Setting Up Jumbo Frames on a VMware ESX Hosts

Jumbo Frames can be an important part of a IP Storage network, it reduces the overhead for a TCP/IP packet by increasing the MTU from 1500 to 9000 per packet. Now there are some strict requirements you need to follow to make this happen, or you will have MTU miss match errors that will actually slow down your storage network instead of speeding it up.

First Make sure you configure your SWITCH VLAN that will handle the traffic to use jumbo frames. For example on a HP Procurve from the configuration prompt:

vlan 30

Second make sure that you configure a an interface on the Storage device that is also on this VLAN to use jumbo frames to communicate with your Host device. This depends on your storage vendor, but reading the documentation you should figure it out quickly.

Third configure all your host devices to communicate with your storage device via jumbo frames on the same vlan. Now I keep saying “same VLAN” for a very good reason, as you will quickly run into the dredded MTU missmatch errors if you try to route communications between VLANs. If you need to route to other devices or a device of a WAN that are not using jumbo frames then you must use a dedicated interface to communicate with the other device with MTU 1500. This interface does not have to be physical, on NetApp this can just be a VIF without -9000 configured on it.

Now that you have soem background on Jumbo frames here is how to enable them on a vSwitch on a VMware ESX host.

I created the VMware Networks port group on vSwitch2 called IPStorage before running the following CLI commands on the ESX host

First in the vCenter or Network Configuration add your vSwitch and setup a portgroup, in this example I used vSwitch2 and called the port group IPStorage. Once this is setup use put or login to the console of your ESX host.

Prep the vSwitch with the following command subsitute vSwitch2 with the vSwitch you wish to target

esxcfg-vswitch -m 9000 vSwitch2

now configure the portgroup as you named it earlier and assign it an IP at the same time

esxcfg-vmknic -a -i -n -m 9000 IPStorage

Finally test your configuration by trying to ping your storage interface with a jumbo frame packet:

vmkping -s 9000

If your ping fails make sure that your storage interface is correctly configured and on the same VLAN and subnet, also ensure that you have Jumbo Frames enabled the switch in the VLAN you are using. Also make sure that when you setup your portgroup in the VMware GUI that you input the VLAN number if you are using tagged vlans on the port.


About Paul Cardelli, CISSP
Cyber Security Analyst, and computer guru

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