"Do not fragment" flag stopping Windows Update working

Discussion in 'Windows Update' started by Jason Mann, Nov 27, 2006.

  1. Jason Mann

    Jason Mann Guest

    For a while, I have been unable to use the Windows Update website properly.
    I can browse to
    http://update.microsoft.com/windowsupdate/v6/default.aspx?ln=en-us without
    any problems, where I am presented with the Express and Custom buttons.
    However after I click "Express" I get the "Checking for the latest updates
    for your computer..." progress bar, and then after a minute or so an error
    page is presented stating "The website has encountered a problem and cannot
    display the page you are trying to view."

    At the same time, I noticed numerous "ICMP unreachable - need to frag"
    errors coming back from my router.

    I re-attempted this while running a packet capture on my Windows machine,
    and it appears that my system is attempting to send TLS packets to the
    windows update web servers that are 1514 bytes in size and have the
    do-not-fragment flag set. As the MTU on my Internet connection is 1458,
    this would seem to be the reason why the windows update site is failing for

    Why is my browser attempting to send these large packets with the DF flag

    Windows XP Pro SP2, IE6.


    Jason Mann, Nov 27, 2006
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  2. Jason Mann

    Alias Guest

    Did you try using Custom instead of Express?

    Alias, Dec 2, 2006
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