Outlook clients cannot connect to casarray using Windows NLB - Exchange Server 2010

So I was using Vmware workstation 9 to perform some basic testing on casarray's and I noticed that when I stopped one of casarray nodes in Windows NLB by issuing the "Stop" command and then going to the node properties and changing the "Default State" to Stopped... my outlook clients would disconnect and could not send and receive emails... hmmm very strange!

So I checked the basic stuff what needs to be checked working with Windows NLB's

  • Made sure the binding order of the network cards is correct (MAPI network should be on top and the NLB Heartbeat network should be second)
  • Disabled IPV6 on the NLB network card
  • Make sure you can ping your casarray FQDN (mine was casarray.alstar.com)
  • Make sure the autodiscover host record (autodiscover.alstar.com) can resolve to the FQDN of the casarray

But what really fixed it for me was that I changed the Cluster Operation Mode from Unicast to Multicast and after I did that I stopped by node again from the NLB console and this time none of my clients were disconnected.

I think its something to do with Vmware and I think even they recommend the mode to be set to Multicast but anyway try this out and see if it works for you guys!