VMware ESXi 4.1 Optimizations for Cisco UC on UCS

In my previous post I discussed the importance of installing the latest version of VMware Tools on UC virtual servers in a Cisco UC on UCS deployment. A second and equally important VMware 'tweak' is disabling Large Receive Offload (LRO) on VMware ESXi hosts.

VMware Knowledge Base Article 1027511 addresses some Linux TCP/IP stacks perform poorly when handling LRO-generated packets. This results in poor TCP performance.

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

Your guest VMs should now have normal TCP networking performance.

VMware Knowledge Base - KB Article 1027511
Cisco UC on UCS - Don't Forget VMware Tools