HOW TO: Change the PPPoE MTU Size in Windows XP

SUMMARY

This article describes how to change the 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 need to reduce the MTU size of a PPPoE connection to a value between 1,400 and 1,480 (for example 1,454). Do not set an MTU size smaller than 1,400. For additional information about the default MTU size, click the article number below 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 article number below 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

and add the following registry values:

Value name: ProtocolType
Data Type: REG_DWORD
Value Data: 0x00000800

Value name: PPPProtocolType
Data Type: REG_DWORD
Value Data: 0x00000021

Value name: ProtocolMTU
Data Type: REG_DWORD
Value Data: the appropriate MTU size (in decimal)

To do so:

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

• As a result, 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 need to restart the computer to make the change take effect.

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