MSFS: Set Best Network MTU

You should check your network’s Maximum Transmission Unit (MTU) in order to ensure you have the best configuration for your system.

What is MTU?

MTU stands for Maximum Transmission Unit – its the largest number of bytes that a packet of information can contain and a packet is the smallest transmission unit in a network.

The MTU depends on configuration parameters in your system, so may vary from PC to PC. If your MTU is not optimised you will be wasting network capacity. Check and if necessary optimise the MTU configuration.

You can follow this video by Liron Segev or just the instructions below which may differ a little but ends up at the same place.

Step 1 – Record the Original MTU Size

Just in case you want to go back to the original settings. You can also reset your network interfaces if you need to.

  • Open a Command Window then type:
    netsh interface ipv4 show subinterfaces
  • Hit the return key
  • You will see what MTUs you have set on all your network devices.

Step 2 – Find the Highest Working MTU Size

  • Open a Command Prompt window and type:
    ping -f -l 1500
  • Hit the return key
    In this example 1500 is the MTU size you are checking
  • If the output says ‘packet needs to be fragmented but DF set’ then reduce the MTU size. Press the up-arrow to recall the previous text then edit the MTU size.
  • If the output doesn’t say its fragmented then increase the MTU size.
  • Repeat these steps until you find the largest unfragmented packet size.

Step 3 – Determine the Actual MTU Size to Set

Add 28 to your new MTU size to allow space for the network header.

Step 4 – Set the MTU size

Below is a batch file script you can use to change the current MTU size to your new calculated size (including the header). After the values have been set the numbers will be displayed onscreen for you to check.

A batch file is an executable script that runs from a file. To make a batch file all you will need to do is open notepad, copy the text below, save the file and then rename it from .txt to .bat. You can edit a .bat file at any time with a text editor.

Before you run the batch file, be sure to edit all mentions of ‘mtu=1492’ to whatever your optimal configuration number is.

echo off
echo .
echo Running as Admin?
echo .
netsh int ipv4 set subinterface "Ethernet" mtu=1492 store=persistent
netsh int ipv4 set subinterface "WiFi" mtu=1492 store=persistent
netsh int ipv4 set subinterface "Local Area Connection" mtu=1492 store=persistent
netsh int ipv4 set subinterface "Local Area Connection* 1" mtu=1492 store=persistent
netsh int ipv4 set subinterface "Local Area Connection* 2" mtu=1492 store=persistent
echo .
echo Ready to show what the interfaces are set to?
echo .
echo .
netsh interface ipv4 show subinterfaces
echo          \____ NOTE - The MTU is in the first column
echo .

If you don’t want to make a batch file then open a Command Window and run each line from the file above that starts with ‘netsh’, taking care to insert your corrected MTU each time.

How to Reset Your Network

Just in case you get into a pickle with the above instructions, here’s how to reset your network:

  • In the task bar search for: Network Reset
  • Click on the : Reset Now button