IP Forwarding by Matching the Most Specific Route
Any router’s IP routing process requires that the router compare the destination IP address of each packet with the existing contents of that router’s IP routing table. Often, only one route matches a particular destination address. However, in some cases, a particular destination address matches more than one of the router’s routes.
The following CCENT and CCNA features can create overlapping subnets:
Manual route summarization ...