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Network connectivity keeps dropping out on this switch...

Posted on 2008-10-01
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Last Modified: 2012-05-05
We've got a rack of 3coms, and one in particular (THAT I HAVE ALREADY SWAPPED OUT), seems to be OK for about 10 minutes or so (judging by the Windows 2003 Server DHCP logs), and then nothing.  No connectivity after a few minutes or so.  The LEDs on the switch don't seem to suggest anything weird.

Strangest part is, the computers CANNOT receive an IP when connected through this switch, but can connect when given a static IP.  But I swapped the switch out for another and they all had received dynamic IPs, but now 20 mins later, they are unable to talk to anything...

Any ideas????
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Question by:tru504187211
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by:ccns
ID: 22620370
I would suggest changing the cable that links the switches together ? possible that this could be the issues unless the server is also plugged in to the failing switch?
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by:tru504187211
ID: 22620409
Done that as well...still nothing.
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by:ccns
ID: 22620423
rack of 3coms, do they connect into some sort of backbone thing at the rear of the switch or is it just a rack situation. switches one above the other connected via cable/fibre
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by:tru504187211
ID: 22620447
Yes, the network is a star with a 3com 4200g as the backbone.  All of the other switches com off of here in a star pattern (4200g being the center).
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by:ccns
ID: 22620465
can you log onto the backbone 4200g and possibly look at the status of the port where the trouble switch is plugged into. see if it comes up with errors etc? you have already changed cables.. what about ports?
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by:tru504187211
ID: 22750447
Yes, I've logged into the 4200 backbone and it reports all 28 ports are either open or OK.  NOW, mutliple switches are dropping off with no warning.  Only similarity, is that they are all gigabit switches that are failing...

Also, scrap that idea about static IP's working.  I've now verified that to be false...

Again, the switches are fine for a while after they are power cycled.  Wireshark is not coming up with anything much except all different clients asking who belongs to this or that IP.  Every once in a while, one machine hammers the network with broadcasts, but I cannot figure that one out yet, but it does not seem to force any switches offline at that time, that I can tell...
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tru504187211 earned 0 total points
ID: 22805190
Solution turned out to unplug ONE cable...someone had thrown a loop in the network from a network cable that used to be connected to a computer...

Thanks!
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