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Optimal MTU size

  1. #1
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    Default Optimal MTU size

    Many users complain that some websites do not open, and usual suggestion is to change the MTU values in modem.
    Applications are also recommended for trying different
    values.
    Now the following is another method for MTU selection.


    General instruction for finding your optimal MTU size

    Go to Start and select Run.
    Set router to MTU 1500 to start with.
    Start RUN
    Type in cmd (Windows 2000/XP/Vista/7) or command (Windows 98/ME) into the box .
    Hit the enter key or click OK
    At the DOS prompt,
    type in ping bbc.co.uk -f -l 1492
    and hit the Enter key.
    If you get the response "Packet needs to be fragmented but DF set",
    lower the size the packet in increments of +/-10 (e.g. 1472, 1462, 1440, 1400) until you have a packet size that does not fragment.
    Now increase the packet size from this number in small increments until you find the largest size that does not fragment.
    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 and can be put in your router's settings
    !
    Hope this helps some of you!?

    Source : NETGEAR site.
    Last edited by essbebe; 17th July 2011 at 05:47 PM. Reason: added reason for MTU change in brief.

  2. #2
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    Exclamation ok...but what does MTU do basically??

    Quote Originally Posted by essbebe View Post
    General instruction for finding your optimal MTU size

    Go to Start and select Run.
    Set router to MTU 1500 to start with.
    Start RUN
    Type in cmd (Windows 2000/XP/Vista/7) or command (Windows 98/ME) into the box .
    Hit the enter key or click OK
    At the DOS prompt,
    type in ping bbc.co.uk -f -l 1492
    and hit the Enter key.
    If you get the response "Packet needs to be fragmented but DF set",
    lower the size the packet in increments of +/-10 (e.g. 1472, 1462, 1440, 1400) until you have a packet size that does not fragment.
    Now increase the packet size from this number in small increments until you find the largest size that does not fragment.
    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 and can be put in your router's settings
    !
    Hope this helps some of you!?

    Source : NETGEAR site.
    ok...but what does MTU do basically??

  3. #3
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    Default

    Post No 1 . edited

  4. #4
    The Wizard meetdilip's Avatar
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    Good one

    Can't rep

  5. #5
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    Default

    Quote Originally Posted by rosh50 View Post
    ok...but what does MTU do basically??
    MTU = Maximum Transmission Unit of a communications protocol of a layer is the size (in bytes) of the largest protocol data unit that the layer can pass onwards.

  6. #6
    linda87st
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    Can you update the article to include iti dna-A211-l modem/router

  7. #7
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    Dna-A211-l modem/wifi router
    Usually default MTU will be 1492 .
    ( this modem belongs to the group wa3002_g4 see my signature link.)
    Safe side select default value 0
    No hard and fast rule . Even users have reportedMTU 1400 works .
    Higher the value better.
    2.
    To avoid confusion use tcp/ip optimizer from speedguide.net.

  8. #8
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    How to apply mtu value in windows 7

  9. #9
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    copy/paste result here for further suggestions.
    1) Open an elevated command prompt and type:

    netsh interface ipv4 show subinterfaces

    and hit Enter.

    You should get a list of all your network adapters installed on your PC

  10. #10
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    1400 worked for me to. Now should I change this setting in Router only or in Windows too using TCP optimizer?

  11. #11
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    @amasoun
    Code:
    IF IT works Don't repair 
    Mention modem/router model/number.
    See menu options in TCP/Ip Optimizer.
    http://www.speedguide.net/showpic_hs...r/registry.png

    REcheck with method in Post No 7 after using TCP/IP optimizer.
    ONLY for AdVANCED Users.
    Make back up of Registry, before attempting any Changes , or
    Create System Restore Point.
    Last edited by essbebe; 8th December 2011 at 07:26 PM.

  12. #12
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    Modem is Netgear DG834GUv5, ISP BSNL Punjab, I rechecked coz largest value should be used, 1432 works and 1433 doesnt. It means I should use 1432+28=1460.

    TCP Optimizer doesnt suggest anything. If you select Does it?

    My question was, should I change MTU size in router only or using TCP Optimizer custom settings I should change it in Windows too?????????

  13. #13
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    See Post No 9. and post the results.

  14. #14
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    Default Problems connecting to Yahoo and Hostmonster.com

    Hi all,

    Greetings on the New Year!

    I am facing a similar problem with my BSNL WiFi router, a UT Starcomm WA3002-g1. I am unable to access Yahoo as well as Hostmonster.com (need for my website).

    I am using a win 7 laptop to connect. I also have a desktop and another laptop (Win XP) but none of these can connect, either over WiFi or LAN.

    I tried 'ping bbc.co.uk -f -l xxxx' and see a fragmented message until 1473 bytes. however, as soon as I drop to 1472 bytes, I start getting a 'request timed out message'?

    Next, I tired setting the router's MTU to 1472+28=1490 but this didnt' work. I changed to 1492 on the router setting and still no luck. HJowever, if I reduced to 1490 or lower, some other websites e.g. timesofindia.com stopped working as well. *sigh*

    I will really appreciate any help. I need to reach my Yahoo mail and more importantly to hostmonster.com

    Thanks.

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  16. #16
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    One more earlier useful link. by @deepmohan. in this forum.
    http://www.indiabroadband.net/broadb...mtu-value.html

  17. #17
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    Talking Mtu 1350

    MTU 1350 worked for me. Everything is just fine now.

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