I'm needing some help proving that it's ATT's fault.

Hey everyone.

I manage a couple Cisco ISR 4000 series routers that are connected to ATT's ciena service switches that they use to provide their ASE service.

My customer's internet was upgraded, so I went to go double check the duplex settings.

They were 100 megabit/half duplex that were gained from autonegotiation.

Since I was directed to set the settings to 1000 megabit full duplex, I did. All of a sudden, traffic on that interface ground to a halt, and I gained a whole host of network problems. So I set it back to what it was, thinking it was a duplex mismatch that caused the problem, and the traffic was fine.

I thought that ATT had statically set their duplex settings, which was why my router interface had so many issues when I changed the settings. But when I reached out to the customers IT department, they refused to do anything about it and said I was uninformed and they are refusing to open up a ticket with ATT.

Am I utterly wrong? Is there something I'm missing?

If not, how can I prove that ATT statically set their duplex settings?