How to manually set the MTU size in Windows XP 2003 2000 Vista

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Maximum Transmission Unit (MTU) in simple words is the maximum IP packet size in bytes, that can be transmitted over the underlying network. While most of time this never has to be changed from the default values there are instances when you need to alter the MTU sizes to fix certain network performance issues. A best and classic example would be with a Windows Exchange Server being accessed over an Internet VPN setup. This in most of the cases demonstrate the problem with MTUs and related issues.

In Windows, changing the MTU value from the defaults, require you to modify the TCP/IP parameters for the adapter in Windows Registry.

WARNING: Editing Windows Registry incorrectly can cause serious problems that may require you to reinstall your operating system. I do not guarantee that you can solve problems that result from editing registry. Use Registry Editor at your own risk.

1. Click Start - RUN and type “regedit” and press enter.

2. Navigate to the following Registry Key

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\<AdapterID>

HKEY_LOCAL_MACHINE
\SYSTEM
\CurrentControlSet
\Services
\Tcpip
\Parameters
\Interfaces
\<AdapterID>

In the right-panel, create a new DWORD named “MTU” with the value (say 1350 in decimal)

NOTE: To create a new DWORD, right-click, select New and select “DWORD Value” and enter the name (MTU here)

This sets the Maximum Transmission Unit (MTU) for that particular network adapter.