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Large packet loss at the guest operating system level on the VMXNET3 vNIC in ESXi (2039495)

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When using the VMXNET3 driver on ESXi 4.x, 5.x or 6.0, you see significant packet loss during periods of very high traffic bursts.


This issue occurs when packets are dropped during  high traffic bursts. This can occur due to a lack of receive and transmit buffer space or when receive traffic which is speed-constrained. For example, with a traffic filter.


To resolve this issue, ensure that there is no traffic filtering occurring (for example, with a mail filter). After eliminating this possibility, slowly increase the number of buffers in the guest operating system.

To reduce burst traffic drops in Windows Buffer Settings:
  1. Click Start > Control Panel > Device Manager.
  2. Right-click vmxnet3 and click Properties.
  3. Click the Advanced tab. 
  4. Click Small Rx Buffers and increase the value. The default value is 512  and the maximum is 8192.
  5. Click Rx Ring #1 Size and increase the value. The default value is 1024 and the maximum is 4096.

  • These changes will happen on the fly, so no reboot is required. However, any application sensitive to TCP session disruption can likely fail and have to be restarted. This applies to RDP, so it is better to do this work in a console window.
  • This issue is seen in the Windows guest operating system with a VMXNET3 vNIC. It can occur with versions besides 2008 R2.
  • It is important to increase the value of Small Rx Buffers and Rx Ring #1 gradually to avoid drastically increasing the memory overhead on the host and possibly causing performance issues if resources are close to capacity.
  • If this issue occurs on only 2-3 virtual machines, set the value of Small Rx Buffers and Rx Ring #1 to the maximum value. Monitor virtual machine performance to see if this resolves the issue.
  • The Small Rx Buffers and Rx Ring #1 variables affect non-jumbo frame traffic only on the adapter.


Windows 2008 R2, Exchange 2010, Packet drops, Packet loss

See Also

Update History

07/29/2013 - Added notes to Resolution section.

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