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Windows Server 2000/2003 Thread, DHCP problems - help needed in Technical; Originally Posted by witch We do use a proxy. So does that mean that the yellow exclamation mark isn't a ...
  1. #16

    Michael's Avatar
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    Quote Originally Posted by witch View Post
    We do use a proxy. So does that mean that the yellow exclamation mark isn't a problem?
    We have about 40 free IP addresses at present. We have three main switches (the Server, ITsuite and WAPS are all connected to one of the three - there are a couple of little switches elsewhere but only the odd machine is connected)
    and I have plugged a laptop in to all of them with no issues - BUT then again the issues are intermittent so how would I know they were OK!
    I haven't heard any issues re the teacher's laptops - but they have reserved IPs
    Windows can mis-report network/internet connectivity time to time, but if you're getting this problem on 80% of devices I would say the issue looks like a DNS/DHCP server database problem to me.

    If you try releasing and re-issuing an IP as others have suggested and this fails, you may end up with a 169.x.x.x address. If this is the case, try setting a static IP address. If this works, then I would say your switches are fine and that you should take a look at DHCP server closely.

  2. #17

    m25man's Avatar
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    Quote Originally Posted by witch View Post
    unfortunately 24 of the 33 IT suite computers which intermittently suffer, are hardwired to the same switch as the DHCP server, as are four of the WAPS
    That sentence would bring me straight back to that particular switch then... or something connected to it!

    What make/model is it? Is it Manageable? Is it really suited to the position it occupies in the topology?
    You say you have 4 WAPs plugged in to it, each WAP port will have many MAC addresses associated with it remember each WAP link is effectively a Switch uplink some budget switches are equipped with CPU's RAM and the processing power of calculator they can struggle with just the 24 clients that they have ports to service show them 30+ MAC addresses on several ports and they fall over.
    Remember cheap switches have a place (at the very end of the cable run)!
    Any switch that has to service a busy interchange must be capable of coping with the traffic thrown at it, you should set up a test node at the very furthest edge of the network and ping -t the DHCP server whilst that is going on fire up a few of the troublesome machines what happens to the latency over the ping path?
    Last edited by m25man; 23rd April 2012 at 09:43 AM. Reason: typo

  3. #18

    witch's Avatar
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    We have 4 main switches in the IT suite cabinet:
    3 x Level One GSW 3456
    1 x D Link Web Smart DGS-1210-24
    All Gigabit switches
    I have just spent goodness knows how long moving all the IT suite computers to the newest switch.(the D Link)
    No go - still had a random three or four not picking up an IP.

    Googling tells me that the D Link can be managed but I still can't see how
    Last edited by witch; 23rd April 2012 at 12:11 PM.

  4. #19
    bandgeekmafia78's Avatar
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    We had a similar problem that turned out to be a faulty switch. It might be worth taking one of the troublesome PCs to another area of the school I(i.e. so that it's networked to another comms cabinet) and see if it picks up an IP there. That will at least narrow down your problems to a network issue rather than a network card issue.

  5. #20

    Michael's Avatar
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    I have to be honest - Level One networking equipment from my experience are absolute junk, poor quality and just generally not worth it. D-Link aren't far behind either, but it's interesting you're still having a few problems, even with the newest D-Link switch.

    Looking on their website, I cannot find a Level One GSW 3456. Could you double check this?

  6. #21

    witch's Avatar
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    Can't spell - GSW2456 - sorry
    I know the switches arent good but I didnt choose them.
    I can't move a troublesome PC very easily because it isnt always the same machines - it can be one of 70 at any time. We only have one main cabinet - all things are connected to it. We have a small switch in one part of the school connected to the main cab by fibre and that is about it.
    When one PC couldnt get an IP I did move the connection to another switch and it worked, but a few days later the same thing happened.
    I have just been handed a list of 9 netbooks that "can't get on the internet" which probably means they were working locally and didnt know it.
    But I have gone and picked up one and it picked up an IP fine....
    Last edited by witch; 23rd April 2012 at 12:38 PM.

  7. #22

    SYNACK's Avatar
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    D-Link are excrement, just finnished pulling most of them out and they can cause all sorts of interesting issues like screwing up multicasts and randomly dropping frames/links when they get older.

    To manage is easy enough, the D-Link will have a default IP, you could set a station to that subnet and go to the webpage directly or possibly use the smartconsole utility to find it on the network from here: D-Link Support Resources

    It may be a case that the D-Link is choking the DHCP requests due to its partial managment and you may do better if you could connect the DHCP server into one of the unmanaged switches as this can't get in the way of the traffic. The D-Link is only partially managed but I have seen weird stuff like this happen on that level of their switches.

  8. #23

    Michael's Avatar
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    If you haven't already, try switching the switches off and remove the plug for up to 60 seconds. This will drain any existing power left in the switches, then power up as normal.

    I still can't see the GSW-2456 but there is a GSW-2457. This may have replaced your model possibly.

    Do you use a single DHCP range and what IP range is it? Class C for example.

  9. #24

    witch's Avatar
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    How do I find out the D Link's default IP? It certainly isnt obvious from my DHCP?
    i don't know how the switches are configured and I cannot see very well as the cables are so tight and the cab is way above my head - I should imagine they are cascaded but that is merely a guess.
    Cant remember the IP range off the top of my head but it is something like 10.44.52.100 - 10.44.52.300
    I think
    have switched the switches off for a couple of minutes. No difference - the netbooks failed after this as did the computer I am trying to image.
    It seems unlikely it is the D Link because it is new and only has a few things on it It was bought because we ran out of space (I didnt choose it) and so currently it has one WAP and about 5 of the IT suite connected.

  10. #25

    Michael's Avatar
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    From what you're saying, it does look more and more like a DHCP Server database corruption.

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    MicrosoftTechy's Avatar
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    Maybe database corruption, re install the DHCP service

  12. #27

    witch's Avatar
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    I would really like it to be a DHCP issue as we are having a shiny shiny new 2008R2 server at half term. But I really need to make sure that it ISN'T a switch or network issue - it would be awful if we got a new server and the problems persisted.

  13. #28

    Michael's Avatar
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    Try rebuilding the DHCP database as follows.

  14. #29

    witch's Avatar
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    Quote Originally Posted by Michael View Post
    Try rebuilding the DHCP database as follows.
    But if the database is corrupt, and you just save it and then restore it, won't you restore the problem as well? How long would it take?
    Anyway, I wouldnt dare do this on my own - I just know that it wouldnt restore or something. Thanks for the help though. The other issue is that I cannot take the system down really.
    What about reserved IPs? Presumably these would have to be recreated? If so, bit of an issue as most staff laptops are on reserved IPs so that they are allowed through the firewall/trust to access SIMS on the admin network
    *don't mean to sound so negative - I just can't see a way around this issue
    Last edited by witch; 24th April 2012 at 08:16 AM.

  15. #30

    plexer's Avatar
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    If you export the dhcp db settings as a txt file you can use the xls file on my website to create the netsh commands needed to insert the reservations into the new db.

    Then if you create a new blank dhcp server setup that would avoid there being any db corruption transfer possibility.

    Ben

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