How to Disable Transport Control Protocol (TCP) Checksum Offloading

Products

• Endpoint Protection
• Network Access Control

Issue/Introduction

What are the steps for disabling TCP checksum offloading

Symptoms
Slow network throughput. Packet captures show many "Bad Checksum" packets. Server/Client communication problems.

Cause

Possible cause is TCP Checksum Offloading

Resolution

Disable TCP Checksum Offloading

1. Click on <start><Control Panel><Network Connections>.
2. Right-click on the applicable network connection and select “Properties”.
3. Next to the name of the NIC being used, click on “Configure”.
4. Now click on the “Advanced” tab.
5. If the NIC’s checksum offloading can be configured through the GUI it will show up in the left-hand box. If it doesn’t show up, perform the following:
6. Open “regedit” from the “run” line
7. Browse to HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters and verify that “DisableTaskOffload=1” exists.
   If it does not, or if it is set to “DisableTaskOffload=0”, add the registry key, or change to “DisableTaskOffload=1", respectively.
   Please Note
   : One test box had a Broadcom NIC and experienced communication problems. In a packet capture, it was evident that checksum offloading was enabled, but when checked, the NIC properties Checksum offloading was not listed. After adding the key described in step 7 (“DisableTaskOffload=1”), the problem went away.