It is extremely improbable that the internet will shut off completely. The network infrastructure comprises off numerous redundant connections. Therefore, bringing the whole internet inadvertently or accidentally very difficult. Internet traffic is robust, with the ability to proactively reroute around every issue. There’s not a massive on/off switch. There really is no appropriate way to switch off the internet. It is a diverse platform with many distinct networks connecting to one another. So, Internet shutdown is not feasible.
The internet is a huge dispersed network over which no single entity has complete control. An effort would most probably result in the internet fragmentation (broken down into several networks). This hasn’t been undertaken to our knowledge, but it’s reasonable to assume that some political actors have invested substantial resources in developing internet death switches.
It is however possible to shut down a certain website or online media platform. It’ll require high level of coding and hacking knowledge if done from the user end. Moreover, from the owner’s end shutting down their sites is fairly possible. Reasons for such shut down could be anything ranging from low traffic to heavy internet load.
Closing down the network would be comparable to closing down all of the world’s highways, an example I’ll use later.
An attacker may disrupt a large amount of internet traffic by cutting several of the main fiber-optic cables that serve as the internet’s core with a bulldozer and/or submarines. To successfully shut down the network, all networks (wired and wireless) throughout the world needs disruption. This would need a large, devastating catastrophe, such as the destruction of much of the planet by a meteor. If this occurs, whether or not internet is entirely offline will be the least of our concerns.