Simple registry edit improves TCP/IP performance

Here's a tip to enhance your TCP/IP's performance.





Brien M. Posey

If your organization uses the PPPoE protocol to attach to the Internet, then there's a good chance that your organization's Internet connection isn't performing anywhere near as well as it should be. You might have noticed that when you attempt to access some Web sites that Internet Explorer tends to time out a lot. If you dismissed this problem as low bandwidth, then you'll be happy to know that the problem is easy to correct.

PPPoE stands for PPP over Ethernet. The reason that PPPoE tends to be so problematic is that by default Windows 2000 sets the TCP/IP MTU size (the maximum TCP/IP packet size) to 1500 bytes. 1500 bytes is fine for standard Ethernet, but it is too large for most PPPoE connections, which have a maximum MTU size of 1492 bytes. The trick to boosting TCP/IP's performance is to find an MTU size that's as high as possible without becoming problematic.

I recommend opening a command prompt window and entering the following command:

PING –F –I <MTU size> <default gateway IP address>

Start by using an MTU size of 1454. If the PING fails, try a lower number. If the PING is successful, keep trying higher numbers until the PING does fail. You should use an MTU size that's slightly lower than the failure point, but your MTU size should never be above 1492 or lower than 68.

Once you've found a value that works, open the Registry Editor and navigate to HKEY_Local_MachineSYSTEMCurrentControlSetServicesTcpipParametersInterfacesadapter ID. If the MTU registry key doesn't exist in this location, you'll have to create it. The new value should be REG_DWORD key whose value is the MTU size.

As always, exercise extreme caution when editing the registry. Making an incorrect change to the registry can destroy Windows and/or your applications.

ABOUT THE AUTHOR

Brien Posey, CEO, Posey Enterprises
Brien Posey is a freelance technical writer and has been working with computers for about 15 years. Before going freelance, Brien served as the Director of Information Systems for a large, nationwide healthcare company. He has also served as a network engineer / security consultant for the Department of Defense. You can access Brien's Web site, which contains hundreds of his articles and white papers, at http://www.brienposey.com.

This was first published in June 2002

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