Alexandre POLOZOFF's
Maximum Transmission Unit (MTU)


The Problem

Having trouble doing ftp uploads in Windows 95? or sending mail? Yet ftp downloads work flawlessly? Odds are more likely than not your MTU setting is skewed because Microsoft doesn't seem to have a good idea what networking is all about.


Helpful applications

While I haven't tried this application out, you can go to the Ziff-Davis Network and download it. According to the description, it seems to have everything you need for optimizing TCP/IP settings including the vital MTU variable.

http://hotfiles.zdnet.com/cgi-bin/texis/swlib/hotfiles/info.html?fcode=000R0B

If you are still using the command line FTP application, try WS_FTP. This is a robust graphical FTP application which helps in debugging these kinds of problems.

Additionally, Net.Medic has proven useful to evaluate internet problems. Continued below...



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Changing MTU settings in the registry manually

Otherwise, for those willing to play with their registry settings manually, follow the instructions below.

Setting the MTU size in Windows '95, follow the instructions below;

1. Start the program regedit.exe

2. Go to the following registry-key
Hkey_Local_Machine\System\CurrentControlSet\Services\Class\Nettrans\000n
where n represents the number where the Drivedesc contains TCP/IP.

3. Choose Edit/New/String from the menu and type MaxMTU followed by two hits of
the Enter key. Then type in 1006. You should see a line like:
MaxMTU "1006"
If that doesn't work then highlight the label MaxMTU and select Edit/Modify from the menu which then should allow you to edit the value to 1006.

4. Next go to the registry key
Hkey_Local_Machine\System\CurrentControlSet\Services\Vxd\MSTCP\
Create a new string variable DefaultRcvWindow with a value 4048.

5. Shutdown and reboot your PC.

If this still hasn't worked then the only thing I can suggest is try using lower MaxMTU values. Some values to try are 576, 256 and 512. Good luck and happy ftp'ing!


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Copyright @ 1996, 1997, 1998 Alexandre Polozoff. All Rights Reserved. Last Update June 19, 1998