How to change the PPPoE MTU size in Windows XP (283165)


The information in this article applies to:

  • Microsoft Windows XP Home Edition
  • Microsoft Windows XP Professional
This article was previously published under Q283165

IN THIS TASK

IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

SUMMARY

This article describes how to change the Point-to-Point Protocol over Ethernet (PPPoE) Maximum Transfer Unit (MTU) size.

The default and maximum PPPoE MTU size is 1,480 bytes. With some Internet service providers (ISPs), you may have to reduce the MTU size of a PPPoE connection to a value between 1,400 and 1,480 (for example, to 1,454). Do not set an MTU size smaller than 1,400.

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

314496 Default MTU size for different network topology

For additional information about how to determine if you have to lower the MTU size of a PPPoE connection, click the following article number to view the article in the Microsoft Knowledge Base:

159211 Diagnoses and treatment of black hole routers


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Modify the MTU size

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

To modify the PPPoE MTU size, create the following registry key:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Ndiswan\Parameters\Protocols\0

Then add the following registry entries.
Entry nameData typeValue data
ProtocolTypeREG_DWORD0x00000800
PPPProtocolTypeREG_DWORD0x00000021
ProtocolMTUREG_DWORDthe appropriate MTU size (in decimal)
To do this:
  1. Click Start, click Run, type regedit, and then click OK.
  2. Locate and then click the following key in the registry:

    HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Ndiswan\Parameters

  3. On the Edit menu, point to New, and then click Key.
  4. Type Protocols, and then press ENTER.
  5. On the Edit menu, point to New, and then click Key.
  6. Type 0, and then press ENTER.
  7. On the Edit menu, point to New, and then click DWORD Value.
  8. Type ProtocolType, and then press ENTER.
  9. On the Edit menu, click Modify.
  10. Type 800, and then click OK.
  11. On the Edit menu, point to New, and then click DWORD Value.
  12. Type PPPProtocolType, and then press ENTER.
  13. On the Edit menu, click Modify.
  14. Type 21, and then click OK.
  15. On the Edit menu, point to New, and then click DWORD Value.
  16. Type ProtocolMTU, and then press ENTER.
  17. On the Edit menu, click Modify.
  18. Type the appropriate MTU size (decimal value), and then click OK.
  19. Quit Registry Editor.
Notes
  • Therefore, if the MTU size is set to 1460 (decimal), the max value of NUM in the following command line can be 1432:

    ping IP_address -f -l NUM

  • You may have to restart the computer to make the change take effect.
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Modification Type:MinorLast Reviewed:1/15/2006
Keywords:kbRegistry kbenv kbhowto KB283165
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