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Table of Contents
Switching Loop
Switching loops are caused when ethernet cables get plugged in willy-nilly-wack-a-mole. That's technical speak for randomly.
The #1 symptom is network connections (like phones, sound systems, etc..) work intermittently, freezing/halting/breaking up every few seconds to minutes as the switches involved reset because of insane load.
Example of Switch Loop and Fix
In this video, a witch loop is created because the top switch is connected to the router as well asffmpeg -i SwitchLoop1.mp4 Switchloop3.mp4 the switch below. Removing either redundant ethernet cable and connection will solve the issue. At the beginning of the video, notice how often and consistent the switch lights are. The redundant cable is unplugged and the network traffic returns to normal.
A proper network design can be simple or complex, the trick is that it is hierarchical and not more than one path. Yes, there are exceptions using special equipment and configuration, but if you are reading this page, you will probably not be using multi-path link aggregation or OSPF routers. You would already know about switch loops.
Finding Switch Loops
This might be simple, just examining most network cables for cross connects may show you 2 or three cables between switches. In the video above, there is a 3rd switch off camera that both bottom switches are plugged into, as well as a cross connect. Initial level: try unplugging cables one at a time and waiting for 30-90 seconds to see if the blinky light chaos stops and your internet connections as well as device to device connections improve.
It could be so bad that you decide that it's time to clean up and label cables, this is a good time to unplug everything, and plug them in one by one watching for that tell-tale switch blinking light chaos.
Sometimes, the problem is created by a remote switch or device (like a switch or router/firewall/WiFi access point) under a desk or stuck in a ceiling that is part of the cross-connect. These might be harder to find.
And probably our best advice: Hire a professional. If you are having such problems, a little technology tune-up from a professional can be the start of a wonderful mutually beneficial relationship.