Routing Policy Configuration Task List 417order of node sequence number. Once a node is matched, the routing policy ispassed and the packet will not go through the next node.Each node comprises a set of if-match and apply clauses. The if-match clausesdefine the match criteria. The matching objects are some attributes of routinginformation. The different if-match clauses on a node is in logical ANDrelationship. Only when the matching conditions specified by all the if-matchclauses on the node are satisfied, can routing information pass the node. Theapply clauses specify the actions to be performed after the node is passed,concerning the attribute settings for routing information.Routing PolicyApplicationA routing policy is applied in two ways:■ When redistributing routes from other routing protocols, a routing protocolaccepts only routes passing the routing policy.■ When receiving or advertising routing information, a routing protocol uses therouting policy to filter routing information.Routing PolicyConfiguration TaskListComplete the following tasks to configure a routing policy:Defining Filtering ListsPrerequisites Before configuring this task, you need to decide on:■ IP-prefix list name■ Matching address range■ Extcommunity list sequence numberDefining an IPv4 prefixListIdentified by name, each IPv4 prefix list can comprise multiple items. Each itemspecifies a matching address range in the form of network prefix identified byindex number.During matching, the system compares the route to each item identified by indexnumber in the ascending order. If one item matches, the route passes the IP-prefixlist, without needing to match against the next item.Follow these steps to define an IPv4 prefix list:Task“Defining Filtering Lists” on page417“Defining an IPv4 prefix List” on page 417“Defining an AS Path List” on page 418“Defining a Community List” on page 418“Defining an Extended Community List” on page 419“Configuring a Routing Policy” onpage 419“Creating a Routing Policy” on page 419“Defining if-match Clauses for the Routing Policy” onpage 420“Defining apply Clauses for the Routing Policy” on page421
