Microsoft KB Archive/917489

Knowledge Base

You cannot view some Web sites in Virtual PC for Mac Version 7

Article ID: 917489

Article Last Modified on 5/6/2006

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APPLIES TO

• Microsoft Virtual PC for Mac Version 7

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Notice

Important This article contains information about how to modify the registry. Make sure to back up the registry before you modify it. Make sure that you know how to restore the registry if a problem occurs. For more information about how to back up, restore, and modify the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows registry

SYMPTOMS

In Microsoft Virtual PC for Mac Version 7, you cannot view some Web sites in a browser window. This issue occurs even though you can view these Web sites in a browser in Mac OS X.

CAUSE

This issue occurs because of an incompatible Maximum Transfer Unit (MTU) network setting. The default maximum transmission size in Microsoft Windows is 1500. The PPPoE network protocol uses a maximum transmission unit size of 1454 or 1492.

Additionally, this issue may occur if the Macintosh computer is configured as a Point-to-Point Protocol over Ethernet (PPPoE) client.

RESOLUTION

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

To resolve this issue, modify the MTU size in the virtual machine. To do this, follow these steps:

1. Back up the Virtual PC for Mac Version 7 virtual machine. For information about how to back up a virtual machine in Virtual PC for Mac Version 7, follow these steps:
   1. Start Virtual PC for Mac Version 7.
   2. On the Help menu, click Virtual PC Help.
   3. In the Search box, type backup, and then press ENTER.
2. In the Virtual PC List window, click the virtual machine that you want, and then click Start Up.
3. In the virtual machine, click Start, click Run, type cmd, and then click OK.
4. At the command prompt, type ipconfig, and then press ENTER. Note the Default Gateway and IP Address addresses that appear.
5. At the command prompt, type ping -f -l 1500 defaultgateway, and then press ENTER. In this command, defaultgateway is the default gateway address that you noted in step 4.
   
   Note In this command, the "l" character is a lowercase "L".
6. If you do not receive a reply that resembles Reply from defaultgateway, go to step 7. If you receive a reply that resembles Reply from defaultgateway, go to step 10. In this scenario, defaultgateway is the default gateway address that you noted in step 4.
7. At the command prompt, type ping -f -l 1454 defaultgateway, and then press ENTER. In this command, defaultgateway is the default gateway address that you noted in step 4.
   
   Note In this command, the "l" character is a lowercase "L".
8. If you do not receive a reply that resembles Reply from defaultgateway, go to the next step. If you receive a reply that resembles Reply from defaultgateway, go to step 10. In this scenario, defaultgateway is the default gateway address that you noted in step 4.
9. At the command prompt, type ping -f -l 1492 defaultgateway, and then press ENTER. In this command, defaultgateway is the default gateway address that you noted in step 4.
   
   Note In this command, the "l" character is a lowercase "L".
10. When you receive a reply that resembles Reply from defaultgateway, note the MTU size in the command. The MTU size can be 1500, 1492, or 1492.
11. At the command prompt, type exit, and then press ENTER.
12. Click Start, click Run, type regedit, and then click OK.
13. Locate and then click the follow registry key:

    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces

14. Expand Interface.
15. Under Interface, click each subkey, and then note the DhcpIPAddress value in the right-pane.
16. When you locate a subkey that has the same DhcpIPAddress value as the IP Address that you noted in step 4, click the subkey in the left pane.
17. On the Edit menu, point to New, and then click DWORD Value.
18. Type MTU, and then press ENTER.
19. Click MTU, click Edit, and then click Modify.
20. In the Value Data box, type the MTU size that you noted in step 10, click Decimal, and then click OK.
21. Restart the virtual machine.

REFERENCES

For more information about how to change the Default Maximum Transmission Unit (MTU) Size Settings for PPP Connections or for VPN Connections, click the following article number to view the article in the Microsoft Knowledge Base:

826159 How to change the default Maximum Transmission Unit (MTU) size settings for PPP connections or for VPN connections

For more information about the default MTU size in network topologies, click the following article number to view the article in the Microsoft Knowledge Base:

314496 Default MTU size for different network topology

Keywords: kbtshoot kbnetwork kbprb KB917489

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