Important Note: Windows Vista has an auto-tuning function that automatically adjusts your settings, so tweaking is not possible. You can disable auto-tuning for troubleshooting connectivity issues. Click here to find out how.

Step 1
Download DrTCP here and open the application.

Step 2
Enter the desired MTU in the appropriate field. Very Important Note: Due to additional overhead you must use an MTU of 1492 or less when utilizing PPPoE connectivity (which is the default standard for BellSouth connectivity). Some applications may require an even lower MTU to work properly. Additional information about finding your optimum MTU can be found here.


Pictures by Andy Houtz

Step 3
Enter the desired RWIN in the appropriate field and click on Save. RWIN should always be an even multiple of your MSS. MSS is always your MTU size minus 40 bytes. Additional information on proper RWIN sizing can be found here. An example of proper RWIN size is shown below as well as recommended settings based on your service:

1452 MSS
x 26 Even Multiple
37752 RWIN

Recommended RWIN initial settings (assuming an MTU of 1492):
FastAcces Extreme 6.0 (6000/512) = 63888
FastAcces Extreme 3.0 (3000/384) = 63888
FastAccess Ultra (1500/256) = 63888
FastAccess Lite (256/128)= 63888

Step 4
There may be more than one network adapter showing in the pull down menu for your PC. Additionally, if you have a network with more than one computer, all NICs, adpaters, and router(s) must have the the same MTU setting. Use the Adapter Settings pulldown and select any other network adapter (if available) and enter the proper values as needed. Repeat Steps 2 and 3 for all adapters until they have the correct information.

Step 5
Restart your computer!!! The changes will not take effect until you do so!

Additional information:
Please reference the links below to learn how to change the MTU on some popular routers:
•MTU change on a Linksys Router
•MTU change on a D-Link Router

Andy Houtz DSL