• Preetam Zare

TCP Segmentation Offload and Jumbo Frames

You can enable jumbo frames on a vSphere distributed switch or vSphere standard switch by changing the maximum transmission units (MTU). TCP Segmentation Offload (TSO) is enabled on the VMkernel interface by default, but must be enabled at the virtual machine level.

Enabling TSO

To enable TSO at the virtual machine level, you must replace the existing vmxnet or flexible virtual network adapters with enhanced vmxnet virtual network adapters. This replacement might result in a change in the MAC address of the virtual network adapter.

TSO support through the enhanced vmxnet network adapter is available for virtual machines that run the following guest operating systems:

· Microsoft Windows 2003 Enterprise Edition with Service Pack 2 (32 bit and 64 bit)

· Red Hat Enterprise Linux 4 (64 bit)

· Red Hat Enterprise Linux 5 (32 bit and 64 bit)

· n SUSE Linux Enterprise Server 10 (32 bit and 64 bit)

Enable TSO Support for a Virtual Machine

You can enable TSO support on a virtual machine by using an enhanced vmxnet adapter for that virtual machine.


1. Log in to the vSphere Client and select the virtual machine from the inventory panel.

2. Click the Summary tab, and click Edit Settings.

3. Select the network adapter from the Hardware list.

4. Record the network settings and MAC address that the network adapter is using.

5. Click Remove to remove the network adapter from the virtual machine.

6. Click Add.

7. Select Ethernet Adapter and click Next.

8. In the Adapter Type group, select Enhanced vmxnet.

9. Select the network setting and MAC address that the old network adapter was using and click Next.

10. Click Finish and then click OK.

11. If the virtual machine is not set to upgrade VMware Tools at each power on, you must upgrade VMware Tools manually.

TSO is enabled on a Vmkernel interface. If TSO becomes disabled for a particular VMkernel interface, the only way to enable TSO is to delete that VMkernel interface and recreate it with TSO enabled.

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