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Thread: Analyzer and Optimizer show different MTU

  1. #1
    Junior Member bege's Avatar
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    Unhappy Analyzer and Optimizer show different MTU

    Hi everybody,

    I am quite confused about the results of the Analyzer and Optimizer.

    My ISP (T-Online Business) requests a special MTU of 1456. So are the settings in my computer and the router.
    This is what the Optimizer finds out in the Largest MTU tab:

    Pinging [66.230.207.58] with 40 bytes ->bytes=40 time=218ms TTL=45
    Pinging [66.230.207.58] with 750 bytes ->bytes=750 time=240ms TTL=45
    Pinging [66.230.207.58] with 1125 bytes ->bytes=1125 time=254ms TTL=45
    Pinging [66.230.207.58] with 1312 bytes ->bytes=1312 time=260ms TTL=45
    Pinging [66.230.207.58] with 1406 bytes ->bytes=1406 time=273ms TTL=45
    Pinging [66.230.207.58] with 1453 bytes -> ..fragmented
    Pinging [66.230.207.58] with 1430 bytes -> ..fragmented
    Pinging [66.230.207.58] with 1418 bytes ->bytes=1418 time=262ms TTL=45
    Pinging [66.230.207.58] with 1424 bytes ->bytes=1424 time=262ms TTL=45
    Pinging [66.230.207.58] with 1427 bytes ->bytes=1427 time=276ms TTL=45
    Pinging [66.230.207.58] with 1428 bytes ->bytes=1428 time=269ms TTL=45
    Pinging [66.230.207.58] with 1429 bytes -> ..fragmented
    The largest possible non-fragmented packet is 1428 (1456 - 28 ICMP & IP headers).
    You can set your MTU to 1456


    But the Analyzer shows an MTU of 1416:

    SpeedGuide.net TCP Analyzer Results
    Tested on: 04.02.2010 14:57
    IP address: 80.129.xxx.xxx
    Client OS: Windows XP

    TCP options string: 020405600103030101010402
    MSS: 1376
    MTU: 1416
    TCP Window: 124608 (NOT multiple of MSS)
    RWIN Scaling: 1 bits (2^1=2)
    Unscaled RWIN : 62304
    Recommended RWINs: 63296, 126592, 253184, 506368, 1012736
    BDP limit (200ms): 4984kbps (623KBytes/s)
    BDP limit (500ms): 1994kbps (249KBytes/s)
    MTU Discovery: ON
    TTL: 45
    Timestamps: OFF
    SACKs: ON
    IP ToS: 00000000 (0)


    How come?

    Does anybody have an idea?
    Regards

  2. #2
    SG Enthusiast Rollingstone's Avatar
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    Try the following with TCP Optimizer & see if MTU will change:

    General Settings tab:
    Custom settings - check
    Modify All Network Adapters - check
    network adapter selection - your NIC
    MTU - 1500
    TTL - 64
    Windows Scaling - uncheck
    TCP Receive Window - leave blank
    MTU Discovery - Yes
    Black Hole Detect - No
    Selective Acks - Yes
    Max Duplicate ACKs - 2
    TCP 1323 Options:
    Timestamps - uncheck

    Advanced Settings tab:
    Max Connections per Server - 10
    Max Connections per 1.0 Server - 10
    LocalPriority - 5
    Host Priority - 6
    DNSPriority - 7
    NetbtPriority - 8
    Lan Browsing speedup - optimized
    QoS: NonBestEffortLimit - 0
    ToS: DisableUserTOSSetting - 0
    ToS: DefaultTOSValue - 0
    MaxNegativeCacheTtl - 0
    NetFailureCacheTime - 0
    NegativeSOACache Time - 0
    LAN Request Buffer Size - 32768
    Firefox Extreme Speed Edition

    What makes you: "...waking up in the morning so excited about & wanna FLY out of the door ?"

  3. #3
    Junior Member bege's Avatar
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    Rollingstone, thank you for your answer.
    (Sorry for the long delay. I didn't get an e-mail notification of your answer and forgot to come back to the forum until today.)

    Unfortunately the strange MTU is still shown by the Analyzer, plus a weird RWIN
    By the way, I just notice that the TTL shown by Optimizer and Analyzer also differ. The Analyzer shows 45, the Optimizer 64.

    SpeedGuide.net TCP Analyzer Results
    Tested on: 04.15.2010 10:04
    IP address: 80.129.xxx.xxx
    Client OS: Windows XP

    TCP options string: 020405600103030e01010402
    MSS: 1376
    MTU: 1416
    TCP Window: 1073725440 (NOT multiple of MSS)
    RWIN Scaling: 14 bits (2^14=16384)
    Unscaled RWIN : 65535
    Recommended RWINs: 63296, 126592, 253184, 506368, 1012736
    BDP limit (200ms): 42949018kbps (5368627KBytes/s)
    BDP limit (500ms): 17179607kbps (2147451KBytes/s)
    MTU Discovery: ON
    TTL: 45
    Timestamps: OFF
    SACKs: ON
    IP ToS: 00000000 (0)

  4. #4
    Junior Member bege's Avatar
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    ... and this is what the Analyzer shows with the standard windows settings:

    SpeedGuide.net TCP Analyzer Results
    Tested on: 04.15.2010 10:30
    IP address: 80.129.xxx.xxx
    Client OS: Windows XP

