Routing TCP/IP, Volume I (CCIE Professional Development)

Fundamentals of Default Routes

When a router is connected to the Internet, a default route is immensely useful. Without a default, the router will have to have a route entry for every destination address reachable over the Internet. As of this writing, such a routing table consists of more than 55,000 entries. With a default route, the router need only know about the destinations internal to its own administrative system. The default route will forward packets destined for any other address to the Internet service provider. In dealing with large routing tables, topology changes are an even bigger concern than the demands on memory. In a large internetwork, topology changes will occur more frequently, resulting in increased system activity to ...