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Weird network problems > time outs & DHCP not working correctly !?

Posted on 2013-12-28
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Last Modified: 2014-01-04
When I try to  ping my servers then I'm getting sometimes immediately a ping reply and sometimes time outs ... the patterns often seem to be ping reply, timeout, ping reply, timeout etc. This happens when pinging anyone of my servers.

Any ideas why?

Also, most of my PCs are not getting IP addresses from the DHCP servers ... how could I find out why that's the case??

Thanks a lot!
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Question by:Xeronimo
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by:John Hurst
ID: 39743603
The first thing I would try is to restart the Server, make sure DHCP started and is running properly and then test again.

If the Server is working well, take a good PC to a switch very near the server and try it. You could have a  problem in the switch network that would take some process of elimination to determine where.

.... Thinkpads_User
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by:John Hurst
ID: 39743613
I assume from your question this used to work. Nonetheless, make sure (somehow) DHCP scope did not change and that you have enough DHCP addresses to hand out.

.... Thinkpads_User
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Author Comment

by:Xeronimo
ID: 39743665
Hi,

Yes, all of this worked fine until an electric blackout recently ...  the DHCP scope is correct and it also has enough free addresses.

It seems though that one or more switches could be the problem, or part of it. I'm able to ping one server correctly that's very close to me (only one switch, let's call it switch A), but not servers further away. What's weird though is that I sometimes get a ping timeout on switch A as well, although much less ... only 1 in 10 or something like that. The others give me 1 timeout for each successful ping ...
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by:John Hurst
ID: 39743671
So then given your further explanation above, you appear to have a network problem, and the power outage (or the surge on power back) may have damaged a switch. I have seen that before. So you need to get one or two new switches and begin replacing and testing suspect switches.

.... Thinkpads_User
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by:Mahesh
ID: 39743919
This is definitely switch problem (malfunctioning).
You can reboot the switch (probably rebuild its configuration) where DHCP server is connected and test other computers on the same switch
Post switch reboot, the client computers on the same switch should get DHCP lease hopefully

Mahesh
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Expert Comment

by:ChiefIT
ID: 39745625
Make sure the duplex settings on the switches and routers are not mismatched. Use Auto negotiate.

Your DHCP problem may be a different problem. It might stem from having a rogue DHCP server on the network. Use your servers for DHCP and make sure the switches/routers are not providing DHCP. There is a reason for the servers.
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Accepted Solution

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Xeronimo earned 0 total points
ID: 39745842
Ok, I've finally found the problem ... for some reason the link aggregation didn't work correctly anymore and was creating a loop on the switch, thus flooding the network with broadcasts.

I've corrected this and now everything works fine again, including the DHCP!
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Author Closing Comment

by:Xeronimo
ID: 39755811
I solved it myself
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