    TCP options string: 02040560
    MSS: 1376
    MTU: 1416
    TCP Window: 16512 (multiple of MSS)
    RWIN Scaling: 0 bits
    Unscaled RWIN : 16512
    Recommended RWINs: 63296, 126592, 253184, 506368, 1012736
    BDP limit (200ms): 660kbps (83KBytes/s)
    BDP limit (500ms): 264kbps (33KBytes/s)
    MTU Discovery: ON
    TTL: 109
    Timestamps: OFF
    SACKs: OFF
    IP ToS: 00000000 (0)

  5. #5
    Junior Member bege's Avatar
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    ... and after having set the MTU in the router to 1492 (the maximum the router allows) Analyzer shows MTU 1452 (computer settings still are windows default = no MTU setting).

    So Analyzer always shows 40 less than the router and/or the computer are set to.

  6. #6
    SG Enthusiast Rollingstone's Avatar
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    What's brand & model of your router ? What speed are you paying for ?
    Firefox Extreme Speed Edition

    What makes you: "...waking up in the morning so excited about & wanna FLY out of the door ?"

  7. #7
    Junior Member bege's Avatar
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    Quote Originally Posted by Rollingstone View Post
    What's brand & model of your router ? What speed are you paying for ?
    The router is Netgear WGR614 v7

    The speed is 3000kBit/s

  8. #8
    SG Enthusiast Rollingstone's Avatar
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    Try the following with TCP Optimizer:

    General Settings tab:
    Custom settings - check
    Modify All Network Adapters - check
    network adapter selection - your NIC
    MTU - 1376
    TTL - 64
    Windows Scaling - uncheck
    TCP Receive Window - 63296
    MTU Discovery - Yes
    Black Hole Detect - No
    Selective Acks - Yes
    Max Duplicate ACKs - 2
    TCP 1323 Options:
    Timestamps - uncheck

    Advanced Settings tab:
    Max Connections per Server - 10
    Max Connections per 1.0 Server - 10
    LocalPriority - 5
    Host Priority - 6
    DNSPriority - 7
    NetbtPriority - 8
    Lan Browsing speedup - optimized
    QoS: NonBestEffortLimit - 0
    ToS: DisableUserTOSSetting - 0
    ToS: DefaultTOSValue - 0
    MaxNegativeCacheTtl - 0
    NetFailureCacheTime - 0
    NegativeSOACache Time - 0
    LAN Request Buffer Size - 32768
    Firefox Extreme Speed Edition

    What makes you: "...waking up in the morning so excited about & wanna FLY out of the door ?"

  9. #9
    Junior Member bege's Avatar
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    Now Analyzer and Optimizer show the same MTU. Looks a bit like wizardry to a "layperson" like me.

    Please, can you explain to me why this was not the case with different MTU values?

    Why did you recommend this MTU value? It is now the same in Optimizer and Analyzer, but not the one the ISP requires.

    And what does the low RWIN value mean? It's below the windows standard which is for slower connection, I think, and far less than what the Optimizer recommends.

    Why is the LAN Request Buffer Size double the size as in the optimal settings of the Optimizer?
    Last edited by bege; 04-20-10 at 09:55 AM.

  10. #10
    SG Enthusiast Rollingstone's Avatar
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    Now Analyzer and Optimizer show the same MTU. Looks a bit like wizardry to a "layperson" like me.

    Please, can you explain to me why this was not the case with different MTU values?

    Why did you recommend this MTU value? It is now the same in Optimizer and Analyzer, but not the one the ISP requires.

    And what does the low RWIN value mean? It's below the windows standard which is for slower connection, I think, and far less than what the Optimizer recommends.

    Why is the LAN Request Buffer Size double the size as in the optimal settings of the Optimizer?
    MTU : In some cases, your modem/router is MTU Limitation !

    RWIN Forumula : Bandwidth * Max.latency / 8

    Your case : 3000 * 150 /8 = 56250 then compare with Recommened RWINS (in ANalyzer) ! The Closest Number is 63296

    LAN Request Buffer Size : Why dont you try max number possible ?
    Firefox Extreme Speed Edition

    What makes you: "...waking up in the morning so excited about & wanna FLY out of the door ?"

  11. #11
    Junior Member bege's Avatar
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    Quote Originally Posted by Rollingstone View Post
    MTU : In some cases, your modem/router is MTU Limitation !
    Thank you!
    Still one thing not clear:
    When the router was set to MTU 1456 (ISP), the max. MTU tab in Optimizer showed the same value, but the Analyzer showed 1416.
    I still don't understand, what the real MTU is and why they are different in Analyzer and Optimizer. (Ingoing and outgoing different?)
    When the router was set to 1492 (maximum of the router), the Analyzer showed 1452. What do you mean is the limitation of the router? The router settings tell it's 1492, so 1456 shouldn't be a problem.

  12. #12
    SG Enthusiast Rollingstone's Avatar
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    What do you mean is the limitation of the router?
    For some reasons, your modem/router is not compatible with your ISP ! So the MTU will not be max ! But we can try maximizing our modem's MTU !
    Firefox Extreme Speed Edition

    What makes you: "...waking up in the morning so excited about & wanna FLY out of the door ?"

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