Single Ethernet Cable Crashes Network?

By don.schult ·
I got to work on Monday morning to discover the entire network at one of our branches had crashed. After doing the usual trouble-shooting I still could not find tha cause. Eventually I saw an ethernet fly-lead cable plugged into two seperate ethernet points along one wall, effectively creating a loop in the network connection. When I unplugged the cable, the network started functioning again. Can anyone explain what was happening? I've never seen this before.

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by .Martin. In reply to Single Ethernet Cable Cra ...

In my non-technical wisdom, i believe this is what it may have been:

because the server was effectively connected to itself in a loop, the server could send out a message, but when it received it, because it was using a patch cable not a crossover, it receive a jumbled message, confusing it sending it spiraling.

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Switching/Bridging Loop

by NetMan1958 In reply to Single Ethernet Cable Cra ...

I suspect you had a switching/bridging loop which wreaks havoc on a network.

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Switching/Bridging Loop

by don.schult In reply to Switching/Bridging Loop

Thanks for the reply. This is exactly what happened

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Reoccurring fault

by mjd420nova In reply to Single Ethernet Cable Cra ...

I've seen this happen before when an unskilled "IT" person made a wrong connection. It causes the network server to "busy: itself trying to get the jumbled message resent and puts itself into a loop that holds off all other traffic until it can resolve the fault. I came to find out later that it was done by mistake but this could have been an attempt by a prankster to take down the network. Actually was pretty effective and would have been overlooked by all but a true diagnostic tech who knew how to identify the cables and the connectors on the patch panel. One cure to prevent this from happening in the future would be to seperate the panels from each other that would make a cross link like this very apparent. Cable and jack labels would also make it a little simpler to trace these faults. A patch cable diagram would also help but it might just sound like busy work to some but is really important that things get identified.

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Reoccuring fault

by don.schult In reply to Reoccurring fault

Thanks for the reply. The actual patch cable was not connected in the server room but actually into two LAN sockets in one of the department's offices so it wasn't easily identifiable and pretty confusing until I "stumbled" upon it...

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And the light went on

by mjd420nova In reply to Reoccuring fault

In the Navy they used to call that type of troubleshooting "easter egging". Looking for something that is out of place or doesn't look right. Actually took them a while to find the right approach of inserting faults without actually doing any damage to other components. We used to use tape over a connection in a plugin card or tape between contacts on a relay.

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