VMware Support AlertBefore upgrading your environment to vSphere 6.0 Update 1, VMware would like everyone to read the following KB article for important information.

After installing or upgrading to ESXi 6.0 and 6.0 Update 1, customers network connectivity is lost randomly with the error: NETDEV WATCHDOG: vmnic0: transmit timed out. This issue has been resolved.

Please proceed to KB article: ESXi 6.0 network connectivity is lost with NETDEV WATCHDOG timeouts in the vmkernel.log (2124669)

This issue is resolved in ESXi 6.0 Update 1a, available at VMware Downloads. For more information, see the VMware ESXi 6.0 Update 1a Release Notes.

Any updates to this information will be made in the KB article itself.