Troubleshooting network issues; General inquiry

Question

I work as a junior network admin at an ISP and I would like your help in resolving an issue whose cause is not readily apparent. Rn I am trying to troubleshoot a case where a switch interface randomly goes down for about 3-5 and then right back up. It is a poe switch and the connected device is a wireless point to point antenna getting power from the switch itself.

PROBLEM SUMMARIZED

1. switch interface goes down
2. switch interface goes back up and connectivity resumes as normal
3. autonegotiation sometimes results in 100mbit full duplex but is mostly 1gbit full duplex

Now the problem can be one of many things: nic of the point to point antenna, cable, switch interface, the switch itself (correct if I'm wrong and please add other possible causes). Is there a way I can tell which of the above is to blame without having to physically go to the location and start changing stuff? What errors should I be looking for in each case? Obviously, an on-site inspection might be of help but it is not certain and requires people

For the record, I have looked at the statistics provided by the switch but the only errors I get in this case are fifo errors which increment when the interface autonegotiates to 100mbit and cannot support all traffic passing through it. But that is expected. I have not gone into much detail about the specific equipment used because I would like a more general approach.

Answer 1

There is no common cause for that problem. Possible problems include cabling, especially with PoE, a defective device or switch port.

autonegotiation sometimes results in 100mbit full duplex but is mostly 1gbit full duplex

That's a near giveaway for a cable problem. Check grade, termination, length, gauge for PoE, and indicated error rates (on both sides and especially in 1000BASE-T mode).