Article ID: 888750 - View products that this article applies to.
When you try to access resources on your Microsoft Virtual Server 2005 host computer from a guest virtual machine, the performance is very slow. When you try to copy a large file, the file copy may take minutes when you expect it to take seconds. Or, the large file transfer may not be completed. You may also experience that the guest virtual machine or other guest virtual machines that are attached to the same virtual network may disconnect from the virtual network.
This problem may also cause actual non-virtual network connections to the host machine to be disconnected. You may see an event log entry that is similar to the following event log entry :
Event ID: 2025
This problem may occur if you have Transmission Control Protocol (TCP) segmentation offloading enabled on the host computer's network adapter. The Digital Equipment Corporation (DEC)/Intel 21140A chipset that Virtual Server 2005 emulates does not support TCP segmentation offloading. Therefore, the Virtual Server Network Driver Interface Specification (NDIS) filter driver must offload the TCP segmentation on the network adapter. This may cause slow performance and other network problems when you use Virtual Server 2005.
To work around this problem, use one of the following methods:
Note If you have any network adapters that Virtual Server 2005 guests use, Microsoft recommends that you disable TCP segmentation offloading.
Method 1Enable local area network (LAN) routing on the host computer, and then move the virtual network to the Microsoft Loopback Adapter.
Note To perform this procedure, your host computer must be running Microsoft Windows Server 2003.
To enable LAN routing on the host computer, follow these steps:
Method 2Disable TCP task offloading in the registry of the host computer. To do this, follow these steps.
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:
(http://support.microsoft.com/kb/322756/ )How to back up and restore the registry in Windows
Method 3If you do not want to disable TCP segmentation offloading on the whole system, and you want to only disable TCP segmentation offloading on the network adapters that Virtual Server 2005 guests use, you must not add the DisableTaskOffload registry entry that is described in Method 2. Instead, you can disable the task offload properties on the Advanced tab of the Properties dialog box of the network adapter.
Warning When you disable the task offload properties, guest virtual machines that are attached to the same virtual network may temporarily disconnect from the virtual network.
To disable the task offload properties, follow these steps:
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Article ID: 888750 - Last Review: November 2, 2007 - Revision: 3.2