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If you can access some, but not all websites or parts of some websites, experience FTP problems and/or cannot send and/or receive email, it may be caused by your MTU (maximum transmission Unit) size being set too high. Reducing the Maximum MTU size setting on the PC might correct this problem.

To determine the maximum MTU size for your Windows PC use the following procedure:
    •Open a Command or "DOS" Window.

    •Ping a known "pingable" address with the command:
    ping -f -l 1500 somesite.com

    •If the ping fails with the message "packet needs to be fragmented but DF set", keep trying the ping command but lower the packet size (1490, 1480, etc.) each time until you find a size that is successful.

    Add 28 more to this (since you specified ping packet size, not including IP/ICMP header of 28 bytes) And this is your MaxMTU.

    •Set the MaxMTU registry key on the PC to the successful packet size + 28. You can edit the registry manually or you can use a program such as DrTCP that will help you change the setting.

    •Reboot the PC.

    •Test the changes by trying to access a problem website or send/receive email.

Read this page for full details.
»Tweaking FAQ »Max MTU: How do I find mine?

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by leevis See Profile edited by Doctor Olds See Profile
last modified: 2005-01-17 12:33:12