Routers can be manually configured to advertise abbreviated versions of reachable addresses, which are called summary addresses. By aggregating many routes into one summary address, route computation and lookup can be made more efficient. If packets arrive at the router as a result of the summary address but have no actual route (as a result of the summary address covering more address space than is actually used), the packets are discarded.
For instructions on managing summary addresses, see Managing IP Summary Addresses.