O'Reilly logo
  • muha med thinks this is interesting:

This means that the router will use the default route when trying to reach this device. If there is no default route, it will drop the packets. Note that this assumes that we are using classless routing. If we had enabled classful routing on the router, then, if it has a route for any subnet of the classful network, it will also have an entry for the entire network. In this case the classful network would be 172.15.0.0/16.

From

Cover of Cisco IOS Cookbook, 2nd Edition

Note

Classful Vs. Classless routing output