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

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 well-known expert on Windows Server administration and cloud computing technologies. He has published over a thousand articles on information technology topics and has written, contributed to or been series editor for over 50 books.

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