Microsoft KB Archive/826159

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

Article ID: 826159

Article Last Modified on 10/30/2006

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APPLIES TO


 * Microsoft Windows Server 2003, Enterprise Edition (32-bit x86)
 * Microsoft Windows 2000 Server
 * Microsoft Windows XP Professional

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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

IN THIS TASK
 SUMMARY 

Change the MTU Settings for PPP Connections 

Change the MTU Settings for VPN Connections REFERENCES



SUMMARY
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.

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Change the MTU Settings for PPP Connections
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.

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.  Click Start, click Run, type regedit in the Open box, and then click OK. Locate and then click the following subkey in the registry:

 

</li> Add a  subkey (if it does not already exist). To do so: <ol style="list-style-type: lower-alpha;"> On the Edit menu, point to New, and then click Key.</li> Type Protocols, and then press ENTER.</li></ol> </li> Add a  (zero) subkey to the   subkey. To do so: <ol style="list-style-type: lower-alpha;"> Click the   subkey that you created step 3.</li> On the Edit menu, point to New, and then click Key.</li> Type 0 (zero), and then press ENTER.</li></ol> </li> Click the   subkey that you created in step 4.</li> On the Edit menu, point to New, and then click DWORD Value.</li> In the Value data box, type ProtocolType, and then click OK.</li> On the Edit menu, click Modify.</li> In the Value data box, type 800, make sure Hexadecimal is selected under Base, and then click OK.</li> On the Edit menu, point to New, and then click DWORD Value.</li> Type PPPProtocolType, and then press ENTER.</li> On the Edit menu, click Modify.</li> <li>In the Value data box, type 21, make sure Hexadecimal is selected under Base, and then click OK.</li> <li>On the Edit menu, point to New, and then click DWORD Value.</li> <li>Type ProtocolMTU, and then press ENTER.</li> <li>On the Edit menu, click Modify.</li> <li>Under Base, click Decimal, type the MTU size that you want in the Value data box, and then click OK.</li> <li>Quit Registry Editor.</li> <li>Restart your computer.</li></ol>

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Change the MTU Settings for VPN Connections
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.

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. <ol> <li>Click Start, click Run, type regedit in the Open box, and then click OK.</li> <li>Locate and then click the following subkey in the registry:

 

</li> <li>Add a  subkey (if it does not already exist). To do so: <ol style="list-style-type: lower-alpha;"> <li>On the Edit menu, point to New, and then click Key.</li> <li>Type Protocols, and then press ENTER.</li></ol> </li> <li>Add a  (zero) subkey to the   subkey. To do so: <ol style="list-style-type: lower-alpha;"> <li>Click the   sub key that you created in step 3.</li> <li>On the Edit menu, point to New, and then click Key.</li> <li>Type 0 (zero), and then press ENTER.</li></ol> </li> <li>Click the   subkey that you created in step 4.</li> <li>On the Edit menu, point to New, and then click DWORD Value.</li> <li>In the Value data box, type ProtocolType, and then click OK.</li> <li>On the Edit menu, click Modify.</li> <li>In the Value data box, type 800, make sure Hexadecimal is selected under Base, and then click OK.</li> <li>On the Edit menu, point to New, and then click DWORD Value.</li> <li>Type PPPProtocolType, and then press ENTER.</li> <li>On the Edit menu, click Modify.</li> <li>In the Value data box, type 21, make sure Hexadecimal is selected under Base, and then click OK.</li> <li>On the Edit menu, point to New, and then click DWORD Value.</li> <li>Type TunnelMTU, and then press ENTER.</li> <li>On the Edit menu, click Modify.</li> <li>Under Base, click Decimal, type the MTU size that you want in the Value data box, and then click OK.</li> <li>Quit Registry Editor.</li> <li>Restart your computer.</li></ol>

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