10000 routers are connected in a network, we have various connections at routers, not just one, so no need to go in a linear fashion going through every router. Take example of the Internet There's like no limit to how many routers are there but still we can find them, send and receive data from them, Like the thread in the link mentioned the advanced and complex mechanisms of finding shortest paths bound the path length to 30 -35 routers, i.e, we can reach any router/server by making approx 30-35 routers max(in general).