Jumbo Frames and Maximum MTU

[vmproteau]

I have set maximum MTU to 9000 in the past for VMkernel vSwitches and portgroups but not on the VM portgroups. There was a reason at the time that I can't recall. I am reconsidering in my new environment and wanted to get some guidance for those famailiar with or already configured with a maximized MTU. I'd appreciate any guidance for or against this configuration.

1. Do you use it for your  vSwitches and vDS port groups that pass VM traffic? I assume there are no issues with this setup but that VMs generally won't take adavntage of the larger frames unless configured within the guest to do so.
2. Providing all associated networking hardware supports and is configured to use it, are there any circumstances where I would not want to set the maximum MTU on the ESXi Host?
3. It's been a while but if I recall the places where MTU should be set are:
   • The physcial switches
   • The vSwitch or vDS
   • The port group
   • The pNIC

[ramkrishna1]

Hi

Welcome to the communities.

Please go through below link and conform all settings are fine and retrive the config after restart .

http://pubs.vmware.com/vsphere-50/index.jsp?topic=%2Fcom.vmware.vcli.examples.doc_50%2Fcli_manage_ne....

Take care!

[homerzzz]

Whether or not you configure jumbo frames really depends on if you have a business justification and positive testing results.

You are correct on the locations where you need to configure...basically end-to-end.

[vmproteau]

Thanks. How about the specific question about the interfaces passing guest VM traffic? As mentioned before my assumption is that guest traffic won't take advantage of any increase in maximum MTU unless they are configured to do so in the OS. My other assumption is that there is no negative affect for guests that aren't configured.for with a larger MTU. I suspect we will have a mix.

Interested in hearing comments and experiences from those who have maximized MTU in their environments.

[NetRock]

Hi,

We usually use Jumbo Frames to maximize the throughput of IP-Based storage systems, for example iSCSI SAN storage. And it has a positive

affect on iSCSI traffic that being transmitted on the network.

The important thing about Jumbo Frames is that you should configure it End-to-End. I mean you should configure it on your VMKernel port, vSwitch,

Physical Switch and finally SAN storage. And setting the Jumbo Frame with just configure the Maximum size of frames and it wouldn't affect traffic

and VMs with lower frames being transmitted.

You can also refer to the following VMware blog post for more info:

Jumbo Frames in vSphere 4.0 | VMware vSphere Blog - VMware Blogs

Hope it helps,

NetRock

[vmproteau]

Thanks NetRock,

I do know that that IP based storage will see the most benefit from the larger MTU size. Appreciate the response on the VM interfaces. I assumed as much but just wanted to make sure before standardizing on this configuration.