Comments on: How To Adjust MTU (Jumbo Frames) on Hyper-V and Windows Server 2012

By: Eric Siron

Eric Siron — Fri, 25 Oct 2013 13:03:00 +0000

Physical switches usually talk about it in terms of the Ethernet frame. I’ve never owned a switch that required me to specify a frame size. Jumbo frames were either off or on. If yours is asking you for a specific number, I would use a minimum size of 9022.

By: kardy

kardy — Fri, 25 Oct 2013 06:22:00 +0000

Hi Eric ,
Thank you for your replay.
I think I need a bit of clarification here . Are talking about ethernet MTU or ip MTU? In my previous comment I refer to the physical switch (Ethernet farme MTU).

By: Eric Siron

Eric Siron — Thu, 24 Oct 2013 15:03:00 +0000

In reply to kardy. Are you talking about the physical switch? Values to use for MTU settings are always defined by the device manufacturer. I can't really be any more specific than that. Usually though, you don't have to set MTU directly on a port. You can usually just set jumbo frames on or off for the entire switch.

By: kardy

kardy — Thu, 24 Oct 2013 15:00:00 +0000

If the Jumbo frame size on the nic is 9014 what should be the mtu for the switch port.

By: ashwin

ashwin — Tue, 15 Oct 2013 08:56:00 +0000

Fantastic post! Short and to the point. I liked the way you made it interesting with story telling. Though this post is about 2012 teaming and jumbo frames, it also covered virtual nic and virtual switch concept.

After I finished reading, the first thing popped up into my mind was regarding MPIO, but then I scrolled down, and it was already answered. In a way I am happy that MPIO query came up, b’cos I am sure lot of us would have had the similar confusion. Thanks Eric. Looking forward to more such articles.

By: Eric Siron

Eric Siron — Wed, 24 Jul 2013 13:11:00 +0000

In reply to Jason Schwark. Nicely done! A word of caution, though: You may not want to enable jumbo frames on adapters that have Internet connections or go through other routers that have a standard frame size as it will impair performance and sometimes cause transmission failures.

By: Jason Schwark

Jason Schwark — Wed, 24 Jul 2013 00:48:00 +0000

Awesome find/tip… I spent some time trying to automate this process, since the key shows up in different locations, depending on how many NICs you have installed, and came up with a powershell script that worked for me – posting here in case it might help someone else:

get-childitem -path “HKLM:SYSTEMCurrentControlSetControlClass{4d36e972-e325-11ce-bfc1-08002be10318}” -recurse -ea SilentlyContinue | where-object {(get-itemproperty -path $_.PSPath) -match “vms_mp” -and (get-itemproperty -path $_.PSPath) -match “1514”} | foreach-object {set-itemproperty -path $_.PSPath -Name “*JumboPacket” -value”9014″}

By: Eric Siron

Eric Siron — Thu, 07 Mar 2013 21:21:00 +0000

In reply to Sergey Mozhzhukhin.

That’s correct. However, there is an abstraction layer here that confuses things.

What Server Manager is referring to is teaming two NICs and then making an iSCSI connection directly over them. That team is represented by a single IP address straddling two ports and trying to engage in multi-path conversations with storage. That is not what is happening here.

In this type of setup, if multi-path is desired, an iSCSI connection would be created by using two vNICs, each with their own IPs, with MPIO enabled. This results in a dual-NIC MPIO iSCSI connection to a switch that then connects to another switch over a multi-port LACP connection that then connects to the back-end storage. This is not an unusual configuration in the real world. The only difference is that one of the switches in this case is virtual.

The setup as presented above does not include MPIO. The lone “Storage” vNIC is the only path to storage and it will never use more than a single pNIC at a time. However, this post is about getting Windows Server 2012 teaming and jumbo frames to work together, not MPIO. I am regretting ever mentioning it.

By: Sergey Mozhzhukhin

Sergey Mozhzhukhin — Thu, 07 Mar 2013 21:04:00 +0000

Server manager help on Server 2012 has this:
“For iSCSI, you cannot use network adapter teaming (also called load balancing and failover, or LBFO), because they are not supported with iSCSI. You can consider using MPIO software instead.”

Number of iSCSI vendors also do not recommend using LBFO with iSCSI.