Don’t plug a cable tester into a switch. Our team just spent the entire day diagnosing this
The network symptoms were increased latency, ping times to wired devices should be under 1ms but they fluctuated between 6-10ms. Some network ports wouldn’t connect at their full speed and duplex when set to auto, don’t know if this is related or just more bad cabling.
The remote method to figure out what’s wrong was to disable 1 port at a time and see if the network improves.
There were a few hints; port 9 would blink on intermittently and go back off. I don’t know if the PoE was trying to power up the cable tester or if the device still had battery powering it.
Label your ports so you know if something is missing
Lock the door to the DC; only allow those inside that have gone through the “don’t Fk with Shit” training
Troubleshooting step 1 is disable all ports that are not in use, narrow down the problem by dis/enabling half the remaining ports.
Don’t hire the cheapest wiring contractor; you get what you pay for
Ubiquiti Cloudkey made this fairly easy to troubleshoot remotely. if this was a “dumb” system we may never have found the root cause