I have a pair of Win2K3/Exchange 2007 VMs running on different Esxi5 hosts and seem to have a spurious network issue. An SMTP application keeps randomly (once every day or every-other day) switching over to the other Exchange server with a 'Socket Closed' error. I've run Wireshark on the machine running the SMTP application, as well as both Exchange VMs and thought I figured out the problem was TCP offloading. I disabled that but still the issue persists. I've run ESXTOP on the host and haven't found any dropped packets with it either. I've switched from E1000 to vmxnet3 adapters and still no change.
I'm at a loss now as to what the problem could be. The only clue I do still have that the problem might be in VMWare is that if I run Wireshark on one of the VMs (but not the other one, oddly), when the the 'Socket Closed' error occurs on the SMTP app, Wireshark stops capturing. It doesn't give an error, there just aren't any more packets in the logs after that point. There's some sort of hiccup going on but I can't figure out a solution. Any ideas?