Time to revisit recommendations around Windows networking enhancements usually called Microsoft Scalable Networking Pack

Update 1/3/2012: We have had a few reports of customers re-enabling SNP features and running into problems because hardware drivers on systems were very old. Please make sure to update your network-related drivers before re-enabling (or enabling) those features!

Over the years, there has been a lot of debate around features in Windows which are usually referred to as Microsoft Scalable Networking Pack (individual features are known as Receive Side Scaling (RSS) and Chimney/TCP Connection Offload/TOE), and the effect of having them enabled or disabled on our servers.

Taking the trip down the memory lane – while it is true that when the features were released in Windows 2003 SP2, there were some issues to work out (in both Microsoft and 3rd party code such as network drivers) – the situation has improved dramatically over the years, to the point where disabling them can have significant impact on the performance of your servers.

Here is an example:

The following screenshot shows one of CPUs being overly taxed while others are not sharing the load. This is quite typical on a server with busy networking connection and RSS feature turned off:


The following shows a bit better what happens when RSS is in fact enabled on the server. The point of enabling it is illustrated by the red circle. Note how a single processor was very busy with networking traffic while the rest were not nearly as busy, and what happens after RSS was enabled:


Now that I have your attention – I wanted to point you to an article that one of my counterparts from Windows team, Tod Edwards, has written recently – which goes in depth on what those features are, why you should enable them, how to do so and also – how to make sure that you are in a good place when you do. Please go here to read it:

Give Microsoft’s Scalable Networking Pack Another Look


(It should go without saying but: please make sure that your network card drivers are updated!)


Nino Bilic

Comments (3)
  1. Brendan says:

    This article indicates that RSS should be enabled for exchange servers and TOE disabled.  Microsoft support had previously instructed me to disable both RSS and TOE.  What is your recommendation regarding RSS?  Is there any benefit to enabling it if you are not hitting 100% utilization on s single core when it is disabled?

  2. Nino Bilic says:

    Brendan – there is a lot of "tribal knowledge" that has been passed around those features over the years; generally speaking, our guidance now is that it is benificial to have those features turned on. I am aware of the fact that in many a support case in the past, support would guide you to disable the features and in depending on timeframe of the case, servie pack levels and drivers used – they were likely right to do so. We are working with support internally too, to help guide away from disabling the features in cases where there is no reason to do so anymore. The linked article really does represent the latest thoughts around it all.

  3. Grimson says:

    Thanks for the information!

    So Microsoft indirectly approves the proactive installation of the mentioned hotfixes?

    (As the article is not directly a MS article, most 3rd party advices must be taken the official road or at least some precaution when it comes to applying hotfixes.)

    For me I will apply these hotfixes accordingly.

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