Today I have been troubleshooting problems with a Microsoft ISA array. The array didn’t function anymore after moving the Configuration Storage Server and one array member from a VMware 3.5 environment to a VMware 4.0 environment. After moving the array member the VMware Tools were upgraded and also the Virtual Hardware was upgraded. After rebooting the moved array member the customer received multiple error messages, like duplicate IP addresses and users not able to access resource through the reverse proxy.
A Microsoft ISA array uses Network Load-Balancing and NLB was the cause of all problems. After upgrading the VMware Tools and the Virtual Hardware, NLB needs to be reconfigured. The complete configuration of NLB was lost. I reconfigured NLB (multicast with IGMP support) and the problem was resolved. The array members were functioning properly again.
Moving and upgrading the second array member resulted in the same problems with the same cause. Reconfiguring NLB on the second array member did the trick. So be careful when moving ISA array members with NLB configured from a VMware 3.5 to a VMware 4.0 environment, especially when upgrading VMware Tools and the Virtual Hardware.