Here’s how to find the optimum MTU from a Windows PC to a server. Note that you can’t really have an optimum MTU that works to ALL servers, because some of them will be on networks with unusual MTUs, so pick a server and tune to it. In the discussion which follows, I’ve assumed your server is at 10.11.12.13. Substitute the address of YOUR server.

• ping 139.76.90.5 -f -l 1500
  • Note that is a lower case F and a lower case L.
  • This will almost certainly produce a fragmentation error message.</ul>
  • Reduce the ping length ( the “1500” in the step above) by 25 and repeat the ping. If you get a fragmentation error, repeat this step, reducing by 25 each time, until you get a successful ping.
  • Increase the ping length by 4, and repeat the ping. If you DON’T get a fragmentation error, repeat this step, increasing by 4 each time until you get a failed ping.
  • Reduce the ping length by 1, until you do NOT get a fragmentation error. </ul> That last number is your MTU. If you want to change your PC's MTU, update HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\\MTU in your registry.