HOW TO: Change the Default Maximum Transmission Unit (MTU) Size Settings for PPP Connections or for VPN Connections

This step-by-step article describes how to edit the registry to change the default maximum transmission unit (MTU) size settings for Point-to-Point Protocol (PPP) connections or for virtual private network (VPN) connections.

Microsoft Windows Server 2003, Microsoft Windows 2000, and Microsoft Windows XP use a fixed MTU size of 1500 bytes for all PPP connections and use a fixed MTU size of 1400 bytes for all VPN connections. This is the default setting for PPP clients, for VPN clients, for PPP servers, or for VPN servers that are running Routing and Remote Access.

PPP connections are connections such as modem connections, Integrated Services Digital Network (ISDN) connections, or direct cable connections over null serial cable or over parallel cable. VPN connections are Point-to-Point Tunneling Protocol (PPTP) connections or Layer 2 Tunneling Protocol (L2TP) connections.

Note Use the methods in this article to edit the registry to modify the MTU size settings. If you experience any problems or any performance-related issues after you modify the MTU size settings, remove the registry keys that you added.

Change the MTU Settings for PPP Connections

To have us change the MTU Settings for PPP Connections for you, go to the "Fix it for me" section. If you prefer to fix this problem yourself, go to the "Let me fix it myself" section.

Fix it for me

To fix this problem automatically, click the Fix it button or link. In the File Download dialog box, click Run and then follow the steps in the Fix it Wizard.




Notes

• Please type the desired MTU size between 1 and 1500 when asked during the installation process
• This wizard may be in English only. However, the automatic fix also works for other language versions of Windows.
• If you are not on the computer that has the problem, save the Fix it solution to a flash drive or a CD and then run it on the computer that has the problem.

Then, go to the "Did this fix the problem?" section.

Let me fix it myself

To change the MTU settings for PPP connections, add the DWORD value, the DWORD value, and the DWORD value to the following registry key: To do so, 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:

1. Click Start, click Run, type regedit in the Open box, and then click OK.
2. Locate and then click the following subkey in the registry:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NdisWan\Parameters
3. Add a
   Protocols
   subkey (if it does not already exist). To do so:
   1. On the Edit menu, point to New, and then click Key.
   2. Type Protocols, and then press ENTER.
4. Add a
   0
   (zero) subkey to the
   Protocols
   subkey. To do so:
   1. Click the
      Protocols
      subkey that you created step 3.
   2. On the Edit menu, point to New, and then click Key.
   3. Type 0 (zero), and then press ENTER.
5. Click the
   0
   subkey that you created in step 4.
6. On the Edit menu, point to New, and then click DWORD Value.
7. In the Value data box, type ProtocolType, and then click OK.
8. On the Edit menu, click Modify.
9. In the Value data box, type 800, make sure Hexadecimal is selected under Base, and then click OK.
10. On the Edit menu, point to New, and then click DWORD Value.
11. Type PPPProtocolType, and then press ENTER.
12. On the Edit menu, click Modify.
13. In the Value data box, type 21, make sure Hexadecimal is selected under Base, and then click OK.
14. On the Edit menu, point to New, and then click DWORD Value.
15. Type ProtocolMTU, and then press ENTER.
16. On the Edit menu, click Modify.
17. Under Base, click Decimal, type the MTU size that you want in the Value data box, and then click OK.
18. Quit Registry Editor.
19. Restart your computer.

Change the MTU Settings for VPN Connections

To have us change the MTU Settings for VPN Connections for you, go to the "Fix it for me" section. If you prefer to fix this problem yourself, go to the "Let me fix it myself" section.

Fix it for me

To fix this problem automatically, click the Fix it button or link. In the File Download dialog box, click Run and then follow the steps in the Fix it Wizard.




Notes

• Please type the desired MTU size between 1 and 1500 when asked during the installation process.
• This wizard may be in English only. However, the automatic fix also works for other language versions of Windows.
• If you are not on the computer that has the problem, save the Fix it solution to a flash drive or a CD and then run it on the computer that has the problem.

Then, go to the "Did this fix the problem?" section.

Let me fix it myself

To change the MTU settings for VPN connections, add the DWORD value, the DWORD value, and the DWORD value to the following registry key: To do so, 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:

1. Click Start, click Run, type regedit in the Open box, and then click OK.
2. Locate and then click the following subkey in the registry:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NdisWan\Parameters
3. Add a
   Protocols
   subkey (if it does not already exist). To do so:
   1. On the Edit menu, point to New, and then click Key.
   2. Type Protocols, and then press ENTER.
4. Add a
   0
   (zero) subkey to the
   Protocols
   subkey. To do so:
   1. Click the
      Protocols
      sub key that you created in step 3.
   2. On the Edit menu, point to New, and then click Key.
   3. Type 0 (zero), and then press ENTER.
5. Click the
   0
   subkey that you created in step 4.
6. On the Edit menu, point to New, and then click DWORD Value.
7. In the Value data box, type ProtocolType, and then click OK.
8. On the Edit menu, click Modify.
9. In the Value data box, type 800, make sure Hexadecimal is selected under Base, and then click OK.
10. On the Edit menu, point to New, and then click DWORD Value.
11. Type PPPProtocolType, and then press ENTER.
12. On the Edit menu, click Modify.
13. In the Value data box, type 21, make sure Hexadecimal is selected under Base, and then click OK.
14. On the Edit menu, point to New, and then click DWORD Value.
15. Type TunnelMTU, and then press ENTER.
16. On the Edit menu, click Modify.
17. Under Base, click Decimal, type the MTU size that you want in the Value data box, and then click OK.
18. Quit Registry Editor.
19. Restart your computer.

Did this fix the problem?

• Check whether the problem is fixed. If the problem is fixed, you are finished with this section. If the problem is not fixed, you can contact support (http://support.microsoft.com/contactus) .
• We would appreciate your feedback. To provide feedback or to report any issues with this solution, please leave a comment on the "Fix it for me (http://blogs.technet.com/fixit4me/) " blog or send us an email (mailto:fixit4me@microsoft.com?Subject=KB) message.

For additional information about MTU size in Microsoft Windows NT 4.0, click the following article number to view the article in the Microsoft Knowledge Base: For more information about PPP, see Request for Comments (RFC) 1548. To do so, visit the following Internet Engineering Task Force (IETF) Web site: