All cluster hosts in a cluster receive all incoming client requests that are destined for the virtual IP address that is assigned to the cluster. The Network Load Balancing load-balancing algorithm, which runs on each cluster host, is responsible for determining which cluster host processes and responds to the client request.
You can distribute incoming client requests to cluster hosts by using unicast or multicast methods. Both methods send the incoming client requests to all hosts by sending the request to the cluster’s MAC address.
When you use the unicast method, all cluster hosts share an identical unicast MAC address. Network Load Balancing overwrites the original MAC address of the cluster adapter with the unicast MAC address that is assigned to all the cluster hosts.
When you use the multicast method, each cluster host retains the original MAC address of the adapter. In addition to the original MAC address of the adapter, the adapter is assigned a multicast MAC address, which is shared by all cluster hosts. The incoming client requests are sent to all cluster hosts by using the multicast MAC address.
Select the unicast method for distributing client requests, unless only one network adapter is installed in each cluster host and the cluster hosts must communicate with each other. Because Network Load Balancing modifies the MAC address of all cluster hosts to be identical, cluster hosts cannot communicate directly with one another when using unicast. When peer-to-peer communication is required between cluster hosts, include an additional network adapter or select multicast mode. When the unicast method is inappropriate, select the multicast method.
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