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Setting Correct MTU Value

  1. #1
    Its Time To Change ! deepmohan's Avatar
    Join Date
    Jan 2009

    Default Setting Correct MTU Value

    As we all might be knowing that while using internet or broadband there is a data transmission between our computer and ISP, these data transmissions take place in a form of packets of various size. The maximum size of packet which we can send and receive varies from ISP to ISP and even on the type of service we have subscribed.

    This packet size is refereed to as "Maximum Transmission Unit" (MTU), if this value is not correct for your connection type then your TCP protocol may get bottle necked and may result in poor speeds. MTU is rated in "octets" a group or set of eight bits.

    In Windows MTU value is set to default 1500 this value is ok but might not be optimal for your connection type.

    Recommended MTU Values

    • 576 - Dial-up Connections

    • 1492 - PPPoE Broadband Connections

    • 1500 - Ethernet, DSL and Cable Broadband Connections

    Now how to find the Largest MTU Value.

    Go to Command Prompt (Start > Programs > Accessories > Command Prompt)

    and type the following and press enter:

    ping -f -l 1472
    C:\>ping -f -l 1472

    Pinging [] with 1472 bytes of data:
    Reply from Packet needs to be fragmented but DF set.
    Packet needs to be fragmented but DF set.
    Packet needs to be fragmented but DF set.
    Packet needs to be fragmented but DF set.

    Ping statistics for
    Packets: Sent = 4, Received = 1, Lost = 3 (75% loss),

    Then reduce 1472 by 10 until you no longer get the "packet needs to be fragmented" error message. Then increase by 1 until you are 1 less away from getting the "packet need to be fragmented" message again, Add 28 more to that value and that will be your MAX MTU.

    If your dont get "packet needs to be fragmented" error message at value 1472 then add 28 to it and your MAX MTU is 1500.

    Now when you have found the MTU Value for your connection type you will have to apply the same to your windows, this can be done in two ways one is making changes in windows registry and the second one is using a third party software.

    Registry Setup:

    1). Go to START > RUN and type regedit.exe, it will open registery editor.

    2). Now select the following registery values:
    HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\ Tcpip\ Parameters\ Interfaces

    3). Under interfaces you will find multiple keys you will have to find the one which

    belongs to your network interface, the key which will have your network ip address will be

    the most correct one.

    4). Once you have found it create a new DWORD (for 32 bit) or QWORD (for 64 bit)by selecting the EDIT > NEW > DWORD/QWORD value and name it MTU.

    5). Double click on MTU to open its settings and choose the Decimal Option and type the MTU value that we have already found that is 1492 etc...

    6) Click OK and close the Registry Editor window and RESTART your PC.

    You are now done with setting your correct MTU Value.

    Else you can download TCP Optimizer, you dont have to install it just run and make the needed changes. You just have to select your Network interface, provide the MAX MTU value, select Custom settings radio button and press apply changes button, it will make the changes in your registry.
    Last edited by Admin; 2nd August 2014 at 01:20 PM.

  2. #2
    Admin's Avatar
    Join Date
    Jan 2006


    I didint realise you had already posted this. I wrote another one which some people may find easier to follow : How to find the correct MTU value.

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