MTU won't change

Get help and discuss anything related to tweaking your internet connection, as well as the different tools and registry patches on the site. TCP Optimizer settings and Analyzer results should be posted here.
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CBFH
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MTU won't change

Post by CBFH »

hi!

My MTU value is set to 1492 in the router and also in OS.
Used stuff like Dr. TCP, TCPOptimizer and DFUE-Speed.
speedguide.net always shows me 1448. would be glad if you could give me some ideas!
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mccoffee
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Post by mccoffee »

what dsl modem do you own?
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cdf216
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Post by cdf216 »

CBFH wrote:hi!

My MTU value is set to 1492 in the router and also in OS.
Used stuff like Dr. TCP, TCPOptimizer and DFUE-Speed.
speedguide.net always shows me 1448. would be glad if you could give me some ideas!
One question,

Do you have Path MTU discovery enabled? if so it could be your provider has hard set the 1448 MTU in their Routers and that is what the analyzer is picking up. Path MTU discovery reads the fastest MTU the along the entire path between you and the target site and adjusts your MTU automatically to compensate, the 1500 you set is just a suggested. You could turn Path MTU Discovery off but I wouldn't reccommend it.
CBFH
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Post by CBFH »

My dsl modem is integrated into the router (Siemens SX541 WLAN). All I can say is, that I have turned off path mtu discovery. When I set the mtu value in the router below 1448, then speedguide shows exactly the value i configured. But above 1448 there seems to be no other value possible. As I have noticed, there are many more people in the www having exactly the same problem. But I didn't find a solution for that. I don't know whether this depends on my ISP (Freenet/germany) or is a limit of the rasppoe driver that came with win xp. Someone mentioned something with pppoA protocol, but I have no experiences referring to that. I also read about registry entries in wrong directories set by Dr TCP and some other tools. Maybe you can tell me, where the values and strings have to be. .. Finally I'm very confused because I can't figure out where the problem is. Hope you can help. If you need system specs, please tell me. Thank you! edit: I can remember the time, when the ISP recommended the MTU at 1454. To this time the MTU at 1454 was working... when I remember right.Then the limit of 1454 was put aside by the ISP... as I have read in the forums...if it's true, then maybe this is the reason for that. Maybe the router overwrites the values set in the OS also for path mtu discovery in the same way as he does for mtu value. mhpf... I don't know - now I depend on you :)
CBFH
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Post by CBFH »

has no one a sloution or any idea?
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mccoffee
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Post by mccoffee »

see if there is any frimware for router contact semans might br a way to get themtu higher
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