With the release of the Scalable Networking Pack that is included with Windows 2003 SP2, we in Exchange support have been seeing some connectivity issues once the new networking features are enabled. These new features are enabled by default and are only used if your network card driver supports them. Some of the new architectural additions that were introduced with the Scalable Networking Pack are TCP Chimney Offload, Receive-side Scaling (RSS) and NetDMA. These were introduced because of the Microsoft Scalable Networking Initiative that was designed to help reduce OS bottlenecks caused by network packet processing. More information regarding the Scalable Networking initiative can be found at www.microsoft.com/snp.
What this is does essentially is to offload TCP/IP packet processing to the network card, thus freeing up valuable CPU cycles for your applications. The throughput increases that you can get from having these enabled are quite significant.
To support these new features, the NDIS miniport driver had to be redesigned to handle this, thus NDIS 6.0 was born. For more information regarding the updated NDIS miniport driver, see http://msdn2.microsoft.com/en-us/library/ms798546.aspx from the Windows Driver Kit NDIS Miniport Driver Reference. With the NDIS 5.1 driver, the Operating System was limited to processing network traffic on a single CPU which impacted CPU performance quite significantly. The new NDIS driver design allows for processing this same information across multiple processors which will improve performance quite significantly.
This appears like this would actually increase the performance of Operating System, but what does this have to do with Exchange? Well, some of the issues surrounding the problems are documented in 936594 and a short list of what may affect Exchange is listed below.
Microsoft, Exchange, Server, Exchange Server 2007, Windows 2003, SP2, Scalable Networking, Troubleshooting, Tips and Tricks, Knowledgebase