We have two buildings connected by a 30m network cable with a switch on either end. Last week we upgraded some old equipment to support gigabit speeds. One of the two switches was an old 10/100 switch so we upgraded it. Right away the connection between the buildings stopped working.
What we've tried
Plug the old 10/100 switch back in in-between the long run and new gigabit switch. This works, but obviously destroys the upgrade.
The cable was a Cat5e that was installed 4 years ago. It's within the spec, but we thought it might be low quality / damaged, so we ran a brand new Cat7 cable. Same exact behavior as the old Cat5e (ie, it works on the 10/100 switch but not the gigabit switch).
We tried using different gigabit switches on both sides of the cable. Same behavior.
We plugged one end of the cable directly into a gigabit ethernet computer and the other end into the new switch. This worked fine, leading us to suspect there might be an Auto-MDI negotiation problem. We rewired the new Cat7 to be a crossover cable to avoid the need for Auto-MDI. Same behavior.
We connected both of the new switches using a short (2m) patch and cross cables. The connection works perfectly with either one.
What other troubleshooting options do we have at this point?
- Old 10/100 switch - TP-Link
- New gigabit switch - TP-Link
TL-SG1008D(produced in 2018)
- Old gigabit switch in building 2 - TP-Link
TL-SG1008D(produced in 2016)
- Replacement gigabit switches we used to test - DLink