Disable LRO

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VMware vSphere ESXi 4.1 introduced a new setting called "Large Receive Offload (LRO)". When enabled on VMs running ESXi 4.1 or later, you may experience slow TCP performance on certain operating systems (depending on which Collaboration application and version). This setting usually needs to be disabled on an ESXi host running Collaboration app VMs (either new install of ESXi 4.1+, or upgrade from ESXi 4.0 to 4.1+ followed by upgrading VMwareTools in app VMs to 4.1+).


Collaboration Application & Version VMware vSphere ESXi Version Disable LRO required?
CUCM 8.0(2) to 8.5 4.1 Yes
CUCM 8.6 or higher 4.1 No
CUCCX / IPIVR 8.0 to 8.5 4.1 Yes
CUCCX / IPIVR 9.0 or higher 4.1 No
Finesse 9.1(1) or earlier 4.1 Yes
All others

Disable LRO if on ESX 4.1 and app version < 8.6.

Otherwise disable LRO is optional.  If you experience FTP/TCP latency, then disable LRO.


To disable LRO, follow this procedure:

  1. Log into the ESXi host or its vCenter with vSphere Client.
  2. Select the host > Configuration > Advanced Settings.
  3. Select Net and scroll down slightly more than half way.
  4. Set the following parameters from 1 to 0:
    • Net.VmxnetSwLROSL
    • Net.Vmxnet3SwLRO
    • Net.Vmxnet3HwLRO
    • Net.Vmxnet2SwLRO
    • Net.Vmxnet2HwLRO
  5. Reboot the ESXi host to activate these changes.

Your guest VMs should now have normal TCP networking performance.



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