Windows Network Load Balancing does not work in an Exchange Server cluster

Consider the following scenario:

• You have multiple servers that are running Microsoft Exchange Server.
• The servers that are running Exchange Server are hosted in a VMware ESX environment.
• The servers that are running Exchange Server are part of a Windows Network Load Balancing cluster.
• Windows Network Load Balancing is configured to run in unicast mode.

In this scenario, Windows Network Load Balancing may not work correctly. For example, network traffic is routed to one node in the cluster.

This issue can occur if the Reverse Address Resolution Protocol (ARP) is enabled in the VMware host.

To resolve this issue, disable Reverse ARP on the VMware ESX host. For information about how to disable Reverse ARP on the VMware ESX host, visit the following VMware website:

For more information about how to implement Network Load Balancing in a VMware environment, visit the following VMware website:

For more information about load balancing in Microsoft Exchange Server 2010 Service Pack 1, visit the following Microsoft TechNet website:

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