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?
Yes, the packet passes through routers at each stage and they direct the packet to the ‘closest’ path based on its destination, until the final router has the destination on its network. This can happen a few times (for something in your ISP network), or 10-30+ times for something further away.