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i have an exchange test environment sitting on vmware. i have 2 mailbox servers, 2 CAS/HUB servers, and an AD server on a 2 physical host VMWare HA cluster. If I have all 5 servers on one host, everything works peachy. If I move 2 hosts off to the other server via vmotion, even though there is a switch between the two hosts that both are connected to, one of my CAS servers becomes unreacheable via ping from the other servers on the other host, but can still be reached by the other exchange guest on the same host, and it can get to other resources on that host. Firewalls have been ruled out. The switch between the two physical hosts has vlans on it, but all the ports specified for that network on BOTH hosts are plugged into the same vlan segment. Does anyone have any ideas???

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Have you tried rebooting the CAS server while it's on the second host? VMware sends a reverse ARP when it vmotions a VM and it's possible that your switch thinks it's still on the first host. – Scott Keck-Warren Oct 13 '11 at 12:34
It was all Microsoft Network Load Balancing's fault. The article I referenced from microsoft said to install that on both of the CAS servers because I wanted to create a CAS Array. Then I come to find out they don't recommend using NLB for exchange anymore and recommend using a 3rd party load balancer. I installed a new load balancer and all is well. – user664408 Nov 17 '11 at 22:44

Either the virtual switch on the second host is misconfigured, or the physical port configuration is incorrect. You haven't stated whether these machines are on different VLANS. Assuming that VLANs are mostly the same, I would verify the correct VLANs are trunked on the switch port.

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