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.

Basically you must disable reverse ARP on the respective VMware ESX hosts to resolve the issue.

Read more in this new MS KB article.

Until later,

Henrik Walther
Technology Architect/Writer/MS Vendor
MCM: Exchange Server | MVP: Exchange Architecture

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