Overview
Routing policy determines how the system handles the routes it receives from and sends to neighboring routers. In many cases, routing policy consists of filtering routes, accepting certain routes, accepting and modifying other routes, rejecting some routes, and determining the routing protocol used to distribute the routes. You can think of routing policy as a way to control the flow of routes into and out of the system.
The decision about which routes to accept from and advertise to various neighbors has an important impact on the traffic that crosses a network. Routing policy is used to enforce business agreements between two or more ISPs concerning the amount and type of traffic that is allowed to pass between them.
You can use one or more of the following mechanisms to configure routing policy: