How to change MTU in Windows 7
I can’t reach website xyz.com, what should I do?
If you can’t reach a certain websites, but the same site is working for others, you should consider changing the MTU value as well. If the MTU value is set too high you will not be able to successfully ping the site and is then unreachable.
Change MTU via Software
One of the easiest way to change the MTU in Windows 7 is to use software like Ashampoo’s Internet Accelerator 3, which is currently available for free: Ashampoo Internet Accelerator 3 Giveaway.
There are other tools available that allow you to change the MTU quite easily. However, I prefer to do it manually.
Change MTU Manually
Tip: If you don’t have any problems with loading websites, you should properly not mess around with the MTU value or you might not be able to reach some websites. If you decide to change the MTU value anyway, keep this in mind so that you will know the reason why a certain website might be unreachable.
Let’s do it the good old-fashioned way!
1. Open the Network Connections
Here’s how: Control Panel / Network and Internet / Network and Sharing Center. In the sidebar click on Change adapter settings
2. Write down the name of your main adapter or remember it. E.g. Local Area Connection
4. Enter ping www.thisdoesnotexist234.com -f -l 1460 … where 1460 is the number of bytes of the package that we are sending out to ping the site. Make sure the site thisdoesnotexist234.com is actually a site that you can’t reach, because your MTU is too high.
Finding The Optimal MTU Value
6. Now, what we do next is to find out the best MTU value for your setup. We have to increase or lower the value 1460 until we find the correct value. The correct value is the highest number that still gets a successful ping Reply.
If you the first one (fragmented) then lower the number 1460 until you get a Reply from. If you get the second one (Reply) then increase the number 1460 until you get a fragmented packet. The highest package size that is not fragmented and gets a successful reply is the best MTU value. Found the package size? Mine is 1464 bytes.
7. Add 28 to the package size (for the header that we send together with the package). 1464 + 28 = 1492 bytes
8. The optimal MTU value for my setup is 1492 bytes
9. Enter netsh interface ipv4 set subinterface “Local Area Connection” mtu=1492 store=persistent and replace Local Area Connection with the network from step 1-2.
10. You have successfully change the MTU in Windows 7! It’s now the optimal MTU value for your setup and all websites should be reachable.
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