Why was the speed cut on the debian internet gateway?

Question

Computer networks

The speed at the gateway is completely according to the tariff. Until now, the computer had an identical speed. But in an instant, everything was gone. According to the speedtest - 9 Mbps out of 100. From Yandex it downloads 500 kilobytes, although everything is ok on the server. I saw that the light on the network card switched to 10 Mbit mode. I set it to 1000 Mbps using ethtool, the light is now on, but the local speed has not changed. Ping became unstable over the wire. Changed wires.

Answer 1

Since replacing the cable did not help, replace the network card.
Also, check the other end of the cable to see if that port is working properly.