Gigabit Network only connects @ 100Mbit on startup

Discussion in 'Windows Networking' started by Nick Hatzichristos, Dec 25, 2004.

  1. Hi everybody,

    I am having a rather serious networking problem that I hope someone can help
    me with.

    I have a small network, consisting of an ADSL router with a 100mbit hub, a
    Gigabit switch, one machine with a 100mbit NIC and two machines with gigabit

    The 100mbit machine is directly connected to the router, and the router is
    connected to the gigabit switch.
    The other two PCs are directly connected to the gigabit switch.
    All machines run WinXP Pro, SP2. All cabling is CAT-5, certified for Gigabit
    The router is an SMC Barricade 7404BRA, and the gig switch an SMC EZSwitch
    10/100/1000 8505T.

    Now the problem I have is weird, and it goes like this : When I first boot
    any of the two Gig PCs, they will not connect to the Gig switch. They will
    not connect at all, they will just keep trying and keep failing. If I
    manually set them to 100Mbit/Full duplex, they instantly connect, but even
    then the connection is ridiculously slow. Anything more than 100/full set in
    the NICs' settings will fail to even connect at all.

    Now, the really weird thing is that after a couple of hours of running time,
    I can go to the NICs' settings and either set them to Auto Negotiate or
    directly to 1000/full, and they connect fine, with perfect Gig speeds, too -
    without changing *anything* else ! But I repeat, that can only happen after
    both machines have been on for a while. At that point, I can reboot the PCs,
    or even shut them down and turn them on again after a few minutes, and there
    is no problem. If I shut them down for a few hours and boot them up again,
    the problem appears again.

    I 've looked everywhere, and tried anything I could think of. I
    reinstalled/updated drivers, replaced all cabling, reset the router and
    switch, even changed NICs (tried with the on-board intel Pro/1000 CT ones,
    and then disabled those and used 3Com gigabit NICs instead. The same thing
    happens. I also eliminated the possibility of a faulty switch, since I
    tested it on another network and it worked fine every time.
    I should also mention that connecting the two gig PCs directly with a
    crosswired cable works perfectly every time too (which points to a faulty
    switch, but like I said... I tested it and it worked fine on another setup).

    I 'm really confused here... I 've searched all over the place but couldn't
    find anything. I would appreciate any help I can get from anyone !

    Thanks, and apologies for the kinda long post - I wanted to make the whole
    setup and problem clear from the start.



    Nick Hatzichristos
    nixx /at/ animatethis /dot/ gr

    ICQ# : 48636115
    Nick Hatzichristos, Dec 25, 2004
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  2. Nick Hatzichristos

    CJT Guest

    That _is_ weird. I'll start the brainstorming:

    It sounds like something thermal; that you've swapped NICS with no
    change suggests it's the switch. Might the other network in which
    you tested the switch be environmentally different (either in
    temperature or perhaps line voltage)? Also, FWIW, my impression is
    that switches heat up as they are actually called upon to perform
    their function (more than just being powered up).

    Out of curiosity, when you say you replaced all the cables, does that
    include the drop cables? Since we're plumbing the depths of the weird,
    it occurs to me that a bimetallic interaction at the drop cable
    connections could generate a small bias voltage that might be
    temperature sensitive, and might tip the balance in a marginal system.

    In the mode where they won't connect at all, do the status lights on
    the NICs and switch reveal anything?

    How long are the cable runs?

    Clearly one thing you could try is replacing the switch (at least
    temporarily) and see whether the problem disappears.
    CJT, Dec 25, 2004
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  3. Hi CJT, thanks for replying and brainstorming with me on this... I 'll try
    to clear some things more.

    Good, at least I haven't got mad or anything... : )

    Yes, it was a completely different environment actually - line voltage was
    most probably the same, but everything else could have been different.

    I see. But still, it should work right away, shouldn't it ?

    I see what you mean, but I don't think I get what you mean by "drop cables"
    (sorry). What I meant by "all cables" was all PC<>switch CAT5 cables,
    PC<>router and router<>switch. The only thing I haven't tried replacing, now
    that I think of it, is the ADSL line cable from the wall outlet to the
    router, but this is completely irrelevant, isn't it ?

    They light up (indicating 1gig connections) for a second or two, while the
    PCs try to connect, and they turn off when the connection fails. And then
    they light up again, then turn off, and so on. No troubleshooting signal I
    'm afraid (checked the manual, too).

    100mbit PC > Router, 6-7 feet (~2-2,5m)
    Router > Switch, around 45 feet (~15m, that's the longest one)
    "Problematic" gig PCs > Switch, 10-12 feet (~3-4m) each.

    I think I will try that anyway... I meant to, but abandoned the idea when I
    saw the very same piece work perfectly on another network.

    One other thing I just realised, is that when I took the switch for testing,
    it could have been after it had already worked for a few hours (I can't
    remember, but it could). That would point to your heat-up theory (since it
    may have been already heated up when it was tested), but what if that theory
    is correct ? Would it mean that the switch is actually defective or
    something ? That can't be the "right" way a switch works, can it ?

    Thank you for trying to tackle this with me, I appreciate your help a lot :)



    Nick Hatzichristos
    nixx /at/ animatethis /dot/ gr

    ICQ# : 48636115
    Nick Hatzichristos, Dec 25, 2004
  4. Nick Hatzichristos

    CJT Guest

    It should. Then again, the whole system _should_ work. <g>
    Some electronics tend to work better when warmed up. Some NICs
    are more tolerant of variances than others, too.
    [I might not be envisioning this quite like it is. To me, a drop cable
    is one from, e.g., a PC to the wall, or from the wall to the switch.
    Then there's the in-wall wiring. That you said you had certified the
    cables suggested to me that there was some in-wall wiring involved,
    since normally people don't certify drop cables on-site. What you just
    wrote suggests I might not be understanding completely.]

