Use the following procedure to configure the Network Load Balancing (NLB) cluster operation mode.

You can also perform the task described in this procedure by using Windows PowerShell. For more information about using Windows PowerShell for NLB clusters, see

When you are using Network Load Balancing (NLB) Manager, you must be a member of the Administrators group on the host that you are configuring, or you must have been delegated the appropriate authority. If you are configuring a cluster or host by running NLB Manager from a computer that is not part of the cluster, you do not have to be a member of the Administrators group on that computer.

To configure the Network Load Balancing cluster operation mode
  1. To open NLB Manager, click Start, click Administrative Tools, and then click Network Load Balancing Manager. You can also open NLB Manager by typing Nlbmgr at a command prompt.

  2. If NLB Manager does not already list the cluster, connect to the cluster.

  3. Right-click the cluster and choose Cluster Properties.

  4. On the Cluster Parameters tab, in Cluster operation mode, select Unicast or Multicast. If appropriate, you can also enable Internet Group Management Protocol (IGMP) support by selecting the IGMP multicast check box.

Additional considerations

  • The cluster operation mode parameters specify whether a multicast media access control (MAC) address should be used for cluster operations. If multicast is enabled, NLB converts the cluster MAC address for the cluster adapter into a multicast address. It also ensures that the cluster's primary IP address resolves to this multicast address as part of the Address Resolution Protocol (ARP). The adapter can now use its original, built-in MAC address that was disabled in unicast mode.

  • You must first enable multicast support before enabling Internet Group Management Protocol (IGMP) support. IGMP support can also be enabled on the network adapter.

  • The IGMP multicast check box enables IGMP support for limiting switch flooding by limiting traffic to "Network Load Balancing ports" only. That is, enabling IGMP support ensures that traffic intended for an NLB cluster passes through only those ports serving the cluster hosts and not all switch ports.

Additional references