Use Jumbo Frames

Unanswered Question
Apr 19th, 2010

We have six 2960 48 port switches in our stack. We just added a pair of 3560 48 port switches to run iSCSI over. These two switches are uplinked to our 2960 switches via the GB ports.

One of my techs wants to enable jumbo frames on both the 3560 units to increase the iSCSI performance. My fear is the larger frames won't play nice with the 2960 switches along with all the 10/100 devices on my network.

Are my concerns valid or will the switches negotiate and operate correctly?


I have this problem too.
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Collin Clark Mon, 04/19/2010 - 11:51

You should only enable jumbo frames when it's 1gb end to end. Your network will work if you have a 10/100 link in between (no jumbo frames though), but it then defeats the purpose of jumbo frames.

dennylester Mon, 04/19/2010 - 11:58

Hi Collin,

Thank you for your respone. I want to make sure I understand you correctly, so my GB attached servers talking to my GB attached iSCSI drive array will communicate fine using Jumbo Frames, but when a 10/100 client tries to communicate with my GB attached server it will work okay too?

I thought I read somewhere we might have issues with UDP traffic since an MTU isn't negotiated. does this make sense?

Thank you,


Collin Clark Mon, 04/19/2010 - 12:16


You are understanding correctly. The jumbo will be windowed down (TCP) until <1500. I have not heard of any app that sends jumbo UDP frames, but that would be a concern when traveling across a 100mb link.


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