[PeterisP]

It doesn't really imply harming the DNS, but rather the actual core infrastructure - network connections.

If they disable/crack/overwhelm the major routers connecting different ISPs (e.g. zero-days or backdoors for router OSes, BGP attacks with cooperation or cracked credentials from some major ISP insiders), then the internet is not going to work for you because your ISP will be simply unable to route your data to where you want.

Are there any good reasons to believe that all major router models don't have backdoors inserted by state actors, either by bribing an insider engineer ten years ago, or even having a manufacturer of some secondary on-board chip (that has direct memory access) insert a hardware backdoor ? We've detected such attempts before, there's all reason to expect that there are some of them active and undetected right now.