We have few Windows 2012 servers running on vsphere 5.1 that has strange network problem.
Sometimes VM just losts connection. Vcenter shows on summary tab everything OK, but you cannot ping the VM, you cannot connect to it with RDP etc...
Rebooting the VM corrects the problem, or using Vmware console and disabling the network card and enabling.
We have tried moving VM to different host, tried different version network card (E1000 and E1000E), tried different power options on VM and nothing seems to work.
One server that has this problem is Veeam Backup and Recovery server, another one is running SQL and another is running file shares.
Any ideas what is crashing network on these 2012 servers? With 2008R2 servers and most of the 2012 we don't have same issues.