Enabling Jumbo Frames

Jumbo frames allow ESXi to send larger frames out onto the physical network. The network must support jumbo frames end-to-end. Jumbo frames up to 9kB (9000 bytes) are supported. Before enabling Jumbo frames, check with your hardware vendor to ensure that your physical network adapter supports jumbo frames.

Enable Jumbo Frames for a VMkernel Interface on a vSphere Standard Switch

Jumbo frames reduce the CPU load caused by transferring data. Enable jumbo frames on a VMkernel network interface by changing the maximum transmission units (MTU) of the VMkernel interface.

Procedure

1. Log in to the vSphere Client and select the Hosts and Clusters inventory view.

2. On the host Configuration tab, click Networking.

3. Click Properties for the vSphere standard switch associated with the VMkernel to modify.

4. On the Ports tab, select the VMkernel interface and click Edit.

5. Set the MTU to 9000, and click OK.

Enable Jumbo Frames on a vSphere Distributed Switch

Enable a vSphere distributed switch for jumbo frames by changing the MTU size for that distributed switch.

Procedure

1. Log in to the vSphere Client and select the Networking inventory view.

2. Right-click the vSphere distributed switch in the inventory pane, and select Edit Settings.

3. On the Properties tab, select Advanced.

4. Set the Maximum MTU to the largest MTU size among all the virtual network adapters connected to the vSphere distributed switch, and click OK.

 

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.

Procedure

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.