Creating Routing Policies

The following are typical circumstances under which you might want to preempt the default routing policies in the routing policy framework by creating your own routing policies:

• You do not want a protocol to import all routes into the routing table. If the routing table does not learn about certain routes, they can never be used to forward packets and they can never be redistributed into other routing protocols.
• You do not want a routing protocol to export all the active routes it learns.
• You want a routing protocol to announce active routes learned from another routing protocol, which is sometimes called route redistribution.
• You want to manipulate route characteristics, such as the preference value, AS path, or community. You can manipulate the route characteristics to control which route is selected as the active route to reach a destination. In general, the active route is also advertised to a router’s neighbors.
• You want to change the default BGP route flap-damping parameters.
• You want to perform per-packet load balancing.
• You want to enable class of service (CoS).