At its core, the Internet is an interconnected fabric of separate networks. Each network which makes up the Internet is operated independently and only interconnects with other networks in clearly defined places.

For smaller networks like your home, the interaction between your network and the rest of the Internet is usually pretty simple: you buy an Internet service plan from an ISP (Internet Service Provider), they give you some kind of hand-off through something like a DSL or cable modem, and give you access to “the entire Internet”. Your router (which is likely also a WiFi access point and Ethernet switch) then only needs to know about two things; your local computers and devices are on one side, and the ENTIRE Internet is on the other side of that network link given to you by your ISP.

For most people, that’s the extent of what’s needed to be understood about how the Internet works. Pick the best ISP, buy a connection from them, and attach computers needing access to the Internet. And that’s fine, as long as you’re happy with only having one Internet connection from one vendor, who will lend you some arbitrary IP address(es) for the extend of your service agreement, but that starts not being good enough when you don’t want to be beholden to a single ISP or a single connection for your connectivity to the Internet.

That also isn’t good enough if you are an Internet Service Provider so you are literally a part of the Internet. You can’t assume that the entire Internet is that way when half of the Internet is actually in the other direction.

This is when you really have to start thinking about the Internet and treating the Internet as a very large mesh of independent connected organizations instead of an abstract cloud icon on the edge of your local network map.