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How do I disable Large Send Offload on Server 2008 Core w/ Broadcom NICs?

Posted on 2010-08-14
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This is for a virtual environment.  Two host servers running Server 2008 R2 Core.  After some research I've determined that I need to disable Large Send Offload on the NICs of my hosts.  I'm trying to determine how and where to do the disabling.  I see in the Broadcom utility where I can disable it.  I also see in the VM's where I can go into the properties of the NIC and disable it (not sure if its needed here).  I'm seen other posts regarding running a NETSH command and editing the registry.  Can anyone shed some light on this?
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Question by:chome81
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by:Blake_1
ID: 33439372
Is http://support.microsoft.com/kb/951037 what you are referring to?  The chimney configuration is pertinent to Broadcom adapters.
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by:chome81
ID: 33439381
No, that is TCP Chimeny Offload.  I am referring to Large Send Offload.  It is different.
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by:Blake_1
ID: 33439396
netsh int ip set global taskoffload=disabled
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by:chome81
ID: 33439405
Blake_1, thank you, but I think there's more to it than that, hense the reason why I'm posting this.  I've seen that command as well, but I'm looking for a more detailed explanation.
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by:msmamji
ID: 33440518
chome81 is right.
The above command will disable offloading on the OS. In order to completely get rid of it you also have to disable it at NIC level.
The problem with this is that you don't have any remote tool only allow you to view the network configuration and core doesn't have any command to change the properties of the NIC.

Luckily I landed on an article about jumbo frames on windows Server 2008 core R2 some time ago. The guy uses Broadcom Management Application Suite on core 2008 R2 to change Jumbo frame properties of broadcom NIC.
http://mrshannon.wordpress.com/2010/01/13/jumbo-frames-on-hyper-v-server/

You can use the article to disable the needed settings of broadcom NIC to completely disable offloading.

Regards,
Shahid
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by:chome81
ID: 33441174
Thanks msmamji.  If I simply disable it in the broadcom utility, won't that alone be sufficient?  Its my understanding that the command will also effect other offloading, such as TCP Chimney Offloading, which I don't want to change.  Is that not correct?
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by:msmamji
ID: 33448776
Sorry for the late reply. Well to answer both you questions, I am copying a part of Ethernet NIC FAQs from broadcom website.
http://www.broadcom.com/support/ethernet_nic/faq_drivers.php#

What is Large Send Offload?Normally the TCP segmentation is done by the protocol stack. By enabling the Large Send Offload value, the TCP segmentation can be done by the Gigabit Ethernet Adapter.How can I configure Large Send Offload?   1. In Microsoft Windows, right-click the Network Adapter in Network Connections and then click Properties.   2. Click the Configure button and then the General tab.   3. Set the "Large Send Offload" parameter to Disable or Enable.
So it seems that the settings alone in the NIC hardware would take care of it. And yes as it seems disabling from NIC settings would disable all offloading features including TCP chimney.

Hope that helps.
Regards,
Shahid
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by:chome81
ID: 33455987
This is where I'm missing it.

This command "netsh int ip set global taskoffload=disabled" will disable ALL offloading, just just LSO, correct?

I only want to disable LSO (Large Send Offloading)
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msmamji earned 500 total points
ID: 33479862
Again sorry for the delay.
task offload is enabled/disabled through ip context and chimney is controlled by tcp context, so I think one should not effect the other. With that being said you can be sure by checking the results of the following commmands.

net int ip show global
should give you the status of task offload among other things and

net int tcp show global
should give you the status of chimney among other things.

check the results of above commands both before and after applying the taskoffload=disabled switch.  

I hope that is what you were asking. The above command (netsh) only gives enabled or disabled control over taskoffload, not granular then that.

Regards,
Shahid
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