I saw a map of undersea internet cables the other day and it’s crazy how many branches there are. It got me wondering - if I’m (based in the UK) playing an online game from someone in Japan for example, how is the route worked out? Does my ISP know that to get to place X, the data has to be routed via cable 1, cable 2 etc. but to get to place Z it needs to go via cable 3, 4?
So at a basic level, well only talk about routers. Every computer/server on a network has an address. When your computer wants to talk to another it attaches the IP address of the destination computer to every piece of data that leaves your computer saying where that data wants to go.
It goes from your computer to your router which has a table of the addresses it knows (your network at your house) and then an address of another router that it sends everything that it doesn’t know.
It does this a few times before your data gets to a router that says “oh, I know a router that knows someone that knows where that is” and it sends it that way. Until it reaches a router that knows the specific computer to send it to.