Routing Policy Configuration Task List 993Each node comprises a list 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 performed after the node is passed, concerningthe attribute settings for routing information.The filter relation among different route policy nodes is logical OR. Once a node ismatched, the routing policy is passed and the packet will not go through the nextnode.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 TaskListTo configure a routing policy, perform the tasks described in the followingsections:Defining Filtering ListsPrerequisites Before configuring this task, you need to decide on:■ IP-prefix list name■ Matching address range■ Extcommunity list sequence numberDefining an IP-prefix List Define an IPv4 prefix listIdentified 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.Task“Defining Filtering Lists” on page993“Defining an IP-prefix List” on page 993“Defining an AS Path ACL” on page 995“Defining a Community List” on page 995“Defining an Extended Community List” on page 995“Configuring a Routing Policy” onpage 996“Creating a Routing Policy” on page 996“Defining if-match Clauses for the Routing Policy” onpage 996“Defining apply Clauses for the Routing Policy” on page998
