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Wireless Networks Thread, Machines dropping like flies in Technical; Hi everyone (just joined) I'm having an issue on my network (2x win2k3 servers with xp & win2k workstations), basically ...
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    Machines dropping like flies

    Hi everyone (just joined)
    I'm having an issue on my network (2x win2k3 servers with xp & win2k workstations), basically one by one machines are failing to connect to the network and the problem seems to be spreading. On some they will be 'limited or no connectivity' and will not be able to aquire a network address, if I give them a valid static IP the limited connectivity alert goes (obviously) but they will not be able to contact the domain or any machines. On others they will not logon to the domain so I log in locally and give them a static IP, they can now ping the domain controller but cannot see the domain.
    This has been going on for a few days but seems to be getting worse, I have given the servers a reboot this morning in an attempt to kickstart the dhcp and dns services but no joy.

    I've now checked my even viewer and have this error 'The DNS server has encountered a critical error from the active directory.....' . I've opened up the AD and had a poke aound but it doesn't look out of order and isn't presenting any problems.
    Any help would be much much appreciated!
    Thanks

    Dave

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    SYNACK's Avatar
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    What event ID or IDs do the errors have in the event viewer, that may help us narrow it down. It is possible that the DNS zone files stored in AD have become corrupted in which case DNS would need to be setup again.

    Are you able to open the DNS app and see which hosts are allocated names?

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    contink's Avatar
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    I'd be looking for output from DCDIAG and NETDIAG... good places to start for diagnostics on this

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    Check the switches... if they are flickering like mad (if you have the activity LED's enabled) then try rebooting them. If there's a dodgey link somewhere causing a loop in the switches then broadcast packets could be building up and eventually... cause this.

    Shot in the dark, but it's a shot!

    If that fails, try linking a machine/laptop directly into the switch the server is connected to, or even better (if you can take the server down) do a crossover cable to your dhcp/dns server and see if it gets anything.

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    Hi

    I had this a while back at one school and it turned out to be a switch playing up because a network card in a old printer had gone mad and was broadcasting so much rubbish that it made the switches crash.

    What I would do is think is this the entire network or just one branch.

    Now take a broken machine and plug it into the switch that the server is plugged into. If this works then the client and the server must me working.
    Try releasing and renewing and see if you get anything in the evenyid on the server or the client.

    Now slowly work your way back to the original location one switch at a time. I had to resort to turning off all switches and test then turn one on and test till I found the switch. I changed it for a more modern one that would cut off a port if it was being bombarded and that stopped working so it was easy to identify.

    I have also seen it when computers are plugged into a new gig switch and the card will stop working correctly. I had to update the driver to the latest and still it does it. But if you plug the client into a 10/100 switch it will work ok. Then I put them back and they are ok for x time sometimes for months and months.

    Lastly I have had a dhcp server at one place that would startup ok but for some reason the dhcp service had to be restarted after each reboot. I never worked out why.

    I dont know if any of this helps any but good luck.

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    Thanks for all your advice guys, initially I did think a switch as the light are blinking in an odd fashion. The problem is the affected machines seem to be only plugged into my secondary cab at the other end of the building from my server. So plugging the affected clients into the first switch then the second etc. is going to be difficult. I think I'll try popping round with a laptop first. Before that I'll replace the second switch in my network (suspicious of it for some reason).

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    Netdiag & dcdiag seems to error :S
    Last edited by dave20046; 12th January 2009 at 09:03 AM.

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    Machines Dropping

    We have had this happen to us, we thought it was a faulty switch also, we found out it was the DNS that was playing up. We corrected the problem by deleting and rebuilding the forward and reverse lookup zones. Things went fine for a couple of months, but it came back, in the end we had to rebuild the whole of the dns from scratch and repair part of the AD (with the help of microsoft). I would not rule out DNS and advise you check it and test it properly it can be costly getting microsoft in (fortunatley I had the sense to continue our server maintenance contract, which my boss now realises was a good move as he saw it as an expense which we hardly used, so we hadnt got to find the repair bill)

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    tmcd35's Avatar
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    A quick note on DNS, just had some issues here, you might want to check the scavange rules are set up correctly and DNS is actually getting rid of stale enteries. Also double check DHCP is always updating DNS records.

    Had the problem here were DNS was not deleting old records and DHCP was not updating DNS. End result - ping/nslookup returned the wrong IP, made VNC quite interesting!

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    Thanks, I'm hoping it won't come to having to rebuild the dns !

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    Right I've tested each switch with my laptop
    1st switch (that the servers are plugged into): working, getting and IP and able to contact server
    2nd switch: same
    3rd switch (via fibre link to 1st): not working, 'limited or no connectivity', can't ping the server.

    I then swapped the 3rd and fourth switches round so the switch I'd just tested was at the very bottom.

    New 3rd switch: working

    4th switch: after plugging my laptop into a fair few random locations on the switch it appears to be not working on any port but the left most two; ports 1 & 25.

    What do you guys think? Reckon it's safe to say it's a knackered switch. I'm extremely dubious of ordering things unnecesarily as the IT budget in this school has already been exceeded.

    Thanks

    Dave
    Last edited by dave20046; 12th January 2009 at 09:33 AM.

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    Event numbers in my DNS log are 4004 & 4015

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    I'm starting to think it may well be the DNS and not the switches as I've just visited a classroom with 4 machines in. 1 machine is patched into switch 4 and the other 3 machines are plugged into a miniswitch that was patched into switch 4. I just patched the miniswitch into switch 3 but there was no change so I unplugged the uplink to the mini switch and put it in the back of the machine, that machine worked. I plugged the uplink back into the miniswitch and the machine back into the miniswitch and now that machine works but none of the others on the 5 port switch will.

    However saying that the port lights on the switches are all flickering in unison pretty rapidly.
    Last edited by dave20046; 12th January 2009 at 10:13 AM.

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    We had a smiler problem with network being flooded out. tunes out it was a dodgy network printer adapter causing the problem.

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