6-16 IP Routing Policy ConfigurationWhen configuring an IP routing policy, go to these sections for information you are interested in:z IP Routing Policy Overviewz IP Routing Policy Configuration Task Listz Displaying IP Routing Policyz IP Routing Policy Configuration Examplez Troubleshooting IP Routing PolicyThe term router in this chapter refers to a router in a generic sense or an Ethernet switch running arouting protocol.IP Routing Policy OverviewIntroduction to IP Routing PolicyRouting policy is technology used to modify routing information to control the forwarding path of datapackets. Routing policy is implemented by changing the route attributes such as reachability.When a router distributes or receives routing information, it may need to implement some policies tofilter the routing information, so as to receive or distribute only the routing information meeting givenconditions. A routing protocol (RIP, for example) may need to import the routing information discoveredby other protocols to enrich its routing knowledge. While importing routing information from anotherprotocol, it possibly only needs to import the routes meeting given conditions and control someattributes of the imported routes to make the routes meet the requirements of this protocol.For the implementation of a routing policy, you need to define a set of matching rules by specifying thecharacteristics of the routing information to be filtered. You can set the rules based on such attributes asdestination address and source address of the information. The matching rules can be set in advanceand then used in the routing policies to advertise, receive, and import routes.FiltersA routing protocol can reference an ACL, IP-prefix, as-path, community-list, or routing policy to filterrouting information. The following sections describe these filters.ACLYou can specify a range of IP addresses or subnets when defining an ACL so as to match thedestination network addresses or next-hop addresses in routing information. You can reference an ACLinto a routing policy to filter routing information.For ACL configuration, refer to the part discussing ACL.
