and from NLB clusters.

  • Configuring NLB to load balance multiple web sites or applications on the same NLB Cluster, including adding all Cluster IP Addresses to TCP/IP and controlling traffic sent to specific applications on specific hosts in the cluster.

  • Diagnosing misconfigured clusters.


You cannot use Network Load Balancing Manager to manage Windows 2000 clusters or mixed clusters, including clusters containing only hosts running Windows 2000 Server operating systems or clusters containing both Windows 2000 and Windows Server 2003 Server operating systems.

Q. Can I Use WMI to Remotely Bind and Configure NLB?

A. No.

Q. Can I Use WMI to Remotely Add an IP Address to TCP/IP?

A. Yes, call the following method:

  • Namespace: root\cimv2

  • Class name: Win32_NetworkAdapterConfiguration

  • Method name: EnableStatic

Q. What is the MaskSourceMAC Registry Key Used For?

A. To work correctly, every packet directed to the virtual IP address must reach all NLB hosts. Each NLB host then filters those packets. When the cluster network adapter of each NLB host connects to a port on a Layer 2 switch, the switch tries to determine the MAC address of the hosts connected to each of its ports. As a result, the switch can associate a MAC address with a given port. Ethernet switches send frames to a MAC address through the port associated with the destination MAC address. If a switch associates the clusters MAC addresses with one of its ports, NLB cannot correctly load-balance the traffic because the traffic will reach only a single NLB host.

In unicast mode NLB utilizes a technique called MAC address masking. NLB substitutes MAC addresses when it sends packets through the switch. The switch maps these substitute MAC address with individual ports, but does not associate the cluster MAC address with any port and therefore sends the traffic to the cluster MAC address to all the ports in the switch. Cluster MAC address masking prevents the switch from learning the association of cluster MAC address with a particular port. If a switch does not have a MAC address associated to a port, it sends the frames to all ports. This is known as port flooding. MAC address masking is possible only when the MaskSourceMAC registry key is set to its default value of one. When it is set to 0, NLB does not perform automatic MAC address masking. Therefore, other techniques must be used to prevent a Layer 2 switch from learning the cluster MAC address.

Q. Where Can I Learn More About NLB Setup and Configuration Options?

A. There are many resources to help you out with setting up and configuring NLB clusters.

First, you should read the Microsoft Windows Server 2003 Deployment Kit ( chapters that explain how to design and deploy NLB clusters: Chapter 10 Designing Network Load Balancing and Chapter 11 Deploying Network Load Balancing of the Planning Server Deployments section.

Once you have familiarized yourself with designing and deployment of NLB clusters, you can use a step-by-step checklist that allows you to set up and configure NLB clusters. The checklist is located in the Windows Server 2003 ( (all versions) online help on your CD, or on the Internet at:

There are many white papers and helpful documentation at Clustering Services in Windows Server 2003, ( There you can find white papers that provide a general overview of Load Balancing, the NLB architecture, configuration information for specific scenarios, troubleshooting and much more.

You should also refer to online Help as often the information you need is located right there.

If you have specific questions that are not answered in the resources listed here, please visit the Clustering Communities page and post your question on one of the NLB or clustering newsgroups. For more information about Microsoft communities, see the Microsoft communities Web site, (