Ask HN: What does a fatal attack on the internet look like?

I've always been worried about the fragility of infrastructure in the scenario of a real war. I'm under the impression that it wouldn't be too hard for e.g. Russia to take down the European power grid with a cyber attack. In the last couple of years Russia has been spending effort to disconnect from the global internet, and thus the following question naturally arises: "What does a fatal attack on the global internet look like and how feasible is it"?