The cluster operation mode determines how you configure the cluster's network address and how that address relates to the existing network adapter addresses. You can configure the operation mode of an NLB cluster by editing the cluster properties, as shown in Figure 16-4. All nodes within a cluster must use the same cluster operations mode. This tab also displays the virtual MAC address assigned to the cluster by using this dialog box.
The cluster operations modes, and the differences between them, are as follows:
■ Unicast Mode When an NLB cluster is configured to work in the unicast cluster operation mode, all nodes in the cluster use the MAC address assigned to the virtual network adapter. NLB substitutes the cluster MAC address for the physical MAC address of a network card. If your network adapter does not support this substitution, you must replace it. When nodes in a cluster have only a single network card, this limits communication between nodes but does not pose a problem for hosts outside the cluster. Unicast mode works better when each node in the NLB cluster has two network adapters. The network adapter assigned the virtual MAC address is used with the cluster; the second network adapter facilitates management and internode communication. Use two network adapters if you choose unicast mode and use one node to manage others.
■ Multicast Mode Multicast mode is a suitable solution when each node in the cluster has a single network adapter. The cluster MAC address is a multicast address. The cluster IP address resolves to the multicast MAC address. Each node in the cluster can use its network adapter's MAC address for management and internode communication.
You can use multicast mode only if your network hardware supports multicast MAC addressing.
■ IGMP Multicast Mode This version of multicast uses Internet Group Membership Protocol (IGMP) for communication, which improves network traffic because traffic for an NLB cluster passes only to those switch ports the cluster uses, not to all switch ports. The properties of IGMP multicast mode are otherwise identical to those of multicast mode.
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