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We see WinPoet with MTUs at 1362, 1454 and 1462. Ideally, they should be 1492. This is a 3-step process to get them up to 1492. Please complete one step at a time and make sure that what should happen does happen. After step 1, MTU should be 1454, regardless of whether it was 1362 or 1462 prior to completing that step.
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Step 1:
To be sure that the adapters and otherwise are set to default and well prepared for what is to come, do this first:
Download DRTCP from the top of this forum ("Links") to your desktop. Open it and enter 18000 (starting point) for TCP Receive Window (RWIN). Set everything else to Default with the tabs. Then clear TTL and Max Duplicate ACKs.
Using the drop-down menu in DRTCP, set your basic dial-up adapter (usually simply named "Dial-up adapter") to 1492. Set any other dial-ups to 0, then clear (blank) any value showing for NICs (Ethernet adapters). Tab to Apply and click it. Exit, reboot, retest and repost.
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If MTU is now 1454 on Tweaks Tester readout (not DRTCP), move on to step 2. If not, find out why.
Note: Your MTU should now be 1454 (not 1492), which is fine. (If yours was 1362, then this is very good.)
Step 2:
Here is a new tweak just for WinPoet. It allows the user to break that 1454 barrier. Go to Start/Run and type in "regedit" (no quotes). Click OK and then click down through here:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Class\Net\000n
(Where "n" is a number like 0001, 0002, etc.) Look for the 000? folder with the "iVasion PoET Adapter" in it. (To the left of which will say "DriverDesc.")
You should see TunnelMode = 1.
Double click on TunnelMode and change the 1 to a 0.
Reboot, retest and you should now have an MTU of 1492.
Note: Some lines do not support this step. If you cannot connect after setting Tunnelmode to 0, simply reset it to 1. This will leave your MTU at 1454. There is no other way to raise it to 1492.
Note: This setting is not available in Win2K/XP.
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If all went well, and MTU is now indeed 1492, run this ping test to ensure that your line supports MTU of 1492.
Step 3:
To find the correct MTU (maximum transmission unit) for your line, do this:
Go to Start/ Programs/ MSDOS-PROMPT, and type:
ping -f -l 1464 www.dslreports.com
(That is a dash lower case "L," not a dash "1." Also notice the spaces in between each section.)
Press Enter. Then reduce 1464 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 "packet need to be fragmented" message again.
Add 28 more to this (since you specified ping packet size, not including IP/ICMP header of 28 bytes), and this is your MaxMTU.
Note: If you can ping through with the number at 1464, you are done. Stop right there. Add 28 and your MaxMTU is 1492.
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edited by JMGullett 
last modified: 2007-02-26 15:28:26 |
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