Finding the Max MTU of your ISP

MaxMTU - Maximum Transmission Unit - is the largest packet size that your ISP will allow you to send.  Anything larger than that gets fragmented into multiple packets.  These multiple packest waste Bandwidth because the last one is usually small.  For efficient use of your bandwidth, you want to send packets that are just a tad below the MTU, to be safe.  This document does not tell you how to adjust that value, but there are any number of utilities available on the web to do this.

The MaxMTU value has to be discovered on an individual basis. To do that follow this: Go to Run and type Command, you'll get a DOS window. Type this:

C:\ping -f -l [value] [your ISP]

I started like this

C:\ping -f -l 1420 www.pacbell.net

And kept going in increments of 5 until the message read that the packets needed to be fragmented. So the idea is to imput the highest value b4 the data gets fragmented. In my case it was 1426, and to the highest value you then add 28, so I reached my ISP's MaxMTU of 1454 and that's the value that I entered in every instance in:

HKLM\SYSTEM\CURRENT CONTROL SET\SERVICES\CLASS\NETTRANS

When you get there and expand the NetTrans key, you'll find a lot of keys like this 0000, 0001, 0002, etc, in each one of them the value MaxMTU may be  present and you need to right click on it and choose Modify and then enter the value you discover to be the best for your ISP The values you pick up in websites are good but generic, so you need to find the value where the data doesn't get fragmented and at the same time you are sending the max amount of data b4 that occurs. It's pretty simple and that way you'll have the optimal value for your connection :-)