Last Thursday, VMware distributed a rush post regarding an issue with Windows Server and VMware Tools. The issue pertains to packets being dropped on virtual machines running Windows as the guest OS and VMware Tools versions 9.10.0 through 10.1.5. For reference, 9.10.0 through 10.1.5 were packaged with ESXi 6.0 and 6.5, respectively. The increased rate of dropped packets stems from a malfunction in Windows Receive Side Scaling (RSS) on Windows 2012 and later guests. RSS normally works to distribute network processing across multiple CPUs. However, the fault in RSS causes all network traffic to run through one CPU on these Windows guests.

VMware notes that this situation results in performance degradation for the applications and services hosted on the affected virtual machine. I have already seen a post of this possibly affecting Veeam backup proxies and subsequent jobs. These proxies already experience extremely busy CPU’s and when compounded with this issue could be the cause intermittent job failures.

VMware is working on a fix and recommends downgrading VMware Tools to version 9.4.15 if you are experiencing the issue.