Monday, February 22, 2010 9:04 AM
When you connect to a guest system running in Hyper-V or some other 3<sup>rd</sup> party virtual software via Remote Desktop Connection or RemoteApp Web Access, the performance is very slow. The performance of the guest system itself is fine.
There is a known issue with Hyper-V and the virtual networks when task offload is enabled in VM.
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 How to back up and restore the registry in Windows
To work around this problem, disable the Large Send Offload on the virtual machine via the following steps:
1. Open Network Connections.
2. Right-click the icon of the NIC which is responsible for the connection to terminal clients and select Properties.
3. In Networking tab, click Configure… button.
4. In the next window, switch to Advanced tab.
5. Click the Large Send Offload Version 2 (IPv4) and change the value to Disabled.
6. Click Start , click Run , type regedit , and then click OK .
7. Locate and then click the following registry subkey:
8. In the right pane, make sure that the DisableTaskOffload registry entry exists. If this entry does not exist, add the entry:
<samp>DWORD Value: DisableTaskOffload
Value Data: 1</samp>
9. Exit Registry Editor.
For more information about the DisableTaskOffload registry entry, visit the following Microsoft Web site:
TCP/IP Task offload allows tasks normally performed by the transport layer to be processed by the network adapter. This reduces the overhead required of the system CPU for these tasks. This allows the system CPU to do more work, possibly increasing the throughput to the network. A special query is made by the transport driver to find out if the network adapter supports the offload of the computation of TCP/IP checksums, TCP/IP segmentation (large send), Fast Packet Forwarding and IPSec Offload. If one or more of these conditions is detected, the transport can request that the network adapter furnish these services.
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