Windows 8 and 8.1 Forums

Changing MTU value.

  1. #1

    Changing MTU value.

    I am trying to change my MTU value, after changing in cmd(admin) it says "Ok" but when I reboot, the value switches back to the default value(1500), could someone help me change it to the value(1492) I have set in my router please. Thanks.

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  2. #2

    I was under the assumption that the MTU was strictly a router setting. Is this not so? If not, where in the OS would it be located?
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  3. #3
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  4. #4

    You haven't mentioned which methods you have already tried for this?

    To see the current MTU values, elevated command prompt > netsh interface ipv4 show subinterface

    To change wireless MTU > netsh interface ipv4 set subinterface "Wireless" mtu=xxxx store=persistent

    For wired connections > set subinterface "Local Area Connection" mtu=xxxx store=persistent

    Or try > nestsh interface ipv4> set subinterface "Local Area Connection" mtu=xxxx store=persistent

    If you need to mess with the MTU values it' likely that something else is causing the problem.
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  5. #5

    Thanks guys, I tried wireless MTU setting: netsh interface ipv4 set subinterface "Wireless" mtu=xxxx store=persistent
    I am trying to change the MTU because I have found out the optimum value for my router is 1492, can I leave the MTU value in OS as default?
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  6. #6

    I've never changed the MTU value in either the router on the OS and mine runs fine.
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  7. #7

    Posts : 70
    windows 8.1

    if you really want to change MTU, first you need to evaluate what is the optimum. Never assume arbitrary correct parameter.
    1) start with
    ping -f -l 1492
    steady decrease value by 10 until no packed is fragmented - see picture
    Click image for larger version

    I would not bother though. I does not matter what target you will ping of course as long as it is pingable. MTU value change makes sense only if you have DSL connection and it may affect upload speed. Before and after each change run network speed test to see if these is any improvement or degradation of network performance. One more thing actual MTU value to enter equals highest not fragmented MTU + 28
    Last edited by Michal; 08 Jan 2014 at 21:31.
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  8. #8

    Quote Originally Posted by brummyfan View Post
    Thanks guys, I tried wireless MTU setting: netsh interface ipv4 set subinterface "Wireless" mtu=xxxx store=persistent
    I am trying to change the MTU because I have found out the optimum value for my router is 1492, can I leave the MTU value in OS as default?
    This is a pseudo science at best and in most cases will make no difference.

    Network speed tests typically have to much inherent variation to either prove or disprove if changing the MTU actually worked or not.
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  9. #9

    Posts : 70
    windows 8.1

    shrug, why then you even post it? As I mentioned MTU change affects only DLS users and only uploads. Not to mention that this will have more impact in the countries with better telecommunication infrastructure (than US). He is from England so he may see some improvements in specific conditions. If he runs several tests and gets average upload improvement of meaningful value then good for him. Personally I would not bother, but for game players this may be helpful (if it works at all).
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  10. #10

    Thanks chev65 & Michal for the contributions, I take your advice and leave as it is
      My System SpecsSystem Spec

Changing MTU value.

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