I have two CAS/HUB servers (CAS1 & CAS2) and two Mailbox servers (MBX1 & MBX2). All four servers live on ESXi 4.0 hosts. CAS1 and MBX1 are on ESXA and CAS2 and MBX2 on ESXB. I am using the Microsoft NLB for my CAS Array. I have configured the NLB with the correct ports according to CAS template Microsoft has provided. My problem is this: CAS2 who is the primary CAS server that takes requests is unable to ping or access anything on MBX1 but is able to get to MBX2 And MBX1 can't talk to CAS2 but can talk to MBX2. MBX2 is able to ping MBX1. CAS1 can ping CAS2, MBX2, & MBX1. Going through a lot of different iterations on what could be causing this problem I moved all VM's to a single ESX host, ESXA, and everything started talking like it should. As soon as I moved one MBX, and it didn't matter which one, to the other ESX host communication to that MBX is lost. So my first thought would be a network problem with the ESX host. I rebuilt the vSwitch, and it didn't correct the problem. This only happens when a MBX server is moved. If I moved a CAS server no problems.
So my question, I think, revolves around Microsoft NLB. Is NLB the problem or is it some deep down network issue? and is the issue in the VM or on the ESX host?