4.4. Route Manipulation
Let's take a look at a couple a ways that you can filter or control the routing information that leaves or enters a router. There are many reasons you may want to do this. I haven't completely covered all of them yet, but not to worry; I'm going to.
One of those big reasons is to control routes coming through a redistribution configuration. Another might be to prevent routing information from leaving the internetwork, say preventing it from going into an ISP network. Sometimes there are links that, because of the bandwidth, you just don't want to have the updates being sent across.
There are a few ways that you can accomplish these filtering affects on the network. These include passive interface configuration, distribute ...