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.

The Author — Mitch Tulloch

Mitch Tulloch is a widely recognized expert on Windows administration, networking, and security. He has been repeatedly awarded Most Valuable Professional (MVP) status by Microsoft for his outstanding contributions in supporting users who deploy and use Microsoft platforms, products and solutions. Mitch has published over two hundred articles on different IT websites and magazines, and he has written or contributed to almost two dozen books and is lead author for the Windows 7 Resource Kit from Microsoft Press. For more information, see www.mtit.com .

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