CCNP exam success, particularly on the BSCI exam, demands you understand the details of route summarization. This skill not only requires that you have a comfort level with binary conversions, but you have to know how and where to apply route summarization with each individual protocol. You also have to know the "side effects" of route summarization. With OSPF, there will actually be an extra interface created at the point of summarization, and this catches a lot of CCNP candidates by surprise. Let's take a look at the null0 interface and how it relates to OSPF summarization. On R1, the following networks are redistributed into OSPF, and then summarized. interface Loopback16 ip address 16.16.16.16 255.0.0.0 interface Loopback17 ip address 17.17.17.17 255.0.0.0 interface Loopback18 ip address 18.18.18.18 255.0.0.0 interface Loopback19 ip address 19.19.19.19 255.0.0.0 R1(config)#router ospf 1 R1(config-router)#redi