View source for Changing Windows MTU

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[[Category:MTU]]

The MTU (Maximum Transmission Unit) is the size of the largest network packet that can be transferred in a single network transmission without any fragmentation happening.

We have a separate page on testing your [[MTU]].

Sometimes you may have a reason to change the MTU on your windows computer. Here is how. 

We will show you how to show the existing MTU, and then how to change it, and then how to revert it back to what it was originally. We're using Windows 10 in this example.

===1. Open Command Prompt, as Administrator===
# Click <SyntaxHighlight inline>start</SyntaxHighlight>
# Type <SyntaxHighlight inline>cmd</SyntaxHighlight>
# On the Right hand side, click <SyntaxHighlight inline>'Run as administrator'</SyntaxHighlight>

<gallery widths=600  heights=300>
Windows-mtu-1.png|Open command prompt, as Administrator
</gallery>

===2. Show the current MTU and the interface name ===
#Enter in the command: <SyntaxHighlight inline>netsh interface ipv4 show subinterfaces </SyntaxHighlight>
#Make a note of the existing MTU (probably <SyntaxHighlight inline>1500</SyntaxHighlight>)
#Make a note of the interface name - eg <SyntaxHighlight inline>Ethernet</SyntaxHighlight>

<gallery widths=700   heights=300>
Windows-mtu-2.png|Show the current MTU and interface name
</gallery>

===3. Change the MTU for the interface===
#Enter the command: <SyntaxHighlight inline>netsh</SyntaxHighlight>
#Then: <SyntaxHighlight inline>interface</SyntaxHighlight>
Then: <SyntaxHighlight inline>ipv4</SyntaxHighlight>
Then: <SyntaxHighlight inline>set subinterface "Ethernet" mtu=1320</SyntaxHighlight>
Then: <SyntaxHighlight inline>exit</SyntaxHighlight>

<gallery widths=700  heights=400>
Windows-mtu-3.png|Changing the MTU to 1320
</gallery>

===5. Check the MTU ===
#Run the first command to show the Interface details again: <SyntaxHighlight inline>netsh interface ipv4 show subinterfaces </SyntaxHighlight>
#It should now show <SyntaxHighlight inline>1320</SyntaxHighlight>

===6. Reverting back===
# Restarting the computer should change the MTU back to default
# Or, you can run the commands above, but set <SyntaxHighlight inline>1500</SyntaxHighlight> instead of <SyntaxHighlight inline>1320</SyntaxHighlight>

===7. Keeping the MTU change permanent===
If you want to keep thje lower MTU even after a reboot, then re-run the commands, but when you come to change the MTU add <SyntaxHighlight inline>store=persistent</SyntaxHighlight> to the command.

eg <SyntaxHighlight inline>set subinterface "Ethernet" mtu=1320 store=persistent</SyntaxHighlight>