Let's say you have one or more IP routes that you don't want appearing in a router's IP routing table. The reason might be for security or for router performance, as a couple of examples. With OSPF, there are three primary ways to accomplish this route filtering:
This video discusses these three approaches, and it demonstrates the configuration of two of these approaches (because redistribution is a topic unto itself).
Enjoy the video!
Kevin Wallace, CCIEx2 (R/S and Collaboration) #7945