@HariDDoS protection is not just a switch, or one component. It’s a collection of different and often disparate technologies that when grouped together form the basis of a combined toolset that can be used in defence.
Typically these consist of IDS (Instrusion Detection System) and IPS (Intrusion Prevention System) components that detect irregularities in network traffic, and will take decisive action based on predefined rulesets, or in the case of more modern systems, AI and ML.
Traditional “traffic shaping” technology is also deployed, so if an attack cannot be easily identified as malicious, the bandwidth available to that connection is severely limited to nothing more than a trickle rather than a full flow.
Years ago, ISP’s used traffic shaping (also called “policers”) as an effective means of stopping applications such as BearShare, eDonkey, Napster, and other P2P based sharing systems from functioning correctly - essentially reducing the “appeal” of distributing and seeding illegal downloads. This was essentially the ISP’s way of saying “stop what you are doing please” without actually pulling the plug.
These days, DDoS attacks are designed to overwhelm - not assume control of - webservers and other public facing components. It’s rare for small entities to be attacked unless there is some form of political agenda driven by your site or product. A classic example is governmental institutions or lawmakers who effectively are classed as “enforcers” and those who disagree are effectively making a statement in the form of Denial of Service.
DDoS protection is effectively the responsibility of the hosting provider, but you shouldn’t just assume that they will protect you or your site. Their responsibility stops at their infrastructure, so it’s then up to you too decide how you full the gap in between your host and the website.
Typically, you’d leverage something like Imunify360 which you can get for Plesk (and something I’d strongly recommend) but it’s not free, and is a paid (not expensive per month) subscription. If you want to use VirtualMin then there are a variety of tools readily available out of the box such as firewalls and fail2ban.