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Thread: Please help - MTU Stuck at 1454

  1. #1
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    Please help - MTU Stuck at 1454

    I have been trying for a few days to show 1492 in the analyzer without any luck - have tweaked reg with TCP/IP optimizer(and checked reg manually for changes) Have checked settings in my router, MRU=1492 there as well. I have tried added some reg entries for TCP/IP that are supposed to increase MTU, but still stays at 1454. I have 2 PCS on the rounter, both are "set" in registry at MTU=1492 but both analyze at 1454.

    I am on a 512/128 connection ISP is iprimus (Australian provider)
    I do not use PPPoE software on the PC, this is handled in the router/modem
    I am running Win XP home SP2
    My route/modem model is a D-Link DSL-504T

    Any help is appreciated

    TCP options string = 020405860103030001010402
    MTU = 1454
    MTU is not fully optimized for broadband. Consider increasing your MTU to 1500 for better throughput.
    MSS = 1414
    MSS is not fully optimized for broadband (although it might work well for slower connections). Consider increasing your MTU value.

    Default Receive Window (RWIN) = 33936
    RWIN Scaling (RFC1323) = 0 bits
    Unscaled Receive Window = 33936

    RWIN is a multiple of MSS
    Other values for RWIN that might work well with your current MTU/MSS:
    520352 (MSS x 46 * scale factor of 8)
    260176 (MSS x 46 * scale factor of 4)
    130088 (MSS x 46 * scale factor of 2)
    65044 (MSS x 46)
    bandwidth * delay product (Note this is not a speed test):

    Your RcvWindow limits you to: 1357.44 kbps (169.68 KBytes/s) @ 200ms
    Your RcvWindow limits you to: 542.976 kbps (67.872 KBytes/s) @ 500ms
    MTU Discovery (RFC1191) = ON
    Time to live left = 49 hops

    TTL value is ok.
    Timestamps (RFC1323) = OFF
    Selective Acknowledgements (RFC2018) = ON
    IP type of service field (RFC1349) = 00000000 (0)

  2. #2
    fem the retarded rabbit mccoffee's Avatar
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    it's probably stuck in the modem what modem you have??
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  3. #3
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    Quote Originally Posted by mccoffee
    it's probably stuck in the modem what modem you have??
    Hi, thanks for the reply

    My route/modem model is a D-Link DSL-504T

    MRU= 1492

    Last edited by lavers; 10-04-05 at 02:57 AM.

  4. #4
    Administrator Philip's Avatar
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    Still, there has to be something limiting the MTU if it is set in your Registry but not reaching our server... Even if you can't increase it, you'll still be pretty close to the being tweaked, the TCP Window is the most important setting.

  5. #5
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    ok, so it is possible that it is ISP set?

    Could you tell me if the TCP Window setting looks alright? Im not really sure how to work out maximum latency to come up with the correct setting.

    Default Receive Window (RWIN) = 33936
    RWIN Scaling (RFC1323) = 0 bits
    Unscaled Receive Window = 33936


    My ADSL speed is 512/128

  6. #6
    Administrator Philip's Avatar
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    Yes, your TCP Window is allright... It is multiple of MSS (1414 * 24 = 33936)...

    And according to the Analyzer and the bandwidth*delay product: Your RcvWindow limits you to: 542.976 kbps (67.872 KBytes/s) @ 500ms .

    In other words, you will be able to get your 512kbps with latency as high as 500ms.

  7. #7
    fem the retarded rabbit mccoffee's Avatar
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    what opitons do you have under connection types just wondering ??
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  8. #8
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    The connection types i can use are

    PPPoE LLC
    PPPoA LLC
    PPPoA VC-MUX


    I can actually connect using any of these connection types, it would appear that the Australian ISP's are like that anyway.

    Could i ask which is the recommended connection type?

    I have heard PPPoA is slightly quicker, but i have also heard ISP's recommend the PPPoE

    As my MTU is stuck at 1454 i dont think the connection type would matter would it?

  9. #9
    fem the retarded rabbit mccoffee's Avatar
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    i think you are stuck with that mtu i ran into this mtu promblem befrore with austrialan's and dlinks
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