Help needed from maccabi or any other network person (MTU)

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Help needed from maccabi or any other network person (MTU)

when i do this test ping -f -l 1472 www.google.com    i have to lower it all the way down to 1332 to be able to recieve all packets +28 for header=1360 (NOT enough to connect to XBL)

Any reason why my mtu needs to be so low?is my router going bad? i have road runner extreme(30 down 5 up )

Level 5
Likes: 30
Posts: 162
Registered: ‎02-12-2011
30 REPLIES

Re: Help needed from maccabi or any other network person (MTU)

in reply to Zacinnc781

When you run that test, 1472 will only work if your router is set to 1500.  What ever your router setting, you must subtract 28 (or 8 if using DSL) from that for the test to run correctly.    For example, if your router was at 1455, the test settings would need to be at 1427 for it to finish without showing fragmentation. I think Mac needs to clarify that a bit in his elagaphant article. It may be confusing some people.

Level 21
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Posts: 1360
Registered: ‎16-12-2011

Re: Help needed from maccabi or any other network person (MTU)

in reply to Nubdub

so you are saying i have to change my MTU setting on the router itself everytime i change it in DOS??

i thought the whole point of the DOS test is to see what i NEED to set my router at ,which tests the packets outside of the router settings?

Level 5
Likes: 30
Posts: 162
Registered: ‎02-12-2011

Re: Help needed from maccabi or any other network person (MTU)

in reply to Zacinnc781

What ever you set your router at, you need to subtract 28 from that number to put in for your test number.  For example, if your router is set at 1500, for the test to run without fragmenting, you would do the test at ping -f -l 1472 www.google.com

If you have your router at 1500 and try ping -f -l 1480 www.google.com, it will fragment. Unless you are using DSL, then subtract 8 instead of 28.

Also be aware its the letter "L" in the test script, not an "i".

Level 21
Likes: 252
Posts: 1360
Registered: ‎16-12-2011

Re: Help needed from maccabi or any other network person (MTU)

in reply to Nubdub

alright i maually set the router to 1500 and reran test at 1472 and sent 4 recieved 0 100% loss and i went down by 10 all the way to 1332 until it actually works the way it is supposed to(thanks for the replies btw)

Level 5
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Posts: 162
Registered: ‎02-12-2011

Re: Help needed from maccabi or any other network person (MTU)

in reply to Zacinnc781

Cool. I know Mac is not going to appreciate being corrected, especially not by me but he really needs to fix that piece of the article.

Level 21
Likes: 252
Posts: 1360
Registered: ‎16-12-2011

Re: Help needed from maccabi or any other network person (MTU)

in reply to Nubdub

do u see what my problem is though?   i would have to set my mtu to 1360 (1332+28) which wont allow me to connect to xbl.....

Level 5
Likes: 30
Posts: 162
Registered: ‎02-12-2011

Re: Help needed from maccabi or any other network person (MTU)

in reply to Nubdub

Sorry to jump in on this, but can I also please ask....my router is set at 1500, when I do the test at 1472 I. Get 0% packet loss which is what I want. So my question is should I change the MTU from 1500 to 1472? Because I'm pretty sure if I do I start getting packet loss. It's all a bit confusing lol.

Thanks for your help in advance!

Level 2
Likes: 11
Posts: 50
Registered: ‎19-10-2011

Re: Help needed from maccabi or any other network person (MTU)

in reply to Zacinnc781

Would you mind running another script and let me know the results? Try    "ping www.google.com -t"  without the quotes of course. Let it run for about 1 minute then press "Ctrl + C" to stop the test. Let me know what you come up with. Make sure you right click the command prompt and choose "run as administrator" when you bring up the window.   

By the way, if your line is DSL 1492 should be the highest number you set your router at. You would most likely have trouble trying to use 1500 DSL (pppoe) connection

Level 21
Likes: 252
Posts: 1360
Registered: ‎16-12-2011

Re: Help needed from maccabi or any other network person (MTU)

in reply to Nubdub

it jsut keeps pinging over and over

Level 5
Likes: 30
Posts: 162
Registered: ‎02-12-2011

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