Changing the mtu size in windows vista, 7 or 8 changing the mtu size in windows vista, 7 or 8. setting the mtu size: once the command prompt window is open follow the steps below to change the mtu size: type netsh interface ipv4 show subinterface; press enter.. In the mtu size field, enter a value from 64 to 1500. click the apply button. your settings are saved. if you suspect an mtu problem, a common solution is to change the mtu to 1400. if you are willing to experiment, you can gradually reduce the mtu from the maximum value of 1500 until the problem goes away.. Add 28 to that number (ip/icmp headers) to get the optimal mtu setting. for example, if the largest packet size from ping tests is 1462, add 28 to 1462 to get a total of 1490 which is the optimal mtu setting. change the mtu on the routers wan setup..
The last successful value plus 28 will be your mtu value. in my case a packet size of 1430 succeeds but 1431 fails, so 1430 + 28 = 1458. step 3: set your mtu. now you have identified the interface you need to change and the ideal mtu for you, now it is time to make the change.. Learn how to change, set or lower mtu size value settings of your network connections like router, wifi, modem, ethernet & lan using command prompt..