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Broadband Connection Tweaking Guide

By: TweakTown Staff | Guides | Posted: Aug 24, 2001 4:00 am

Tweaking: MTU


The first thing you need to know is MTU, which stands for Maximum Transmission Unit. It is the maximum packet size, in bytes, that can be transmitted across a link. The MTU determines the size of your packets, so if it is too small, your computer will be responding often. If it is too big, errors will cause each packet to be resent. What we need to do is find your maximum MTU which does NOT return a fragment message such as the below screenshot. In a minute I will talk about which is the maximum MTU size for different types of connections you want to set at!



Typically, all cable modem connections should be set to 1500 MTU, while DSL connections can vary. For example, ADSL PPPOE needs to be set at 1492, while ADSL STATIC needs to be set at 1500. Any other type of DSL connection should use an MTU of 1500, just like cable modem. Confused? Well I will make it easier for you.






SDSL = 1500


VDSL = 1500


HDSL = 1500


IDSL = 1500


CABLE = 1500


Now you are wondering "How the heck am I going to "change" my MTU?" Well that step is through the registry, or a simple to use program called Dr. TCP - Click here to download Dr.TCP.


When you have downloaded Dr. TCP, run it. This program may seem confusing but it does wonders. Take a look at the screenshot below. Tab to the maxmtu field and delete the current number that may be shown. Then type in the specific MTU that is for your connection, example: 1500, for ADSL static IP.



Note: Those people who are behind an ADSL PPPOE connection, know that even if you do set your MTU to 1492, Windows will limit you to 1454. How can you still set it at 1492 without windows limiting it? Read the instructions below carefully in setting your MTU to 1492 in Windows 9x. This is a 3 step plan so follow carefully. These instructions are for Winpoet users. Please scroll down for Ethernet users. Winpoet, Ethernet, and RASPPPOE are software that connects your ADSL PPPOE or PPPOA connection to the Internet. Your ISP requires you to use it.


PPPoE stands for Point-to-Point Protocol over Ethernet


PPPoA stands for Point-to-Point Protocol over ATM


For Winpoet v2.x+


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 do 1 step at a time, and make sure that what should happen, does. After step 1, MTU should be 1454, regardless of if it was 1362, or 1462 prior to.




Step #1.


To be sure that the adapters and otherwise are set to default and prepared well for what is to come, do this first:


Open Dr.TCP. Using the drop-down menu in DR. TCP, set your basic dial-up adapter (usually simply named "Dial-up adapter") to 1492. Set any other dial-ups to 0, and clear (blank) any value showing for NICs (Ethernet adapters). Tab to Apply and click it, Exit, re-boot, re-test, re-post.




If MTU is now 1454 (if not, find out why), move on to step #2


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, then click down through here:




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