    (As I read further, I realized this [] is probably irrelevant, anyway,
    since you've apparently just got short cables connecting the offending
    PCs to the switch)

    BTW, what's the nature of the certification that was done?

    The only thing I haven't tried replacing, now
    I wouldn't worry about that one.
    I don't claim to be an expert on this particular aspect, but that sounds
    to me like a failure negotiating. Is the switch one that auto-detects
    both speed and the need for a crossover connection? If so, can it be
    forced to non-crossover mode (i.e. skip the X vs. II determination)?
    It seems to me that for the problem described, just that last bit
    counts, since presumably you could disconnect the router from the
    switch and things would be the same on the LAN.

    Are those 3-4m cables "store bought?" Or were they fabricated on-site?
    I'm always suspicious of cabling, because so many people get it wrong.
    Out of curiosity, if they were fabricated on-site, to which standard
    do they adhere -- 568A or 568B?
    They should work cold, but that's no guarantee this particular one does.
    Even a switch that meets specs could have intermittent problems if
    something else (e.g. cabling) is marginal.
    Merry Christmas. :)
    CJT, Dec 25, 2004
  5. I probably mislead you about the certification - all cables are store
    bought, no in-wall wiring, and by "certified" I meant that they all have
    "gigabit ethernet certified" printed across :)
    No on-site certification, and certainly no on-site fabrication of wires...

    It auto-detects speed, but only works with II cables (tried crossover and it
    failed, and that was in "working OK" mode).

    Exactly (I tried that too). I think it's clear that my problem is with the
    Like I mentioned above, they're store-bought and they are of the 568B
    standard ("568B.2" is printed across, along with other tech specs).

    I 'll do some more hot/cold tests to see if that's actually the case, and
    then I 'll see if I can get some other make/model for testing.

    Merry Christmas to you too (and everyone else !) and a happy, speedy,
    bottleneck-free new year ! ;)

    thank you once again :)



    Nick Hatzichristos
    nixx /at/ animatethis /dot/ gr

    ICQ# : 48636115
    Nick Hatzichristos, Dec 25, 2004
  6. Nick Hatzichristos

    CJT Guest

    It sounds like you've done everything right, and it should "just work."

    I'm fresh out of ideas right now, and it's almost dinner time in Texas,
    so I'll just say "best of luck with it!" Maybe something we've
    discussed will trigger some thoughts in other readers.
    CJT, Dec 25, 2004
  7. Nick Hatzichristos

    Yousuf Khan Guest

    Now, having glanced through some of the other discussions you've had in
    this thread, have you tried fiddling with any of the the other advanced
    network card configuration settings available to you? These parameters
    are all different depending on adapter, but in my 100BT NICs I also have
    settings for Adaptive Interrupt, Flow Control, Network Address, Receive
    Buffers, Transmit Buffers, and Validate Packet Length. I've left all of
    those at defaults in my case, since everything is working fine. In your
    case, you may want to check into them?

    Now it's entirely possible that you've run into one of those early
    teething issues with new technology. This sort of thing used to occur
    with 100BT hardware too in the early days, though these days that
    technology has been around so long that we don't remember them. I'm sure
    they even occurred in the really old days with 10BT, when people were
    switching away from coax Ethernet to twisted-pair, but I was barely
    cognizant of networking back in those days.

    Yousuf Khan
    Yousuf Khan, Dec 26, 2004

  8. Hi Yousuf, thanks for replying :)

    There are, of course, advanced settings in the NIC's control panel, and I
    have tried changing a couple of them. But seeing as I don't know the exact
    effect of each setting, and given that the possible combinations are
    endless, I haven't tried playing with more than just a couple - you know, I
    could make things worse ;)
    Plus, the fact that after a while the whole thing settles down and works as
    expected is a good indication that none of those settings need fiddling

    I 'll keep looking into this, I really hope I find what's wrong - it's
    frustrating, to say the least, to have to wait a few hours every morning
    before I get my LAN working :(

    Anyway, thanks again for sharing your idea : ) Merry Christmas !



    Nick Hatzichristos
    nixx /at/ animatethis /dot/ gr

    ICQ# : 48636115
    Nick Hatzichristos, Dec 26, 2004
  9. Nick Hatzichristos

    CJT Guest

    It might be worth checking that you have the most recent firmware in
    the switch:

    Interestingly, that page indicates it does auto MDI-I/X.
    CJT, Dec 26, 2004
  10. For the record :

    I ended up replacing the SMC switch with a different one (a 3com). It worked
    perfectly right away, and still works perfectly on the third day of testing,
    right from the start (no need to "warm up" !).

    The really weird thing is, however, that the SMC switch still worked
    perfectly in a different environment than my own. It seems that whatever it
    was that was affecting it, the 3Com one is immune to ;)

    I still can't explain it, but the problem is gone now so I think I 'll just
    seal this and archive it away in my "X-files" drawer : )

    Big thanks to all who tried to help me get to the bottom of this.

    Happy new year !



    Nick Hatzichristos
    nixx /at/ animatethis /dot/ gr

    ICQ# : 48636115
    Nick Hatzichristos, Dec 28, 2004
  11. Nick Hatzichristos

    dg Guest

    In the past there have been particular nics that didn't pair well with
    specific hubs/switches. That kind of stuff happens sometimes, even with all
    of the standards that exist. Yep, sometimes its easiest to just be happy it
    works now and use the SMC switch in a different situation where it works all
    the time.

    dg, Dec 30, 2004
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