A default route is a special route that matches all packet destinations.  Default routes can be particularly useful when only one physical path exists from one part of the network to another, and in cases for which one enterprise router provides connectivity to the Internet for that enterprise.

Default Routes Using the ip route Command
When a router knows about at least one default route, the router notes that route with an asterisk in the routing table.  If a router learns about multiple default routes – either through static configuration or from routing protocols – the router notes each default route with an asterisk in the routing table.  The router chooses the best default route, noting that choice as the gateway of last resort.

Default Routes Using the ip default-network Command
ip default-network lists a classful IP network as its parameter, telling the router to use the routing details of the route for that classful network as the forwarding details for a default route.


Default Route Summary
- Default static routes can be statically configured using the ip route 0.0.0.0 0.0.0.0 next-hope-address or the ip default-network net-number command.

- When a router only matches a packet with the default route, that router uses the forwarding details listed in the gateway of last resort line.  Default routes are used according to the rules of classless or classful routing.