Simple mechanisms for introducing hierarchy into the interdomain routing system, making it practical to route a truly large Internet, are described. It is shown that addresses need to be assigned along network topological lines to maximise the reduction in routing overhead. Simplifying the mechanisms for changing hot addresses makes it possible to renumber a network so that it has a topologically significant address when the site changes position within the routing system. These proposals make it possible to significantly increase the utilization of addresses and extend the time the Internet can use the Internet Protocol (IP) Version 4. >