Network Loop

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What is the best way to diagnose a network loop on a switch?
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Commented:
If you suspect Loop, the first thing I would do is inspct wall jacks for somone plugging in a small 4 or 8 Port Netgear HUB, or similar.  That would cause it a loop.
If you are not running Spanning-Tree Protocol there are a few applications out there that you can use that help you identify a loop in your network like solarwinds or capsa network analyzer. Other then that sometimes it takes good ole fashioned detective work. Identifying all your cable drops and switch uplinks.

You can enable STP and put your switch ports that you know are not uplinks to other switches in a bpdu block state this should stop your loop as well. This will disable the interface if it gets a bpdu. Simply put a bpdu is what switches send to each other to say hey I am a switch.
Commented:
Network Sniffer will help you. e.g. snorby
Top Expert 2014
Commented:
Physically look at the switches... if there's a loop you'll usually see solid lights rather than flashing activity lights when a storm is occuring.

A quick way to tell if that's the case is to remove the uplink to a switch and see if the lights settle down and flicker as usual.  If they do, it's usually a storm which indicates a loop.

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