TCP Chimney Offload and Windows Server 2008

by Mitch Tulloch [Published on 24 Feb. 2009 / Last Updated on 31 Oct. 2008]

How to verify that your server is utilizing the capabilities of a NIC that supports TCP Chimney Offload.

NDIS 6.0 supports full TCP offload or "chimney offload" which provides a direct connection (a "chimney") between applications and a TCP offload-capable NIC. This feature enables such a NIC to perform TCP processing for offloaded connections which reduces processor overhead and makes network communications more efficient. For details, see http://msdn.microsoft.com/en-us/library/aa503758.aspx.

How can you verify whether this feature is enabled on a Windows Server 2008 server that has a TCP Offload Engine (TOE) NIC installed? Use the Netsh command as follows:

C:\>netsh int tcp show global

Querying active state...

TCP Global Parameters

----------------------------------------------

Receive-Side Scaling State : enabled

Chimney Offload State : enabled

Receive Window Auto-Tuning Level : normal

Add-On Congestion Control Provider : ctcp

ECN Capability : disabled

RFC 1323 Timestamps : disabled

If TCP Chimney Offload is disabled, you can enable it using this command:

netsh int tcp set global chimney=enabled

Note that you must reboot your server after running the above command.

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