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.

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http://msexchangeteam.com/archive/2007/07/18/446400.aspx