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3COM 4500 - Network Loops Kill LAN

3COM 4500 - Network Loops Kill LAN

3COM 4500 - Network Loops Kill LAN

Greetings all,

My organisation uses 3COM 4500 LAN switches at the office I'm located.  We've had two incidents where a network loop has brought the whole LAN to its knees - in one case, a simple 8-port switch was connected to the LAN and somebody "looped" a cable by mistake and in another case, an RJ-45 jack was accidentally smashed up.  In both cases, LAN traffic ground to a halt - pings were intermittent and most applications stopped responding.

My understanding is that STP should isolate ports in such instances, but I've not been able to find information to confirm this 100%.  Are there any additional configs I can apply to our LAN switches to prevent such incidents in future?

Thanks for any info,


RE: 3COM 4500 - Network Loops Kill LAN

enable STP globally on the switch and "stp edged-port enable" on all ethernetports and you'll do fine


RE: 3COM 4500 - Network Loops Kill LAN

STP will work on all ports configured with STP. So lets say you take port 1 of your 4500 switch and plug it into port 2 of the 4500, since both ports have stp configured, STP will take over and shut one down.  But, if you go from port 1 to a hub then back to port 2 on your 4500....stp wont work.  The moment that traffic passes through the hub, there are no stp instructions, therefore causing the loop.  If you have a voip telephone system, the PC port on the back of a voip phone can also be a culprit.  I have seen dumbasses plug both the ethernet port and the pc port into thier lan in the past. hope this helps

RE: 3COM 4500 - Network Loops Kill LAN

Thanks for the info, bio777 and cknipe.  I have got a couple of spare 4500's - I will set up a little lab and try various configurations.

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