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How do I change the PPTP MTU size?

    Question

  • I have a remote router that I connect to using PPTP.  The particular router does not like PPTP MTU > 1300.  Per Microsoft, in Windows XP and in Vista I'm able to add the following lines to my registry to limit the PPTP MTU size to 1300:


    [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NdisWan\Parameters\Protocols\0]
    "PPPProtocolType"=dword:00000021
    "ProtocolType"=dword:00000800
    "ProtocolMTU"=dword:00000514

    When I add the same lines in Windows 7 x64 and reboot, it does not appear to reduce the MTU as desired.

    The symptoms are a successfull connection but then any attempt to move a large block of data over the tunnel times out.  Small blocks of data (browsing a directory with 6 items in it, for example) work.

    I'm pretty sure the problem is the MTU because the symptoms are identical to the problem that I was having on XP and Vista until I found and applied the fix above.  So it appears that the tunnel driver for PPTP has changed in some way in Windows 7 and it is not picking up the information from the registry.

    Any suggestions would be appreciated.
    Saturday, March 07, 2009 10:40 PM

Answers

  • Hi,

    I suggest that you create a value “MTU” in the following branch in Registry.

    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\ID for Adapter

    The following KB article can be referred.

    KB314053
     


    Arthur Xie - MSFT
    Monday, March 09, 2009 9:26 AM
    Moderator

All replies

  • Hi,

    I suggest that you create a value “MTU” in the following branch in Registry.

    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\ID for Adapter

    The following KB article can be referred.

    KB314053
     


    Arthur Xie - MSFT
    Monday, March 09, 2009 9:26 AM
    Moderator
  • Arthur,
        Thank you.  Your suggestion worked.  Howver neither KB314053 nor your response descibes how to determin the "ID for Adapter" for the particular PPTP tunnel adapter.  The KB article describes a method that appears to work only for physical adapters.  I was able to determine which adapter ID to use by connecting, and then noticing which Adapter ID had the right remote IP address.  Is there an easier way to determine the "ID for Adapter" for virtual adapters?
    Wednesday, March 11, 2009 7:25 PM