I’ve had a couple of occurances of this where a server 2003 R2 vm will seemingly just loose network connectivity. Attempting to ping either in or out will not work. Whilst sometimes powering off and on the vm will resolve the issue it wont stop it randomly happening again (naturally during production hours).
I’ve noted that there is a VMware kb on the issue (which I found after i’d resolved the issue) however it states that it occurs when you have jumbo frames enabled within the guest vm. This however is not the case in my experience.
To resolve this issue just add another vnic to the vm using either the e1000 or vmxnet2 and remove the vmxnet3 vnic the re-enter the vm’s ip information in the newly added card. Another choice would (as a #lonvmug colleague of mine had discovered) be to reinstall vmware tools and reboot the vm Link . Reinstalling the tools is the best bet but I was unable to do that as the vm in question was a terminal services box so I hot added another vnic to avoid rebooting and loosing the disconnected sessions.
There will be some cases where you will need to reboot the vm afterwards such as network sensitive app that cannot handle a short amount of network disruption.