Suppose IP routers learned about IP networks and subnets the way Ethernet learning bridges learn about hosts: by noting the appearance of new ones and the interface by which they arrive. Compare this with existing distance-vector router learning

(a) for a leaf site with a single attachment to the Internet, and

(b) for internal use at an organization that did not connect to the Internet

Assume that routers only receive new-network notices from other routers, and that the originating routers receive their IP network information via configuration